Susceptibility towards Enterotoxigenic Escherichia coli F4ac Diarrhea Is Governed by the MUC13 Gene in Pigs

Enterotoxigenic Escherichia coli (ETEC) F4ac is a major determinant of diarrhea and mortality in neonatal and young pigs. Susceptibility to ETEC F4ac is governed by the intestinal receptor specific for the bacterium and is inherited as a monogenic dominant trait. To identify the receptor gene (F4acR), we first mapped the locus to a 7.8-cM region on pig chromosome 13 using a genome scan with 194 microsatellite markers. A further scan with high density markers on chromosome 13 refined the locus to a 5.7-cM interval. Recombination breakpoint analysis defined the locus within a 2.3-Mb region. Further genome-wide mapping using 39,720 informative SNPs revealed that the most significant markers were proximal to the MUC13 gene in the 2.3-Mb region. Association studies in a collection of diverse outbred populations strongly supported that MUC13 is the most likely responsible gene. We characterized the porcine MUC13 gene that encodes two transcripts: MUC13A and MUC13B. Both transcripts have the characteristic PTS regions of mucins that are enriched in distinct tandem repeats. MUC13B is predicated to be heavily O-glycosylated, forming the binding site of the bacterium; while MUC13A does not have the O-glycosylation binding site. Concordantly, 127 independent pigs homozygous for MUC13A across diverse breeds are all resistant to ETEC F4ac, and all 718 susceptible animals from the broad breed panel carry at least one MUC13B allele. Altogether, we conclude that susceptibility towards ETEC F4ac is governed by the MUC13 gene in pigs. The finding has an immediate translation into breeding practice, as it allows us to establish an efficient and accurate diagnostic test for selecting against susceptible animals. Moreover, the finding improves our understanding of mucins that play crucial roles in defense against enteric pathogens. It revealed, for the first time, the direct interaction between MUC13 and enteric bacteria, which is poorly understood in mammals.产肠毒素大肠杆菌（Enterotoxigenic Escherichia coli，ETEC）F4ac是引发新生仔猪与幼龄仔猪腹泻及死亡的关键致病因子。仔猪对ETEC F4ac的易感性由该菌特异性肠道受体介导，并以单基因显性遗传的方式传递。为鉴定该受体基因（F4acR），研究团队首先利用194个微卫星标记开展全基因组扫描，将该基因座定位至猪13号染色体上一段7.8厘摩（cM）的区域内。后续通过13号染色体上的高密度标记进行扫描，将该基因座的定位区间缩小至5.7厘摩的范围。通过重组断点分析，将该基因座进一步限定在2.3兆碱基（Mb）的区域内。进一步利用39720个信息性单核苷酸多态性（SNPs）开展全基因组定位分析，结果显示在该2.3Mb区域内，最具显著性的标记位点紧邻MUC13基因。针对多个不同远交群体的关联分析研究，有力证实MUC13是最有可能的致病基因。研究团队对猪MUC13基因进行了表征分析，该基因可编码两种转录本：MUC13A与MUC13B。两种转录本均具备黏蛋白（mucins）特征性的PTS结构域，且该结构域富含独特的串联重复序列。MUC13B被预测可发生大量O-糖基化修饰，从而形成该菌的结合位点；而MUC13A则不具备O-糖基化结合位点。与此一致的是，来自多个不同品种的127头MUC13A纯合仔猪均对ETEC F4ac具有抗性；而来自广泛品种群体的718头易感个体均至少携带一个MUC13B等位基因。综合上述结果，研究团队得出结论：猪对ETEC F4ac的易感性由MUC13基因调控。该研究成果可直接应用于育种实践，借此可建立高效精准的诊断检测方法，用于筛选抗ETEC F4ac的仔猪、淘汰易感个体。此外，该研究加深了人们对黏蛋白在抵御肠道病原体过程中关键作用的认知。本研究首次揭示了MUC13与肠道细菌之间的直接相互作用，而这一过程在哺乳动物中此前鲜有深入研究。