Comparative Study On MRNA Expression And DNA Polymorphism Of Corticotropin Releasing Hormone In Pigs

This study was aimed to analyze the breed-specific characteristics of pigs in reponse tobacktest and loading stress, through comparison of the behavior and blood biochemicalmeasures between Erhualian (EHL) and Pietrain (PIE) pigs. Hypothalamic CRH andpituitary CRHR1 mRNA expressions were measured by RT-PCR to investigatebreed-specific responses of these two genes in response to transport stress. Furthermore, thepolymorphism of CRH gene in Erhualian, Pietrain and Pietrain×Erhualian F2 pigs wasmeasured by PCR-SSCP, and the correlation between the polymorphism of CRH gene andthe meat quality of F2 pigs was also analyzed, in order to illuminate the relationshipsbetween the expression of hypothalamic CRH and pituitary CRHR1 and thebreed-specific coping characteristics, and to identify the potential molecular marker forselecting stress resistance in pigs.1 Breed specific characteristics of stress responses in Erhualian andPietrain pigsErhualian (Hal^NN) and Pietrain (Halⁿⁿ) pigs were subjected to both backtest and loadingtrial, the behavior indexes responding to backtest (Backtest score, BS), as well as theplasma levels/activities of cortisol, creatine kinase (CK) and lactate dehydrogenase (LDH)before and after loading were observed as response criteria. The results showed that: (1) thebacktest score of Erhualian pigs was significantly lower than Pietrain pigs (P＜0.001); (2)before loading, Erhualian pigs exhibited significantly higher basal plasma cortisol level, butremarkably lower plasma CK activity, compared with Pietrain pigs (P＜0.01). No breeddifference in plasma LDH activity was observed; (3) plasma cortisol levels increasedsignificantly in Pietrain pigs immediately after loading (P＜0.05), whereas that in Erhualianpigs remained unchanged. Plasma CK and LDH activities in two breeds of pigs did notshow significant changes upon loading. The above results indicate that Erhualian andPietrain pigs respond to backtest and loading stress differently, Erhualian pigs seem to be less stress sensitive compared with Pietrain pigs.2 Expression of hypothalamie CRH and pituitary CRHR1 mRNA in pigsErhualian and Pietrain pigs were respectively allocated to control and transport groups.Pigs in the transport groups were subjected to 2 h transport. After transport, 4 groups ofpigs were sacrificed in parellel and the hypothalami and pituitaries were excised for RNAextraction. RT-PCR was used to determine the expression of hypothalamic CRH andpituitary CRHR1 mRNA. The results showed that: (1) there was a tendency that Erhualianpigs expressed higher level of CRH mRNA as compared with Pietrain pigs irt controlgroups. The expression of hypothalamic CRH gene in Erhualian pigs increasedsignificantly in transported groups (P＜0.05), but no notable difference was found inPietrain pigs. (2) the expression of pituitary CRHR1 in Pietrain pigs decreased significantly(P＜0.05) whereas no difference were found in Erhualian pigs in transported group. Theseindicated that there were breed-specific difference of hypothalamic CRH and pituitaryCRHR1 mRNA expressions in Erhualian and Pietraln pigs under transport stress, and thedifference may account for the difference of stress susceptibility between breeds.3 Polymorphisms of CRH gene in pigsThe polymorphism of CRH gene in Erhualian, Pietrain and Pietralin×Ehualian F2 pigswas detected with PCR-SSCPs. The results showed that: (1) no mutation of CRH on c.83was found in pigs; (2) a polymorphic site in CRH on g.233 was identified in Pietrain and F2pigs, with the gene frequency of 0.46 and 0.29, respectively, and the mutation was notmeasured in Erhualian pigs; (3) the mutation was correlated with shear force of thelongissimus dorsi (P=0.05) in F2 pigs after transportation, implying the potentialapplication of CRH g.233 for selecting stress resistance in pigs.