Australasian Science: Australia's authority on science since 1938

“Alternative RNA” Switches Reptile Gender

Many reptiles don’t have sex chromosomes like humans and other mammals. Instead, their gender is set by the temperature at which their eggs are incubated. Researchers studying Australia’s bearded dragon lizard have now discovered the master switch by which this occurs: a temperature-sensitive molecular signature in a family of genes that control the expression of many other genes. The findings have been published in Science Advances.

“The dragon lizard has sex chromosomes similar to birds that determine sex at normal temperatures. But at high temperatures, embryos with male sex chromosomes reverse sex and hatch as females,” said lead author Dr Clare Holleley of CSIRO and The University of Canberra’s Institute for Applied Ecology.

“Our work looked at all the messenger RNA molecules that were made by dragons that were functional females, even though genetically they were male. We compared these molecules with RNA made by normal males and normal females,” Holleley explained.

Co-lead author Ira Deveson, a PhD student from the Garvan Institute of Medical Research, said this line of inquiry uncovered a unique difference. “We found that sex-reversed females produce a unique message, with their RNA retaining a chunk of sequence that is normally spliced out of the message. This means that the gene won’t make a normal protein. Somehow that throws a spanner in the works when it comes to making a male,” he said.

Even more surprising was the finding that the same gene retains this chunk in crocodiles and turtles. This suggests that temperature-determined sex depends on this “alternative RNA” in all reptiles.

“We think our discovery will spark a whole new approach to understanding how to make males and females – in all animals,” added La Trobe University Distinguished Professor and University of Canberra Adjunct Professor Jenny Graves, who collaborated on the research. “There are many different ways males and females are determined throughout nature. This breakthrough moves us all a step closer to understanding the whole picture of sex.”