Haplotype variability in the bovine MITF gene and association with piebaldism in Holstein and Simmental cattle breeds

Candidate gene analysis, quantitative trait locus mapping in outbreed and experimental cross populations and a genome wide association study in Holstein reported that a few chromosome regions contribute to explain a large quote of variability of the white/black degree of spotting in cattle. In particular, an important region affecting this trait was localized on bovine chromosome 22 in the correspondence of the microphthalmia-associated transcription factor (MITF) gene. We sequenced a total of 7,258 bp of the MITF gene in 40 cattle of different breeds, 20 animals from spotted breeds (10 Italian Holstein and 10 Italian Simmental) and 20 animals from solid coloured breeds (10 Italian Brown and 10 Reggiana) and identified 17 single nucleotide polymorphisms (SNPs). Allele frequencies of one polymorphism (g.32386957A>T) were clearly different between spotted (A = 0.875; T = 0.125) vs non spotted breeds (A = 0.125; T = 0.875) (P=8.2E-12). This result was confirmed by genotyping additional animals of these four breeds (P<1.0E-20). A total of 21 different haplotypes were inferred from the sequenced animals. Considering similarities among haplotypes, spotted and non-spotted groups of cattle showed significant differences in their haplotype distribution (P=0.001), that was further supported by analysis of molecular variance (AMOVA) of two genotyped SNPs in an enlarged sample of cattle. Variability in the MITF gene clearly explained differences between spotted and non-spotted phenotypes but, at the same time, it was evident that this gene is not the only genetic factor determining piebaldism in Italian Holstein and Italian Simmental cattle breeds.