|Chase, Chadwick - Chad|
|Krininger Iii, C.|
Submitted to: Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2002
Publication Date: 1/20/2003
Citation: Paula-Lopes, F.F., Chase, C.C., Al-Katanani, Y.M., Krininger Iii, C.E., Rivera, R.M., Tekin, S., Majewski, A.C., Ocon, O.M., Olson, T.A., Hansen, P.J. 2003. Genetic divergence in cellular resistance to heat shock: differences between breeds developed in temperate vs. hot climates in responses of preimplantation embryos, reproductive tract tissues & lymphocytes to elevated culture. Reproduction.125:285-294. Interpretive Summary: Exposure to heat stress has less deleterious effects on fertility of breeds of cattle adapted to hot climates than breeds from temperate climates. This breed difference has been attributed to the superior ability of heat-tolerant cattle to regulate body temperature in the presence of heat stress. Here it was demonstrated that genetic adaptations exists at the cellular level as well and that Brahman and Senepol cattle have evolved to acquire mechanisms to protect cells against the deleterious effect of high temperature. In particular, embryos from Brahman cattle were better able to survive after exposure to elevated temperature than embryos from Angus and Holstein, two heat sensitive breeds of cattle. Additionally, lymphocytes (white blood cells) from Brahman and Senepol cattle experienced less apoptosis (cell death) following heat shock than lymphocytes from the other breeds (Angus and Holstein). Thus, Brahman and Senepol cattle cannot only regulate body temperature in the face of heat stress more effectively than breeds from temperate climates, but hyperthermia that does result from heat stress is less likely to have severe effects on death of white blood cells. It is likely that the evolutionary forces that led to the Brahman and Senepol breeds being adapted to hot climates resulted in selection of genes controlling resistance to cellular heat shock. Identification of the genes controlling cellular thermotolerance in Brahman cattle, may, therefore lead to genetic strategies for improving embryonic survival during heat stress in breeds that are not thermotolerant.
Technical Abstract: The detrimental effects of heat stress on fertility in cattle are less pronounced in heat-tolerant breeds. Although these genetic differences reflect differences in thermoregulation, cells from heat-tolerant breeds are less adversely compromised by elevated temperature (i.e., heat shock) than cells from heat-sensitive breeds. Experiments were performed to test the hypothesis that cells and tissues from two thermotolerant breeds (Brahman and Senepol) are better able to survive and function after exposure to elevated temperature than cells and tissues from two thermosensitive breeds (Holstein and Angus). Exposure of embryos (greater than 8 cell stage) at day 5 after insemination to heat shock of 41 C for 6 h decreased development to the blastocyst stage and embryo cell number. However, the deleterious effect of heat shock on blastocyst formation and embryo cell number was less pronounced for Brahman than for Holstein and Angus. Senepol embryos had very low development and it was not possible to determine heat shock effects in this breed. In contrast to the sensitivity of embryos to heat shock, there was no effect of a 41 C heat shock on [3H]leucine incorporation into proteins secreted by oviductal or endometrial explants. Brahman and Senepol lymphocytes were more resistant to heat-induced apoptosis than the other breeds. Heat shock reduced lymphocyte glutathione content but the magnitude of the decrease was not affected by breed. In conclusion, embryos from Brahman are more resistant to heat shock than Angus and Holstein. It is likely that the evolutionary forces that led to the Brahman and Senepol breeds being adapted to hot climates resulted in selection of genes controlling resistance to cellular heat shock.