RUI: The Role of Ret Signaling in Nephric Duct Migration

Rider University, Lawrenceville NJ

Investigators

Abstract

In mammals, it has been demonstrated that glial-derived neurotrophic factor (GDNF) signaling through Ret, a transmembrane protein tyrosine kinase, is required for proper development of the metanephros - the terminal kidney of amniote vertebrates. Our interest in the Ret signaling system was piqued by several observations indicating it may also operate at much earlier steps in renal development: Ret and other components of its signaling complex can be detected in intermediate mesoderm and in nephric duct (ND) epithelia well before formation of the metanephros. In addition, components of the Ret system have been identified in developing excretory systems of fish, frogs and salamanders. These vertebrates don't make a metanephros; their terminal kidney is the mesonephros. So, what function might Ret signaling perform during early excretory system development? The observation that both enteric enervation and kidney development fail in GDNF or Ret knockout mice, provides an important clue. Both the hindbrain neural crest, which generates the enteric nervous system, and the ND, the Ret expressing component of the developing excretory system, must migrate to their final destinations in the embryo by following guidance information distributed along their respective pathways. Furthermore, our experiments in axolotl embryos have revealed that when neural crest of the head is transplanted to the flank of a donor embryo it follows the same trajectory a transplanted ND would take. Thus, the two tissues which require Ret function during development - ND and hindbrain neural crest - can also interpret the same guidance information on the flank. From these studies, we formulated the hypothesis that Ret signaling functions in either promoting or guiding ND cell migration. Dr. Drawbridge's preliminary data reveals that components of the Ret signaling system are present on the migrating ND of axolotl embryos. Furthermore, we have evidence that ectopic application of GDNF in vivo can redirect migration of the axolotl ND. During the course of this project, she will (1) determine the spatio-temporal expression patterns of components of the Ret signaling system via in situ hybridization and immunocytochemistry; (2) determine whether Ret signaling is sufficient for directing ND migration by ectopic placement of GDNF in vivo; and (3) determine whether Ret signaling is necessary for ND pathfinding and motility by performing antibody inhibition and/or chromophore-assisted laser inactivation (CALI) experiments to knockout components of the Ret system during ND migration. These data will provide a rigorous test of the hypothesis that Ret signaling functions in ND pathfinding and motility, as well as provide information about Ret signaling and evolution of the vertebrate excretory system.