A novel polymorphism at the prolactin receptor may be responsible of allele heterogeneity in coat type in Senepol cattle

The prolactin receptor (PRLR) have been described as a candidate gene with a variant allele containing a nonsense/dominant mutation causative of the slick coat (SC) phenotype (chromosome 20:39136558GC>G; p.L462*) in Senepol and SC Holstein cattle of Puerto Rico (PR). However, inconsistencies between p.L462* genotypes and SC phenotype had been observed in Senepol. Therefore, a total of 661 animals [Holstein (230), Senepol (357), Charolais (4), Senepol x Charolais (13), Jersey (34), and Creole (23)] were genotyped by DNA sequencing of a 645 bp PRLR exon 11 fragment that includes 5 reported polymorphic positions. A non-reported cytosine by thymine single nucleotide polymorphism (SNP) was identified at the chromosome 20:39136612 position; 53 bp downstream of the reported p.L462* cytosine insertion/deletion (InDel), also resulting in a nonsense mutation. This SNP incorporates 16 amino acids to the shortened PRLR. Five genotype combinations (CC/CC, CC/CT, C-/CC, C-/CT and --/CC) resulting from both PRLR exon 11 polymorphisms were observed and allelic heterogeneity resulting in SC phenotype was exclusively present in Senepol and Senepol x Charolais. The PRLR InDel/SNP genotype combination CC/CC, were present in non-slick: Senepol x Charolais (3), Charolais (4), Holstein (127), and Jersey (33) cattle with an overall frequency of 0.25. Heterozygote SC animals, genotypes combination CC/CT [Senepol (4), Senepol x Charolais (2)] and C-/CC [Senepol (49), Senepol x Charolais (7), Holstein (103), Jersey (1), and Creole (23)] had frequencies of 0.01 and 0.28, respectively. Meanwhile, homozygous SC animals, C-/CT [Senepol (45) and Senepol x Charolais (1)] and --/CC [Senepol (259)] presented frequencies of 0.07 and 0.39, individually. The novel pyrimidine transition reported herein in SC Senepol that do not possess the PRLR p.L462* responsible InDel suggest a possible more accurate scenario for slick genotype calling within such tropically adapted breed if selection is to be made in favor of such coat type.