A proteomic approach to investigate the qualitative and quantitative polymorphism of β-lactoglobulin in ovine milk: Inference on gene copy-number variations

摘要

The rationale of this work is based on recent evidences suggesting that: 1) both qualitative and quantitative β-lactoglobulin (β-LG) polymorphism may be found in bovine milk; 2) quantitative polymorphisms are often the result of expression gradients in multiple copies of a gene; 3) the β-LG gene is duplicated in the dog and bovine genome; 4) mammary genes are highly conserved across Mammalia. Thus, an investigation was conducted on ovine β-LG polymorphism checking phenotypic evidence for copy-number variants of β-LG in sheep. To the purpose, 206 milk samples were collected, during a small-scale survey within sheep farms breeding Southern Italian breeds. PAGIF screening of the samples revealed that approximately 50% individuals exhibited β-LG polymorphism and 4 different quantitative patterns, which were characterized in detail by a proteomic approach relying on combined chromatographic and mass spectrometric techniques. The expected figures based on the expression gradient models were compared with well-established α-globin gene arrangements in sheep. The different phenotypes suggest the presence of both duplicate and triplicate BLG haplotypes. The occurrence of a triplicate haplotype was supported by population data. The current study supports the helpfulness of up-to-date proteomics for inferring copy number polymorphisms through the characterization of the phenotypic expression.