Disentangling epigenetics and sex determination

For the first time researchers show how environmental temperature is converted into an epigenetic signal that might control sex determination in reptiles.

The bearded dragon has an exceptional sex determination system. Not only do dragons have sex-chromosomes, but they also exhibit male-to-female sex-reversal when embryos are incubated at high temperatures. A study led by IAE Adjunct Dr Clare Holleley and Ira Deveson, from the Garvan Institute of Medical Research, on the Australian Central Bearded Dragon (Pogona vitticeps) identified transcriptional signatures of temperature and sexual development.

“Temperature influences sex in many reptiles, but the mechanism underlying this phenomenon has eluded researchers for fifty years. Our research identifies the first strong candidate mechanism by which temperature could be converted into a molecular signal to direct male and female development,” says Dr Holleley.

Their study identified a link between epigenetic regulation and external temperature controlling sexual differentiation. Two genes from the Jumonji family produced unique alternative transcripts with retained intron sequences in female dragons that have been sex-reversed by temperature, but not in normal chromosomal females or males. The alternative splicing event is predicted to disrupt the normal function of these two genes, or possibly generate a completely new function.

“We made the exciting discovery that temperature influences genes from the Jumonji family. These are key regulatory genes that control the expression of other genes when the embryo is developing inside the egg.  We know from other mammalian studies, that members of the Jumonji family can directly control sex determination genes (e.g. SRY). So we may have illuminated an interesting parallel in reptiles,” says Dr Holleley.

It is now increasingly apparent that intron retention is an important mode of gene regulation. The link between intron retention and this family of epigenetic factors may have far-reaching implications for our understanding of gene-environment interactions and development.

You can find out more about this exciting discovery from their article: Differential intron retention in Jumonji chromatin modifier genes is implicated in reptile temperature-dependent sex determination, published in Science Advances.