Does heat stress provoke the loss of a continuous layer of cortical granules beneath the plasma membrane during oocyte maturation?

Abstract

The objective of the present study was to evaluate the influence of heat stress on bovine oocyte maturation. Both nuclear stage and distribution of cortical granules (CG) were simultaneously evaluated in each oocyte. Oocyte overmaturation under standard conditions of culture was also evaluated. For this purpose, logistic regression procedures were used to evaluate possible effects of factors such as heat stress, overmaturation, replicate, CG distribution and metaphase II (MII) morphology on oocyte maturation. Based on the odds ratio, oocytes on heat stressed (HSO) and overmaturated (OMO) oocyte group were, respectively, 14.5 and 5.4 times more likely to show anomalous MII morphology than those matured under control conditions (CO). The likelihood for an oocyte of showing the CG distribution pattern IV (aging oocyte) was 6.3 and 9.3 times higher for HSO and OMO groups, respectively, than for the CO group. The risk of undergoing anomalous oocyte maturation, considering both nuclear stage and distribution of CG was 17.1 and 18 times greater in oocytes cultured in HSO and OMO groups, respectively, than those in the CO group. In conclusion, heat stress proved to be valuable in aging oocytes. Heat stress advanced age for nuclear and cytoplasmic processes in a similar form to that of oocyte overmaturation.

A Five-Day Progesterone Plus eCG-Based Fixed-Time AI Protocol Improves Fertility Over Spontaneous Estrus in High-Producing Dairy Cows Under Heat Stress

“…This improvement in fertility due to the 5-day progesterone-based protocol has two possible explanations. Firstly, high temperatures have been related to oocyte aging [32]. It seems reasonable to think that regardless of whether the lifespan of a follicular wave is shortened in short protocols, oocyte quality has less time to be affected by heat stress.…”

Disparate consequences of heat stress exposure during meiotic maturation: embryo development after chemical activation vs fertilization of bovine oocytes

“…After direct application of heat stress, Edwards et al (2005) demonstrated that more bovine oocytes progressed to metaphase I by 8 h of in vitro maturation (hIVM), metaphase II by 18 hIVM, and completed cortical granule translocation to the oolemma by 24 hIVM compared with those not exposed to heat stress. Also, heat stress exposure between 18 and 21 hIVM increased the percentage of bovine oocytes exhibiting a type IV cortical granule distribution suggesting earlier exocytosis (Andreu-Vazquez et al 2010).…”

Factors affecting the in vitro embryo production in cattle associated to ovum pick up sistem

“…Moreover, Aroyo et al (2007) in mice and Gendelman et al (2010) in bovine observed a delay in the cleavage rate of embryos produced during the hot season in comparison with embryos produced during the cold season. On the other hand, some findings provided evidence for bovine HSO to mature faster than non-heat-stressed counterparts (Edwards et al, 2005;Schrock et al, 2007; Andreu- Vazquez et al, 2010). In agreement with our results, oocytes heat-stressed during the germinal vesicle stage (bovine: Payton et al, 2004;mouse: LaRosa and Downs, 2007) or during maturation (bovine: Ju et al, 2005;Schrock et al, 2007;Edwards et al, 2009;Zhandi et al, 2009;Rispoli et al, 2011;Payton et al, 2011) have shown competence in overcoming the first cellular division similar to that found in non-HSO.…”