title: Exposure to a physiologically relevant elevated temperature hastens in vitro maturation in bovine oocytes.
abstract: The objective of this study was to evaluate nuclear (progression to metaphase II) and cytoplasmic (translocation of cortical granules to the oolemma) maturation in control (38.5 degrees C) and heat-stressed (41.0 degrees C) oocytes. Hoechst staining indicated that a similar proportion of control and heat-stressed oocytes progressed to meta-phase II. More heat-stressed oocytes had type III cortical granule distribution suggesting that heat stress accelerated cytoplasmic maturation. The kinetics of nuclear maturation was examined in a second experiment in which a higher proportion of heat-stressed oocytes progressed to metaphase I by 8 h and arrested at meta-phase II at 16 and 18 h after placement into maturation medium. However, differences related to maturation temperature were no longer apparent by 21 h. Heat-induced alterations in kinetics of nuclear and cytoplasmic maturation prompted a third experiment to evaluate if earlier insemination of heat-stressed oocytes ameliorates heat-induced reductions in development. A significant temperature x insemination time interaction was noted when evaluating blastocyst development. Blastocyst development was reduced when heat-stressed oocytes were inseminated with sperm 24 h after placement into maturation medium compared with controls. In contrast, blastocyst development was similar to controls when heat-stressed oocytes were inseminated at 19 h. Based on this interaction, earlier insemination in vitro prevented heat-induced reductions in oocyte development. Collectively, these studies suggest a cumulative effect of heat stress to hasten in vitro maturation in bovine oocytes.
authors.affiliation: Department of Animal Science, The University of Tennessee Institute of Agriculture, Tennessee Agricultural Experiment Station, Knoxville, 37996-4574, USA. jedwards@utk.edu
authors.forename: J L
authors.initials: JL
authors.lastname: Edwards
authors.forename: A M
authors.initials: AM
authors.lastname: Saxton
authors.forename: J L
authors.initials: JL
authors.lastname: Lawrence
authors.forename: R R
authors.initials: RR
authors.lastname: Payton
authors.forename: J R
authors.initials: JR
authors.lastname: Dunlap
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology; D002417:Cattle; D002467:Cell Nucleus / Q000502:physiology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000502:physiology; D046149:Embryo Culture Techniques / Q000662:veterinary; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary; D006358:Hot Temperature; D007700:Kinetics; D009865:Oocytes / Q000254:growth & development* / Q000648:ultrastructure; D013997:Time Factors