The two major aspects of germ cell development examined in this proposal are: a) oogenesis per se (the transformation of oogonia into oocytes) and early oocyte development and b) the initiation of vitellogenesis. Both the pipefish, Syngnathus scovelli, and the seahorse, Hippocampus erectus, will be used because of the unique arrangement of developing follicles in their ovaries, where a sequential pattern of oocyte development is observed. This pattern begins on one side of the ovary and a gradient of follicles of increasing developmental age extends to the opposite side. Little is known about the regulation of early events of oocyte formation in embryonic ovaries of most vertebrates and the absence of very early stage oocytes in adult ovaries in many species. The presence of germinal tissue (oogonia and meiotic oocytes) in a restricted but easily accessible region of syngnathan ovaries makes these teleost ideal for studying early germ cell events and their hormonal regulation in an adult vertebrate. The extent of oogonial proliferation and the time for progression of oocytes through meiosis will be determined in vivo. Dr. Selman will then attempt to duplicate both processes in vitro by examining the influence of various hormones and co- cultured tissues on oogonial division and the progression of oocytes from leptotene up to diplotene stages. The process of follicle formation will also be examined. Dr. Selman intends to characterize the transition from previtellogenesis to vitellogenesis in syngnathans and will address the cellular mechanism(s) responsible for the initiation of vitellogenesis. For this she will examine follicular vascularization, vitellogenin accessibility, the ontogeny of functional vitellogenin rectors and the intraoocytic fate of internalized vitellogenin. Studies will be performed both in vivo and in vitro to determine whether a cessation of normal lysosomal synthesis and/or activity or a modification of the endocytic pathway distinguishes previtellogenic form vitellogenic oocytes.
