# Divergent Photoperiodic Responses in Hypothalamic Dio3 Expression and Gonadal Activity Between Offspring and Paternal Brandt’s Voles

## TL;DR

This study finds that young male Brandt’s voles respond to day-length changes with altered gonadal development and gene expression, unlike their fathers, highlighting a key role for the Dio3 gene in seasonal breeding.

## Contribution

The study reveals age-specific photoperiodic responses and the role of Dio3 in regulating gonadal development in Brandt’s voles.

## Key findings

- Offspring under increasing long photoperiods showed higher gonadal development and lower Dio3 expression compared to decreasing short photoperiods.
- Paternal voles did not show significant photoperiodic responses, indicating divergent age-based mechanisms.
- Dio3 expression in offspring correlated with gonadal activity, emphasizing its role in photoperiod interpretation.

## Abstract

This study investigated an age-dependent photoperiod sensitivity mechanism in male Brandt’s voles, a small rodent species. We examined the gonadal development and expression profiles of reproductive-related genes in the hypothalamus of male offspring born under three different photoperiod conditions, as well as in their fathers. The results showed that both artificial and natural increasing long photoperiod treatments led to similar phenotypes and gene expression characteristics in male offspring, specifically a significantly higher level of gonadal development and a notably lower expression of hypothalamic Dio3 compared to the decreasing short photoperiod group. However, paternal voles did not exhibit any significant response to the applied photoperiod. These results suggest divergent photoperiodic responses between the two ages and highlight the crucial role of hypothalamic Dio3 in interpreting photoperiodic signals and regulating gonadal development in Brandt’s voles.

The postnatal development of gonadal glands in seasonal breeders, particularly small rodent species, is influenced by photoperiodic patterns. However, little research has been conducted on the effects of pattern similarity and age differentiation especially in molecular features. This study compares the postnatal development of gonadal glands and the expression of hypothalamic genes related to reproductive regulation in male offspring of Brandt’s voles (Lasiopodomys brandtii) born under three types of changing photoperiodic patterns: increasing long photoperiod (ILP, 12 h + 3 min/day), natural increasing long photoperiods (NLPs), and decreasing short photoperiods (DSPs, 12 h − 3 min/day), as well as in their paternal voles exposed to these patterns at the same period. Results indicate that over the course of 12 postnatal weeks, gonadal development, including organ masses and serum testosterone levels, exhibited similar profiles between the ILP and NLP groups, which were significantly higher than those observed in DSP offspring. Hypothalamic type 3 iodothyronine deiodinase (Dio3) exhibited significantly higher expression in the DSP group from postnatal week 4 to 8 compared to the other two groups. These physiological and molecular differences gradually decreased with age in offspring, but were never observed in the paternal voles, indicating divergent photoperiodic responses between the two ages. The synchronous profiles observed between hypothalamic Dio3 expression and gonadal activities underscore its crucial role in interpreting photoperiodic signals and regulating gonadal development in Brandt’s voles.