title: Patterned collagen fibers orient branching mammary epithelium through distinct signaling modules.
abstract: For decades, the work of cell and developmental biologists has demonstrated the striking ability of the mesenchyme and the stroma to instruct epithelial form and function in the mammary gland, but the role of extracellular matrix (ECM) molecules in mammary pattern specification has not been elucidated. Here, we show that stromal collagen I (Col-I) fibers in the mammary fat pad are axially oriented prior to branching morphogenesis. Upon puberty, the branching epithelium orients along these fibers, thereby adopting a similar axial bias. To establish a causal relationship from Col-I fiber to epithelial orientation, we embedded mammary organoids within axially oriented Col-I fiber gels and observed dramatic epithelial co-orientation. Whereas a constitutively active form of Rac1, a molecule implicated in cell motility, prevented a directional epithelial response to Col-I fiber orientation, inhibition of the RhoA/Rho-associated kinase (ROCK) pathway did not. However, time-lapse studies revealed that, within randomly oriented Col-I matrices, the epithelium axially aligns fibers at branch sites via RhoA/ROCK-mediated contractions. Our data provide an explanation for how the stromal ECM encodes architectural cues for branch orientation as well as how the branching epithelium interprets and reinforces these cues through distinct signaling processes.
authors.affiliation: Department of Bioengineering, University of California Berkeley, Berkeley, CA 94720, USA. dbrownfi@stanford.edu
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Brownfield
authors.forename: Gautham
authors.initials: G
authors.lastname: Venugopalan
authors.forename: Alvin
authors.initials: A
authors.lastname: Lo
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Mori
authors.forename: Kandice
authors.initials: K
authors.lastname: Tanner
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fletcher
authors.forename: Mina J
authors.initials: MJ
authors.lastname: Bissell
mesh_terms: D000818:Animals; D024042:Collagen Type I / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D008321:Mammary Glands, Animal / Q000378:metabolism*; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018613:Microscopy, Confocal; D009479:Neuropeptides / Q000378:metabolism*; D012741:Sexual Maturation; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
chemical_list: D024042:Collagen Type I; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D054460:rho-Associated Kinases; C526380:RhoA protein, mouse; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein
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