P1.88 Wednesday, Jan. 4 A mechanistic understanding of yolk steroid effects PAITZ, RT*; BOWDEN, RM; Illinois St. University; Illinois St. University email@example.com
In oviparous vertebrates, egg yolks contain numerous steroids of maternal origin at the time of oviposition and manipulations of these yolk steroids have been shown to influence the phenotype of the resulting offspring. To date, most research has focused on the phenotypic effects of these maternal steroids while less attention has been paid to the underlying mechanisms. In this poster, we present a series of experiments conducted in red-eared sliders (Trachemys scripta) that characterize the physiological mechanisms underlying yolk steroid effects. First, endogenous levels of yolk progesterone (P), testosterone (T), and estradiol (E2) decline rapidly during the early stages of embryonic development. Second, tritiated P, T, and E2 are all converted to water-soluble metabolites during these same early stages. Using E2 as an example, we demonstrate that these water-soluble metabolites are estrogen sulfates and that they primarily reside outside of the embryo in the extraembryonic fluids and yolk for most of development. During the final stages of development, we observe a decline in levels of E2 metabolites in the extraembryonic fluids and yolks and an increase in the levels found in the embryo. Finally, we show that exogenous estradiol sulfate is capable of inducing sex reversal in embryos suggesting that these sulfonated steroids can produce phenotypic effects. Together, these data illustrate the complex nature of the mechanisms underlying yolk steroid effects and highlight the importance of addressing embryonic processes when attempting to interpret the evolutionary consequences of maternal steroids.