Developmental Changes in the in Vitro Activated Regenerative Activity of Primitive Mammary Epithelial Cells

Maisam Makarem,Afshin Raouf,Peter Eirew,Long V Nguyen,David J H F Knapp,Connie J Eaves,John Stingl,Nagarajan Kannan,Michael D Prater,Sneha Balani,Oksana Nemirovsky,Timm Schroeder

doi:10.1371/journal.pbio.1001630

Abstract

Author SummaryMany adult tissues are maintained by a rare subset of undifferentiated stem cells that can self-renew and give rise to specialized daughter cells that have a more limited regenerative ability. The recent identification of cells in the fetal and adult mammary gland that display the properties of stem cells provides a foundation for investigating their self-renewal and differentiation control. We now show that these stem cell properties can be elicited from single mouse mammary cells placed in 3D cultures if novel factors produced by fibroblasts are present. Moreover, a comparison of the clonal outputs of fetal and adult mammary cells in this in vitro system shows that the fetal mammary cells have superior regenerative activity relative to their adult counterparts. The ability to activate and quantify the regenerative capacity of single mouse mammary epithelial cells in vitro sets the stage for further investigations of the timing and mechanisms that alter their stem cell properties during development, the potential relevance of these events to other normal epithelial tissues, and how these processes might be involved in the genesis of breast cancer.

Highlights

The regenerative properties of individual cells within the mammary gland were first indicated by the retrovirally marked clonal outgrowths shown to develop from mouse mammary tissue fragments transplanted into the cleared mammary fat pad [1,2]
We show that these stem cell properties can be elicited from single mouse mammary cells placed in 3D cultures if novel factors produced by fibroblasts are present
A comparison of the clonal outputs of fetal and adult mammary cells in this in vitro system shows that the fetal mammary cells have superior regenerative activity relative to their adult counterparts

Summary

Introduction

The regenerative properties of individual cells within the mammary gland were first indicated by the retrovirally marked clonal outgrowths shown to develop from mouse mammary tissue fragments transplanted into the cleared mammary fat pad [1,2]. MRUs can be quantified by limiting dilution analysis (LDA) of their ability to regenerate large branched glandular structures when transplanted into the cleared fat pad of prepubertal mice [3,4]. This MRU assay has been widely used to investigate mechanisms that regulate normal adult mammary stem cell differentiation and growth control [6], as well as the effects of various mutations that contribute to the genesis of breast cancer [7]

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Conclusion