Meeting Abstract

103.1  Tuesday, Jan. 7 08:15  Regulation of maternally-derived steroids by developing threespined stickleback embryos PAITZ, RT*; BELL, AM; Univ. of Illinois; Univ. of Illinois rpaitz@illinois.edu

Exposure to maternal steroids during embryonic development influences offspring phenotypes. Recent studies have shown that in several vertebrate taxa, embryos are capable of metabolizing maternal steroids, thereby modulating their exposure to steroids that might otherwise interfere with development. We tested the hypothesis that developing embryos modulate their exposure to maternal steroids by metabolizing them in threespined sticklebacks ( Gasterosteus aculeatus ). Levels of progesterone, testosterone, estradiol, and cortisol were quantified in unfertilized eggs and at six stages following fertilization. All four steroids significantly declined within 72 hours of fertilization. To determine whether the drop in steroid levels reflects embryonic metabolism, eggs were dosed with tritiated cortisol. Immersion in water containing tritiated cortisol for 30 min resulted in an increase in radioactivity within fertilized and unfertilized eggs, suggesting that cortisol entered the eggs via diffusion. However, 72 hr later, radioactivity was essentially non-detectable within eggs, suggesting that cortisol was eliminated from the egg. If eggs were maintained in tritiated cortisol for 72 hr, fertilized eggs still did not contain radioactivity. Thin-layer chromatography analysis of the both the eggs and water found no evidence of cortisol metabolites being formed. The decline in endogenous steroid levels paired with the lack of radioactivity in fertilized eggs following a 72 hr immersion suggests that embryos are regulating their endocrine environment by eliminating steroids from the egg rather than via metabolism. This elimination of maternal steroids from the egg may serve to buffer the embryo from the effects of maternal steroids in much the same manner that metabolism does in other vertebrate taxa.