The Evolution of Endocrine Extraembryonic Membranes
Lori Cruze, Medical University of South Carolina
16 Nov 2012
As amniotes, mammals, reptiles, and birds share common extraembryonic membranes, which function in nutrient and gas exchange, waste removal and shock absorption. In viviparous (live-bearing) amniotes, extraembryonic membranes and maternal uterine tissues alike contribute to the placenta, an endocrine organ that synthesizes, transports, and metabolizes hormones essential for embryonic development. Surprisingly, the endocrine role of extraembryonic membranes has not been investigated in oviparous (egg-laying) amniotes despite similarities in their basic structure, function, and shared evolutionary ancestry. To begin addressing this question, we examined steroidogenesis and steroid hormone signaling in the chorioallantoic membrane (CAM) of chicken, American alligator, and Florida red-belly slider, species that represent three major amniote lineages, which reproduce strictly by oviparity. Collectively, our data indicate that the oviparous CAM is steroidogenic and has steroid hormone signaling capability. This work indicates that endocrine activity of extraembryonic membranes is not a novel characteristic of placental amniotes. Further, we hypothesize that endocrine activity of extraembryonic membranes might be an evolutionarily conserved characteristic of amniotes, which suggests an additional unifying characteristic of amniotes and has implications for evolutionary reproductive biology.
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