It is proposed to analyze early neural development in embryos of the flatworm species Macrostomum sp. And Neochildia fusca that can be raised in the lab so that embryos of all stages can be obtained in sufficient numbers year round. Flatworms are generally believed to have retained several primitive features of the common bilaterian ancestor and therefore represent a highly relevant system to study basic developmental processes, such as establishment of the body axes and early neurogenesis. Given the basal phylogenetic position of flatworms the proposed experiments will contribute to our understanding of neural development and the evolution of molecular networks controlling this process.
Our first aim is to reconstruct normal neurogenesis. Questions are the origin and pattern of neural progenitors, their proliferation and migration, and the pattern of axon tracts that emerges as neurons differentiate. These studies will provide a framework of data in which to interpret the expression pattern of genes that will be identified as part of the following aims. Aim 2 is the generation of a cDNA library for both species, which will greatly facilitate the screen for genes involved in neurogenesis. Aim 3 proposes to use a combined PCI and library screen approach to identify cognates of the following highly conserved genes that play fundamental roles in neural development in vertebrates and invertebrate systems: the regionalization genes vnd, ind, msh, Otx/otd, Tailless, lab and cad; the proneural genes ato and ASC, and the neural fate specifying genes of the POU/Homeodomain and LIM/Homeodomain family. Obtaining probes for these genes will serve two purposes. It will furnish early markers for neural precursors used to analyze normal neurogenesis at a satisfactory level of detail. Secondly, the expression pattern of these conserved genes is expected to provide valuable insight into how they function during neural patterning in flatworms. This in turn will aid in reconstructing how the relationship between specific molecular networks and morphogenetic events in neurogenesis arose during evolution.
