Preliminary Genetic Analysis Of Porcine Skin Wrinkle And Thickness

Pig is one of the important domestic animals, which is also a suitable animal model for biomedical research in human disease and health problems. The skin is the largest organ of the integumentary system in mammals, and plays important roles in protecting the body against pathogens and excessive water loss. Wrinkles are uneven stripes on the skin. Deciphering the genetic mechanisms for porcine skin wrinkle can help people better make clear the underlying formation of skin folds, and may provide a reference to remove wrinkles and keep beauty in human. Molecular genetic researches on skin thickness do also help us better understand the development and morphology structure of skin.The present studies include two parts: one is genome-wide association study(GWAS) for porcine head wrinkle in Erhualian pigs, the other is preliminary genetic study on skin thickness in Bamaxiang pigs.First, wrinkle phenotypes and 60 K SNP genotypes of 333 Erhualian pigs were obtained, and GWASs for skin wrinkle were performed in this Erhualian pig population. Head photos of 333 Erhualian pigs were taken and their wrinkles were traced on translucent copy paper over the photos using HB pencil. The traced wrinkles were scanned and the pixels of the traced wrinkles and head blank outline were calculated by Photoshop software. The pixel ratios of wrinkle to head blank outline were considered as one phenotype of skin wrinkle trait. Meanwhile, three volunteers were convened to score the skin wrinkle in the above 333 Erhualian pigs according to the scoring criteria from 1 to 5. The average values were gained and considered as another phenotype of skin wrinkle trait. Both phenotypes of skin wrinkle spanned large range, their coefficients of variation were 30.15% and 32.63%, respectively. This result suggested that skin wrinkles in the Erhualian pig population had significant differentiation. The heritabilities of these two wrinkle phenotypes were estimated to be 0.41 and 0.81, respectively, based on the pedigree information using MCMCglmm package. So skin wrinkle in Erhualian pigs was high-heritability trait. Genome-wide association studies for porcine skin wrinkle were performed with their 60 K SNP genotype data. The most significant SNP loci(ALGA0040227) were identified at the position of 34835986 bp on SSC7, which was located at the downstream site of 3255 bp to the candidate gene GRM4. The allele A is benefit to reduce the extent of wrinkle in pigs.Second, skin thickness at 9 typical sites of the whole pig body were measured in Bamaxiang pig breed, one of Chinese local miniature pig breeds, and association test was performed between phenotypes of skin thickness and genotypes of 46 SNPs in the QTL region on SSC 7. Fifty Bamaxiang pigs, including 27 females and 23 castrated males, were randomly selected from a Bamaxiang pig population consisting of 319 adult pigs, which were slaughtered at 300 days. The difference of skin thickness between pairwise body sites and the difference between females and castrated males were test using the basic statistic package of R language. Pairwise Pearson's correlation coefficients were calculated between skin thickness at different body sites, meanwhile their significant tests were done. There were no significant correlations between skin thickness at belly and back, between belly and shoulder, and between belly and cheek. Other pairwise combinations had significant positive correlation. Pairwise Pearson's correlation coefficients were calculated between skin thickness at different body sites, meanwhile their significant tests were done. 46 SNPs located in the region from 34.5 to 36.2 Mb on SSC7 were selected and designed for genotyping on a SEQUENOM MassARRAY SNP Genotyping platform. Combined with the above phenotypes of skin thickness, association studies on the target candidate region were performed by a general mixed linear model using SNPasscoc package of R language. Association analysis between skin thickness at 9 different body sites and the above candidate SNPs suggested that the major QTL on SSC7 affecting skin thickness was also identified in Bamaxiang pig population. ANKS1 A and HMGA1 might be positional causal genes affecting skin thickness in pigs.Here variation of head skin wrinkle was investigated in Erhualian pig population, and skin thicknesses on 9 different body sites were measured in Bamaxiang pig population. The candidate genes responding to both traits were preliminary identified. The results in the present studies could make important clues to deeply decipher the molecular genetic mechanism for skin wrinkle and skin thickness, and could provide a reference for studying on skin development and skin wrinkle formation in human.