The findings are detailed in an international study recently published that opens up new perspectives on the evolutionary flexibility of reproduction in the animal kingdom.
An international study involving the Institute of Marine Sciences (ICM-CSIC) has revealed a previously unknown evolutionary mechanism in the reproductive biology of vertebrates. The study, recently published in the prestigious journal Science Advances, shows that a gene crucial for the formation of females has been modified throughout evolution to become the master gene that triggers male development.
Until now, isolated cases were known where certain genes involved in the differentiation of one sex could partially modify their expression to intervene in the differentiation of the opposite sex. However, this research provides the first evidence in vertebrates where a functional component of the female pathway acquires the ability to completely govern the opposite process, acting as a master regulator of masculinity.
The gene involved has been identified as figlaY, located on the Y chromosome of the Mozambique tilapia (Oreochromis mossambicus). In the vast majority of vertebrates, the original homologous gene, called figla, is an essential transcription factor for oocyte development in females. In this fish species, the gene underwent a process of genetic duplication and truncation, subsequently relocating to the male chromosome.
The specific contribution of the ICM-CSIC team, led by researcher Francesc Piferrer, involved the conception and supervision of the study, as well as the interpretation of results and contribution to the drafting of the manuscript.
The role of transposons or "jumping genes"
Genomic analysis revealed that transposons—also known as "jumping genes" due to their nature as mobile elements within the genome—were responsible for this structural reorganisation. These elements altered the regulatory sequence of the duplicated gene, giving it a dominant-negative function. This modification directly blocks the development of the female pathway and imperatively promotes the formation of testes.
To experimentally validate the role of this gene, the research team applied CRISPR-Cas9 gene-editing technology to inhibit the expression of figlaY in genetically male (XY) embryos. The specimens in which the gene was deactivated developed fully functional ovaries and became females, confirming that this factor is both indispensable and sufficient to determine the male sex in this species.
Implications for biology and aquaculture
The discovery highlights that sex determination in vertebrates possesses a far greater molecular flexibility than previously described, proving that gene networks can recruit elements from alternative pathways to establish new regulatory systems.
Aside from its scientific relevance in the field of evolution, the finding is of significant practical interest to the aquaculture sector. Tilapia is one of the most widely farmed fish globally, and the production of single-sex populations is a common practice to optimise the yields of this food resource.