Bovine mammary gene expression profiling during the onset of lactation. Bos taurus

Lactogenesis includes two stages. Stage Ⅰ begins a few weeks before parturition, and stage Ⅱ 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 Ⅰ). 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 Ⅱ). 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.