Bearded dragon embryos can use two different sets of genes to grow into a female lizard – one activated by sex chromosomes and the other activated by high temperatures during development. Sarah Whiteley and Arthur Georges from the University of Canberra report these new findings on April 15 in the journal PLOS Genetics.
In many reptiles and fish, the sex of a developing embryo depends on the temperature of the surrounding environment. This phenomenon, known as temperature-dependent sex determination, was discovered in the 1960s, but the molecular details of how it occurs have eluded scientists despite half a century of intensive research. Researchers investigated the biochemical pathways needed to make a female in the new study by studying this phenomenon in bearded dragons. Male bearded dragons have ZZ sex chromosomes, while females have ZW sex chromosomes. However, warm temperatures can replace the ZZ sex chromosomes, causing a male lizard to develop as a female.
Whiteley and Georges compared genes activated during development in bearded dragons with ZW chromosomes compared to ZZ animals exposed to high temperatures. They found that initially different sets of developmental genes are active in the two types of females, but ultimately the pathways converge to produce ovaries. The findings support recent research suggesting that ancient signaling processes inside the cell help translate high temperatures into sex reversal.
The new study is the first to show that there are two ways to produce an ovary in the bearded dragon and bring us closer to understanding how temperature determines sex. The study also identifies several candidate genes potentially involved in determining sex as a function of temperature. These results lay the groundwork for future experiments to determine the role of each gene in sensing temperature and directing sexual development.
Whiteley adds: “” The most exciting part of this work is the discovery that the mechanism involves ubiquitous and highly conserved cellular processes, signaling pathways and epigenetic chromatin modification processes. This new knowledge brings us closer to how temperature determines sex, so it’s a very exciting time to be in biology. “
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