# Transcriptome analysis reveals the sex-switching mechanism of juvenile hermaphroditism in silver pomfret (Pampus argenteus)

## TL;DR

This study explores how silver pomfret switch from female to male during development, revealing the role of hormones and gene activity in this process.

## Contribution

The study identifies specific genes and metabolic pathways involved in sex-switching during juvenile hermaphroditism in silver pomfret.

## Key findings

- Oocyte apoptosis and testis development occur between 90 and 120 dph in silver pomfret.
- Androgens like 11-KT and estrogen E2 regulate sex differentiation through gene expression.
- Ovarian development involves lipid metabolism and follicular selection processes.

## Abstract

Our previous study on silver pomfret (Pampus argenteus) demonstrated that all gonads initially develop into ovaries by 60 days post-hatch (dph). Between 80 and 120 dph, some oocytes undergo apoptosis, resulting in the development of testes and a transient hermaphroditic stage. This observation indicates a complex molecular mechanism underlying sex differentiation in this species.

Gonadal samples were collected at 90 dph, 120 dph, and 150 dph, with sex identification performed by HE staining and transcriptome sequencing. Morphological traits, including body length and weight, were measured to evaluate sexual size dimorphism. Candidate genes related to with sex differentiation were identified through differential gene expression analysis and feature selection methods, followed by gene set enrichment analysis to identify potential molecular pathways. Heatmaps were generated to visualize gene expression patterns across developmental stages and samples. Sex hormones concentrations were measured using commercial assay kits to assess their role in gonadal differentiation. RT-qPCR validated the sequencing results, while immunofluorescence (IF) examined the expression of related genes in testes and ovaries.

Histological and transcriptomic analyses identified the period between 90 and 120 dph as critical for sex differentiation in silver pomfret. At 90 dph, apoptotic signals trigger the apoptosis of early-stage oocytes. During this period, both testis-preferential and ovary-preferential genes exhibit high expression, leading to spermatogonia differentiation and the emergence of a juvenile hermaphroditic stage. The study established that androgens 11-KT and estrogen E2 regulate sex differentiation through modulation of related gene expression, with 11-KT serving a crucial role. This process involved significant enrichment of the steroid hormone biosynthesis pathway and the metabolism of xenobiotics by cytochrome P450 in the testes. Ovarian development is characterized by fatty acid metabolism and PPAR signaling pathway activation, along with energy metabolism pathways including the citrate cycle (TCA cycle) and cell degradation processes, such as lysosome activity and ubiquitin-mediated proteolysis, suggesting that ovarian development encompasses lipid accumulation and follicular selection.

This investigation illuminates the molecular processes underlying this distinctive pattern of gonadal differentiation, providing novel insights into sex differentiation in fish exhibiting a juvenile hermaphroditic stage.

The online version contains supplementary material available at 10.1186/s13293-025-00736-1.

Juvenile hermaphroditism represents an uncommon sex differentiation pattern, characterized by testis differentiation following oocyte apoptosis and a juvenile hermaphroditic phase. This study reveals that metabolic changes and increased expression of testis differentiation-related genes (dmrt1, wt1, gsdf, ect) contribute significantly to oocyte apoptosis and juvenile hermaphroditism in 90 dph male fish. The research demonstrates that sex hormones 11-KT and E2 influence gonadal differentiation through regulation of sex differentiation-related gene expression, with 11-KT serving a central role. The simultaneous elevated expression of 11-KT and E2 potentially explains the sustained juvenile hermaphroditic phase in certain fish. Conversely, ovarian development encompasses energy accumulation and oocyte natural selection. This investigation provides comprehensive understanding of sex-switching mechanisms in juvenile hermaphroditic fish, establishing groundwork for future research into this distinctive gonadal differentiation pattern.

The online version contains supplementary material available at 10.1186/s13293-025-00736-1.

Histological evidence of sexual differentiation was examined in silver pomfret.

Metabolic changes and the expression of apoptotic signals are the primary causes of early-stage oocyte apoptosis.

The simultaneous high expression of testis and ovary differentiation-related genes led to the formation of juvenile hermaphroditism.

Sex hormones play a crucial role in regulating the sex differentiation of silver pomfret.

The online version contains supplementary material available at 10.1186/s13293-025-00736-1.