The Evolution of Endocrine Function
in Extraembryonic Membranes
I am interested in the evolution of the placenta and extraembryonic membranes. My research questions focus on how these structures evolved as endocrine organs in placental animals. To investigate this evolutionary relationship, I am studying extraembryonic membranes of non-placental amniotes such as alligator, turtle, and chicken to determine if these shared structures play an endocrine role in the development of oviparous avian and reptilian species. The mammalian placenta performs numerous functions crucial for embryonic survival and development including the synthesis, transport, and metabolism of steroid hormones. Yet, the evolution and development of this critical endocrine organ remains poorly understood. A key defining characteristic of all amniotes (mammals, reptiles, and birds) is the formation of extraembryonic membranes during embryonic development: the amnion, chorion, allantois, and vitelline. Two of these membranes, the chorion and allantois fuse and form the chorioallantoic placenta in viviparous (live-bearing) species, or the chorioallantoic membrane in oviparous (egg-laying) species. Recent studies investigating the individual components of the mammalian chorioallantoic placenta have discovered that both extraembryonic membranes and maternal tissues contribute to hormone synthesis and metabolism. Is this trait a mammalian innovation? At present, no studies have examined the endocrine activity of specific cell types in the extraembryonic membranes of oviparous or viviparous non-mammalian amniotes.
Extraembryonic Membranes as a Target of Endocrine Disruption
As amniotes, mammals, reptiles, and birds share common extraembryonic membranes that are critical for embryonic survival and development. While the placenta and accompanying extraembryonic membranes of eutherian mammals are classified as an endocrine organ, the endocrine role of extraembryonic membranes in birds and reptiles is relatively unknown. Despite many studies demonstrating the presence of endocrine disrupting contaminants in the chorioallantoic membrane of reptilian and avian species, extraembryonic membranes have not been established as targets of endocrine disruption. As such, we are investigating the endocrine role of extraembryonic membranes in oviparous amniotes to better understand the impact of environmental contaminants on these tissues. as an indicator of endocrine function, we examined steroidogenesis in the chicken (Gallus gallus) chorioallantoic membrane. Steroid enzyme mRNA expression, protein localization, and hormone synthesis have been examined using quantitative real-time RT-PCR (QPCR), in situ hybridization, immunohistochemistry, and explant tissue culture. Our work suggests that the chick chorioallantoic membrane (CAM) has endocrine capability and further indicate that endocrine disrupting contaminants could be interfering with development through a novel mechanism in birds and reptiles; via the endocrine pathway of the extraembryonic membranes themselves