GREWAL, A.K*; SIBLE, J; BELDEN, L.K; Virginia Tech, Blacksburg Va; Virginia Tech, Blacksburg Va; Virginia Tech, Blacksburg Va: Examining developmental responses to environmental insults in early stage amphibian embryos

Amphibian population declines remain a major concern among ecologists and scientists around the world. Some of these declines may occur due to embryonic mortality in response to environmental insults at the earliest stages of development. Studies of the popular laboratory model organism, Xenopus laevis, have revealed that a developmental program of cell suicide (apoptosis) is engaged after the midblastula transition (MBT) in response to a range of environmental factors, including radiation. However, little is known about whether this response is common to all amphibians or represents a developmental strategy that has evolved in specific lineages. In preliminary studies, the embryonic response to ionizing radiation was investigated in three species of frogs: spring peepers (Pseudacris crucifer), grey treefrogs (Hyla versicolor), and green frogs (Rana clamitans). Early embryos from each species were collected from natural ponds and were separated based on their embryonic stages of development: Pre-MBT, MBT, and Post-MBT. All three groups were then divided into an irradiated group (40 Gy) and a control group. Following irradiation, development of the embryos was monitored for two hours. Assays for apoptosis as measured by the activation of apoptotic caspase enzymes was preformed with each set of embryos. No caspase activity was detected in any of the species studied. Thus, apoptosis may not be a common response to irradiation in all amphibians. Studies are underway to determine whether these embryos engage a cell cycle arrest checkpoint prior to the MBT, a program that is not functional in X. laevis until after the MBT. Continuation of these studies will identify the range of responses of amphibian embryos to environmental mutagens.