Phosphoproteome Reveals the Lactation Mechanism in Caprine Mammary Gland Tissues in Peak and Late Lactation Stages

Background: Protein phosphorylation plays an important role in lactation. Differentially modified modification sites between peak lactation (PL, 90 days postpartum) and late lactation (LL, 280 days postpartum) were investigated using an integrated approach, namely, liquid chromatography with tandem mass spectrometry (LC-MS/MS) and tandem mass tag (TMT) labelling, to understand the molecular biological mechanisms in goat breast tissues. Results: : A total of 1,938 (1,111 up-regulated, 827 down-regulated) differentially modified modification sites of 1,172 proteins were identified ( P values 1.5). In addition, the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that ribosome (chx03010), RNA transport (chx03013), protein export (chx03060), calcium signalling pathway (chx04020), oxytocin signalling pathway (chx04921), RNA degradation (chx03018) and MAPK signalling pathway (chx04010) were enriched in relation to energy metabolism and protein translation. The results of western blot showed phosphorylation levels of ACACA, EIF4EBP1 and IRS1 increased and JUN decreased in PL compared with LL. The result was consistent with phosphoproteome. Conclusions: : Overall, these data indicate that protein phosphorylation is closely related to lactation and differentially modified modification sites might have potential research value in the regulation of goat lactation.