A SNP in Intron 8 of CD46 Produces a Novel Mastitis-Associated Transcript in Holsteins

The membrane protein CD46, a ubiquitous cell surface pathogen receptor, can bind Streptococcus to trigger cell autophagy, which is a critical step in the control of infection. In this study, we found a new splice variant designed as CD46-AS, characterized by a retention of a 48 bp sequence from intron 8 of the bovine CD46 gene, which encodes a putative protein enlarged by 16 amino acids. CD46-AS mRNA was found to be over represented in mastitis-infected mammary gland tissue relative to healthy tissues. A single nucleotide polymorphism (SNP) (c. 1033+2184 C>T) in the exonic splicing enhancer (ESE) motif region was shown to result in the CD46-AS aberrant splice variant that caused by the C allele through constructing alternative alleles using the pSPL3 exon capturing vector and transfecting these into 293T cells. Allelic frequency in 56,452 individuals belonging to 112 cattle, buffalo, yak and bison breeds suggested that the C allele (80.13%) is the advantageous and ancestral allele. Association analysis showed that genomic estimated breeding value (gEBV) of milk somatic cell score (SCS) and clinical mastitis (CM) of Chinese Holsteins with the CT genotype was lower than that of individuals with either the CC or TT genotypes. The gEBV of udder health synthesis (STMA) of TT genotype was higher than that of the CC or CT genotypes. Our finding suggests that the CD46 gene likely plays a critical role in the risk of mastitis caused by Streptococcusin dairy cows via an alternative splicing mechanism caused by a functional mutation in intron 8.  Our data also underline the importance of variation within ESEs in regulating transcript processing.

Acknowledgements

We thank Professor J.F. Taylor from the Division of Animal Sciences, University of Missouri for providing SNP frequency data in different cattle breeds and his criticisms and editing of this manuscript. This study was supported by grants from the National Natural Science Foundation of China (31371255, 31271328 and 31000543), the Support Program of the Ministry of Science and Technology, P. R. China (2011BAD19B02 and 2011BAD19B04), the Major Project of National Transgene in China (2013ZX08007-001), and the Program of National Cow Industrial Technology System (CARS-37).