Fig. 1. Lef1 expression in the mammary placode 3 between E11.5 and E11.75. Whole-mount in situ hybridization on embryos between E11.5 and E11.75 with dig-labeled antisense riboprobe for Lef1. (A) Lef1 is not expressed at significant level at E11.5 between the forelimb and hindlimb. (B) First evidence of Lef1 expression in the forming mammary placode (P3) occurs as a discrete line (between the 2 black arrows). (C and D) At E11.75, Lef1 is now expressed as a comet-like shape with the tail of the comet being localized caudally (between the 2 arrows) and then as a round like structure (P3). (E) Scanning electron microscopy of E11.5 embryo showing placode 3 as a knob of cells slightly elevated above the surface of the epidermis. (F) High magnification of placode 3. P: mammary placode. Scale bar, A-D, 785 µm; E, 980 µm; F, 390 µm.