Graduation Term

2019

Degree Name

Master of Science (MS)

Department

School of Biological Sciences

Committee Chair

Ryan T. Paitz

Committee Member

Rachel M. Bowden

Abstract

Maternal steroids transferred to eggs can elicit permanent effects on various aspects of offspring phenotype. Although, testosterone was thought to be a key mediator of maternal effects in birds, we now know that vertebrate embryos actively regulate their exposure to maternal testosterone through steroid metabolism, suggesting testosterone metabolites may elicit the observed phenotypic effects. To address the role steroid metabolism plays in mediating yolk testosterone effects, we used European starling (Sturnus vulgaris) eggs to characterize the timing of testosterone metabolism and determine whether etiocholanolone, a prominent testosterone metabolite in avian embryos, is capable of influencing early embryonic development. Tritiated testosterone (3H-T) was injected into freshly laid eggs to characterize the movement and metabolism during early development. Varying levels of etiocholanolone were also injected into starling eggs and incubated for either three or five days to test whether etiocholanolone influences the early growth of embryonic tissues. Interestingly, the conversion of testosterone to etiocholanolone is initiated within the first 12 hours of embryonic development, but the increase in etiocholanolone is transient; etiocholanolone is also subject to metabolism, suggesting embryos are exposed to elevated levels of etiocholanolone for a short period of time in early development. We found exogenous etiocholanolone manipulation had no significant effect on the growth rate of the embryos or extra-embryonic membranes early in development. These findings suggest the conversion of yolk testosterone to etiocholanolone may be an inactivation pathway that buffers the embryo from the effects of maternal steroids and the observed effects of yolk testosterone may be modulated by the fraction of testosterone that escapes metabolism.

Access Type

Thesis-Open Access

DOI

http://doi.org/10.30707/ETD2019.Campbell.N

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