# Specificity of Key Sex Determination Genes in a Mammal with Ovotestes: The European Mole Talpa europaea

## TL;DR

This study explores how the European mole develops mixed male and female gonads by analyzing specific genes involved in sex determination.

## Contribution

The paper is the first to analyze the structure of key sex determination genes in the European mole, revealing unusual features in the Sry gene.

## Key findings

- The Sry gene in European moles has an unusual two-exon structure with a large intron containing a LINE retroposon.
- Double peaks in DNA sequencing suggest possible multiple copies of the Sry gene.
- The Rspo1 gene in moles has five exons and is similar to that in T. occidentalis.

## Abstract

Simple Summary: The genetics of sex determination in mammals has been studied mainly in humans and mice. However, some animals develop in other ways, like moles, whose females have mixed gonads that combine two parts: male (testes) and female (ovaries). In other animals and humans, such gonads are known but they are formed due to pathologies and disturb the ability to reproduce up to sterility. We first characterized the structural features of some genes and hypothesized that changes in the structure of the key gene for testis development Sry may be responsible for the ovotestes formation in European moles. Here, we considered the presence of the intron-containing fragments of the retroposon and presumably the existing copies of the Sry gene along with features of the placenta structure.

Here, for the first time, the structure of genes involved in sex determination in mammals (full Sry and partial Rspo1, Eif2s3x, and Eif2s3y) was analyzed for the European mole Talpa europaea with ovotestes in females. We confirmed male-specificity for Eif2s3y and Sry. Five exons were revealed for Rspo1 and the deep similarity with the structure of this gene in T. occidentalis was proved. The most intriguing result was obtained for the Sry gene, which, in placental mammals, initiates male development. We described two exons for this canonically single-exon gene: the first (initial) exon is only 15 bp while the second exon includes 450 bp. The exons are divided by an extended intron of about 1894 bp, including the fragment of the LINE retroposon. Moreover, in chromatogram fragments, which correspond to intron and DNA areas, flanking both exons, we revealed double peaks, similar to heterozygous nucleotide sites of autosomal genes. This may indicate the existence of two or more copies of the Sry gene. Proof of copies requires an additional in-depth study. We hypothesize that unusual structure and possible supernumerary copies of Sry may be involved in ovotestes formation.