Diverse regulation of mammary epithelial growth and branching morphogenesis through noncanonical Wnt signaling

Proc Natl Acad Sci U S A. 2017 Mar 21;114(12):3121-3126. doi: 10.1073/pnas.1701464114. Epub 2017 Mar 7.


The mammary gland consists of an adipose tissue that, in a process called branching morphogenesis, is invaded by a ductal epithelial network comprising basal and luminal epithelial cells. Stem and progenitor cells drive mammary growth, and their proliferation is regulated by multiple extracellular cues. One of the key regulatory pathways for these cells is the β-catenin-dependent, canonical wingless-type MMTV integration site family (WNT) signaling pathway; however, the role of noncanonical WNT signaling within the mammary stem/progenitor system remains elusive. Here, we focused on the noncanonical WNT receptors receptor tyrosine kinase-like orphan receptor 2 (ROR2) and receptor-like tyrosine kinase (RYK) and their activation by WNT5A, one of the hallmark noncanonical WNT ligands, during mammary epithelial growth and branching morphogenesis. We found that WNT5A inhibits mammary branching morphogenesis in vitro and in vivo through the receptor tyrosine kinase ROR2. Unexpectedly, WNT5A was able to enhance mammary epithelial growth, which is in contrast to its next closest relative WNT5B, which potently inhibits mammary stem/progenitor proliferation. We found that RYK, but not ROR2, is necessary for WNT5A-mediated promotion of mammary growth. These findings provide important insight into the biology of noncanonical WNT signaling in adult stem/progenitor cell regulation and development. Future research will determine how these interactions go awry in diseases such as breast cancer.

Keywords: epithelial morphogenesis; mammary stem cells; noncanonical Wnt signaling; receptor tyrosine kinase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Differentiation / genetics
  • Cell Proliferation / genetics
  • Epithelium / metabolism*
  • Female
  • Gene Expression Regulation
  • Mammary Glands, Animal / cytology
  • Mammary Glands, Animal / growth & development
  • Mammary Glands, Animal / metabolism*
  • Mice
  • Mice, Knockout
  • Morphogenesis* / genetics
  • Receptor Tyrosine Kinase-like Orphan Receptors / genetics
  • Receptor Tyrosine Kinase-like Orphan Receptors / metabolism
  • Receptors, Wnt / metabolism
  • Wnt Proteins / genetics
  • Wnt Proteins / metabolism
  • Wnt Signaling Pathway*
  • Wnt-5a Protein / genetics
  • Wnt-5a Protein / metabolism


  • Receptors, Wnt
  • Wnt Proteins
  • Wnt-5a Protein
  • Wnt5b protein, mouse
  • Receptor Tyrosine Kinase-like Orphan Receptors
  • Ror2 protein, mouse