Submitted to: Biology of Reproduction
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2002
Publication Date: July 1, 2002
Citation: Block, J., Chase, C.C., Hansen, P.J. 2002. Importance of maternal versus paternal contributions for resistance of bovine preimplantation embryos to heat shock [abstract]. Biology of Reproduction.66(1):154.
Brahman embryos are more resistant to inhibition of development caused by heat shock than Angus or Holstein embryos. Two experiments were conducted to test whether the superior thermotolerance of Brahman embryos was the result of the genetic and cellular contributions from the oocyte, spermatozoa, or both. In experiment 1, Brahman (n=6 replicates) and Holstein oocytes (n=8) were fertilized with spermatozoa from an Angus bull. On day 4 after fertilization, embryos >9 cells were collected and randomly assigned to control (38.5°C) or heat shock (41°C for 6 h) treatments. There were significant breed x temperature interactions affecting the proportion of embryos that developed to the blastocyst (BL) and advanced blastocyst (expanded or hatched; ABL) stages at day 8 after fertilization (p<0.001 and 0.01, respectively). Heat shock reduced the proportion of Angus x Holstein embryos that developed to BL (55.6 ± 4.2% vs. 29.8 ± 4.2%) and ABL (37.7 ± 3.6% vs. 12.2 ± 3.6%) as compared to controls. In contrast, heat shock did not affect development of Angus x Brahman embryos (BL = 42.1 ± 4.8% vs. 55.6 ± 4.8% for 38.5 and 41°C, respectively; ABL = 17.6 ± 4.2% vs. 32.4 ± 4.2%). For experiment 2, oocytes from Holstein cows (n=7) were fertilized with semen from Brahman or Angus bulls. Heat shock of embryos >9 cells reduced development to BL (P<0.002) and ABL (p<0.005) for embryos sired by both Brahman (BL = 54.3 ± 7.7% vs. 23.4 ± 7.7%; ABL = 43.0 ± 7.4% vs. 7.9 ± 7.4%, for 38.5 and 41°C, respectively) and Angus bulls (BL = 57.9 ± 7.7 vs. 31.0 ± 7.7%; ABL = 33.6 ± 7.4% vs. 18.4 ± 7.4%, for 38.5 and 41°C, respectively). There were no breed x temperature interactions. Results suggest that the oocyte plays a more important role in the resistance of Brahman embryos to deleterious effects of heat shock than the spermatozoa. Either the oocyte transmits a cytoplasmic factor conferring thermotolerance or genes controlling thermotolerance are paternally imprinted.