title: The Wnt co-receptor Lrp6 is required for normal mouse mammary gland development.
abstract: Canonical Wnt signals are transduced through a Frizzled receptor and either the LRP5 or LRP6 co-receptor; such signals play central roles during development and in disease. We have previously shown that Lrp5 is required for ductal stem cell activity and that loss of Lrp5 delays normal mammary development and Wnt1-induced tumorigenesis. Here we show that canonical Wnt signals through the Lrp6 co-receptor are also required for normal mouse mammary gland development. Loss of Lrp6 compromises Wnt/beta-catenin signaling and interferes with mammary placode, fat pad, and branching development during embryogenesis. Heterozygosity for an inactivating mutation in Lrp6 is associated with a reduced number of terminal end buds and branches during postnatal development. While Lrp6 is expressed in both the basal and luminal mammary epithelium during embryogenesis, Lrp6 expression later becomes restricted to cells residing in the basal epithelial layer. Interestingly, these cells also express mammary stem cell markers. In humans, increased Lrp6 expression is associated with basal-like breast cancer. Taken together, our results suggest both overlapping and specific functions for Lrp5 and Lrp6 in the mammary gland.
authors.affiliation: Laboratory of Cell Signaling and Carcinogenesis, Van Andel Research Institute, Grand Rapids, Michigan, United States of America. Charlotta.Lindvall@vai.org
authors.forename: Charlotta
authors.initials: C
authors.lastname: Lindvall
authors.forename: Cassandra R
authors.initials: CR
authors.lastname: Zylstra
authors.forename: Nicole
authors.initials: N
authors.lastname: Evans
authors.forename: Richard A
authors.initials: RA
authors.lastname: West
authors.forename: Karl
authors.initials: K
authors.lastname: Dykema
authors.forename: Kyle A
authors.initials: KA
authors.lastname: Furge
authors.forename: Bart O
authors.initials: BO
authors.lastname: Williams
mesh_terms: D000818:Animals; D002469:Cell Separation; D005260:Female; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006239:Haplotypes; D026502:LDL-Receptor Related Proteins / Q000378:metabolism / Q000502:physiology*; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; C555475:LRP6 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555483:Lrp5 protein, mouse; C555476:Lrp6 protein, mouse; D051153:Wnt Proteins