ABSTRACT. This study aimed to estimate changes in HSF3 and HSP70 mRNA expression in stress-sensitive tissues of 2 chicken breeds during acute heat stress. Lingshan chickens (LSC) and White Recessive Rock (WRR) (24 chickens of each breed) were randomly divided into 4 groups (0, 2, 3, and 6 h of heat treatment). With increasing heat treatment time, both HSF3 and HSP70 expression first declined and then showed a significant increase in both breeds. However, HSP70 expression decreased in the heart following 6 h of heat treatment, whereas HSF3 expression continued to increase. After 2 h of heat treatment, HSF3 expression was significantly higher in the brain and leg muscle of LSC compared to WRR (P < 0.05, P < 0.01). In comparison, HSP70 expression was significantly higher in the liver and leg muscle of WRR compared to LSC (P < 0.01, P < 0.05). After 3 h of heat treatment, HSF3 expression was significantly higher in the brain and leg muscle of LSC compared to WRR (P < 0.01). In comparison, HSP70 expression was significantly higher in the liver and heart of LSC compared to WRR (P < 0.01). These results indicate that the expression of HSF3 and HSP70 mRNA in LSC and WRR exhibit species-specific and tissue-specific differences during heat treatment.

ABSTRACT. Studying thermotolerance is important for the prevention of thermostress in chickens. This study aimed to analyze the effect of mutations in the heat shock protein 70 (HSP70) gene on chicken thermotolerance. The C.-69A>G SNP in the 5'-flanking region of the HSP70 gene was genotyped in Lingshan and White Recessive Rock (WRR) chickens. Association of this SNP with thermotolerance traits revealed it to be significantly associated with CD4+/CD8+, and potentially associated with heterophil-to-lymphocyte ratio in WRR chickens exposed to thermoneutral temperature (15°C). Online prediction detected a putative myeloid zinc finger protein 1 binding factor in the C.-69A>G mutation. Under acute thermostress, mRNA levels of HSP70 in individuals with different C.-69A>G genotypes varied in the heart, leg muscle, and liver tissues. The HSP70 protein was expressed at higher levels in individuals with the GG genotype than in those with the AA genotype. In heart and liver, protein expression of HSP70 in individuals with the GG genotype was significantly higher than in those with the AA genotype. In leg muscle, protein expression was higher in birds with the GG genotype than in those with the AA and AG genotypes. Luciferase activity of the GG genotype was significantly higher than that of the AA genotype, suggesting that the C.-69A>G SNP regulates HSP70 gene expression. These results indicate that the C.-69A>G SNP in the 5'-flanking region of the HSP70 gene might affect chicken thermotolerance and that the GG genotype might be advantageous for the prevention of thermostress.