All ETDs from UAB

Advisory Committee Chair

Rosa Serra

Advisory Committee Members

Anupam Agarwal

Chenbei Chang

Andra Frost

Christopher Klug

Jianbo Wang

Document Type

Dissertation

Date of Award

2010

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Transforming growth factor-beta (TGF-beta) negatively regulates mammary gland development and requires Wnt5a to exert some of these effects on mammary gland development. Wnt5a is a non-canonical signaling Wnt that is expressed in all stages of mammary gland development except lactation. Using slow release pellets containing Wnt5a, as well as Wnt5a null tissue, we previously showed that Wnt5a also acts to limit mammary development. Initial studies revealed a potential role for TGF-beta and Wnt5a in regulating mammary gland progenitor cells, indicating they may act to regulate the stem and progenitor cell population. In order to study the role of Wnt5a on mammary stem and progenitor cell maintenance, we wanted to create a new mouse model. Here, we generated transgenic mice that overexpress Wnt5a in the mammary epithelium using the MMTV promoter (M5a mice). Lactation was impaired in two high Wnt5a expressing lines. Lactation defects could not be explained by differences in apoptosis, lineage differentiation, milk synthesis or secretion. Instead, Wnt5a overexpression led to a failure in oxytocin response and milk ejection, similar to mice with a mutation in Connexin43 (Cx43), we examined Cx43 phosphorylation and localization in M5a mice. In wild type mice, Cx43 switched from a phosphorylated to a more hypophosphorylated form after parturition. In contrast, Cx43 was maintained in the phosphorylated form after parturition in M5a mice. Similarly, mammary myoepithelial cells grown in culture and treated with Wnt5a exhibited altered Cx43 phosphorylation relative to vehicle treated control cells. We propose that Wnt5a inhibits the response to oxytocin and prevents milk ejection through regulation of Cx43 phosphorylation. Additionally, we examined the effects of Wnt5a and TGF-beta on mammary stem cell populations and found no direct, significant effects on stem cell number. Although Wnt5a and TGF-beta may not regulate stem cell number, we hypothesize they may direct other aspects of stem or progenitor cell maintenance, such as progenitor proliferation or stem cell self-renewal. Overall, we conclude that Wnt5a and TGF-beta may regulate the mammary progenitor cell population. Additionally, Wnt5a overexpression can alter mammary Cx43 phosphorylation at parturition, inhibiting the milk ejection response.

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