Transcriptome analysis of mammary tissues reveals complex patterns of transporter gene expression during pregnancy and lactation

As a complex Ca²⁺‐rich fluid mixture of water, casein, lactose and several ions, milk secretion requires a number of unknown transporters, which can be identified by a genome‐wide microarray study in mammary tissues of lactating animals. Ca²⁺ was reported to be secreted across mammary epithelial cells through the transcellular pathway, presumably involving TRPC (canonical transient receptor potential) channels. In the present study, we have used quantitative real‐time PCR to demonstrate that the human mammary cell line MCF‐7, as well as rat mammary tissues from pregnant and lactating rats, expressed TRPC1, TRPC5 and TRPC6. Expression of TRPC1, TRPC5 and TRPC7 were markedly up‐regulated, whereas that of TRPC3 and TRPC4 was down‐regulated in the early lactating period. To further identify other transporter genes affected by lactation, a highly sensitive Illumina microarray featuring Bead Array technology was performed on RNA samples from mammary tissues of lactating rats. We found that, of the 384 transcripts changed during lactation, 31 transcripts were involved in the transport of water and electrolytes, such as Ca²⁺, Na⁺, K⁺, Cl^?, I^?, Fe²⁺, sulfate and phosphate. The present study, therefore, provides information for further investigation of the mechanism of lactation‐induced transport adaptation in mammary epithelial cells.