The effect of kinetic heat shock on bovine oocyte maturation and subsequent gene expression of targeted genes

Abstract

The exposure of oocytes to heat stress during the maturation process results in harmful effects to their internal organelles, low fertilization capability and higher embryonic losses. In the present experiment the effect of heat shock (HS) during the maturation process was assessed. In Assay 1, oocytes from winter (December-March; n = 100) and summer (June-September; n = 100) months were collected and matured to analyse their HS tolerance. Total RNA was extracted from matured oocytes and cDNA synthesis was performed, followed by qPCR for selected genes (Cx43, CDH1, DNMT1, HSPA14), compared with two reference genes (GAPDH and SDHA). In Assay 2, oocytes collected during the winter were subjected to kinetic HS by stressing them at 39.5°C for 6, 12, 18 or 24 h and were afterwards matured at control temperature (38.5°C), and subsequently subjected to the previously described gene analysis procedure. Results of Assay 1 show that summer-collected oocytes exhibited lower maturation rate than winter-collected oocytes, which may be due to the down-regulation of the HSPA 14 gene. Assay 2 showed that 6 h of HS had no effect on gene regulation. CDH1 and DNMT1 up-regulation was observed starting at 12 h, which may represent the effect of heat shock on oocyte development.

Effect of Cortisol on Bovine Oocytes Maturation and Further Embryonic Development After In vitro Fertilization

“…Several research developed in vivo show cortisol as a stressful hormone, affects bovine metabolism, in general, and reproduction in particular [30][31]. Previously studies showed that in the Azores, fertility of bovine decreases drastically to 35% in the summer period, achieving 78% in the non-hot periods as spring and autumn [44][45]. Several hypotheses have been purposed to explain this shut in the hot periods [18,32,45].…”

“…Previously studies showed that in the Azores, fertility of bovine decreases drastically to 35% in the summer period, achieving 78% in the non-hot periods as spring and autumn [44][45]. Several hypotheses have been purposed to explain this shut in the hot periods [18,32,45]. Heat stress genes, such HASP14 and Cx34 are activated during summer, when outside temperature rises over 25 ºC.…”

“…Heat stress genes, such HASP14 and Cx34 are activated during summer, when outside temperature rises over 25 ºC. As these genes are also related to the apoptosis, one can speculate that, among other mechanisms, apoptosis can play a crucial role in the embryonic as well as in the follicle/oocyte development from the beginning to metaphase II [32,45]. Besides in the literature, cortisol levels on cattle are not very clear, these values were chosen according several authors in which cortisol can reach a maximum of about 250 µM when cattle are exposed for long time to stress conditions such high environmental temperature [28][29].…”

Heat stress, a serious threat to reproductive function in animals and humans

“…Summer‐collected oocytes exhibited lower IVM rates than winter‐collected oocytes. This observation has been associated with HS‐induced downregulation of the HSPA14 gene (Pavani et al, ). Oocytes collected during the summer showed more than 20 times higher incidence of anomalous metaphase II morphology than control oocytes.…”

Consequences of assisted reproductive techniques on the embryonic epigenome in cattle

“…In addition, treatment-specific effects have been observed for IVM oocytes. For example, Kahlon (2016) has shown that exposure to bisphenol A can decrease the total amount of DNMT1 protein in oocytes, whereas prolonged heat shock and melatonin increase transcript amount Pavani et al 2017). Further, work from Van Hoeck et al (2011) identified increased levels of DNMT3A transcript in blastocyst stage embryos that developed from oocytes exposed to nonesterified fatty acids (NEFA) during IVM.…”