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Fig. 1. TOPGAL expression during mammary gland development. (A) Development of
mammary buds (red circles) from the presumptive mammary line (broken red line)
during mouse embryogenesis (E10.5-E12.5). Mammary buds 1 and 5 develop
underneath the limb buds and are depicted as open circles with a broken
circumference. Placodes arise asynchronously, with placode pair number 3
detected first, followed by number 4, then numbers 1 and 5, and finally pair
number 2 (Veltmaat et al.,
2003). (B-G) Whole-mount X-gal stained TOPGAL embryos at E10.5
(B,C); E11.5 (D-F); and E12.5 (G). Cells expressing the TOPGAL transgene
appear blue. At E10.5, TOPGAL activity appears as a streak in the mammary
region between the fore- and hind-limb buds (lb), indicated by arrows (B,C).
By E11.5, TOPGAL-positive cells accumulate in placodes at defined locations
that are reproducible between different embryos (D-F). D' shows a higher
magnification view of placode number 3 from the embryo shown in D.
Blue-stained cells are seen on the surface of the embryo adjacent to the
developing placode (arrows). At E12.5, almost all the blue-staining cells in
the mammary region are concentrated within well-defined mammary buds (G,
arrows). (H) X-gal-stained whole-mount of E17.5 ventral skin showing punctate
staining throughout the mammary epithelial ducts. (I) 20 µm section through
the area of the mammary line in an E10.5 TOPGAL embryo. Note TOPGAL activity
in both the surface epithelium and the underlying mesenchyme (arrow). (J) 5
µm section through a mammary bud from an E13.5 embryo. The epithelial cells
and a few surrounding mammary mesenchymal cells (arrow) express TOPGAL. (K) 5
µm section through the mammary ducts from an E17.5 embryo. A subset of
epithelial cells and a few mesenchymal cells express TOPGAL (arrows). (L)
Whole-mount preparation of X-gal and carmine aluminum (red)-stained mammary
gland from a TOPGAL transgenic mouse on day 13 of pregnancy. TOPGAL is active
in developing alveoli (arrow). (M) 5 µm section through the mammary gland
shown in L. TOPGAL is active in epithelial cells of developing alveolar
structures (arrows).
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