Recent work indicates that members of the Eph-related receptor tyrosine kinase (RTK) family and their ligands play key roles in neural development. Eph-related receptors are a large subgroup of RTKs that have spatial and cell-type restricted expression in the developing nervous system; several are segmentally expressed in the hindbrain and/or expressed in neurons and their targets. Ligands for Eph-related kinases (LERKs) are a family of polypeptides that are anchored in the plasma membrane, and active only when membrane-bound, and thus mediate contact-dependent signalling between cells. Previous work by members of the network has identified novel members of these receptor and ligand families, analysed developmental expression and binding specificities, mapped regulatory elements, and provided initial insights into function of specific genes. The Sek-1 RTK regulates the segmental identity or restricts the movement of cells between hindbrain segments; preliminary results also suggest a role in correct migration of specific neural crest cells. The LERK RAGS repels retinal axons and has graded expression in the tectum consistent with a role in establishing the retino-tectal map of neuronal connections. Gene knockout reveals the Sek-4 RTK is required for formation of specific axon tracts. Thus, these gene products are involved in two critical aspects of neural development: sharpening of domains with distinct regional identity and establishment of patterns of neuronal connections. We propose to build upon the initial studies by approaches at the molecular, cellular and whole embryo levels that take major steps towards understanding the roles and regulation of these receptors and ligands in the developing nervous system. In addition to using general strategies to uncover gene function, we will study roles in two specific aspects of neural development: patterning of the hindbrain and neural crest, and establishment of the retino-tectal map. The strategies are based upon our complementary expertise and take advantage of the different experimental assets of the mouse, chick and Xenopus systems.
(1) We will screen for further novel members of the LERK family expressed in the nervous system. (2) We will further study the developmental expression of Eph-related RTKs and LERKs. (3) We will analyse regulatory elements that drive segmental expression in the hindbrain. (4) We will characterise receptor-ligand interactions and screen for cytoplasmic binding proteins. (5) We will use in-vitro systems to analyse roles of LERKs in retinal axon pathfinding and neural crest migration. (6) We will carry out gene knockouts of further Eph-related RTKs and analyse cooperative functions by generating double mutants. (7) We will analyse function of Eph-related RTKs and LERKs by overexpression and dominant negative strategies, using transgenic, viral and microinjection approaches in the mouse, chick and Xenopus embryo.
Funding SchemeCSC - Cost-sharing contracts