AREG-/- mice demonstrate impaired mammary development and form only rudimentary ductal epithelial trees, however, AREG-/- glands are still capable of undergoing alveologenesis and lactogenesis during pregnancy. Transplantation of AREG-/- mammary epithelial cells into cleared mouse mammary fat pads results in a diminished capacity for epithelial growth (∼15%) as compared to wild type mammary epithelial cells. To determine whether ERα and/or AREG signaling were necessary for non-mammary cell redirection, we inoculated either ERα-/- or AREG-/- mammary cells with non-mammary progenitor cells (WapCre/Rosa26LacZ+ male testicular cells or GFP+ embryonic neuronal stem cells). ERα-/- cells possessed a limited ability to grow or reprogram non-mammary cells in transplanted mammary fat pads. AREG-/- mammary cells were capable of redirecting both types of non-mammary cell populations to mammary phenotypes in regenerating mammary outgrowths. Transplantation of fragments from AREG-reprogrammed chimeric outgrowths resulted in secondary outgrowths in 6 out of 10 fat pads, demonstrating the self-renewing capacity of the redirected non-mammary cells to contribute new progeny to chimeric outgrowths. Nestin was detected at the leading edges of developing alveoli suggesting its expression may be essential for lobular expansion.