MOLE GENOME REVEALS WHY FEMALES HAVE OVARIES AND TESTICLES

Moles are some of the most peculiar animals out there. Largely seen as pests due to their intricate tunnel systems, moles are found on every continent except South American and Antarctica. Despite the pervasive myth, moles aren’t blind, but they do see very poorly and are colorblind and they have an extra finger in their forepaws. But here’s one fact that you probably didn’t know: the females are intersexual. That’s because they simultaneously have both ovarian and testicular tissues — and now scientists think they know why.

Like in any mammal, the key to muscle growth is testosterone. And although female moles are equipped with two X chromosomes, they grow both ovarian and testicular tissues united in one organ known as the ovotestis. This unique organ enables females to grow strong muscles like males, Tibi Puiu wrote for ZME Science. 

“The trick of evolution here is to equalize males and females. For life underground you need strength and due to scarce resources, you have to defend your territory. Females would be here at a dramatic disadvantage, they are less strong and less aggressive. By making females more male-like evolution compensated this disadvantage, moles are unique in that respect. Female hyenas also have very high androgen levels, but I do not think that they have ovotestes,” Prof. Stefan Mundlos, Research Group leader at the Max Planck Institute for Molecular Genetics (MPIMG) and Director at the Institute for Medical Genetics and Human Genetics at Charité – Universitätsmedizin Berlin, told ZME Science. 

Mundlos and colleagues completely sequenced the genome of the Iberian mole (Talpa occidentalis) for the first time. Upon examining the 3D structure of the genome, the scientists found that changes in this structure alter genetic activity. When combined with sequences that encode testicular development, these changes in both genes and “regulatory regions belonging to these genes” stimulate enzymes for male hormone production in the female moles.

The development of sexual organs in mammals typically goes in either of two directions: male or female. But in female moles, their development is somewhat right in the middle. In fact, when comparing the genome of the mole to other animals, including humans, the researchers discovered an inverted genomic segment in a region known to be involved in testicular development. This inversion was responsible for additional DNA segments in the regulatory domain of the FGF9 gene, thereby reorganizing the control and regulation of the gene. The FGF9 gene is responsible for the development of testicular tissue in addition to ovarian tissue in the female moles. Additionally, regulatory sequences are appended to the adrogen production gene CYP17A1, ultimately increasing the production of male sex hormones in the ovotestes of female moles.