In previous work we and others confirmed that conditional deletion of either Pkd1 or Wwtr1 in osteoblasts has a direct role in osteoblast-mediated bone formation.6,25 Our current studies extend these findings by demonstrating the additive osteopenia phenotypes in double Pkd1/Wwtr1Oc-cKO null mice are due to direct loss of both PC1 and/or Wwtr1 signaling in the osteoblast lineage. Here, WWTR1 is linked to Osteopenia.