Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/12/2010
Publication Date: 7/1/2010
Citation: Choudhary, R.K., Li, R.W., Clover, C.M., Capuco, A.V. 2010. Bovine mammary stem cells: Transcriptome profiling and the stem cell niche [abstract]. Journal of Dairy Science. 93 (E-Suppl. 1):ii-iii.
Technical Abstract: Identification and transcriptome analysis of mammary stem cells (MaSC) are important steps toward understanding the molecular basis of mammary epithelial growth, homeostasis and tissue repair. Our objective was to evaluate the molecular profiles of four categories of cells within the bovine mammary epithelium, two subpopulations of putative stem cells and two subpopulations of control cells, with the goal of localizing and characterizing MaSC in situ. Putative MaSC were identified based upon their ability to retain the thymidine analog, bromodeoxyuridine (BrdU), for an extended period. Five Holstein calves were injected with BrdU, tissue was harvested 45 d later and label retaining epithelial cells (LREC) were identified in mammary cryosections by immunostaining. Using laser microdissection, LREC from basal (LRECb) and embedded (LRECe) layers of mammary epithelium were isolated along with adjacent control epithelial cells (EC). Cells (6-13) in each category per heifer were lysed, cDNA synthesized, amplified and labeled for microarray hybridization. Data analysis revealed 592 differentially expressed genes (P = 0.05; = 2-fold change) between LRECb and basal EC, and 110 genes between LRECe and their embedded EC. Of these, 387 genes with enriched expression in LRECb were involved in cell growth and proliferation, cell cycle, and post-translational modifications. Low expression of estrogen receptor-a and high expression of aldehyde dehydrogenase 3B1 in LRECb were consistent with stem cell character. We found high expression of NR5A2 (pluripotency transcription factor) and no expression of XIST (X-chromosome inactivation factor) in LRECb. Comparison between LRECb and LRECe showed down-regulation of cell survival and proliferation factors (IGF2, HSPB6, LAMC1), nestin (stem cell marker), epigenetic modifiers (JRID2, METTL33, SMARCC2), and up-regulation of apoptotic genes (SFRS5, THAP3) and XIST in LRECe. We conclude that BrdU label retention identifies stem and progenitor cells, wherein MaSC (LRECb) are located in the basal region of the mammary epithelium and committed progenitor cells (LRECe) are localized in more apical layers.