![]() The initial dorsoventral patterning of the neural tube exemplifies a classical induction from neighboring tissue. Similarly, Wnt and Bmp signaling is active from the dorsal pole of the neural tube and from the superficial ectoderm. The shh gradient in turn induces a gradient of GliA and GliB transcriptional factor activity, which together with Sox2 participates in the formation of distinct gene expression domains. Sonic hedgehog (shh) forms a ventral-to-dorsal gradient and is expressed in the floor plate and the notochord. The unique gene expression in the progenitor domains is suggested to be the result of fine-tuned signaling activities related to gradients of secreted morphogens. Differences are derived from unique combinatorial gene expression in the progenitor domains of the neural tube, which leads to development of distinct types of neurons. The brain and spinal cord display characteristic functional and structural differences along the dorsoventral axis. Furthermore, we propose that the mode of the floor plate induction adapts to the variant topography of interacting tissues during gastrulation and notochord formation and thereby reveals evolutionary plasticity of early embryonic induction. laevis and chick embryos may be initially induced by planar interaction within the ectoderm or epiblast. Our results indicate that the floor plate in X. Intriguingly, this alternative sequence of domain induction is related to the asymmetrical morphogenesis of the primitive node and other axial organs in the chick. laevis embryos are roughly compatible with the classical view of “ventral to dorsal induction” of the floor plate, the early shh expression in the chick floor plate challenges this model. While shh expression patterns in rabbit and X. laevis, shh is expressed at the beginning of gastrulation in a distinct area dorsal to the dorsal blastopore lip and adjacent to the prospective neuroectoderm, whereas the floor plate expresses shh at the end of gastrulation. ![]() Neither indian hedgehog nor desert hedgehog are expressed in these midline structures although mRNA of both genes was detected in other structures of the early chick embryo. Our analysis reveals a markedly divergent pattern within these vertebrates: whereas in the rabbit shh is first expressed in the notochord and its floor plate domain is then induced during subsequent somitogenesis stages, in the chick embryo shh is expressed in the prospective neuroectoderm prior to the notochord formation and, interestingly, prior to mesoderm immigration. We therefore studied the expression dynamics of shh in rabbit, chicken and Xenopus laevis embryos (as well as indian hedgehog and desert hedgehog as possible alternative functional candidates in the chicken). However, reported data are inconsistent and the spatiotemporal development of the relevant shh expression domains has not been studied in detail. This activity has been attributed to sonic hedgehog (shh) signaling, which originates in the notochord, forms a gradient, and autoinduces shh expression in the floor plate. The notochord has organizer properties and is required for floor plate induction and dorsoventral patterning of the neural tube.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |