KRECH, J.P.*; VANDERGON, T.L.: Photolyase mRNA levels measured by RT-PCR vary significantly among individual eggs and during embryonic stages of development in the Pacific treefrog, Hyla regilla

Recent worldwide declines in amphibian populations have led researchers to explore hypotheses that might explain this phenomenon. One hypothesis suggests that rising levels of ultraviolet (UV) radiation may be impacting amphibian survival in early stages of development. Ultraviolet radiation has been shown to affect the development of many amphibians, but not the Pacific treefrog, Hyla regilla. Pacific treefrogs lay eggs in sunny areas in shallow to medium depth pools where UV exposure may be high. Studies have shown a correlation between the survival of other amphibian larvae and the level of activity of the DNA repair enzyme, photolyase. We examined the levels of photolyase mRNA found in individual H. regilla eggs and embryos at various stages of development. Photolyase mRNA was found in all stages of development from newly laid eggs through hatching, but at varying levels. There was a 16-fold difference in photolyase mRNA expression among individual newly laid eggs. Initial levels are high but decrease significantly from newly laid eggs to day two embryos and increase to significantly higher levels by day four. These data suggest that embryos actively up-regulate the photolyase gene expression in early stages of development perhaps triggered by falling levels of endogenous photolyase mRNA or photolyase protein.