# Androgen Receptor Expression Governs the Seasonal Inhibition of Testicular Development and Subsequent Recovery in Rattus norvegicus caraco

## TL;DR

This study shows that androgen receptor expression controls seasonal changes in testicular development in a subspecies of brown rats from Northeast China.

## Contribution

The study identifies androgen receptor (Ar) expression as a key regulator of seasonal testicular development in Rattus norvegicus caraco.

## Key findings

- Ar expression increases during the nonbreeding season in rats with small testes and specific body weights.
- Sertoli cell maturation depends on upregulated Ar expression, regardless of age or environmental conditions.
- Suppression of Ar expression hinders testicular development and reduces spermatogenesis.

## Abstract

This study explores the role of androgen receptor (AR) in regulating testicular development in Rattus norvegicus caraco, a subspecies of brown rats from Northeast China with seasonal breeding patterns. The research found that Ar expression increases during the nonbreeding season, particularly in rats with small testes and body weights between 80 and 100 g. The maturation of Sertoli cells relies on the upregulation of Ar expression, regardless of age or environmental conditions. When Ar expression was suppressed, testicular development was hindered, leading to decreased spermatogenesis and slower testis growth. These results suggest that brown rats can modulate testicular development by regulating Ar expression as a response to seasonal environmental changes.

Commonly in seasonal breeding animals, testicular development is inhibited prior to Sertoli cell maturation when environmental conditions become unfavorable, with recovery occurring once conditions improve. However, the precise molecular mechanisms governing this process remain unclear. We investigated the role of androgen receptor (AR) in the seasonal regulation of testicular development in a wild population of Rattus norvegicus caraco, a subspecies of brown rats in Northeast China residing in high-latitude regions, known for its seasonal reproductive patterns. Our results revealed a significant increase in Ar mRNA expression in wild rats with small testes less than 0.2 g and body weights ranging between 80 and 100 g during the nonbreeding season. Further examinations of Ar expression in the testicular development of R. n. caraco in the laboratory under different day lengths and temperatures that simulating breeding and nonbreeding seasons suggest that the maturation of Sertoli cells depends on the upregulation of Ar expression around a testis weight of 0.07–0.18 g, regardless of age and conditions, synchronously accompanying the initiation of the meiotic phase. When Ar expression was suppressed, testicular development was impeded around the stage of Sertoli cell maturation, resulting in decreased spermatogenesis and hindered growth in testis weight. Our findings elucidate how animals control the seasonal inhibition and subsequent recovery of testicular development by regulating Ar expression in R. n. caraco.