Home About us Contact
|
Home About us Contact | ||
|
|
||
Developmental Mechanisms (developmental + mechanism)
Selected AbstractsDevelopmental mechanisms of digit reductionEVOLUTION AND DEVELOPMENT, Issue 4 2002Mark W. Hamrick No abstract is available for this article. [source] NG2 proteoglycan is expressed exclusively by mural cells during vascular morphogenesisDEVELOPMENTAL DYNAMICS, Issue 2 2001Ugur Ozerdem Abstract Immunofluorescence mapping demonstrates that the NG2 proteoglycan is invariably expressed by the mural cell component of mouse neovascular structures. This pattern is independent of the developmental mechanism responsible for formation of the vasculature (vasculogenesis or angiogenesis). Thus, NG2 is expressed in the embryonic heart by cardiomyocytes, in developing macrovasculature by smooth muscle cells, and in nascent microvessels by vascular pericytes. Due to the scarcity of proven markers for developing pericytes, NG2 is especially useful for identification of this cell type. The utility of NG2 as a pericyte marker is illustrated by two observations. First, pericytes are associated with endothelial tubes at an early point in microvessel development. This early interaction between pericytes and endothelial cells has important implications for the role of pericytes in the development and stabilization of microvascular tubes. Second, the pericyte to endothelial cell ratio in developing capillaries varies from tissue to tissue. Because the extent of pericyte investment is likely to affect the physical properties of the vessel in question, it is important to understand the mechanisms that control this process. Additional insight into these and other aspects of vascular morphogenesis should be possible through use of NG2 as a mural cell marker. © 2001 Wiley-Liss, Inc. [source] Sexual size dimorphism in the two spot ladybird beetle Adalia bipunctata: developmental mechanism and its consequences for matingECOLOGICAL ENTOMOLOGY, Issue 4 2002Hironori Yasuda Abstract ,1. The literature on ladybirds indicates that males are consistently smaller than females but take the same length of time to complete their development. Rearing Adalia bipunctata at 20 and 25 °C confirmed that protandry cannot account for sexual size dimorphism in this species, nor can a difference in egg size. 2. Female larvae consumed more food and had a higher relative growth rate in the fourth instar than did male larvae. 3. When food is limited, small males appear to be more successful at mating than are large males. 4. To account for these results, it is hypothesised that the gonads of male larvae compete more strongly with the soma for resources and that this reduces the growth potential of the soma of male larvae relative to that of female larvae. The greater mating success of small males when food is limited supports the eat or mate hypothesis, which predicts that when food is limited small males will spend less time feeding and more time mating than will large males. [source] Activation of class I metabotropic glutamate receptors limits dendritic growth of Purkinje cells in organotypic slice culturesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006Alexandra Sirzen-Zelenskaya Abstract The development of the dendritic tree of a neuron is a complex process which is thought to be regulated strongly by signals from afferent fibers. We showed previously that the blockade of glutamatergic excitatory neurotransmission has little effect on Purkinje cell dendritic development. We have now studied the effects of glutamate receptor agonists on the development of Purkinje cell dendrites in mouse organotypic slice cultures. The activation of N -methyl- d -aspartate receptors had no major effect on Purkinje cell dendrites and the activation of (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid receptors was strongly excitotoxic so that no analysis of its effects on dendritic development was possible. The activation of metabotropic glutamate receptors led to a very strong inhibition of dendritic growth, resulting in Purkinje cells with very small stubby dendrites. This effect was specific for the activation of class I metabotropic glutamate receptors and could not be reduced by blocking synaptic transmission in the cultures, indicating that it was mediated by receptors present on Purkinje cells. Pharmacological experiments suggest that the signaling pathway involved does not require activation of phospholipase C or protein kinase C. The inhibition of dendritic growth by activation of class I metabotropic glutamate receptor could be a useful negative feedback mechanism for limiting the size of the dendritic tree of Purkinje cells after the establishment of a sufficient number of parallel fiber contacts. This developmental mechanism could protect Purkinje cells from excitotoxic death through excessive release of glutamate from an overload of parallel fiber contacts. [source] Development and evolution of adaptive polyphenismsEVOLUTION AND DEVELOPMENT, Issue 1 2003H. Frederik Nijhout SUMMARY Phenotypic plasticity is the primitive character state for most if not all traits. Insofar as developmental and physiological processes obey the laws of chemistry and physics, they will be sensitive to such environmental variables as temperature, nutrient supply, ionic environment, and the availability of various macro- and micronutrients. Depending on the effect this phenotypic plasticity has on fitness, evolution may proceed to select either for mechanisms that buffer or canalize the phenotype against relevant environmental variation or for a modified plastic response in which some ranges of the phenotypic variation are adaptive to particular environments. Phenotypic plasticity can be continuous, in which case it is called a reaction norm, or discontinuous, in which case it is called a polyphenism. Although the morphological discontinuity of some polyphenisms is produced by discrete developmental switches, most polyphenisms are due to discontinuities in the environment that induce only portions of what is in reality a continuous reaction norm. In insect polyphenisms, the environmental variable that induces the alternative phenotype is a token stimulus that serves as a predictor of, but is not itself, the environment to which the polyphenism is an adaptation. In all cases studied so far, the environmental stimulus alters the endocrine mechanism of metamorphosis by altering either the pattern of hormone secretion or the pattern of hormone sensitivity in different tissues. Such changes in the patterns of endocrine interactions result in the execution of alternative developmental pathways. The spatial and temporal compartmentalization of endocrine interactions has produced a developmental mechanism that enables substantial localized changes in morphology that remain well integrated into the structure and function of the organism. [source] Consequences of maternal yolk testosterone for offspring development and survival: experimental test in a lizardFUNCTIONAL ECOLOGY, Issue 3 2007T. ULLER Summary 1Hormone-mediated maternal effects and developmental plasticity are important sources of phenotypic variation, with potential consequences for trait evolution. Yet our understanding of the importance of maternal hormones for offspring fitness in natural populations is very limited, particularly in non-avian species. 2We experimentally elevated yolk testosterone by injection of a physiological dose into eggs of the lizard Ctenophorus fordi Storr, to investigate its roles in offspring development, growth and survival. 3Yolk testosterone did not influence incubation period, basic hatchling morphology or survival under natural conditions. However, there was evidence for increased growth in hatchlings from testosterone-treated eggs, suggesting that maternal hormones have potential fitness consequences in natural populations. 4The positive effect of prenatal testosterone exposure on postnatal growth could represent a taxonomically widespread developmental mechanism that has evolved into an adaptive maternal effect in some taxa, but remains deleterious or selectively neutral in others. 5A broader taxonomic perspective should increase our understanding of the role of physiological constraints in the evolution of endocrine maternal effects. [source] P1 Regionalisation of the brain as an evolutionarily conserved developmental mechanism.JOURNAL OF ANATOMY, Issue 1-2 2001E. GALE Comparative studies of chordate neural connectivity and gene families have provided evidence for evolutionary conservation of the patterning mechanisms in brain development (review Holland & Holland, Curr. Opin. Neurobiol.9, 1999). Based on expression patterns of ascidian and amphioxus homologues of the Otx gene and the Hox1 gene and of the ascidian Pax-2/5/8, the chordate brain has been suggested to have tripartite development (Wada et al., Development125, 1998; Kozmik et al., Development126, 1999). Primitively, the chordates have regions homologous to the vertebrate forebrain, anterior midbrain and posterior hindbrain while the posterior midbrain/anterior hindbrain region seems to be a vertebrate innovation. The extent of the homologies within each of these regions between the vertebrates and their ancestors is not fully determined but the similarity of Hox gene expression patterns suggests organisational constants over evolutionary time within the posterior hindbrain region. Identification of the posterior hindbrain region as a developmental unit in vertebrates is demonstrated in the retinoid-deficient quail. Embryos laid by quails fed a retinoid-deficient diet have no posterior hindbrain while the anterior hindbrain is specified normally. Through DiI cell lineage tracing and a temporal analysis of gene expression characteristic of this region (Krox-20, Hoxb-1, mafB, and fgf3), we have followed the development of this region of cells. From the initial formation of the neural plate phenotype in the retinoid-deficient quail, there is no evidence of a posterior hindbrain. This region is never specified and all the cells of the hindbrain participate in an anterior hindbrain fate. A single retinoid injection in ovo during early development completely rescues the posterior hindbrain ensuring that the phenotype was the result of a single stimulus. Therefore cells from the posterior hindbrain respond in a coordinated regional manner to the presence or absence of a single gene inducer, retinoic acid. We present evidence of regionalisation of the vertebrate head that is up stream of segment specification. In combination with data from amphioxus and ascidians, this may represent a common mechanism for head development throughout chordate evolution. Interestingly, regional deletion with enlargement of the adjacent region is very reminiscent of the gap gene phenotype in Drosophila. It would be disregarding millions of years of divergent evolution to suggest that vitamin A is identical to a Drosophila gap gene inducer; nevertheless this data supports the hypothesis of common underlying regulation of axial regionalisation and gene hierarchies. [source] Testosterone, growth and the evolution of sexual size dimorphismJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 8 2009R. M. COX Abstract The integration of macroevolutionary pattern with developmental mechanism presents an outstanding challenge for studies of phenotypic evolution. Here, we use a combination of experimental and comparative data to test whether evolutionary shifts in the direction of sexual size dimorphism (SSD) correspond to underlying changes in the endocrine regulation of growth. First, we combine captive breeding studies with mark-recapture data to show that male-biased SSD develops in the brown anole lizard (Anolis sagrei) because males grow significantly faster than females as juveniles and adults. We then use castration surgeries and testosterone implants to show that castration inhibits, and testosterone stimulates, male growth. We conclude by reviewing published testosterone manipulations in other squamate reptiles in the context of evolutionary patterns in SSD. Collectively, these studies reveal that the evolution of SSD has been accompanied by underlying changes in the effect of testosterone on male growth, potentially facilitating the rapid evolution of SSD. [source] Clinicopathological study of scirrhous hepatocellular carcinomaJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 9 2006Mina Kurogi Abstract Background and Aims:, Scirrhous hepatocellular carcinoma (SHCC) is characterized by diffuse fibrosis of the tumor, however, its clinicopathological features are not fully clarified. This study aimed to clarify the clinicopathological features of SHCC. Methods:, Among 546 consecutively resected HCC without preoperative anticancer therapies, 25 SHCC were selected for the study and compared with 521 cases without scirrhous as the control. Results:, SHCC accounted for 4.6% of cases. On diagnostic imagings, SHCC was frequently misdiagnosed as cholangiocarcinoma (CC), combined HCC-CC or metastatic carcinoma. Overall survival rate was significantly higher than the control. The average (±SD) tumor size of SHCC was 3.4 ± 1.8 cm without significant difference to the control. The majority of SHCC (88%) were located close to the liver capsule. SHCC was characterized by stellate fibrosis (84%), no encapsulation (100%), no necrosis and hemorrhage (100%), intratumoral portal tracts (80%), remarkable lymphocyte infiltration (84%), clear cell change (84%), and hyaline bodies (52%). The number of ,-smooth muscle actin-positive myofibroblast-like cells (activated stellate cells) in the tumor was about three times more than that in the control. Regarding the developmental mechanism of scirrhous change, a close correlation with unique tumor location and activation of stellate cells was suggested. Conclusion:, SHCC presents with characteristic clinicopathological features and the recognition of SHCC is important for both clinicians and pathologists. [source] Children's understanding of certainty and evidentiality: Advantage of grammaticalized forms over lexical alternativesNEW DIRECTIONS FOR CHILD & ADOLESCENT DEVELOPMENT, Issue 125 2009Tomoko Matsui In verbal communication, the hearer takes advantage of the linguistic expressions of certainty and evidentiality to assess how committed the speaker might be to the truth of the informational content of the utterance. Little is known, however, about the precise developmental mechanism of this ability. In this chapter, we approach the question by elucidating factors that are likely to constrain young children's understanding of linguistically encoded certainty and evidentiality, including the types of linguistic form of these expressions, namely, grammaticalized or lexical forms. © Wiley Periodicals, Inc. [source] Basal metabolic rate in the Yakut (Sakha) of SiberiaAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2005J. Josh Snodgrass Human indigenous circumpolar populations have elevated basal metabolic rates (BMRs) relative to predicted values; this metabolic elevation has been postulated to be a physiological adaptation to chronic and severe cold stress. The present study examines BMR in the Yakut, an indigenous high-latitude population from the Sakha Republic of Russia to determine (1) whether the Yakut show evidence of an elevated BMR, (2) if the Yakut display evidence of age-related changes in BMR, and (3) whether lifestyle differences influence BMR. BMR was measured during the late summer in 75 women and 50 men (ages 18,56 years) from the Siberian village of Berdygestiakh. Measured BMR (± SEM) of the entire sample was significantly elevated (+6.5%) compared to predictions based on body mass (6,623.7 ± 94.9 vs. 6,218.2 ± 84.7 kJ/day; P < 0.001). Additionally, measured BMR for the entire sample was significantly higher than predictions based on fat-free mass (+20.8%) and surface area (+8.9%). Males and females both showed significant elevations relative to all three standards. The elevated BMR of the Yakut does not appear to be attributable to extreme levels of protein, since the Yakut consume a mixed diet with a substantial proportion of carbohydrates. No significant age-related changes in BMR were found when controlled for body composition. No significant relationship was found between lifestyle variables and BMR, suggesting the possibility of a genetic or developmental mechanism. This study provides additional evidence of metabolic elevation in indigenous circumpolar groups and has important implications for estimating the nutritional requirements of these populations. Am. J. Hum. Biol. 17:155,172, 2005. © 2005 Wiley-Liss, Inc. [source] The Cnidarian and the Canon: the role of Wnt/,-catenin signaling in the evolution of metazoan embryosBIOESSAYS, Issue 5 2004Alex Primus In a recent publication, Wikramanayake and colleagues have implicated the canonical Wnt/,-catenin signaling pathway as a mediator of axial polarity and germ-layer specification in embryos of the cnidarian Nematostella.1 In this anthozoan, ,-catenin is localized in nuclei of blastomeres in one region of the 16- to 32-cell embryo whose descendants subsequently form the entoderm of the embryo. They claim that the pattern of nuclear localization is significant for two reasons: (1) when nuclear localization of ,-catenin was inhibited, gastrulation does not occur, and (2) when localization of ,-catenin took place in all cells of the pregastrula embryo, the number of entodermal cells increases. Since the Wnt/,-catenin signaling pathway also plays a role in establishing axial polarity and specifying endoderm and mesoderm in a number of bilaterians,2,6 Wikramanayake et al. imply that this developmental mechanism is an evolutionary inheritance from a radially symmetrical ancestor. Some of the gaps in the current evidence, which must be filled to evaluate their interpretation, are discussed. BioEssays 26:474,478, 2004. © 2004 Wiley Periodicals, Inc. [source] WHY DOES A TRAIT EVOLVE MULTIPLE TIMES WITHIN A CLADE?EVOLUTION, Issue 1 2006REPEATED EVOLUTION OF SNAKELINE BODY FORM IN SQUAMATE REPTILES Abstract Why does a trait evolve repeatedly within a clade? When examining the evolution of a trait, evolutionary biologists typically focus on the selective advantages it may confer and the genetic and developmental mechanisms that allow it to vary. Although these factors may be necessary to explain why a trait evolves in a particular instance, they may not be sufficient to explain phylogenetic patterns of repeated evolution or conservatism. Instead, other factors may also be important, such as biogeography and competitive interactions. In squamate reptiles (lizards and snakes) a dramatic transition in body form has occurred repeatedly, from a fully limbed, lizardlike body form to a limbreduced, elongate, snakelike body form. We analyze this trait in a phylogenetic and biogeographic context to address why this transition occurred so frequently. We included 261 species for which morphometric data and molecular phylogenetic information were available. Among the included species, snakelike body form has evolved about 25 times. Most lineages of snakelike squamates belong to one of two ecomorphs, either short-tailed burrowers or long-tailed surface dwellers. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of these two ecomorphs on different continental regions (including multiple origins of the burrowing morph within most continents), with very little dispersal of most limb-reduced lineages between continental regions. Overall, the number of repeated origins of snakelike morphology seems to depend on large-scale biogeographic patterns and community ecology, in addition to more traditional explanations (e.g., selection, development). [source] Is retinoic acid genetic machinery a chordate innovation?EVOLUTION AND DEVELOPMENT, Issue 5 2006Cristian Cañestro SUMMARY Development of many chordate features depends on retinoic acid (RA). Because the action of RA during development seems to be restricted to chordates, it had been previously proposed that the "invention" of RA genetic machinery, including RA-binding nuclear hormone receptors (Rars), and the RA-synthesizing and RA-degrading enzymes Aldh1a (Raldh) and Cyp26, respectively, was an important step for the origin of developmental mechanisms leading to the chordate body plan. We tested this hypothesis by conducting an exhaustive survey of the RA machinery in genomic databases for twelve deuterostomes. We reconstructed the evolution of these genes in deuterostomes and showed for the first time that RA genetic machinery,that is Aldh1a, Cyp26, and Rar orthologs,is present in nonchordate deuterostomes. This finding implies that RA genetic machinery was already present during early deuterostome evolution, and therefore, is not a chordate innovation. This new evolutionary viewpoint argues against the hypothesis that the acquisition of gene families underlying RA metabolism and signaling was a key event for the origin of chordates. We propose a new hypothesis in which lineage-specific duplication and loss of RA machinery genes could be related to the morphological radiation of deuterostomes. [source] Short and long germ segmentation: unanswered questions in the evolution of a developmental modeEVOLUTION AND DEVELOPMENT, Issue 6 2005Paul Z. Liu Summary The insect body plan is very well conserved, yet the developmental mechanisms of segmentation are surprisingly varied. Less evolutionarily derived insects undergo short germ segmentation where only the anterior segments are specified before gastrulation whereas the remaining posterior segments are formed during a later secondary growth phase. In contrast, derived long germ insects such as Drosophila specify their entire bodies essentially simultaneously. These fundamental embryological differences imply potentially divergent molecular patterning events. Numerous studies have focused on comparing the expression and function of the homologs of Drosophila segmentation genes between Drosophila and different short and long germ insects. Here we review these comparative data with special emphasis on understanding how short germ insects generate segments and how this ancestral mechanism may have been modified in derived long germ insects such as Drosophila. We break down the larger issue of short versus long germ segmentation into its component developmental problems and structure our discussion in order to highlight the unanswered questions in the evolution of insect segmentation. [source] Diverse developmental mechanisms contribute to different levels of diversity in horned beetlesEVOLUTION AND DEVELOPMENT, Issue 3 2005Armin P. Moczek Summary An ongoing challenge to evolutionary developmental biology is to understand how developmental evolution on the level of populations and closely related species relates to macroevolutionary transformations and the origin of morphological novelties. Here we explore the developmental basis of beetle horns, a morphological novelty that exhibits remarkable diversity on a variety of levels. In this study, we examined two congeneric Onthophagus species in which males develop into alternative horned and hornless morphs and different sexes express marked sexual dimorphism. In addition, both species differ in the body region (head vs. thorax) that develops the horn. Using a comparative morphological approach we show that prepupal growth of horn primordia during late larval development, as well as reabsorption of horn primordia during the pupal stage, contribute to horn expression in adults. We also show that variable combinations of both mechanisms are employed during development to modify horn expression of different horns in the same individual, the same horn in different sexes, and different horns in different species. We then examine expression patterns of two transcription factors, Distal-less (Dll) and aristaless (al), in the context of prepupal horn growth in alternative male morphs and sexual dimorphisms in the same two species. Expression patterns are qualitatively consistent with the hypothesis that both transcription factors function in the context of horn development similar to their known roles in patterning a wide variety of arthropod appendages. Our results suggest that the origin of morphological novelties, such as beetle horns, rests, at least in part, on the redeployment of already existing developmental mechanisms, such as appendage patterning processes. Our results also suggest, however, that little to no phylogenetic distance is needed for the evolution of very different modifier mechanisms that allow for substantial modulation of trait expression at different time points during development in different species, sexes, or tissue regions of the same individual. We discuss the implications of our results for our understanding of the evolution of horned beetle diversity and the origin and diversification of morphological novelties. [source] Gene expression and digit homology in the chicken embryo wingEVOLUTION AND DEVELOPMENT, Issue 1 2005Monique C. M. Welten Summary The bird wing is of special interest to students of homology and avian evolution. Fossil and developmental data give conflicting indications of digit homology if a pentadactyl "archetype" is assumed. Morphological signs of a vestigial digit I are seen in bird embryos, but no digit-like structure develops in wild-type embryos. To examine the developmental mechanisms of digit loss, we studied the expression of the high-mobility group box containing Sox9 gene, and bone morphogenetic protein receptor 1b (bmpR-1b),markers for precondensation and prechondrogenic cells, respectively. We find an elongated domain of Sox9 expression, but no bmpR-1b expression, anterior to digit II. We interpret this as a digit I domain that reaches precondensation, but not condensation or precartilage stages. It develops late, when the tissue in which it is lodged is being remodeled. We consider these findings in the light of previous Hoxd-11 misexpression studies. Together, they suggest that there is a digit I vestige in the wing that can be rescued and undergo development if posterior patterning cues are enhanced. We observed Sox9 expression in the elusive "element X" that is sometimes stated to represent a sixth digit. Indeed, incongruity between digit domains and identities in theropods disappears if birds and other archosaurs are considered primitively polydactyl. Our study provides the first gene expression evidence for at least five digital domains in the chick wing. The failure of the first to develop may be plausibly linked to attenuation of posterior signals. [source] Why is limb regeneration possible in amphibians but not in reptiles, birds, and mammals?EVOLUTION AND DEVELOPMENT, Issue 2 2003Frietson Galis SUMMARY The capacity to regenerate limbs is very high in amphibians and practically absent in other tetrapods despite the similarities in developmental pathways and ultimate morphology of tetrapod limbs. We propose that limb regeneration is only possible when the limb develops as a semiautonomous module and is not involved in interactions with transient structures. This hypothesis is based on the following two assumptions: To an important extent, limb development uses the same developmental mechanisms as normal limb development and developmental mechanisms that require interactions with transient structures cannot be recapitulated later. In amniotes limb development is early, shortly after neurulation, and requires inductive interactions with transient structures such as somites. In amphibians limb development is delayed relative to amniotes and has become decoupled from interactions with somites and other transient structures that are no longer present at this stage. The limb develops as a semi-independent module. A comparison of the autonomy and timing of limb development in different vertebrate taxa supports our hypothesis and its assumptions. The data suggest a good correlation between self-organizing and regenerative capacity. Furthermore, they suggest that whatever barriers amphibians overcame in the evolution of metamorphosis, they are the same barriers that need to be overcome to make limb regeneration possible in other taxa. [source] Microevolutionary analysis of the nematode genus Pristionchus suggests a recent evolution of redundant developmental mechanisms during vulva formationEVOLUTION AND DEVELOPMENT, Issue 4 2001Jagan Srinivasan SUMMARY To identify the mechanisms by which molecular variation is introduced into developmental systems, microevolutionary approaches to evolutionary developmental biology have to be taken. Here, we describe the molecular and developmental characterization of laboratory strains of the nematode genus Pristionchus, which lays a foundation for a microevolutionary analysis of vulva development. We describe 13 laboratory strains of the Pristionchus genus that are derived from natural isolates from around the world. Mating experiments and ITS sequence analysis indicated that these 13 strains represent four different species: the gonochoristic species P. lheritieri and three hermaphroditic species, P. pacificus, P. maupasi, and an as yet undescribed species Pristionchus sp., respectively. P. pacificus is represented by five different strains isolated from California, Washington, Hawaii, Ontario, and Poland. Developmental differences during vulva formation are observed between strains from different species but also between strains of P. pacificus, like the strains from California and Poland. In particular, redundant developmental mechanisms present during vulva formation in P. pacificus var. California are absent in other strains. Amplified restriction fragment length polymorphism (AFLP) analyses of the P. pacificus strains revealed that the American strains are highly polymorphic. In contrast, the developmentally distinct strain from Poland is identical to the Californian strain, suggesting that the developmental differences rely on a small number of changes in developmental control genes rather than the accumulation of changes at multiple loci. [source] Germ-line transformation and RNAi of the ladybird beetle, Harmonia axyridisINSECT MOLECULAR BIOLOGY, Issue 4 2006H. Kuwayama Abstract To elucidate the molecular mechanisms underlying the tremendous diversity of insect wing colour patterns, it is imperative to identify and functionally characterize the genes involved in this developmental process. Here we report the first successful germ-line transformation using the transposable element vector piggyBac in the ladybird beetle Harmonia axyridis, which demonstrates typical genetic polymorphism in its wing colour patterns. The transformation efficiency by piggyBac was 3.7% per fertile G0. We investigated the effectiveness of RNAi in Harmonia by injecting EGFP (enhanced green fluorescent protein) dsRNA into early transgenic EGFP-expressing embryos and observed substantial reduction of EGFP fluorescence in 87.2% of hatched larvae. Application of these new genetic tools to non-model insects such as Harmonia will facilitate the broad understanding of developmental mechanisms and evolutionary processes that are inaccessible using established model systems. [source] Micro-magnetic resonance imaging of avian embryosJOURNAL OF ANATOMY, Issue 6 2007Xiaojing Li Abstract Chick embryos are useful models for probing developmental mechanisms including those involved in organogenesis. In addition to classic embryological manipulations, it is possible to test the function of molecules and genes while the embryo remains within the egg. Here we define conditions for imaging chick embryo anatomy and for visualising living quail embryos. We focus on the developing limb and describe how different tissues can be imaged using micro-magnetic resonance imaging and this information then synthesised, using a three-dimensional visualisation package, into detailed anatomy. We illustrate the potential for micro-magnetic resonance imaging to analyse phenotypic changes following chick limb manipulation. The work with the living quail embryos lays the foundations for using micro-magnetic resonance imaging as an experimental tool to follow the consequences of such manipulations over time. [source] Symposium on the evolution of developmental mechanismsJOURNAL OF ANATOMY, Issue 1-2 2001Anthony Graham No abstract is available for this article. [source] Imbalanced genomic imprinting in brain development: an evolutionary basis for the aetiology of autismJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2006C. BADCOCK Abstract We describe a new hypothesis for the development of autism, that it is driven by imbalances in brain development involving enhanced effects of paternally expressed imprinted genes, deficits of effects from maternally expressed genes, or both. This hypothesis is supported by: (1) the strong genomic-imprinting component to the genetic and developmental mechanisms of autism, Angelman syndrome, Rett syndrome and Turner syndrome; (2) the core behavioural features of autism, such as self-focused behaviour, altered social interactions and language, and enhanced spatial and mechanistic cognition and abilities, and (3) the degree to which relevant brain functions and structures are altered in autism and related disorders. The imprinted brain theory of autism has important implications for understanding the genetic, epigenetic, neurological and cognitive bases of autism, as ultimately due to imbalances in the outcomes of intragenomic conflict between effects of maternally vs. paternally expressed genes. [source] Understanding challenging behaviour in people with severe and profound intellectual disability: a stress-attachment modelJOURNAL OF INTELLECTUAL DISABILITY RESEARCH, Issue 6 2002C. G. C. Janssen Abstract Background Advances in our knowledge of attachment, stress and coping may foster new explanations for the development of challenging behaviour in people with intellectual disability (ID). Method Research on stress and coping among people with ID was reviewed initially, and then studies on the security of the attachment relationships of people with ID with their caregivers were analysed. Results There is evidence that people with ID are more vulnerable to stress and use less effective coping strategies. Furthermore, the body of studies on attachment indicates that people with ID are at risk for developing insecure, especially disorganized attachment. There is evidence from other populations that the combination of stress, and insecure or disorganized attachment may put people at risk for developing behaviour problems. Conclusion A stress-attachment model of the development of challenging behaviour among people with ID shows promise as an explanatory framework. The uncovering of these developmental mechanisms may be particularly useful for the prevention of behavioural problems. [source] Development of the vertebrate central nervous system: formation of the neural tubePRENATAL DIAGNOSIS, Issue 4 2009Nicholas D. E. Greene Abstract The developmental process of neurulation involves a series of coordinated morphological events, which result in conversion of the flat neural plate into the neural tube, the primordium of the entire central nervous system (CNS). Failure of neurulation results in neural tube defects (NTDs), severe abnormalities of the CNS, which are among the commonest of congenital malformations in humans. In order to gain insight into the embryological basis of NTDs, such as spina bifida and anencephaly, it is necessary to understand the morphogenetic processes and molecular mechanisms underlying neural tube closure. The mouse is the most extensively studied mammalian experimental model for studies of neurulation, while considerable insight into underlying developmental mechanisms has also arisen from studies in other model systems, particularly birds and amphibians. We describe the process of neural tube formation, discuss the cellular mechanisms involved and highlight recent findings that provide links between molecular signaling pathways and morphogenetic tissue movements. Copyright © 2009 John Wiley & Sons, Ltd. [source] Microanatomy of the Mandibular Symphysis in Lizards: Patterns in Fiber Orientation and Meckel's Cartilage and Their Significance in Cranial EvolutionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2010Casey M. Holliday Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft-tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here, we present new histological data illustrating the morphology of the joint in a number of taxa including iguanians, geckos, scincomorphs, lacertoids, and anguimorphs. The symphyses of all taxa exhibit dorsal and ventral fibrous portions of the joints that possess an array of parallel and woven collagen fibers. The middle and ventral portions of the joints are complemented by contributions of Meckel's cartilage. Kinetic taxa have more loosely built symphyses with large domains of parallel-oriented fibers whereas hard biting and akinetic taxa have symphyses primarily composed of dense, woven fibers. Whereas most taxa maintain unfused Meckel's cartilages, iguanians, and geckos independently evolved fused Meckel's cartilages; however, the joint's morphologies suggest different developmental mechanisms. Fused Meckel's cartilages may be associated with the apomorphic lingual behaviors exhibited by iguanians (tongue translation) and geckos (drinking). These morphological data shed new light on the functional, developmental, and evolutionary patterns displayed by the heads of lizards. Anat Rec 293:1350,1359, 2010. © 2010 Wiley-Liss, Inc. [source] Descent with modification: the unity underlying homology and homoplasy as seen through an analysis of development and evolutionBIOLOGICAL REVIEWS, Issue 3 2003BRIAN K. HALL ABSTRACT Homology is at the foundation of comparative studies in biology at all levels from genes to phenotypes. Homology similarity because of common descent and ancestry, homoplasy is similarity arrived at via independent evolution However, given that there is but one tree of life, all organisms, and therefore all features of organisms, share degree of relationship and similarity one to another. That sharing may be similarity or even identity of structure the sharing of a most recent common ancestor,as in the homology of the arms of humans and apes,or it reflect some (often small) degree of similarity, such as that between the wings of insects and the wings of groups whose shared ancestor lies deep within the evolutionary history of the Metazoa. It may reflect sharing entire developmental pathways, partial sharing, or divergent pathways. This review compares features classified homologous with the classes of features normally grouped as homoplastic, the latter being convergence, parallelism, reversals, rudiments, vestiges, and atavisms. On the one hand, developmental mechanisms may be conserved, when a complete structure does not form (rudiments, vestiges), or when a structure appears only in some individuals (atavisms). On the other hand, different developmental mechanisms can produce similar (homologous) features Joint examination of nearness of relationship and degree of shared development reveals a continuum within expanded category of homology, extending from homology , reversals , rudiments , vestiges , atavisms , parallelism, with convergence as the only class of homoplasy, an idea that turns out to be surprisingly old. realignment provides a glimmer of a way to bridge phylogenetic and developmental approaches to homology homoplasy, a bridge that should provide a key pillar for evolutionary developmental biology (evo-devo). It will and in a practical sense cannot, alter how homoplastic features are identified in phylogenetic analyses. But rudiments, reversals, vestiges, atavisms and parallelism as closer to homology than to homoplasy should guide toward searching for the common elements underlying the formation of the phenotype (what some have called deep homology of genetic and/or cellular mechanisms), rather than discussing features in terms of shared independent evolution. [source] Fluctuating asymmetry as an indicator of fitness: can we bridge the gap between studies?BIOLOGICAL REVIEWS, Issue 1 2002LUC LENS ABSTRACT There is growing evidence from both experimental and non-experimental studies that fluctuating asymmetry does not consistently index stress or fitness. The widely held , yet poorly substantiated - belief that fluctuating asymmetry can act as a universal measure of developmental stability and predictor of stress-mediated changes in fitness, therefore staggers. Yet attempts to understand why the reported relationships between fluctuating asymmetry, stress and fitness are so heterogeneous , i.e. whether the associations are truly weak or non-existent or whether they become confounded during different stages of the analytical pathways , remain surprisingly scarce. Hence, we attempt to disentangle these causes, by reviewing the various statistical and conceptual factors that are suspected to confound potential relationships between fluctuating asymmetry, stress and fitness. Two main categories of factors are discerned: those associated with the estimation of developmental stability through fluctuating asymmetry, and those associated with the effects of genotype and environment on developmental stability. Next, we describe a series of statistical tools that have recently been developed to help reduce this noise. We argue that the current lack of a theoretical framework that predicts if and when relationships with developmental stability can be expected, urges for further theoretical and empirical research, such as on the genetic architecture of developmental stability in stressed populations. If the underlying developmental mechanisms are better understood, statistical patterns of asymmetry variation may become a biologically meaningful tool. [source] Bladder exstrophy-epispadias complexBIRTH DEFECTS RESEARCH, Issue 6 2009Michael Ludwig Abstract The bladder exstrophy-epispadias complex (BEEC) represents an anterior midline defect with variable expression comprising a spectrum of anomalies involving the abdominal wall, pelvis, urinary tract, genitalia, and occasionally the spine and anus. The vast majority of BEEC cases are classified as non-syndromic and the etiology of this malformation is still unknown. This review presents the current state of knowledge on this multifactorial disorder, including historical retrospect, phenotypic and anatomical characterization, epidemiology, proposed developmental mechanisms, existing animal models, and implicated genetic and environmental components. These published lines of evidence argue strongly that BEEC occurs as a result of strong genetic predisposition that is yet to be deciphered. Birth Defects Research (Part A), 2009. © 2009 Wiley-Liss, Inc. [source] Carbon monoxide-induced axial skeletal dysmorphogenesis in the chick embryo,,BIRTH DEFECTS RESEARCH, Issue 4 2003Peter G. Alexander Abstract BACKGROUND Congenital axial skeletal defects affect two to three individuals per 1,000 live births. Without strong evidence for heritability, the cause is assumed to be multi-factorial. Carbon monoxide (CO), an increasingly prevalent environmental toxicant, is a potential environmental component in the etiology of these defects. The chick embryo is a useful model for the characterization and assessment of the mechanism(s) of action of basic developmental mechanisms. METHODS We have determined a critical period and dose for CO teratogenicity and established a model of CO-induced axial skeletal dysmorphogenesis in the chick embryo. The resulting phenotypes reveal a spectrum of axial skeletal defects ranging from minor defects of the vertebral canal and inter,vertebral discs, to thoraco,lumbar scoliosis, to a tailless phenotype reminiscent of caudal dysgenesis syndrome. These axial skeletal defects have been related to earlier developmental defects in somitogenesis, including errors in segmentation and epithelialization and the expression of the somitic epithelialization factor, Paraxis. We have examined patterns of cell death and apoptosis in CO exposed chick embryos to assess the target tissue(s) involved in the teratogenicity of CO. RESULTS With respect to the embryonic axis, the neural tube was found to be the most sensitive to CO-induced apoptosis, followed by the somitic mesoderm and Hensen's node. CONCLUSIONS We hypothesize that the somitic defects and the resulting axial skeletal dysmorphogenesis are caused by disrupted neural tube or ectoderm functions related to somite formation and maintenance. We also hypothesize that CO-induced dysmorphogenesis at this critical period of somitogenesis is caused by the overabundance of CO acting endogenously as a cellular signal, while coincidentally exerting its influence as a toxicant of oxygen delivery or utilization. Birth Defects Research (Part A) 67:219,230, 2003. Published 2003 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||