# Expression of Insl3 Protein in Adult Danio rerio

## TL;DR

This study explores the expression of the Insl3 protein in zebrafish testes and its role in reproduction.

## Contribution

The study reveals an autocrine and paracrine function of Insl3 in zebrafish testis and suggests a conserved mechanism of action across vertebrates.

## Key findings

- Insl3 is expressed in Leydig and germ cells of zebrafish testes.
- Insl3 and Rxfp2 share conserved amino acid residues across vertebrates.
- The hormone's function in zebrafish testis involves autocrine and paracrine signaling.

## Abstract

Insulin-like peptide 3 (INSL3) is a biomarker for Leydig cells in the testes of vertebrates, and it is principally involved in spermatogenesis through specific binding with the RXFP2 receptor. This study reports the insl3 gene transcript and the Insl3 prepropeptide expression in both non-reproductive and reproductive tissues of Danio rerio. An immunohistochemistry analysis shows that the hormone is present at a low level in the Leydig cells and germ cells at all stages of Danio rerio testis differentiation. Considering that the insl3 gene is transcribed in Leydig cells, our results highlight an autocrine and paracrine function of this hormone in the Danio rerio testis, adding new information on the Insl3 mode of action in reproduction. We also show that Insl3 and Rxfp2 belonging to Danio rerio and other vertebrate species share most of the amino acid residues involved in the ligand–receptor interaction and activation, suggesting a conserved mechanism of action during vertebrate evolution.