Bovine mammary gene expression profiling during the onset of lactation
Lactogenesis includes two stages. Stage ? begins a few weeks before parturition, and stage ? begins a few weeks before parturition. In order to better understand the molecular events driving lactogenesis in dairy cows, genome-wide gene expression profiling was conducted using digital gene expression profiling (DGE) on bovine mammary tissue at three time points (on approximately day 35 before parturition (-35d), day 7 before parturition (-7d) and day 3 after parturition (+3d)). Approximately 6.2 million, 5.8 million and 6.1 million 21-nt cDNA tags were sequenced in the three cDNA libraries (-35d, -7d and +3d), respectively. After aligning to the reference sequences, the three cDNA libraries included 8,662, 8,363 and 8,359 genes, respectively. With a fold change cutoff criteria of =2 or =-2 and a false discovery rate (FDR) of =0.001, a total of 812 genes were significantly differentially expressed at -7d compared with -35d (stage ?). There were 234 genes upregulated and 578 genes downregulated, accounting for 28.8% and 71.2% of differentially expressed genes respectively. A total of 1,189 genes were significantly differentially expressed at +3d compared with -7d (stag ?). Of these genes with significant expression changes, 274 (23.0%) genes were upregulated. 915 (77.0%) genes were downregulated. The results suggest that the mammary gland begins to lactate not only by a gain of function but also by a broad suppression of function to effectively push most of the cell's resources towards lactation. Overall design: Examination of genome-wide gene expression profiling using digital gene expression profiling (DGE) on bovine mammary tissue at three time points of approximately day 35 before parturition, day 7 before parturition and day 3 after parturition. There were 6 cows in each group. The mammary tissue from cows in the same group were pooled together for RNA isolation. The total RNA was used to sequence.