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Open Access Research article

Evolution of major milk proteins in Mus musculus and Mus spretus mouse species: a genoproteomic analysis

Nisrine Boumahrou1, Claudia Bevilacqua1, Christian Beauvallet1, Guy Miranda1, Sanda Andrei12, Emmanuelle Rebours1, Jean-Jacques Panthier3, Sylvain Bellier14 and Patrice Martin1*

Author Affiliations

1 INRA, UR1313 Génétique animale et Biologie intégrative UMR 1313, Equipe LGS, F-78350 Jouy-en-Josas, France

2 Universitatea de Stiinte Agricole si Medicina Veterinara Cluj-Napoca, Romania

3 Institut Pasteur, Génétique Fonctionnelle de la Souris; CNRS URA2578, F-75724 Paris, France

4 INRA, UMR955 Génétique Fonctionnelle et Médicale, F-94704 Maisons-Alfort, France

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BMC Genomics 2011, 12:80  doi:10.1186/1471-2164-12-80

Published: 28 January 2011

Abstract

Background

Due to their high level of genotypic and phenotypic variability, Mus spretus strains were introduced in laboratories to investigate the genetic determinism of complex phenotypes including quantitative trait loci. Mus spretus diverged from Mus musculus around 2.5 million years ago and exhibits on average a single nucleotide polymorphism (SNP) in every 100 base pairs when compared with any of the classical laboratory strains. A genoproteomic approach was used to assess polymorphism of the major milk proteins between SEG/Pas and C57BL/6J, two inbred strains of mice representative of Mus spretus and Mus musculus species, respectively.

Results

The milk protein concentration was dramatically reduced in the SEG/Pas strain by comparison with the C57BL/6J strain (34 ± 9 g/L vs. 125 ± 12 g/L, respectively). Nine major proteins were identified in both milks using RP-HPLC, bi-dimensional electrophoresis and MALDI-Tof mass spectrometry. Two caseins (β and αs1) and the whey acidic protein (WAP), showed distinct chromatographic and electrophoresis behaviours. These differences were partly explained by the occurrence of amino acid substitutions and splicing variants revealed by cDNA sequencing. A total of 34 SNPs were identified in the coding and 3'untranslated regions of the SEG/Pas Csn1s1 (11), Csn2 (7) and Wap (8) genes. In addition, a 3 nucleotide deletion leading to the loss of a serine residue at position 93 was found in the SEG/Pas Wap gene.

Conclusion

SNP frequencies found in three milk protein-encoding genes between Mus spretus and Mus musculus is twice the values previously reported at the whole genome level. However, the protein structure and post-translational modifications seem not to be affected by SNPs characterized in our study. Splicing mechanisms (cryptic splice site usage, exon skipping, error-prone junction sequence), already identified in casein genes from other species, likely explain the existence of multiple αs1-casein isoforms both in SEG/Pas and C57BL/6J strains. Finally, we propose a possible mechanism by which the hallmark tandem duplication of a 18-nt exon (14 copies) may have occurred in the mouse genome.