Sequence analysis and genetic variability of Mediterranean river buffalo prolactin gene (PRL)

Prolactin (PRL) is one of the most versatile hormones of the pituitary gland in terms of biological actions. In particular, PRL is essential for mammary gland development, lactogenesis and milk protein gene expression. It has also considered as a potential quantitative trait locus affecting milk performance traits in dairy cattle. Aims of this study were to detect PRL gene polymorphisms and to investigate their effect in Mediterranean river buffalo milk yield. For this purpose, DNA was isolated from the blood collected from 757 unrelated lactating Mediterranean river buffaloes belonging to 14 farms located in Salerno, Caserta and Potenza provinces (Italy). Using primers designed on bubaline genome sequence we amplified and sequenced the entire PRL gene of 5 buffaloes randomly chosen. Seven-thousand one-hundred and fifty-one records for milk yield, measured monthly by the official recording system of the Italian Association of Buffalo Breeders on 1081 lactations of 544 buffaloes, were used. Association between PRL polymorphism and milk yield was investigated with a mixed linear model. The entire panel of Mediterranean river buffalo DNA samples were genotyped in outsourcing ANIMAL BREEDING AND GENOMICS (KBiosciences, Herts, UK) for the exonic SNP. The buffalo PRL gene extends over 8.6 kb including 0.858 kb of exonic regions and 7.741 kb of intronic regions plus 361 bp of the 5′UTR. The main feature of the buffalo PRL gene is simple architecture. It contains 5 exons ranging in size from 82 (exon 1) to 306 bp (exon 5) and 4 introns from 629bp (intron 4) to 2715bp (intron 1). The sequence comparison of buffalo PRL gene showed 34 intronic polymorphisms (11 transversions, 22 transitions and 1 single deletions/insertions) and a transition C→T at the 108th nucle- otide of the exon 5. The frequency of the PRL T108C SNP in the investigated population was 0.88 (genotype distribution: 589 T/T, 156 T/C, 12 C/C). The least-squares means for milk yield indicated a difference of 0.18 kg/day between the genotypes TT (n. subjects 432) and TC (105) or CC (7), whereas both TC and CC showed an average milk production of 8.32 kg/day. However, these differ- ences were not significant. Therefore, this SNP appears to be selectively neutral in relation to milk yield.