Figure 4

Mesenchymal Ltbp 1L activity is upregulated coincident with embryonic nipple formation. (A) The 5-bromo-4-chloro-3-indolyl-β-D-galactoside (X-Gal)-stained skin whole mount (embryonic day16.5) shows robust Ltbp1L-LacZ expression (blue stain) in the mammary rudiments (white arrows) and developing hair follicles (red arrowheads). (B) Nuclear fast red (NFR)-counterstained section of the E16.5 mammary sprout shows strong focal Ltbp1L-LacZ expression in mammary mesenchyme at the onset of nipple induction. (C, D) Postnatal day 1 X-Gal-stained skin whole mount (C) and NFR-stained section (D) show Ltbp1L-LacZ expression in smooth-muscle cells at the base of the nipple shield extending radially into the developing areola. Scale bars represent microns.