title: Seasonal effect on germinal vesicle-stage bovine oocytes is further expressed by alterations in transcript levels in the developing embryos associated with reduced developmental competence.
abstract: Physiological perturbations of bovine follicle-enclosed oocytes during the lengthy period of follicular development can lead to reduced oocyte developmental competence. It is suggested that heat stress-induced alterations in germinal vesicle (GV)-stage oocytes are further expressed in the transcriptional levels of genes involved in oocyte maturation and early embryonic development. Bovine oocytes were collected during cold (December-April) and hot (May-November) seasons, matured, fertilized, and cultured in vitro. The percentage of fertilized oocytes cleaving to the 2- to 4-cell stage was higher in the cold vs. hot season (89.0% ± 2.63% vs. 75% ± 2.63%, respectively; P < 0.05), as was the percentage of cleaved embryos further developing to blastocysts (26.6% ± 0.9% vs. 10.1% ± 1.8%, respectively; P < 0.05). Total RNA and poly(A) mRNA of oocytes and developing embryos were isolated and subjected to semiquantitative and real-time PCR for MOS, GDF9, and POU5F1 genes. In GV-stage oocytes, their mRNA levels did not differ between the seasons. However, following maturation, mRNA levels were higher in oocytes collected in the cold season (P < 0.05). In 4-cell-stage embryos, GDF9 and POU5F1 showed opposite mRNA patterns between seasons (higher and lower levels, respectively) in the hot season (P < 0.05). In both 8-cell-stage embryos and blastocysts, POU5F1 expression was lower during the hot season (P < 0.05). Exposing the ovarian pool of oocytes to environmental stress appears to impair maternal mRNA storage and/or the mechanism of transcription renewal, in turn affecting embryo gene expression before and after embryonic genome activation. Such impairment might partially explain the carry-over effect of summer heat stress on dairy cow conception rates.
authors.affiliation: Department of Animal Sciences, Robert H. Smith Faculty of Agriculture, Food and Environment, the Hebrew University, Rehovot, Israel.
authors.forename: Mirit
authors.initials: M
authors.lastname: Gendelman
authors.forename: Zvi
authors.initials: Z
authors.lastname: Roth
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000378:metabolism; D002417:Cattle; D046149:Embryo Culture Techniques; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology; D005260:Female; D005307:Fertilization in Vitro; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000502:physiology*; D006358:Hot Temperature; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D013312:Stress, Physiological
chemical_list: D012333:RNA, Messenger