The breast cell type enriched transcriptome
The primary function of the breast is to provide milk for newborn babies, and mainly consists of a mixture of glandular and adipose tissue. Glandular tissue is arranged in a branching ductal structure, terminating in alveoli, with adipocytes filling the interstitial space. Both males and females have breast tissue, although only data from female breast tissue is analyzed here.
2094 genes were predicted to have cell type specificity in the breast.
Breast cell type enriched transcriptome: Summary
Genes with predicted cell type specificity within breast are detailed in Table 1. Identified genes are subdivided into 3 specificity categories, based on the difference between the enrichment score in the corresponding cell type, compared to the other cell types profiled in the tissue (see Methods Summary page for details):
Breast cell type enriched transcriptome: Illustrative examples
Breast glandular cells
Glandular cells of the breast, sometimes called luminal cells, line the alveoli and lumen of the glandular tissue, and secrete the majority of proteins and substances that make up milk. In non-lactating women these cells are usually inactive, and are activated by hormonal changes that occur during pregnancy and childbirth in order to promote lactation. Genes classified as having specificity in breast glandular cells include the gluconeogenesis regulator and tumor suppressor Fructose-bisphosphatase 1 (FBP1), as well as proteins with unknown function such as SH3 Domain Containing 21 (SH3D21) and Transmembrane protein 45B (TMEM45B) .
Breast glandular cells (progenitor)
Glandular progenitor cells are a distinct, long lived subset of breast glandular cells that have the ability to generate novel glandular cells, to both expand the glandular population during pregnancy, as well as maintaining homeostasis during other periods. Genes classified as having specificity in glandular progenitor cells include Calmodulin like protein 5 (CALML5), a calcium binding protein thought to be involved in terminal differentiation of cells, and Pleckstrin homology like domain family A member 1 (PHLDA1), a regulator of translation and apoptosis.
Breast myoepithelial cells
Myoepithelial cells, or basal cells, lie underneath the glandular cells, and express many smooth muscle proteins. Myoepithelial cells have contractile ability and can constrict to expel the milk from the ducts and out of the body via the nipple. Myoepithelial cells also help regulate the proliferation and differentiation of glandular cells. Genes classified as having specificity in myoepithelial cells include structural proteins such as Keratin 14 (KRT14), as well as Anoctamin 1 (ANO1), a chloride channel with a diverse range of cellular functions including cell proliferation, survival, secretion, and migration as well as playing a role in the contraction of smooth muscle proteins.
The main function of adipocytes is to store energy in the form of fat and release it between meals, however they also function as endocrine tissue, secreting several growth factors, hormones and inflammatory mediators. During pregnancy and lactation, adipocytes of the breast provide lipids to the glandular cells for milk production, and are also the source of several hormones secreted into the milk. Genes classified as having specificity in Adipocytes include Perilipin 4 (PLIN4), which coats stored lipid droplets to protect them from lipases, as well as Acetyl-CoA carboxylase beta (ACACB), which plays a central role in fatty acid metabolism.