Differentially expressed mammary proteins during lactation in dairy sheep

In this research we wanted to produce a proteomic map of the sheep mammary gland, reflecting the protein variation occurring during lactation, with the purpose to identify the responsible mechanisms for lactation performances. Two-dimensional electrophoresis was applied to the proteins extracted by mammary gland tissues, collected at three different lactation stages. Differentially expressed proteins (22 spots) between two different lactation stages were identified by high-performance liquid chromatography with tandem mass spectrometric detection methods. The expression of more than half of the detected proteins, particularly the proteins of the metabolism pathway, showed the highest photodensity value at lactation peak, in agreement with the higher cellular activity of the mammary gland for milk synthesis and secretion at this lactation stage. The analysis of the remaining proteins highlighted that they are involved in apoptotic processes, which represent the main cause of the declining of milk yield during lactation, because of the imbalance between cell proliferation and apoptosis. Our results showed that the proteomic approach is valuable to understand the biochemical pathways that contribute to specific phenotypic expression.