Developmental and Hormonal Regulation of Wnt Gene Expression in the Mouse Mammary Gland

Abstract

Claudins are a large family of membrane proteins whose classic function is to regulate the permeability of tight junctions in epithelia. They are tetraspanins, with four alpha-helices crossing the membrane, two extracellular loops, a short cytoplasmic N-terminus and a longer and more variable C-terminus. The extracellular ends of the helices are known to undergo side-to-side (cis) interactions that allow the formation of claudin polymers in the plane of the membrane. The extracel-lular loops also engage in head-to-head (trans) interactions thought to mediate the formation of tight junctions. However, claudins are also present in intracellular structures, thought to be vesicles, with less well-characterized functions. Here, we briefly review our current understanding of claudin structure and function followed by an examination of changes in claudin mRNA and protein expression and localization through mam-mary gland development. Claudins-1, 3, 4, 7, and 8 are the five most prominent members of the claudin family in the mouse mammary gland, with varied abundance and intracellular local-ization during the different stages of post-pubertal development. Claudin-1 is clearly localized to tight junctions in mam-mary ducts in non-pregnant non-lactating animals. Cytoplasmic puncta that stain for claudin-7 are present throughout development. During pregnancy claudin-3 is localized both to the tight junction and basolaterally while claudin-4 is found only in sparse puncta. In the lactating mouse both claudin-3 and claudin-8 are localized at the tight junction where they may Electronic supplementary material The online version of this article (

An immunohistochemical evaluation of the proteins Wnt1 and glycogen synthase kinase (GSK)‐3β in invasive breast carcinomas

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“…Previous studies suggested that Wnt4 is expressed only concomitant with high progesterone secretion in the adult and pregnant mammary gland (Gavin & McMahon, 1992;Weber-Hall et al, 1994). The finding that deletion of Wnt4 affected mammary regeneration potential more severely than abrogation of PR signaling suggested that Wnt4 may have PR-independent functions in stem cell stimulation.…”

Interactions between FGF and Wnt signals and Tbx3 gene expression in mammary gland initiation in mouse embryos

“…Wnt genes have been suggested to play key roles in glandular development, including the induction of mouse mammary glands (Gavin & McMahon, 1992;Weber-Hall et al 1994). Evidence in favour of this suggestion comes from the regulated expression of these genes in mammary development as well as their proliferative effects on mammary epithelial cells when overexpressed (Wong et al 1994;Bradbury et al 1995).…”