Research Summary:
One of my research programs focuses on sex determination as a case study in how evolution has produced very different mechanisms for achieving the same end. Here I take advantage of the fact that in many reptiles the sex of the offspring depends on the incubation temperature of the egg, a process known as temperature-dependent sex determination (TSD). One question concerns how the physical stimulus of temperature is transduced into a physiological stimulus that operates ultimately at a molecular level to determine an individual's gonadal sex. In this work I use the red-eared slider turtle as the animal model system. I have demonstrated that sex steroid hormones are the physiological equivalent of incubation temperature, serving as the proximate trigger for male and female sex determination. Temperature appears to accomplish this end by acting on genes coding for steroidogenic enzymes (e.g., steroidogenic factor 1 and aromatase) and sex steroid hormone receptors (e.g., estrogen and androgen receptors), and other transcription factors and signaling molecules (e.g., Sox9, Wnt4, FOXL2, Mis, and Pumilio). Phylogenetic analysis indicates that TSD is the precursor of sex determination by genotypic mechanisms (e.g., sex chromosomes). My other research focuses on epigenetics. There is now evidence that an individual's likelihood of developing health problems involves a combination of that individual's own exposures as well as exposures of ancestors in generations past. This transmission of life experiences across generations represents the newly emerging field of environmental epigenetics.