# Sex-specific gonadal transcriptome during early development of Siberian sturgeon

## TL;DR

This study identifies sex-specific genes in early gonad development of Siberian sturgeon, revealing new candidates for male and female differentiation.

## Contribution

The first transcriptomic analysis of undifferentiated gonads in genetically sexed Siberian sturgeon reveals both established and newly identified genes activated near the onset of sex differentiation.

## Key findings

- Female-biased genes include estrogen-related genes and novel candidates not previously linked to estradiol.
- Male differentiation involves the known gene tbx1 and new candidates like plin1 and nrxn3.
- No sex-biased genes related to androgen production were identified in males.

## Abstract

Sex determination and differentiation are complex processes shaped by a wide variety of molecular factors. In contrast to teleost species, many aspects of these processes remain poorly understood in basal non-teleost fishes such as the Siberian sturgeon (Acipenser baerii). Genetic sexing of this important aquaculture species now enables studies of undifferentiated males and females to identify factors involved in early sexual differentiation.

Twelve undifferentiated Siberian sturgeon (six males, six females) were genetically sexed at 2.5 months of age. High-quality RNA was extracted from gonad samples, and transcriptomes were assembled using a reference dataset. Bioinformatic analyses were performed to identify sex-biased genes through differential expression analysis, Gene Ontology (GO) enriched terms, and classification of coding and non-coding sequences.

Genes potentially associated with sex differentiation were identified in gonadal tissue. Female-biased genes included classical estrogens production genes (hsd17b1, cyp19a1, foxl2) and immediate early response genes known to react rapidly to estrogens (jun-b, c-fos, egr1), as well as genes not previously linked to estradiol (di-ras2, ier2, aanat). The enriched Gene Ontology results suggested that melatonin signaling and hypothalamic pathways may also contribute to female differentiation. In males, the well-known factor tbx1 was upregulated along with novel candidates (plin1, nrxn3, chs2, mmp9). No sex-biased genes related to androgen production were identified.

By 2.5 months of age, sex-specific gonadal differences are already apparent in Siberian sturgeon. This study highlights the estrogen response pathway, including immediate early response genes described here for the first time in the context of fish gonadal differentiation. At the same time, an estrogen-independent ovarian pathway cannot be ruled out. Male differentiation appears to involve tbx1 together with new candidates for testis regulation in the absence of sex-biased androgen-producing enzymes. These novel genes expressed near the onset of sex differentiation merit further investigation.

The online version contains supplementary material available at 10.1186/s13293-025-00810-8.

The first transcriptomic analysis of undifferentiated gonads in genetically sexed Siberian sturgeon reveals both established and newly identified genes activated near the onset of sex differentiation.

Ovarian differentiation involves both estrogen-dependent and estrogen-independent factors.

A novel set of male-biased genes expands the list of potential contributors to testis differentiation in fish.

The online version contains supplementary material available at 10.1186/s13293-025-00810-8.

In animals, the development of ovaries or testes is a key step in their growth. This process involves many complex biological events. For many modern fish species, scientists already know a great deal about how this happens. However, in ancient fish like the Siberian sturgeon, much less is understood. Our goal was to explore how this process begins during early development in this species.

We studied young sturgeons at two and a half months of age, before visible differences in their gonads appeared. Their sex was identified using genetic markers. We examined six males and six females, analyzing the activity of thousands of genes in their gonads using advanced sequencing technologies to see which genes were active early in sexual development.

The female fish showed activation of some genes that respond rapidly to the hormone estrogen, alongside the well-known genes that help produce estrogens. We also detected activation of other genes that do not appear to depend directly on estrogens. These results suggest that additional signals, such as the hormone melatonin and possibly brain-derived factors — may also influence female gonadal development.

In males, we identified new candidate genes that may play important roles in testis development. Interestingly, only one previously known male-related gene was activated, and we found no activation of genes involved in production of male hormones (androgens).

By 2.5 months of age, sturgeons are already beginning to show sex-specific differences in their gonads. Our study uncovered new candidate genes that could explain how sex differentiation occurs in sturgeon, providing a foundation for future research on this ancient fish.

The online version contains supplementary material available at 10.1186/s13293-025-00810-8.