Home About us Contact
|
Home About us Contact | ||
|
|
||
Patterning Mechanisms (patterning + mechanism)
Selected AbstractsDiffering strategies for forming the arthropod body plan: Lessons from Dpp, Sog and Delta in the fly Drosophila and spider AchaearaneaDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 4 2008Hiroki Oda In the insect Drosophila embryo, establishment of maternal transcription factor gradients, rather than cell,cell interactions, is fundamental to patterning the embryonic axes. In contrast, in the chelicerate spider embryo, cell,cell interactions are thought to play a crucial role in the development of the embryonic axes. A grafting experiment by Holm using spider eggs resulted in duplication of the embryonic axes, similar to the Spemann's organizer experiment using amphibian eggs. Recent work using the house spider Achaearanea tepidariorum has demonstrated that the homologs of decapentaplegic (dpp), short gastrulation (sog) and Delta, which encode a bone morphogenetic protein (BMP)-type ligand, its antagonist and a Notch ligand, respectively, are required in distinct aspects of axis formation. Achaearanea Dpp appears to function as a symmetry-breaking signal, which could account for Holm's results to some extent. Experimental findings concerning Achaearanea sog and Delta have highlighted differences in the mechanisms underlying ventral and posterior development between Drosophila and Achaearanea. Achaearanea ventral patterning essentially depends on sog function, in contrast to the Drosophila patterning mechanism, which is based on the nuclear gradient of Dorsal. Achaearanea posterior (or opisthosomal) patterning relies on the function of the caudal lobe, which develops from cells surrounding the blastopore through progressive activation of Delta-Notch signaling. In this review, we describe the differing strategies for forming the arthropod body plan in the fly and spider, and provide a perspective towards understanding the relationship between the arthropod and vertebrate body plans. [source] Cell dissociation experiments reveal that positional information operates in the chicken frontonasal massGENESIS: THE JOURNAL OF GENETICS AND DEVELOPMENT, Issue 3 2006Masayoshi Kawakami Abstract In this study we examined the role of cell,cell affinity in patterning the avian frontonasal mass,the facial prominence that forms the prenasal cartilage and premaxillary bone. Reconstituted cell pellets derived from undifferentiated, frontonasal mass mesenchyme were recombined with facial epithelium and grafted to host embryos to continue development. We determined that the cells reestablished a recognizable frontonasal mass pattern and were able to induce egg teeth in overlying ectoderm. Further analysis revealed there were region-specific differences in the cartilage patterns such that central recombinations were more likely to form a straight cartilage rod, whereas lateral mesenchyme pellets were more likely to form complex, branched cartilage patterns. The basis for the pattern differences was that central mesenchyme cells showed preferential clustering in the cartilage condensations in the center of the graft, whereas lateral cells were spread throughout as determined by dye labeling and quail chicken chimeras. The disruption of cell contacts temporarily delayed onset of gene expression but by 48 h both Msx2 and Dlx5 were expressed. Msx2, in particular, had very clear edges to the expression domains and often the pattern of expression correlated with type of cartilage morphology. Together, these data suggest that an important patterning mechanism in the face is the ability of mesenchymal cells to sort out according to position and that Msx2 may help repress chondrogenic potential in the lateral frontonasal mass. genesis 44:105,114, 2006. © 2006 Wiley-Liss, Inc. [source] Vascular regression is required for mesenchymal condensation and chondrogenesis in the developing limbDEVELOPMENTAL DYNAMICS, Issue 3 2001Melinda Yin Abstract Vascular regression occurs during limb mesenchymal cell condensation and chondrogenesis, but it is unclear whether it is required for these processes or is a secondary phenomenon without major regulatory roles. To address this issue, beads presoaked with the potent angiogenic factor vascular endothelial growth factor (VEGF) were implanted in the vicinity of the prospective digit 2 in early chick embryo wing buds and the effects on angiogenesis and digit development were determined over time. We found that VEGF treatment caused a marked local increase in blood vessel number and density. Strikingly, this was accompanied by inhibition of digit 2 development as revealed by lack of expression of chondrogenic transcription factor Sox9 and absence of Alcian blue staining. Vascular distribution and skeletal development in adjacent areas remained largely unaffected. Inhibition of digit formation and excess vascularization were both reversible upon further embryonic growth and dissipation of VEGF activity. When supernumerary digits were induced at the anterior limb margin by retinoic acid treatment, their development was also preceded by vascular regression; interestingly, cotreatment with VEGF inhibited supernumerary digit development as well. Direct exposure of limb mesenchymal cells in micromass cultures to VEGF caused no obvious effects on condensation and chondrogenesis, indicating that VEGF effects are not due to direct action on skeletal cells. Our results are the first to provide evidence that vascular regression is required for mesenchymal condensation and chondrogenesis. A model of how patterning mechanisms and vascular regression may intersect and orchestrate limb skeletogenesis is proposed. © 2001 Wiley-Liss, Inc. [source] The development and evolution of the pharyngeal archesJOURNAL OF ANATOMY, Issue 1-2 2001ANTHONY GRAHAM abstract A muscularised pharynx, with skeletal support, serving the dual functions of feeding and respiration, is a fundamental vertebrate characteristic. Embryologically, the pharyngeal apparatus has its origin in a series of bulges that form on the lateral surface of the embryonic head, the pharyngeal arches, whose development is complex. These structures are composed of a number of disparate embryonic cell types: ectoderm, endoderm, neural crest and mesoderm, whose development must be coordinated to generate the functional adult apparatus. In the past, most studies have emphasised the role played by the neural crest, which generates the skeletal elements of the arches, in directing pharyngeal arch development, but it has also become apparent that the endoderm plays a prominent role in directing arch development. Neural crest cells are not required for arch formation, their regionalisation nor to some extent their sense of identity. Furthermore, the endoderm is the major site of expression of a number of important signalling molecules, and this tissue has been shown to be responsible for promoting the formation of particular components of the arches. Thus vertebrate pharyngeal morphogenesis can now be seen to be a more complex process than was previously believed, and must result from an integration of both neural crest and endodermal patterning mechanisms. Interestingly, this also mirrors the fact that the evolutionary origin of pharyngeal segmentation predates that of the neural crest, which is an exclusively vertebrate characteristic. As such, the evolution of the vertebrate pharynx is also likely to have resulted from an integration between these 2 patterning systems. Alterations in the interplay between neural crest and endodermal patterning are also likely to be responsible for the evolutionary that occurred to the pharyngeal region during subsequent vertebrate evolution. [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] | ||||||||||