Candidate regulators of mammary branching morphogenesis identified by genome‐wide transcript analysis

Abstract

The mammary gland develops in a process known as branching morphogenesis, whereby a distal epithelial bud extends and bifurcates to form an extensive ductal network. Compared with other branched organs, such as the lung and kidney, little is known about the molecular basis of branching in the mammary gland. Here we report a microarray profiling strategy to identify novel genes that may regulate mammary branching. We microdissected terminal end bud (TEB) and mature duct microenvironments from ␤-actin-green fluorescent protein reporter mice and compared their RNA expression profiles with epithelium-free mammary stroma by means of microarray. We identified 1,074 genes enriched in the TEB microenvironment, 222 genes enriched in the mature duct microenvironment, and 385 genes enriched in both TEB and mature duct microenvironments. The microarray correctly predicted the expression of genes known to be enriched in the epithelium (Ets-5) and stroma (MMP-14) of TEBs and in the mature duct microenvironment (MMP-3). The microarray also correctly predicted the localization of previously uncharacterized genes, such as the TEB-enriched SPRR-1a, the duct-enriched casein-␥, and the general epithelial marker pleiotrophin. Analysis of genes enriched in TEBs revealed several genes in the Wnt (Wnt-2, Wnt-5a, Wnt-7b, Dsh-3, Frizzled-1, Frizzled-2), hedgehog (Dhh), ephrin (Ephrin-B1, Eph-A2), and transcription factor (Twist-1, Twist-2, Snail) families. In situ hybridization verified that these genes were enriched in the TEB epithelium (Wnt-5a, Wnt-7b, Dhh, Eph-A2) or TEB stroma (Wnt-2, Frizzled-1, Ephrin-B1). We discuss the potential roles of these genes in mammary branching morphogenesis. Developmental Dynamics 235:3404 -3412, 2006.

ERα–CITED1 co-regulated genes expressed during pubertal mammary gland development: implications for breast cancer prognosis

“…Our global time course analysis of the entire gland differs from the approach of other research groups who have looked at a single pubertal time point and compared isolated segments of the gland (Kouros-Mehr and Werb, 2006;Morris et al, 2006). While the different approaches complement each other and a degree of overlap was apparent between findings, we identify both key global trends of pubertal development as well as dynamic expression changes for novel genes, not previously associated with pubertal mammary gland development.…”

Eph receptor and ephrin function in breast, gut, and skin epithelia

“…2). [55][56][57] The spatiotemporal expression pattern of Eph receptors and ephrins is important for breast epithelial tissue morphogenesis and function.…”

“…EphA2 expression is enriched in TEBs compared to ducts. 55,56 EphA2 was required for proliferation and hepatocyte growth factor (HGF)-induced branching morphogenesis as post-pubertal mice lacking this receptor exhibited reduced ductal penetration into the fat pad, which is a requirement for TEB formation. These studies suggest that EphA2 is a positive regulator of branching morphogenesis in mammary gland development.…”

Hepatic accumulation of Hedgehog-reactive progenitors increases with severity of fatty liver damage in mice

“…Gli activity promotes epithelial-mesenchymal transitions. 13,18,41,42 Therefore, we compared fibrosis markers in ethionine-treated lean and ob/ob mice. Although others have reported reduced fibrotic responses in ob/ob mice, 43,44 we found that ob/ob mice expressed higher mRNA levels of collagen 1aI (col1aI) (Figure 8a), asma (Figure 8b), and transforming growth factor-b (TGF-b) (Figure 8c) than lean mice after ethionine treatment.…”