Fig. 2. Mammary gland development in wild type (+/+) and heterozygous Tbx3^tm1Pa (+/–) adult females and in wild-type (either +/+ or +/–) and Tbx3^tm1Pa/Tbx3^tm1Pa (–/–) embryos. (A,B) Wholemounts of the right inguinal mammary glands of 6-week-old virgin females showing a similar extent of duct growth within the fat pad (in, inguinal lymph node). (C,D) Mammary glands from pregnant and lactating heterozygous females, respectively, showing normal ductal growth and lactation that was indistinguishable from controls. (E-H) Wnt10b expression in 11.5 and 12.5 dpc embryos. No mammary buds are evident in the mutant embryos (F,H), whereas buds are evident in the wild-type embryos (E,G; arrows). (I-L) Lef1 expression in 12.5 and 13.5 dpc embryos. No mammary buds are evident in the mutant embryos (J,L), whereas they are clearly visible in the wild-type embryos (I,K; arrows). The development of the forelimb and vibrissae in the 13.5 dpc mutant embryo (L) indicates that it is at a similar developmental stage as the 12.5 dpc control (I). (M-P) Sagittal and transverse sections of 12.5 and 13.5 dpc embryos, respectively. No mammary buds were seen in the 12.5 dpc mutant embryos (N), although three buds out of an expected 20 were seen in two mutant embryos at 13.5 dpc (P). Insets are higher magnification images of the boxed area showing details of the mammary bud region.