Meeting Abstract

S5-2.2  Friday, Jan. 4  Toward a Dynamic Model of Yolk Steroid Deposition and Utilization MOORE, Michael*; JOHNSTON, Gwynne; Arizona State University; Arizona State University

The discovery by Schwabl that maternal steroid hormones are transferred to the egg yolk and have effects on offspring phenotype revealed a new pathway for non-genetic maternal effects. The initial model proposed relied on passive transfer. The thinking was that steroids passively entered the lipophillic yolk during vitellogenesis and then were sequestered in the yolk until passively delivered to the embryo as the yolk was used. Subsequent studies have revealed that the system is much more dynamic than that. In this talk we explore questions about how dynamic the system really is. Is transfer of maternal steroids to the yolk passive or actively regulated? At what stages of the maternal reproductive cycle are steroids transferred? During reproduction, how dynamic are yolk steroid levels? Especially in the case of potentially deleterious steroids (such as androgens in females or glucocorticoids), once deposited can the steroids come out of the yolk over time? Can they be metabolized by the yolk? By the embryo? During incubation, how much do steroid levels in the yolk change? Can steroids diffuse from the yolk to the embryo prior to yolk utilization? Does the embryo contribute to yolk steroid levels as it develops? Finally, if some yolk steroids have beneficial effects on offspring phenotype, why has natural selection not caused embryos to produce these beneficial steroids directly? We believe that comprehensive answers to questions like these will eventually allow us to generate a much more accurate and complete model of yolk steroid transfer and utilization, and that this model will be much more dynamic and active than the model initially proposed.