During puberty, hormonal signals initiate epithelial branching morphogenesis in mammary glands, and this study shows that the extracellular matrix has a role in patterning the epithelium. During branching morphogenesis, the epithelium progressed from a random orientation to being oriented along the long axis of the mammary gland, which indicates that a patterning cue for orientation might pre-exist in the stroma. Indeed, tracks of collagen I fibres in the stroma, which are oriented towards the long axis before branching morphogenesis begins, were co-oriented with the direction of epithelial outgrowth in early-stage mammary glands. The orientation of collagen I fibres was found to be sufficient to direct epithelial branch orientation, in a RAC1-dependent manner. RHOA–RHO kinase-mediated actomyosin contractions were not required to sense the orientation of collagen I fibres but they enhanced fibre orientation, which suggests that contractions generated by the branching epithelium could reinforce directional decisions.
ORIGINAL RESEARCH PAPER
Brownfield, D. G. et al. Patterned collagen fibers orient branching mammary epithelium through distinct signaling modules. Curr. Biol. 4 Apr 2013 (doi:10.1016/j.cub.2013.03.032)
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Minton, K. Epithelial patterning in branching morphogenesis. Nat Rev Mol Cell Biol 14, 266 (2013). https://doi.org/10.1038/nrm3575
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DOI: https://doi.org/10.1038/nrm3575