Differential expression and regulation of HSP70 gene during growth phase in ruminants in response to heat stress.

Heat shock proteins regulate the physiological mechanism of heat stress adaptation at cellular level. The present investigation was carried out to analyse the HSP70 gene regulation in various growth stage in ruminants in peripheral blood mononuclear cells (PBMCs). The relationship between HSP gene expression and thermotolerance in age-specific manner in ruminants has not been analysed. Therefore m-RNA HSP70 expression level was examined in different age groups of Jamunpari goat during hot climatic conditions. The experiment was carried out in 32 animals of Jamunapari goat belonging to the age groups of 3-months, 9-months, 12-months, and adults (2-3 year). Total RNA was isolated from peripheral blood mononuclear cells. The physiological response such as rectal temperature (RT), respiration rate (RR) and heart rate (HR) was used as indicator to heat stress. Temperature Humidity Index (THI) was used as an indicator of severity of environmental stress. The THI range varied from 82.00-92.08 during experimental period. The m-RNA HSP70 expression level at 9-month age of animals was up-regulated and significantly higher than other age groups. It was observed that the level of HSP70 transcripts in PBMCs was highest at 9-month age group, and age-related decline in HSP70 expression was observed in adult age. Based on the physiological response, the contrasting heat-stress phenotypes were recognised as heat stress susceptible (HSS) and heat stress tolerant (HST) individuals and the expression of m-RNA HSP70 was analysed at different ages in response to chronic heat stress. The differential mRNA expression of HSS individuals at 3 and 9-month of age showed the highest fold expression than HST. Age and phenotype had significant effect (p < 0.01) on the crossing point (CP) value. The m-RNA HSP70 gene expression in different age groups was correlated with heat stress tolerance and this could be used as biomarker for breeders to analyse the HSP response in -vivo in ruminants.