Heat shock of porcine zygotes immediately after oocyte activation increases viability

Abstract

We evaluated the effect of different timing variations of an applied heat shock on parthenogenetically activated (PA) porcine embryos. PA embryos were heat shocked for 9 hr at 42 degrees C from either 0-9 hr post activation (hpa; 09HS), 13-22 hpa (1322HS), or 22-31 hpa (2231HS). Analysis of 24-hr cleavage rates (P < 0.0001), day 5 cell numbers (P < 0.005), day 7 blastocyst rates (P < 0.0001), and day 7 cell numbers (P < 0.05) showed that 09HS embryos developed more successfully in vitro than did all other treated and control embryos. In vitro fertilized (IVF) embryos were exposed to similar heat treatments as described for PA embryos, and embryos derived from somatic cell nuclear transfer (SCNT) were exposed only to the control and 09HS treatments to assess the effects of the different heat treatments on the timing of first cleavage and development to blastocyst. Embryos derived from both IVF and SCNT showed higher proportions of cleaved embryos on day 1 of development when heat shocked immediately after fertilization or fusion/activation as compared to NHS controls (P < 0.05). Blastocyst rates however, showed only modest (IVF; P = 0.089) or no (SCNT; P > 0.1) improvement as compared with control embryos. In summary, exposing PA embryos to elevated temperatures immediately after oocyte activation results in dramatically enhanced developmental potential. A thorough characterization of this phenomenon may yield findings that can serve to increase the efficiency with which PA, IVF, and SCNT embryos are produced in vitro.