Effect of daily environment and season in a tropical environment on the expression of heat shock protein, and steroidogenic and apoptotic genes in bovine cumulus-oocyte complex

Abstract

The objectives of this study were to determine the differences in the expression of heat shock protein, and
steroidogenic and apoptosis genes by cumulus-oocyte complex (COC) of beef cattle in a tropical environment as
affected by seasonal and day effect of temperature and relative humidity. Real-time reverse transcription-polymerase
chain reaction (RT-PCR) was used to measure gene expression in COC in different seasons including cool (Jan to Feb),
summer (Mar to Apr) and rainy (May to Jul) seasons. Ambient temperature and relative humidity recorded on the day
before oocyte collection were used to classify environment groups as: low temperature and low humidity (LT-LH),
high temperature and low humidity (HT-LH) and high temperature and high humidity (HT-HH). Expression of HSP70
was higher in the cool than rainy season, and for LT-LH than HT-HH (p < 0.05). For the steroidogenic gene, STAR genes
were expressed less in HT-LH than either LT-LH or HT-HH (p < 0.05), but no effect of season was observed. Expression
of MCL-1 was lower (p < 0.05) for HT-LH than LT-LH or HT-HH and BAX was higher (p < 0.05) for HT-LH than LTLH or HT-HH. Except for HSP70, expression of heat shock proteins and steroidogenic and apoptotic genes in COC was
not affected by season. However, expression of these genes in COC was altered when environmental conditions were
characterized by HT-LH. Higher humidity appears to mediate expression of these genes when climates are hot.