ammary glands of MMTV-LRP6 virgin mice and WT littermate controls (12 weeks old) was used for RT-PCR to detect myc-tagged human LRP6 transgene in Founder 4. (b) Quantification of LRP6 transgene expression by q-PCR. Founder 4 has the highest level of LRP6 transgene expression, while Founder 5 has the lowest. (c) Mammary glands from MMTV-LRP6 mice or WT littermate controls (12 weeks old, n=4) were dissected and lysates were prepared. The levels of LRP6 in crude membrane fraction were analyzed by Western blotting with a specific LRP6 antibody. Samples were also probed with an anti-actin antibody to verify equal loading. Lower panel, quantification of the Western blot signals of LRP6 from mammary glands, which were normalized to actin levels. Error bars represent SD. \*P\<0.05 indicates a significant difference compared to mammary glands from WT littermate controls.](nihms146777f1){#F1}

![LRP6 immunohistochemical staining in the mammary glands of MMTV-LRP6 mice. (a--b) LRP6 expression in mammary glands of MMTV-LRP6 virgin mice and WT littermate controls was shown through immunohistochemical staining using human LRP6 polyclonal antibody. Bar, 200 μm. (c--d) H & E staining of mammary glands from MMTV-LRP6 virgin mice and WT littermate controls. Bar, 400 μm, inset, 200 μm.](nihms146777f2){#F2}

![Mammary gland hyperplasia in MMTV-LRP6 mice. (a) Mammary glands from MMTV-LRP6 virgin mice or WT littermate controls (Founder 4 line) at 14 or 21 weeks of age were analyzed by whole mount staining. *Inset*: high magnification of a selected area. Note mammary hyperplasia in MMTV-LRP6 mice. Bar, 500 μm, inset, 400 μm. (b) Quantification of terminal end buds (TEBs) from WT and MMTV-LRP6 mice (Founder 4, n=4) at 14 or 21 weeks of age. Error bars represent SD. \*P\<0.05 indicates a significant difference compared to mammary glands from WT littermate controls.](nihms146777f3){#F3}

![Wnt signaling is up-regulated in HMECs by LRP6 overexpression. HMECs were cultured in 24-well plates. For each well, 0.05 μg of Wnt signaling rep