Estudo de polimorfismos nos genes CSN1S1 e CSN3 em fêmeas bubalinas de padrão racial Murrah.

Abstract

The characteristics of milk are controlled by several genes, with emphasis on the four casein genes, CSN1S1; CSN1S2; CSN2 and CSN3, which are responsible for encoding the four fractions of that protein, are they, α-casein which includes α (S1) and α (S2), β and κ-casein. The study of genetic variants in these genes, seek to investigate alleles, insertions or deletions, which may reflect directly on productive characteristics, indicating differences in the quality, composition and yield of milk. Thus, the objective of this study is to investigate the occurrence of polymorphisms in the CSN1S1 and CSN3 genes, in buffalo females of the Mur-rah racial pat tern. The CSN1S1 and CSN3 genes were analyzed in 41 lactating Murrah buffaloes, using nucleotide sequencing. The primer pairs amplified fragments of 313 base pairs (bp) for the CSN1S1 gene, and 350 bp for the CSN3 gene. An SNP was found in the amplified fragment for the CSN1S1 gene, located in nucleotide number 2.123 of the promoter region (5 'UTR), at position nt-258 (A / G), which does not cause any amino acid alteration. The observed genotypic frequencies of this SNP were different from the expected genotypic frequencies (EHW - Hardy-Weinberg Equilibrium), and in addition, the observed heterosigosity (Ho) was higher than the expected heterosigosity (He). As for the CSN3 gene, two SNPs nt-98 and nt-102 (nucleotides number 377 and 381 of exon number 4, of the CSN3 gene) were identified in codons 33 (ACC / ATC) and 34 (AC C / AC T) of the analyzed fragment, which correspond to codons 135 and 136 of the mature peptide, and which, once translated, result in the amino acids Threonine (Thr) / Isoleucine (Ile), in the case of the ATC / ACT codons and Threonine / Threonine, for the ACC / ACC ha-plotypes. According to the analyzes, the genotypic and observed frequencies were different for the CSN3 gene. And again, the observed heterosigosity (Ho) was greater than the expected heterosigosity (He), thus suggesting an excess of hetero-zygotes in relation to the Hardy-Weinberg equilibrium model. A new SNP was found in the CSN1S1 gene (5 'UTR) in buffaloes, and another 2 polymorphisms in the CSN3 gene (exon 4) not yet described in buffalo of the Murrah racial pattern, raised under tropical climate, were investigated. Thus, the knowledge of candidate gene polymorphisms in dairy buffalo suggests and encourages studies to be carried out that aim to establish associations between such variants and characteristics of milk production and its derivatives, enabling selection assisted by molecular markers.