Enterotoxigenic Escherichia coli (ETEC) F4ab and F4ac are major determinants of piglet diarrhoea. The locus for the ETEC F4ab/ac receptor has been mapped to SSC13q41. MUC13 is a transmembrane mucin expressed predominantly in the epithelial surface of the gastrointestinal tract and the MUC13 gene was assigned to SSC13q41, supporting it as a positional candidate gene for the ETEC F4ab/ac receptor. We herein determined the complete 2679-bp cDNA of pig MUC13, and proved that it was most highly expressed in the jejunum and moderately expressed in the trachea, stomach and liver. Furthermore, 13 MUC13 polymorphisms were identified in 19 founder animals of a White Duroc x Erhualian resource population, and a total of 727 F(2) animals with in vitro ETEC F4ab/ac adhesion phenotypes in this population were genotyped for three identified MUC13 polymorphisms including c.576C>T, c.908A>G and c.935A>C. The transmission disequilibrium test showed that the MUC13 alleles and haplotypes were significantly associated with susceptibility/resistance to ETEC F4ab/ac, especially between haplotype [C;G;A] and susceptibility to ETEC F4ac (P = 8.0e-18). Animals inheriting this haplotype were predominantly susceptible to ETEC F4ac (n = 291/303). Moreover, nearly all animals homozygous for haplotype [T;G;C] (n = 39/41) and a majority of those with the [C;A;A]/[T;G;C] haplotype pair (n = 79/88) were resistant to ETEC F4ab. Our results indicated that MUC13 is in strong linkage disequilibrium with the ETEC F4ab/ac receptor locus and provided potential markers for selection of ETEC F4ab/ac-resistant animals in the pig breeding scheme.

Dongxiang Spotted, Pingxiang Two-End-Black and Yushan Black pigs are three indigenous breeds in Jiangxi Province, China, that have been listed in the national conservation program for Chinese indigenous livestock germplasm. Here, we investigated the genetic diversity and population structure of the nucleus populations of these three breeds in a worldwide context of European and Chinese pigs using Illumina Porcine 60K chips. Our data indicate that Dongxiang Spotted and Yushan Black pigs have recently experienced severe inbreeding. The two breeds show large runs-of-homozygosity values, long-range extents of linkage disequilibrium and reduced observed heterozygosity. In contrast, Pingxiang Two-End-Black pigs are rich in genetic diversity and have few inbred individuals. Both phylogenetic and admixture analyses illustrate that Dongxiang Spotted and Yushan Black pigs are genetically close to their geographical neighbors in East China and that Pingxiang Two-End-Black pigs have a close relationship with three other Two-End-Black breeds in central China. Finally, we reconstructed the family structures of the three breeds and propose a reliable breeding strategy to better conserve these breeds.

Enterotoxigenic Eschoerchia coli (ETEC) F4 is a major cause of diarrhea in neonatal and young pigs. The locus encoding intestinal receptor for ETEC F4ab/ac has been mapped to pig chromosome (SSC) 13q41. We previously assigned mucin 20 (MUC20) to SSC13q41 and considered it a candidate for the ETEC F4ab/ac receptor. In this study, the full-length mRNA sequence of the porcine MUC20 gene was determined, revealing two MUC20 alternative transcripts differing in an 18-bp deletion in the open reading frame (ORF). The longer isoform is 1,927-bp long and contains a 1,572-bp ORF encoding a protein of 523 amino acids. RT-PCR analysis showed that MUC20 mRNA was expressed most highly in the kidney, prostate, epididymis and bladder. Seven single nucleotide polymorphisms in MUC20 were identified in founder animals of a White Duroc × Erhualian cross, and the entire cross population (n = 842) was genotyped for two MUC20 polymorphisms: g.191C>T in intron 5 and c.1600C>T in exon 6. The transmission disequilibrium test (TDT) results revealed that both polymorphisms were significantly associated with in vitro ETEC F4ab/ac adhesion phenotypes in the intercross population, and the most significant association was found between g.191C>T and F4ac adhesion phenotype (P = 1.02 × 10(-9)).