Whole mount analysis of TEBs. (a) High-magnification TEBs in carmine alum stained whole mounts. Large bulbous TEBs are present at the end of the advancing duct in +/+,+/- glands at 4 weeks after transplantation (top left), but have regressed by 7 weeks (middle left) and 20 weeks (bottom left) after transplantation. The TEBs in the -/- glands are present at 4 weeks (top right), they persist at 7 weeks (middle right), and have regressed by 20 weeks (bottom right). Whole mounts at a given time point are contralateral glands from the same recipient mouse at the same magnification. (b) Number and area of TEBs after transplantation. Shown are the number of TEBs in a carmine alum (CA)-stained whole mount (top left) and the average epithelial area of the TEBs (top right) at 4 weeks after transplantation in three mice with paired contralateral outgrowth; and the number of TEBs (bottom left) and the epithelial area of the TEB in stained paraffin-embedded sections (bottom right) at 4 weeks aftertransplantation in six ErbB3-/- glands and six ErbB3+ glands, two of which are paired contralateral outgrowths. Solid lines connect the paired null and wild-type or heterozygous (wt/het) contralateral transplants from the same recipient mouse. Dotted lines connect the mean of the outgrowths from contralateral glands in the complete null-wt/het pairs, and the means are listed at the termini of these lines. Asterisks represent the mean from all recipients of a given genotype, with means listed in italics. Circles mark the TEBs shown in panel c. (c) Representative TEBs in paraffin-embedded sections. An ErbB3+ TEB (bottom right) in an hematoxylin and eosin stained paraffin-embedded section compared with a ErbB3-/- TEB (bottom left) taken at the same magnification. Both TEBs were near average size for the respective genotype. Circles in panel b, lower right, mark the corresponding diamonds. TEB, terminal end bud.