Developmental changes in the in vitro activated regenerative activity of primitive mammary epithelial cells.

Many normal adult tissues contain rare stem cells with extensive self-maintaining regenerative potential. During development, the stem cells of the hematopoietic and neural systems undergo intrinsically specified changes in their self-renewal potential. In the mouse, mammary stem cells with transplantable regenerative activity are first detectable a few days before birth. They share some phenotypic properties with their adult counterparts but are enriched in a subpopulation that displays a distinct gene expression profile. Here we show that fetal mammary epithelial cells have a greater direct and inducible growth potential than their adult counterparts. The latter feature is revealed in a novel culture system that enables large numbers of in vitro clonogenic progenitors as well as mammary stem cells with serially transplantable activity to be produced within 7 days from single fetal or adult input cells. We further show that these responses are highly dependent on novel factors produced by fibroblasts. These findings provide new avenues for elucidating mechanisms that regulate normal mammary epithelial stem cell properties at the single-cell level, how these change during development, and how their perturbation may contribute to transformation.

Isolation of mouse mammary epithelial subpopulations: a comparison of leading methods.

Isolation of mammary epithelial subpopulations, including stem and progenitor cells, has become a standard technique in recent years. However, a number of methods and approaches for this have developed and the relative benefits of the different approaches, and the reason for their development, have not always been clear. Here, three of the leading laboratories working on the separation of mammary cell subpopulations have summarised their methods, highlighted their differences and similarities and also discussed the reasoning behind the approaches they have taken. This article will assist workers establishing mammary cell separation protocols in their laboratories to make informed choices about the methods they should use.

Phenotypic and functional characterisation of the luminal cell hierarchy of the mammary gland.

INTRODUCTION: The organisation of the mammary epithelial hierarchy is poorly understood. Our hypothesis is that the luminal cell compartment is more complex than initially described, and that an understanding of the developmental relationships within this lineage will help in understanding the cellular context in which breast tumours occur. METHODS: We used fluorescence-activated cell sorting along with in vitro and in vivo functional assays to examine the growth and differentiation properties of distinct subsets of human and mouse mammary epithelial cells. We also examined how loss of steroid hormones influenced these populations in vivo. Gene expression profiles were also obtained for all the purified cell populations and correlated to those obtained from breast tumours. RESULTS: The luminal cell compartment of the mouse mammary gland can be resolved into nonclonogenic oestrogen receptor-positive (ER+) luminal cells, ER+ luminal progenitors and oestrogen receptor-negative (ER-) luminal progenitors. The ER+ luminal progenitors are unique in regard to cell survival, as they are relatively insensitive to loss of oestrogen and progesterone when compared with the other types of mammary epithelial cells. Analysis of normal human breast tissue reveals a similar hierarchical organisation composed of nonclonogenic luminal cells, and relatively differentiated (EpCAM+CD49f+ALDH-) and undifferentiated (EpCAM+CD49f+ALDH+) luminal progenitors. In addition, approximately one-quarter of human breast samples examined contained an additional population that had a distinct luminal progenitor phenotype, characterised by low expression of ERBB3 and low proliferative potential. Parent-progeny relationship experiments demonstrated that all luminal progenitor populations in both species are highly plastic and, at low frequencies, can generate progeny representing all mammary cell types. The ER- luminal progenitors in the mouse and the ALDH+ luminal progenitors in the human appear to be analogous populations since they both have gene signatures that are associated with alveolar differentiation and resemble those obtained from basal-like breast tumours. CONCLUSION: The luminal cell compartment in the mammary epithelium is more heterogeneous than initially perceived since progenitors of varying levels of luminal cell differentiation and proliferative capacities can be identified. An understanding of these cells will be essential for understanding the origins and the cellular context of human breast tumours.

Mixed Lymphangioma and Cavernous Hemangioma Within the Ulnar Nerve: A Case Report.

BACKGROUND: Lymphangiomas are benign lymphatic vessel hamartomas typically found in the skin or subcutaneous tissue of the head and neck. Although mostly seen in a congenital context, acquired forms have been reported. By contrast, cavernous hemangiomas are benign hamartomas of endothelial origin. They can arise anywhere in the body, but are typically described as arising from the central nervous system. METHODS: We report the case of a young patient who developed a mixed lymphangioma and cavernous hemangioma within the ulnar nerve. The tumor was removed during an intrafascicular dissection with preservation of all major fascicles. RESULTS: Postoperatively, the patient retained intrinsic motor function and full sensation returned. This is the first published case of this type of mixed tumor occurring in a peripheral nerve. CONCLUSIONS: It could not be ascertained whether trauma was the mechanism by which a lymphangioma developed within the peripheral nerve, as has been proposed. Although this is plausible, alternative mechanisms should be considered.

Mammary stem cells have myoepithelial cell properties.

Contractile myoepithelial cells dominate the basal layer of the mammary epithelium and are considered to be differentiated cells. However, we observe that up to 54% of single basal cells can form colonies when seeded into adherent culture in the presence of agents that disrupt actin-myosin interactions, and on average, 65% of the single-cell-derived basal colonies can repopulate a mammary gland when transplanted in vivo. This indicates that a high proportion of basal myoepithelial cells can give rise to a mammary repopulating unit (MRU). We demonstrate that myoepithelial cells, flow-sorted using two independent myoepithelial-specific reporter strategies, have MRU capacity. Using an inducible lineage-tracing approach we follow the progeny of myoepithelial cells that express α-smooth muscle actin and show that they function as long-lived lineage-restricted stem cells in the virgin state and during pregnancy.

Enzymatic dissociation, flow cytometric analysis, and culture of normal mouse mammary tissue.

Evidence is emerging that the mouse mammary epithelium is arranged as a hierarchy that spans from stem cells to lineage-restricted progenitor cells to differentiated luminal and myoepithelial cells. The use of fluorescence-activated cell sorting (FACS) in combination with quantitative functional clonal assays represents a powerful tool for studying the properties of mouse mammary stem and progenitor cells. This chapter outlines the experimental procedures for generating single viable cell suspensions of mouse mammary epithelial cells, immunostaining cells for flow cytometry, in vitro assays for the detection and enumeration of mouse mammary progenitor cells, and in vivo assays for the detection and enumeration of mouse mammary stem cells.