# RNA-Seq Revealed the Effects of Cold Stress on Different Brain Regions of Leiocassis longirostris

## TL;DR

This study uses RNA-seq to show how cold stress affects different brain regions in an endangered fish, with the mesencephalon being the most responsive.

## Contribution

The study identifies the mesencephalon as the core brain region responding to cold stress in Leiocassis longirostris.

## Key findings

- The mesencephalon showed the most significant molecular changes under cold stress.
- Cold stress disrupted circadian rhythms, spliceosome activity, and ubiquitin-mediated proteolysis in the brain.
- WGCNA analysis linked the mesencephalon to cold stress adaptation through gene co-expression networks.

## Abstract

The endangered fish Leiocassis longirostris suffers is highly susceptible to cold stress during seasonal changes or cold waves, often leading to mass mortality. While the brain regulates thermoregulation, region-specific molecular responses to cold remain poorly understood. This study employed RNA-seq to systematically analyze acute cold stress (4 °C, 24 h) effects across five brain regions in L. longirostris. Results revealed that different brain regions have distinct regional responses. Crucially, the mesencephalon (MB) exhibited the most significant changes and was identified as the core responsive region. Cold stress triggered MB-specific circadian rhythms, spliceosome, and ubiquitin-mediated proteolytic changes to coordinate adaptation to environmental stress.

Cold shock represents a prevalent but harmful environmental stress factor that poses significant threats to fish survival and reproductive success. In fish, the brain acts as a central regulator of thermoregulatory processes. Nevertheless, how different brain regions respond molecularly to cold exposure remains largely unknown. To address this, this study systematically investigated the effects of acute cold stress on five specific brain regions of Leiocassis longirostris using RNA-seq. The findings demonstrated that all five brain regions were significantly impacted by cold treatment, with the mesencephalon (MB) showing the most substantial changes. GO and KEGG enrichment analyses indicated that cold stress disrupted processes including gene expression regulation, circadian rhythms, and immune function within brain tissues. Through Weighted Gene Co-Expression Network Analysis (WGCNA), the MB was identified as the core responsive region, and the brain’s reaction to cold stress was strongly correlated with circadian rhythm, spliceosome, and ubiquitination. In summary, our investigation demonstrates that the MB represents a principal region for cold stress response in L. longirostris, involving alterations in circadian clocks, immune function, and inflammatory responses, alongside suppression of gene expression processes and ubiquitination-mediated proteolysis.