Figure 5

Sustained latent TGFβ binding protein (Ltbp)1L-LacZ expression in the specialized stroma of the adult nipple. (A-E) Robust Ltbp1L-LacZ expression was detected throughout postnatal development by 5-bromo-4-chloro-3-indolyl-β-D-galactoside (X-Gal) staining (blue stain) in bands of smooth-muscle cells (red arrows) at the base of the nipple underlying the areola in the region of the nipple sphincter (A) Histological section through a nipple of a virgin mouse, counterstained with nuclear fast red (NFR). (B, B’) Nipples from a pregnant (P14.5) mouse are shown from below (B) and above (B’). (C) Immunohistochemical detection of SMA 1 (brown stain) colocalizes with Ltbp1L-LacZ in areola smooth muscle, P13.5. Secondary antibody control (C’). (D) Resorcin-fuchsin stain detects elastin fibrils (black arrow to deep purple stain) encompassing Ltbp1L-LacZ-expressing smooth muscle. (E) NFR-stained section shows Ltbp1L-LacZ upregulation in nipple stromal cells during pregnancy, P13.5. (F, F’) Colocalization of Ltbp1L-LacZ expression (black arrow to blue stain) with immunohistochemical detection of vimentin (brown stain) in stromal cells underlying the nipple germinative epithelium (GE) just prior to clefting, during pregnancy (P15.5). NFR-counterstained nipple sections from mice during (G) pregnancy P16.5 and (H) involution. Note the absence of X-Gal staining in the region of the lactiferous duct (LD) within the nipple in G and H and acquisition of reporter expression as the LD enters the fat pad at the base of the nipple (see black arrow in G). Scale bars represent distance in microns.