New research has explored the dynamic genetic changes taking place during the bluehead wrasse’s sex change.

The bluehead wrasse social group consists of one dominant blue male fish and a harem of yellow females. However, when the dominant male is removed from the group the largest female immediately undergoes a full sex change and becomes the new alpha male. The female’s behaviour quickly changes, and the ovaries convert into a fully functioning testis within 10 days.

To understand the genetic changes taking place, female bluehead wrasse’s brains and gonads were investigated at various timeframes of the sex change process. Limited differences were observed in the brain but large changes in gene expression were observed in the gonads.

It was revealed that a stress response triggers the initial transformation, as cortisol production and signalling increased in the early transition stages. This triggers a downregulation of female associated genes and upregulation of protein kinases to reach the intermediate transition stage.

At the intermediate stage it was expected that there would be both male and female differentiated tissue in the gonads, but that the proportion of male tissue would increase further along the transition. However, it was found that there was instead a unique transitional cell type that resembled undifferentiated stem cells.

Gene expression in the intermediate region was also different to the genes expressed in both distinctly female and distinctly male fish. The genes expressed promoted innate immunity, cell proliferation and protein catabolism, all of which are characteristic of the dynamic disassembly and rebuilding of the gonads. Researchers also found that many of the changes were regulated by epigenetics. Interestingly, the entire intermediate stage was found to strongly resemble the early developmental stages of mammals.

Understanding sex changes can aid researchers in both understanding early development and epigenetic mechanisms.