Angiopoietin-2 (ANGPT2) as a candidate gene for somatic cell score in German Holstein cattle

This study evaluated the bovine angiopoietin-2 (ANGPT2) gene as a functional and positional candidate gene underlying a previously fine mapped quantitative trait locus (QTL) for somatic cell score on bovine chromosome 27. The gene product angiopoietin-2 is directly involved in the extravasation of neutrophils, making it a promising candidate to control the amount of somatic cells in milk. A total of 11 polymorphisms were identified within the gene by comparatively resequencing the entire open reading frame of the gene as well as adjacent intronic regions. Four selected variants were genotyped in the same granddaughter design used for QTL mapping and an association study was carried out applying 2 complementary approaches. A variable number of tandem repeats in intron 7 of the gene was found to be significantly associated with cell score in all approaches and explains approximately half of the QTL variance. Analysis of ANGPT2 mRNA expression in different localizations of the udder in animals putatively carrying divergent QTL alleles revealed differential expression in the udder lymph node. Together with the physiological role of angiopoietin-2, these results support a role of ANGPT2 in the genetic control of somatic cell score. Further studies are, however, needed to further underpin this hypothesis.