Figure 2

Histological analyses of mammary glands transplanted into Rag1^-/- mice show that Six1 is not necessary for the normal development of the mammary gland. Developmental stages are shown on the left, and the genotype of the animal from which the glands are derived is shown at the top. (A-B) At 5 weeks post-transplant, Six1^+/+ and Six1^-/- mammary glands were composed of epithelial ducts embedded in a soft connective tissue rich in fat. (C) A view of a Six1^+/+ mammary gland 10 weeks post-transplant shows a normal appearance. (D) The Six1^-/- mammary gland 10 weeks post-transplant demonstrates that the mammary ductal network is unaffected in the absence of Six1. Ten weeks after the transplant procedure, Rag1^-/- mice were mated and the transplanted mammary glands were analyzed at day 5 (E and F), day 12 (G and H) and day 17 (I and J) of pregnancy. Alveologenesis in pregnancy was not affected by Six1 deficiency.