Transient Heat-Shock Disrupts Molecular Signals and Competence of Riverine Bubalus Bubalis Oocytes and Early Embryos in a Stage-Specific Manner

Background Thermal stress elicits detrimental effect in reproduction performance of Bubalus bubalis, buffalo. Riverine buffalo oocytes and early embryos possess differential ability to grow and survive under thermal stress condition. It is interesting to know how precisely the short and transient heat stress impacts growth and development of buffalo oocytes and early embryos in a stage specific manner. In this study, we aim to identify the most sensitive and vulnerable stage of oocytes and early embryos against transient heat stress as well as unravel the underlying molecular signals responsible for the stunted embryo development under thermal stress. It was assessed by utilizing six different groups of oocytes and embryos with an incorporation of 4 h transient heat shock at 40ºC during different stage of in-vitro maturation (IVM) and in vitro culture (IVC). Results The stressed oocytes of group (grp) 1, 2 and 3 exhibit comparable paces of attaining metaphase-II (M-II) phase at different time interval of IVM. The most detrimental effect of heat stress was observed in grp 2 with sharp reduction in morula to blastocysts transition rate (p<0.05). Expression of mRNA transcripts of HSP8, MnSOD and Sirt-3 genes were significantly increased from mid-IVM to 4-cell embryo although subsequently, down-regulated in embryos of 8-16 cells, morulae and blastocysts. Expression of maternal to embryo transition (MET) genes viz. PAP, U2Af and eIF4A was significantly down regulated from 2-cell embryo to morula (p<0.05). Maternal recognition of pregnancy (MRP) and morulae to blastocyst transition genes were poorly expressed in grp 2 than of the other stress groups (p<0.05). Conclusions Disruption of molecular signal has implicated in the poor formation of inner cell mass (ICM) and trophectoderm (TE) cells, this results in compromised development prospects of early buffalo embryos in a stage specific manner. Well-coordinated molecular signals associated with heat stress held responsible for reduced development of early embryo. We establish the most vulnerable stage of buffalo oocytes and presumptive zygotes against transient heat shock and observe a narrow window as the most critical stage for regulating the development potential of the prospective embryos under short heat stress environment.