Analysis Of Copy Number Of MUC13Encoding The Porcine Intestinal Receptor For ETEC F4ac And Its Expression In Adhesive And Non-adhesive Animals

Through a series of genetic analyses including QTL mapping, genome-wide association analysis, fine mapping by breakpoints recombinant analysis, we have demonstrated that MUC13is the causal gene for susceptibility to ETEC F4ac diarrhea in piglets. We also showed that MUC13has two transcription copies:MUC13A and MUC13B. An investigation in a number of Chinese and Western pigs indicated that susceptibility towards ETEC F4ac is solely determined by the MUC13B copy.In this study, we further recorded in vitro ETEC F4ac adhesion phenotypes on275Sutai pigs and260Western commercial breeds. We genotyped these animals for a diagnostic68bp indel marker distinguishing MUC13A and MUC13B copies. The results confirmed that all animals homozygous for MUC13A are resistant to ETEC F4ac, and susceptibility to this bacteria is solely determined by the MUC13B allele.MUC13A and MUC13B has different tandem repeat units in PTS region encoded by exon2. The repeat unit in MUC13A was mainly ASTSAPSA or ASTSAPAAG, while in MUC13B was majorly TPTPTTTP. However, it is unclear whether the two MUC13alleles are encoded by a single copy gene or multiple copy genes in the pig genome. To solve this problem, we employed genomic quantitative PCR to determine the copy number of MUC13in60pigs from Chinese and Western diverse breeds. Our results showed that all pigs only have a single copy of MUC13in the genome. Real-time quantitative PCR analysis of the expression of MUC13B transcripts revealed that there is no difference of MUC13B expression between adhesive and non-adhesive individuals, indicating that MUC13B causal variant is not regulatory mutation. Taken together, these results confirmed that MUC13is the responsible gene for the porcine intestinal receptor for ETEC F4ac, and paved the road into the final characterization of the causal variants of MUC13.