X. Laevis (x + laevi)

Distribution by Scientific Domains

Selected Abstracts

One of the duplicated matrix metalloproteinase-9 genes is expressed in regressing tail during anuran metamorphosis

Kenta Fujimoto
The drastic morphological changes of the tadpole are induced during the climax of anuran metamorphosis, when the concentration of endogenous thyroid hormone is maximal. The tadpole tail, which is twice as long as the body, shortens rapidly and disappears completely in several days. We isolated a cDNA clone, designated as Xl MMP-9TH, similar to the previously reported Xenopus laevis MMP-9 gene, and showed that their Xenopus tropicalis counterparts are located tandemly about 9 kb apart from each other in the genome. The Xenopus MMP-9TH gene was expressed in the regressing tail and gills and the remodeling intestine and central nervous system, and induced in thyroid hormone-treated tail-derived myoblastic cultured cells, while MMP-9 mRNA was detected in embryos. Three thyroid hormone response elements in the distal promoter and the first intron were involved in the upregulation of the Xl MMP-9TH gene by thyroid hormone in transient expression assays, and their relative positions are conserved between X. laevis and X. tropicalis promoters. These data strongly suggest that the MMP-9 gene was duplicated, and differentiated into two genes, one of which was specialized in a common ancestor of X. laevis and X. tropicalis to be expressed in degenerating and remodeling organs as a response to thyroid hormone during metamorphosis. [source]

Comparative and developmental study of the immune system in Xenopus

Jacques Robert
Abstract Xenopus laevis is the model of choice for evolutionary, comparative, and developmental studies of immunity, and invaluable research tools including MHC-defined clones, inbred strains, cell lines, and monoclonal antibodies are available for these studies. Recent efforts to use Silurana (Xenopus) tropicalis for genetic analyses have led to the sequencing of the whole genome. Ongoing genome mapping and mutagenesis studies will provide a new dimension to the study of immunity. Here we review what is known about the immune system of X. laevis integrated with available genomic information from S. tropicalis. This review provides compelling evidence for the high degree of similarity and evolutionary conservation between Xenopus and mammalian immune systems. We propose to build a powerful and innovative comparative biomedical model based on modern genetic technologies that takes take advantage of X. laevis and S. tropicalis, as well as the whole Xenopus genus. Developmental Dynamics 238:1249,1270, 2009. © 2009 Wiley-Liss, Inc. [source]

Xenopus, the next generation: X. Tropicalis genetics and genomics

Nicolas Hirsch
Abstract A small, fast-breeding, diploid relative of the frog Xenopus laevis, Xenopus tropicalis, has recently been adopted for research in developmental genetics and functional genomics. X. tropicalis shares advantages of X. laevis as a classic embryologic system, but its simpler genome and shorter generation time make it more convenient for multigenerational genetic, genomic, and transgenic approaches. Its embryos closely resemble those of X. laevis, except for their smaller size, and assays and molecular probes developed in X. laevis can be readily adapted for use in X. tropicalis. Genomic manipulation techniques such as gynogenesis facilitate genetic screens, because they permit the identification of recessive phenotypes after only one generation. Stable transgenic lines can be used both as in vivo reporters to streamline a variety of embryologic and molecular assays, or to experimentally manipulate gene expression through the use of binary constructs such as the GAL4/UAS system. Several mutations have been identified in wild-caught animals and during the course of generating inbred lines. A variety of strategies are discussed for conducting and managing genetic screens, obtaining mutations in specific sequences, achieving homologous recombination, and in developing and taking advantage of the genomic resources for Xenopus tropicalis. © 2002 Wiley-Liss, Inc. [source]

Effects of 17 ,-estradiol exposure on Xenopus laevis gonadal histopathology

Jeffrey C. Wolf
Abstract The natural estrogen 17 ,-estradiol (E2) is a potential environmental contaminant commonly employed as a positive control substance in bioassays involving estrogenic effects. The aquatic anuran Xenopus laevis is a frequent subject of reproductive endocrine disruptor research; however, histopathological investigations have tended to be less than comprehensive. Consequently, a study was designed to characterize gross and microscopic changes in the gonads of X. laevis as a result of E2 exposure. Additional goals of this study, which consisted of three separate experiments, included the standardization of diagnostic terminology and criteria, the validation of statistical methodology, and the establishment of a half maximal effective concentration (EC50) for E2 as defined by an approximately 50% conversion of presumptive genotypic males to phenotypic females. In the first experiment, frogs were exposed to nominal concentrations of 0, 0.2, 1.5, or 6.0,µg/L E2. From these experimental results and those of a subsequent range finding trial, the EC50 for E2 was determined to be approximately 0.2,µg/L. This E2 concentration was utilized in the other two experiments, which were performed at different facilities to confirm the reproducibility of results. Experiments were conducted according to Good Laboratory Practice guidelines, and the histopathologic evaluations were peer reviewed by an independent pathologist. Among the three trials, the histopathological findings that were strongly associated with E2-exposure (p,<,0.001 to 0.0001) included an increase in the proportion of phenotypic females, mixed sex, dilated testis tubules, dividing gonocytes in the testis, and dilated ovarian cavities in phenotypic ovaries. A comparison of the gross and microscopic evaluations suggested that some morphologic changes in the gonads may potentially be missed if studies rely entirely on macroscopic assessment. Environ. Toxicol. Chem. 2010;29:1091,1105. © 2010 SETAC [source]

Comparative effects of pH and Vision® herbicide on two life stages of four anuran amphibian species,

Andrea N. Edginton
Abstract Vision®, a glyphosate-based herbicide containing a 15% (weight:weight) polyethoxylated tallow amine surfactant blend, and the concurrent factor of pH were tested to determine their interactive effects on early life-stage anurans. Ninety-six-hour laboratory static renewal studies, using the embryonic and larval life stages (Gosner 25) of Rana clamitans, R. pipiens, Bufo americanus, and Xenopus laevis, were performed under a central composite rotatable design. Mortality and the prevalence of malformations were modeled using generalized linear models with a profile deviance approach for obtaining confidence intervals. There was a significant (p < 0.05) interaction of pH with Vision concentration in all eight models, such that the toxicity of Vision was amplified by elevated pH. The surfactant is the major toxic component of Vision and is hypothesized, in this study, to be the source of the pH interaction. Larvae of B. americanus and R. clamitans were 1.5 to 3.8 times more sensitive than their corresponding embryos, whereas X. laevis and R. pipiens larvae were 6.8 to 8.9 times more sensitive. At pH values above 7.5, the Vision concentrations expected to kill 50% of the test larvae in 96-h (96-h lethal concentration [LC50]) were predicted to be below the expected environmental concentration (EEC) as calculated by Canadian regulatory authorities. The EEC value represents a worst-case scenario for aerial Vision application and is calculated assuming an application of the maximum label rate (2.1 kg acid equivalents [a.e.]/ha) into a pond 15 cm in depth. The EEC of 1.4 mg a.e./L (4.5 mg/L Vision) was not exceeded by 96-h LC50 values for the embryo test. The larvae of the four species were comparable in sensitivity. Field studies should be completed using the more sensitive larval life stage to test for Vision toxicity at actual environmental concentrations. [source]

Novel regulation of yolk utilization by thyroid hormone in embryos of the direct developing frog Eleutherodactylus coqui

Srikanth Singamsetty
SUMMARY Thyroid hormone (TH) is required for metamorphosis of the long, coiled tadpole gut into the short frog gut. Eleutherodactylus coqui, a direct developing frog, lacks a tadpole. Its embryonic gut is a miniature adult form with a mass of yolky cells, called nutritional endoderm, attached to the small intestine. We tested the TH requirement for gut development in E. coqui. Inhibition of TH synthesis with methimazole arrested gut development in its embryonic form. Embryos treated with methimazole failed to utilize the yolk in their nutritional endoderm, and survived for weeks without further development. Conversely, methimazole and 3,3,,5-tri-iodo- l -thyronine, the active form of TH, stimulated gut development and utilization and disappearance of the nutritional endoderm. In Xenopus laevis, the receptor for TH, TR,, is upregulated in response to TH. Similarly, EcTR,, the E. coqui ortholog, was upregulated by TH in the gut. EcTR, expression was high in the nutritional endoderm, suggesting a direct role for TH in yolk utilization by these cells. An initial step in the breakdown of yolk in X. laevis is acidification of the yolk platelet. E. coqui embryos in methimazole failed to acidify their yolk platelets, but acidification was stimulated by TH indicating its role in an early step of yolk utilization. In addition to a conserved TH role in gut development, a novel regulatory role for TH in yolk utilization has evolved in these direct developers. [source]

Localization of RNAs in oocytes of Eleutherodactylus coqui, a direct developing frog, differs from Xenopus laevis

Yvonne M. Beckham
SummaryEleutherodactylus coqui develops directly on land to a frog. The large 3.5-mm oocyte of E. coqui has enough yolk to allow development without a feeding tadpole. In the smaller Xenopus laevis oocyte, 1.3 mm in diameter, mRNAs involved in germ layer formation, such as VegT and Vg1, are localized to the vegetal cortex of the oocyte. We hypothesized that an animal shift has occurred in the localization of the E. coqui Orthologs of VegT and Vg1 due to the large egg size. Through a combination of degenerate reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE), we cloned 1634 bp of EcVegT and 1377 bp of EcVg1. Northern blot analysis shows that the lengths of these transcripts are 2.5 kb and 1.3 kb, respectively. This result suggests that we have obtained the complete Vg1 transcript, although this transcript has an extremely short 3, untranslated region compared with X. laevis, 256 bp and 1268 bp, respectively. Zygotic expression of EcVegT closely resembles that of VegT, supporting their orthology. Radioactive RT-PCR and in situ hybridization demonstrated the presence of EcVegT and EcVg1 predominantly near the animal pole of the oocyte. RT-PCR showed that the animal blastomeres, formed from the first horizontal cleavage, inherit half of the EcVegT and EcVg1 transcripts, although they contain only about 1% of the embryo volume. Our results indicate major differences between the molecular organization of the eggs of X. laevis and E. coqui. [source]

Patterns of spatial and temporal cranial muscle development in the African clawed frog, Xenopus laevis (Anura: Pipidae)

Janine M. Ziermann
Abstract The African Clawed Toad, Xenopus laevis, has been a major vertebrate model organism for developmental studies for half a century. Because most studies have focused on the early stages of development, this has had the effect that many aspects of organogenesis and later development remain relatively poorly known in this species. In particular, little is known about cranial muscle development even at the level of morphology and histological differentiation of muscle anlagen and muscle fibers. In this study, we document the morphogenesis and histological differentiation of cranial muscles in X. laevis. We provide a detailed account of the timing of development for each of the cranial muscles, and also describe a new muscle, the m. transversus anterior. The cranial musculature of X. laevis larvae generally develops in a rostrocaudal sequence. The first muscles to differentiate are the extrinsic eye muscles. Muscles of the mandibular and hyoid arches develop almost simultaneously, and are followed by the muscles of the branchial arches and the larynx, and by the mm. geniohyoideus and rectus cervicis. Despite the fact that differentiation starts at different stages in the different muscles, most are fully developed at Stage 14. These baseline data on the timing of muscle differentiation in the X. laevis can serve as a foundation for comparative studies of heterochronic changes in cranial muscle development in frogs and other lissamphibians. J. Morphol., 2007. © 2007 Wiley-Liss, Inc. [source]

Roles of Corticotropin-Releasing Factor, Neuropeptide Y and Corticosterone in the Regulation of Food Intake In Xenopus laevis

E. J. Crespi
Abstract In mammals, hypothalamic control of food intake involves counterregulation of appetite by anorexigenic peptides such as corticotropin-releasing factor (CRF), and orexigenic peptides such as neuropeptide Y (NPY). Glucocorticoids also stimulate food intake by inhibiting CRF while facilitating NPY actions. To gain a better understanding of the diversity and evolution of neuroendocrine feeding controls in vertebrates, we analysed the effects of CRF, NPY and glucocorticoids on food intake in juvenile Xenopus laevis. We also analysed brain CRF and NPY mRNA content and plasma corticosterone concentrations in relation to nutritional state. Intracerebroventricular (i.c.v.) injection of ovine CRF suppressed food intake while CRF receptor antagonist ,helical CRF(9,41) significantly increased food intake relative to uninjected and placebo controls. By contrast, i.c.v. injection of frog NPY and short-term corticosterone treatment increased food intake. Semi-quantitative reverse transcription-polymerase chain reaction analyses showed that CRF and NPY mRNA fluctuated with food intake in the brain region containing the mid-posterior hypothalamus, pretectum, and optic tectum: CRF mRNA decreased 6 h after a meal and remained low through 31 days of food deprivation; NPY mRNA content also decreased 6 h after a meal, but increased to prefeeding levels by 24 h. Plasma corticosterone concentration increased 6 h after a meal, returned to prefeeding levels by 24 h, and did not change with prolonged food deprivation. This postprandial increase in plasma corticosterone may be related to the subsequent increase in plasma glucose and body water content that occurs 24 h postfeeding. Overall, our data support the conclusion that, similar to other vertebrates, CRF is anorexigenic while NPY is orexigenic in X. laevis, and CRF secretion modulates food intake in the absence of stress by exerting an inhibitory tone on appetite. Furthermore, the stress axis is activated in response to food intake, but in contrast to mammals and birds is not activated during periods of food deprivation. [source]