Dale, Jacqueline Kim; (1997) Ventral midline neuroectoderm development along the anteroposterior axis of the vertebrate embryo. Doctoral thesis (Ph.D.), University College London (United Kingdom).

Text Ventral_midline_neuroectoderm_.pdf Download (13MB)

Abstract

During embryonic development the nervous system becomes patterned as a series of inductive interactions occurs, such that distinct cell populations differentiate at different positions within the neural tube. Previous studies have shown that in posterior regions of the central nervous system (CNS), floor plate cells at the ventral midline play an important role in organising adjacent tissue. I have investigated the development of ventral midline neuroectoderm cells along the anteroposterior axis of neurula stage rat and chick embryos and found that they are heterogeneous, posterior ventral midline floor plate cells are distinct from rostral diencephalic ventral midline (RDVM) cells. To understand the basis for this heterogeneity I have examined the spatial relationship of ventral midline cells of the CNS with respect to underlying axial mesodermal cells. Posterior floor plate cells are underlain by notochord, while RDVM cells are underlain by prechordal mesoderm. Previous studies have shown that notochord can induce floor plate cells. I have examined the inductive potential of prechordal mesoderm, and compared it to that of notochord, by analysing the induction of midline markers in neural plate tissue in vitro, using immunocytochemistry or in situ hybridisation techniques. My results reveal that, whereas notochord induces floor plate differentiation, prechordal mesoderm induces RDVM cells. Thus, axial mesoderm at different anteroposterior levels has distinct inducing properties. Recent studies have suggested that expression of the signalling molecule sonic hedgehog (SHH), by notochord cells, mediates its ability to induce floor plate differentiation. Since SHH is also expressed by prechordal mesoderm, I have analysed the requirement for SHH signalling in the differentiation of RDVM cells. Experiments using function-blocking antibodies to SHH-N suggest that SHH expression by prechordal mesoderm is necessary for its inducing activity. Moreover, experiments using purified SHH-N alone, suggest that RDVM cells are induced by a concentration of SHH two-fold higher than that required to induce floor plate cells. However, prechordal mesoderm does not appear to express higher levels of SHH than notochord. Together these studies suggest the presence of a second molecule that is restricted to anterior axial mesoderm and that modulates SHH signalling by prechordal mesoderm.

Download activity - last month

Export as JSONCSVXML

Download activity - last 12 months

Export as CSVJSONXML

Downloads by country - last 12 months

Export as JSONCSVXML

Archive Staff Only

View Item