Thy-1: a differentiation marker of potential mammary myoepithelial cells in vitro

Comprehensive identification, isolation, and culture of human breast cell types

Tissues are formed and shaped by cells of many different types and are orchestrated through countless interactions. Deciphering a tissue's biological complexity thus requires studying it at cell-level resolution, where molecular and biochemical features of different cell types can be explored and thoroughly dissected. Unfortunately, the lack of comprehensive methods to identify, isolate, and culture each cell type from many tissues has impeded progress. Here, we present a method for the breadth of cell types composing the human breast. Our goal has long been to understand the essence of each of these different breast cell types, to reveal the underlying biology explaining their intrinsic features, the consequences of interactions, and their contributions to the tissue. This biological exploration has required cell purification, deep-RNA sequencing, and a thorough dissection of the genes and pathways defining each cell type. While the molecular analysis is presented in an adjoining article, we present here an exhaustive cellular dissection of the human breast and explore its cellular composition and histological organization. Moreover, we introduce a novel FACS antibody panel and rigorous gating strategy capable of isolating each of the 12 major breast cell types to purity. Finally, we describe the creation of primary cell models from nearly every breast cell type-some the first of their kind-and submit these as critical tools for studying the dynamic cellular interactions within breast tissues and tumors. Together, this body of work delivers a unique perspective of the breast, revealing insights into its cellular, molecular, and biochemical composition.

CTGF-D4 Amplifies LRP6 Signaling to Promote Grafts of Adult Epicardial-derived Cells That Improve Cardiac Function After Myocardial Infarction

Transplantation of stem/progenitor cells holds promise for cardiac regeneration in patients with myocardial infarction (MI). Currently, however, low cell survival and engraftment after transplantation present a major barrier to many forms of cell therapy. One issue is that ligands, receptors, and signaling pathways that promote graft success remain poorly understood. Here, we prospectively isolate uncommitted epicardial cells from the adult heart surface by CD104 (β-4 integrin) and demonstrate that C-terminal peptide from connective tissue growth factor (CTGF-D4), when combined with insulin, effectively primes epicardial-derived cells (EPDC) for cardiac engraftment after MI. Similar to native epicardial derivatives that arise from epicardial EMT at the heart surface, the grafted cells migrated into injured myocardial tissue in a rat model of MI with reperfusion. By echocardiography, at 1 month after MI, we observed significant improvement in cardiac function for animals that received epicardial cells primed with CTGF-D4/insulin compared with those that received vehicle-primed (control) cells. In the presence of insulin, CTGF-D4 treatment significantly increased the phosphorylation of Wnt co-receptor LRP6 on EPDC. Competitive engraftment assays and neutralizing/blocking studies showed that LRP6 was required for EPDC engraftment after transplantation. Our results identify LRP6 as a key target for increasing EPDC engraftment after MI and suggest amplification of LRP6 signaling with CTGF-D4/insulin, or by other means, may provide an effective approach for achieving successful cellular grafts in regenerative medicine.

Isolation, purification, culture and characterisation of myoepithelial cells from normal and neoplastic canine mammary glands using a magnetic-activated cell sorting separation system

Mammary gland tumours, the most common malignant neoplasm in bitches, often display myoepithelial (ME) cell proliferation. The aim of this study was to isolate, purify, culture and characterise ME cells from normal and neoplastic canine mammary glands. Monodispersed cells from three normal canine mammary glands and five canine mammary tumours were incubated with an anti-Thy1 antibody and isolated by magnetic-activated cell sorting (MACS). Cells isolated from two normal glands (cell lines CmME-N1 and CmME-N2) and four tumours (cell lines CmME-K1 from a complex carcinoma, CmME-K2 from a simple tubulopapillary carcinoma, and CmME-K3 and CmME-K4 from two carcinomas within benign tumours) were cultured in supplemented DMEM/F12 media for 40days. Cell purity was >90%. Tumour-derived ME cell lines exhibited heterogeneous morphology, growth patterns and immunocytochemical expression of cytokeratins, whereas cell lines from normal glands retained their morphology and levels of cytokeratin expression during culture. Cell lines from normal glands and carcinomas within benign tumours grew more slowly than those from simple and complex carcinomas. This methodology has the potential to be used for in vitro analysis of the role of ME cells in the growth and progression of canine mammary tumours.

Reprogramming non-mammary and cancer cells in the developing mouse mammary gland

The capacity of any portion of the murine mammary gland to produce a complete functional mammary outgrowth upon transplantation to an epithelium-divested fat pad is unaffected by the age or reproductive history of the donor. Likewise, through serial transplantations, no loss of potency is detected when compared to similar transplantations of the youngest mammary tissue tested. This demonstrates that stem cell activity is maintained intact throughout the lifetime of the animal despite aging and the repeated expansion and depletion of the mammary epithelium through multiple rounds of pregnancy, lactation and involution. These facts support the contention that mammary stem cells reside in protected tissue locales (niches), where their reproductive potency remains essentially unchanged through life. Disruption of the tissue, to produce dispersed cells results in the desecration of the protection afforded by the "niche" and leads to a reduced capacity of dispersed epithelial cells (in terms of the number transplanted) to recapitulate complete functional mammary structures. Our studies demonstrate that during the reformation of mammary stem cell niches by dispersed epithelial cells in the context of the intact epithelium-free mammary stroma, non-mammary cells, including mouse and human cancer cells, may be sequestered and reprogrammed to perform mammary epithelial cell functions including those ascribed to mammary stem/progenitor cells.

Tumorigenic WAP-T mouse mammary carcinoma cells: a model for a self-reproducing homeostatic cancer cell system

Background

In analogy to normal stem cell differentiation, the current cancer stem cell (CSC) model presumes a hierarchical organization and an irreversible differentiation in tumor tissue. Accordingly, CSCs should comprise only a small subset of the tumor cells, which feeds tumor growth. However, some recent findings raised doubts on the general applicability of the CSC model and asked for its refinement.

Methodology/Principal Findings

In this study we analyzed the CSC properties of mammary carcinoma cells derived from transgenic (WAP-T) mice. We established a highly tumorigenic WAP-T cell line (G-2 cells) that displays stem-like traits. G-2 cells, as well as their clonal derivates, are closely related to primary tumors regarding histology and gene expression profiles, and reflect heterogeneity regarding their differentiation states. G-2 cultures comprise cell populations in distinct differentiation states identified by co-expression of cytoskeletal proteins (cytokeratins and vimentin), a combination of cell surface markers and a set of transcription factors. Cellular subsets sorted according to expression of CD24a, CD49f, CD61, Epcam, Sca1, and Thy1 cell surface proteins, or metabolic markers (e.g. ALDH activity) are competent to reconstitute the initial cellular composition. Repopulation efficiency greatly varies between individual subsets and is influenced by interactions with the respective complementary G-2 cellular subset. The balance between differentiation states is regulated in part by the transcription factor Sox10, as depletion of Sox10 led to up-regulation of Twist2 and increased the proportion of Thy1-expressing cells representing cells in a self-renewable, reversible, quasi-mesenchymal differentiation state.

Conclusions/Significance

G-2 cells constitute a self-reproducing cancer cell system, maintained by bi- and unidirectional conversion of complementary cellular subsets. Our work contributes to the current controversial discussion on the existence and nature of CSC and provides a basis for the incorporation of alternative hypotheses into the CSC model.

Expression of MAP kinases and connexins in the differentiation of rat mammary epithelial cells

Gap junctional intercellular communication (GJIC) is involved in the regulation of many cellular processes. MAP kinases are known to affect GJIC and phosphorylation of connexin (Cx). MAP kinases can also be a regulator of cell proliferation and growth. This study was undertaken to show the relevance between expression patterns of Cxs and MAP kinases in rat mammary epithelial cells (RMECs). In order to characterize the RMECs, they were stained with Peanut lectin, which indicates most alveolar epithelial cells, and Thy-1.1 was used as a marker of luminal epithelial cells or myoepithelial cells, respectively. We studied the expression patterns of major gap junction proteins, Cx26, 32, and 43 in RMECs. Western blot analysis demonstrated that Cx26 gradually decreased from day 2, while Cx32 was expressed constantly from day 1 to 14. Cx43 dramatically increased on day 5 and decreased thereafter. The expression patterns and phosphorylation of ERK1/2 and JNK were similar to Cx43, but expression of p38 was like that of Cx32. These results showed that the MAP kinases that comprise ERK1/2, p38, and JNK were involved in regulation of Cxs. Our data suggests that GJIC plays an important role during rat mammary differentiation and that MAP kinases may be closely related functionally to regulate the gap junction.

Epithelial to mesenchymal transition in human breast cancer can provide a nonmalignant stroma

A breast carcinoma biopsy showed cytochemical evidence of epithelial mesenchymal transition and an alpha-smooth muscle actin-positive stromal reaction. To study the lineage, and the nature of the cells in the stromal reaction, we derived a novel cell line, HBFL-1, from the explanted biopsy. HBFL-1 cells are immortal and exhibit a shared non-random X-chromosome inactivation pattern with the epithelial tumor of origin. Yet they closely resemble normal, finite-life-span fibroblasts by morphology, lack of tumor formation in nude mice, marker expression profile, protein pattern using two-dimensional gel electrophoresis and the ability to undergo myofibroblast conversion. HBFL-1 interacts reciprocally with tumor cells in collagen gel to induce activation of MMP2, leading to tumor-like behavior of epithelial colonies. In vivo, HBFL-1 cells resembled normal-derived myofibroblasts and conferred a significant 3.5- to 7-fold increase in MCF-7 tumor size in nude mice. However, that they were indeed not normal fibroblasts was revealed by residual keratin expression and formation of epithelial microfoci in a reconstituted basement membrane and in nude mice. We conclude that breast cancer can generate its own nonmalignant stroma and that one function for this is that of a reciprocal interaction with epithelial tumor cells to facilitate tumor growth.

Function of the hydrophobic transmembrane portion of Thy-1 antigen

Thy-1 antigen is anchored in the cell membrane by glycophosphatidyl inositol linkages instead of hydrophobic protein domains. The hydrophobic portion of Thy-1 antigen is cleaved by putative "transamidase." Mutated genes were constructed by using site-directed mutagenesis. One mutant gene codes Thy-1 antigen lacking carboxy terminal amino acids from 112Cys to 143Leu including cell membrane binding amino acid 112Cys. The other mutant gene codes Thy-1 antigen lacking from 124Trp to 143Leu that includes leucine core portion. DNA transfection analysis and Northern blot analysis revealed that hydrophobic portion of Thy-1 antigen is essential to express Thy-1 molecule onto the cell surface.

Dynamics and longevity of the glycolipid-anchored membrane protein, Thy-1

Thy-1 and a number of other proteins are anchored to the outer hemi-leaflet of membranes by a glycolipid moiety containing ethanolamine phosphate, mannose, glucosamine, and phosphatidylinositol. They nevertheless have the striking property of being able to transduce signals across the plasma membrane. We here demonstrate, for the BW5147 murine T lymphoma, that (a) greater than 90% of Thy-1 is at the cell surface, (b) Thy-1 is about one order of magnitude less concentrated in coated pits than the transferrin receptor or H-2 antigens, (c) Thy-1 undergoes at most very limited endocytosis or diacytosis, and (d) Thy-1 has an unusually slow turnover rate. Several similar observations have also been made for a second glycolipid-anchored protein, the T cell activating protein. Thus, the absence of cytoplasmic and trans-membrane domains may result in lipid-anchored proteins being confined to the cell surface and being free from constraints which affect the turnover of transmembrane proteins.

Determination of the molecular nature and cellular localization of Thy-1 in human renal tissue

The molecular nature and cellular localization of Thy-1 antigen in human renal tissue were studied. Strong immunohistochemical staining was observed in frozen sections of human kidney using monoclonal anti-human Thy-1 antibody; this reaction was almost completely abolished by pretreating the kidney section with phosphatidyl inositol (PI)-specific phospholipase C (PI-PLC). Immunohistochemical analysis revealed that the Thy-1 antigen is localized on the proximal tubular epithelial cells and the Bowman's capsule of the glomerulus. Northern blot analysis of renal mRNA using a cloned human Thy-1 gene revealed the presence of human Thy-1 mRNA of a similar size to the one in human brain. When a human kidney cDNA library was screened with the same probe, a cDNA of human Thy-1 was isolated. Moreover, human Thy-1 protein with a molecular weight (MW) of 21,000 was detected in renal tissue by gel electrophoresis and Western blot analysis using monoclonal anti-human Thy-1 antibody. These data demonstrate for the first time the production of human Thy-1 as a PI-anchored protein with a unique cellular location in human renal tissue.

Changes of subcellular localization of Thy-1 antigen during thymic myoid cell differentiation

Using a quantitative enzyme immunoassay, Thy-1 antigen expressed by a rat myoid cell line R615B2 was detected mainly on the cell surface at a single cell stage, whereas at the stage of forming myotubes, Thy-1 was found predominantly in the cytoplasm. The muscle specific creatine kinase activity also increased in association with the shift of Thy-1 from the cell surface to the cytoplasm, suggesting biological significance of Thy-1 redistribution in muscle differentiation from single cells to multinucleated cells.

Differential control of mRNA levels for Thy-1 antigen and laminin in rat mammary epithelial and myoepithelial-like cells

Thy-1 antigen and laminin are two components often associated with the basement membrane of the rat mammary gland and are thought to be synthesized, at least in part, by the adjacent myoepithelial cells in vivo. The relative levels of Thy-1 mRNA and laminin mRNA are compared in a rat mammary cuboidal epithelial cell line and a derivative elongated myoepithelial-like cell line by hybridizing cloned cDNAs to cellular mRNA isolated from these cell types. Although the elongated myoepithelial-like cells synthesize four times as much laminin protein as the cuboidal epithelial cells, there is only a 1.7-fold increase in laminin mRNA between the two cell types. In contrast the 17-fold increase in Thy-1 antigen between the elongated cells and the cuboidal cells can be accounted for completely by a 14-18-fold increase in Thy-1 mRNA, suggesting that changes in the steady-state levels of Thy-1 mRNA in these cell lines are modulated at either a transcriptional or a post-transcriptional level. Run-off transcription by nuclei isolated from the cell lines does not distinguish between these two possibilities. The comparative results on Thy-1 antigen and laminin show that the enhanced production of two proteins often associated with the basement membrane of the rat mammary gland can be controlled at different levels in the elongated myoepithelial-like cells.

Culture and characterization of murine dendritic Thy-1+ epidermal cells

Although numerous advances have been made in characterizing the phenotype, ontogeny, ultrastructure, and cytochemistry of the murine Thy-1+ dendritic epidermal cell (Thy-1+ EC), elucidation of its functional qualities has been hampered by the difficulty in preparing pure populations of these cells. We therefore sought to obtain expanded, purified populations of Thy-1+ EC using culture techniques. Since Thy-1+ EC are bone marrow-derived, density gradient enriched populations of freshly harvested epidermal cells (FH-EC) were placed in culture under conditions known or suspected to promote mitogenesis among leukocyte subsets. FH-EC prepared from truncal skin of C3H/HeN mice (Thy-1.2+) were cultured at 37 degrees C in 5% CO2 in complete medium (CM) of Eagle's Hanks' amino acid with 10% fetal calf serum, nutrients, and antibiotics at 10(6) FH-EC/well in 24-well culture plates. CM was supplemented with one or more of the following: concanavalin A (Con-A), interleukin-1/epidermal cell-derived thymocyte-activating factor (IL-1/ETAF), IL-2, IL-3, gamma interferon, indomethacin (IM), and anti-Thy-1.2 antibody. Media with appropriate supplements were changed every 2-3 days. Freshly isolated, enriched FH-EC contained 7-20% Thy-1+ EC (defined as brightly fluorescing cells readily distinguishable from weakly fluorescing keratinocytes), which also stained with antibodies directed against asialo GM1, Ly 5.1, and vimentin but did not stain with antibodies to other T cell-, B cell- or macrophage phenotypic markers. Analysis of 10 separate cultures revealed a 3- to 10-fold expansion of nonkeratinocyte Thy-1+ cells after 21 +/- 4 days in culture in CM supplemented with Con-A and IM, and 70-100% of viable cells after expansion were Thy-1+. Phenotypic analysis of expanded cells revealed the emergence in 10 separate cultures of one of two mutually exclusive distinct populations: one Thy-1+, asialo GM1+, L3T4- (natural killer phenotype) and the other Thy-1+, asialo GM1-, L3T4+ (T helper phenotype). Experiments designed to explain the emergence of an L3T4+ population suggest that phenotypic modulation occurred in vitro.

Heterogeneity of epidermal Thy-1-positive cells defined by lectin-binding sites

A new cell type that expresses Thy-1 antigen (dendritic epidermal Thy-1-positive cells, d-Thy-1+ EC) was discovered in the murine epidermis in 1983. It is not clear, however, whether all d-Thy-1+EC represent a unitary population. We investigated the cell surface glycoconjugate pattern of d-Thy-1+EC using 6 lectins: concanavalin A (Con-A), Dolichos biflorus agglutinin (DBA), Ricinus communis agglutinin 1 (RCA-1), wheat germ agglutinin (WGA), Ulex europaeus agglutinin (UEA-1), and peanut agglutinin (PNA). These lectins could be divided into 3 groups: lectins binding to most d-Thy-1+EC (Con-A and RCA-1); lectins virtually unreactive with d-Thy-1+EC (DBA and UEA-1); and lectins binding to subpopulation of d-Thy-1+EC (WGA and PNA). For lectins of group 1 and group 2, no difference was observed from strain to strain of mice (C3H/He, BALB/c, and C57B1/6), or from site to site of the body (back, ear, and tail). However, striking difference of percentage of lectin-binding d-Thy-1+EC was observed in group 3 lectins in the tail region compared with the back or the ear, although no strain difference was noted: back or ear, 83.6-95.5% with PNA, 13.6-29.6% with WGA in C3H; tail, 4.0-19.4% with PNA, 30.0-59.1% with WGA in C3H. These results indicate that d-Thy-1+EC are a heterogeneous population and that their distribution is different from site to site in the body.

In vitro characteristics of rat mesangial cells in comparison with aortic smooth muscle cells and dermal fibroblasts

Rat glomerular mesangial cells were cultured and their antigens were compared with those of aortic vascular smooth muscle cells and dermal fibroblasts. Glomeruli, aortic, and dermal explants were cultured for 3 weeks and subcultured in the same conditions. These cultured cells were evaluated by indirect immunofluorescence studies using antibodies against Thy-1 antigen, desmin, and chicken gizzard actin. Most of mesangial cells were positive for Thy-1, desmin, and actin. On the other hand, fibroblasts were negative for desmin, and smooth muscle cells stained Thy-1 scarcely, and were negative for desmin. In the latter two cells, actin-positive fibrils were thinner and fainter than mesangial cells. These results indicated that mesangial cells could be distinguished in vitro from vascular smooth cells and fibroblasts by immunofluorescence microscopy.

Morphological and phenotypical characterization of bone marrow-derived dendritic Thy-1-positive epidermal cells of the mouse

Increasing evidence exists that the spectrum of dendritic cells within the epidermis is more complex than previously thought. In addition to Langerhans cells, Merkel cells, and melanocytes, the murine epidermis contains a dendritic cell population whose most prominent phenotypic feature is the Thy-1 antigen. These cells are now generally referred to as dendritic Thy-1+ epidermal cells (dThy-1+EC). The ultrastructural features of these cells do not resemble those of other resident epidermal cells (EC). In particular, their cytoplasm contains abundant intermediate-sized filaments of the vimentin type as well as membrane-limited organelles with a central granular core. The bone marrow derivation of dThy-1+EC is now well established: dThy-1+EC carry Ly-5 determinants whose expression is restricted to cells of the hemopoietic differentiation pathway, and studies using Thy-1-disparate radiation bone marrow chimeras have revealed the presence of donor-type Thy-1+ cells within the epidermis; by immunoelectron microscopy, these cells represent dThy-1+EC. dThy-1+EC repopulate the epidermis at a slower rate than Langerhans cells as evidenced by a direct comparison of the repopulation kinetics of both cell systems in radiation bone marrow chimeras, and by experiments studying the emergence of either Ia+- or dThy-1+EC in an epidermis which had been previously depleted of either Langerhans cells (glucocorticosteroids) or of dThy-1+EC (PUVA). The phenotypical features of dThy-1+EC differ from those of thymus-derived lymphocytes, B cells, dendritic cells, and mononuclear phagocytes. The surface marker repertoire of dThy-1+EC (Thy-1, Ly-5, asialo-GM1) resembles certain members of the rather heterogeneous natural killer (NK) cell system but functional studies are needed to ascertain this contention.

Origin and function of Thy-1+ dendritic epidermal cells in mice

The epidermis of normal mouse skin incorporates a newly-recognized population of dendritic cells which express relatively large amounts of the cell surface glycoprotein, Thy-1 antigen. These cells, termed Thy-1+dEC, are distinct from both epidermal Langerhans cells (LC) and melanocytes, and they populate cutaneous sites in surface densities which range to as high as 580 cells/mm2, approximately two-thirds that of LC. Studies of lethally irradiated mice which were reconstituted with semiallogeneic bone marrow cells and mice which received grafts of semiallogeneic skin have demonstrated that some, if not all, Thy-1+dEC are of bone marrow origin, and that they are capable of migrating into epidermis from a vascular source. Thy-1+dEC expressed both asialo GM1 and a cell surface determinant recognized by the monoclonal antibody 20-10-5S, further suggesting their functions will be included among those normally ascribed to lymphoreticular cells. Isolation of epidermal cells with the Fluorescence Activated Cell Sorter (FACS) was successful in producing relatively pure populations of Thy-1+dEC and LC. Such technological advances as this should facilitate testing several hypotheses concerning the ultimate function of these cells, including the possibilities that they are antigen-presenting cells which selectively activate down-regulating signals, T lymphocytes, natural killer (NK) cells, or natural suppressor (NS) cells.

Isolation and characterization of mouse Thy-1 genomic clones

The mouse Thy-1.2 gene was isolated from a C57Bl/6 cosmid library and its nucleotide sequence was determined from an 8-kilobase-long EcoRI fragment. The predicted amino acid sequence indicates that the mouse Thy-1 molecule contains a 19 amino acid leader peptide and the 112 amino acids reported previously from protein sequence analysis, plus 31 extra amino acids at the carboxyl terminus. These 31 amino acids contain a stretch of 20 amino acids, at positions 124-143, which is highly hydrophobic. RNA transfer blot analysis of RNA from mouse tissues indicates that the sequence coding for these 31 amino acids is present on poly(A)-containing RNA of brain and thymus tissues. This hydrophobic segment very likely provides the basis for integration of Thy-1 within the plasma membrane. The entire coding sequence of Thy-1 is distributed among three exons, encoding amino acid residues -19 to 8, -7 to 106, and 107 to 143, respectively. Comparison of the mouse and rat Thy-1 genes shows that both have a similar gene organization and encode a highly conserved transmembrane segment.

Thy-1 is a differentiation antigen that characterizes immature murine erythroid and myeloid hematopoietic progenitors

To determine the role of Thy-1 antigen in murine hematopoietic differentiation, bone marrow was treated with anti-Thy-1.2 antibody and complement or complement alone. Growth of immature hematopoietic progenitors, erythroid burst-forming units (BFU-E), and granulocyte/macrophage colony-forming units (CFU-GM) was greatly reduced following antibody and complement treatment and was not restored by mitogen-stimulated spleen cell supernatants. In contrast, more mature erythroid and myeloid progenitors, the erythroid colony-forming unit (CFU-E) and the macrophage progenitor stimulated by L-cell-conditioned media (LCM), were spared by anti-Thy-1.2 antibody and complement treatment. Here, to separate the effects of anti-Thy-1.2 antibody treatment on accessory cells from those on progenitors, splenic T cells and thymocytes were added to treated marrow at ratios of up to 200%. Growth of BFU-E and CFU-GM was not restored. To more precisely replace required accessory cells, male complement-treated marrow was cocultured with female anti-Thy-1.2 antibody and complement-treated marrow. Even marrow cells failed to restore female BFU-E and CFU-GM growth. Fluorescent-activated cell sorting (FACS) and immune sheep red cell rosetting with anti-Thy-1.2-labeled marrow were then performed to determine if immature hematopoietic progenitors bear Thy-1.2. These techniques revealed enrichment of BFU-E and CFU-GM in the Thy-1.2-positive fraction, demonstrating the presence of Thy-1.2 on early murine hematopoietic progenitors. CFU-E and CFU-M were present in the Thy-1.2-negative fraction following FACS separation. These data demonstrate that Thy-1.2 is a differentiation antigen, present on at least some murine BFU-E and CFU-GM and lost as they mature to CFU-E and CFU-M.

Thy-1 antigen-bearing dendritic cells in murine epidermis are derived from bone marrow precursors

Thy-1 antigen is expressed on a dendritic subpopulation of cells in murine epidermis. Numbering between 200 and 500/mm2 surface area in abdominal skin, they are distinct from the dendritic Langerhans cells (LCs) and melanocytes. Since immigrant lymphoid cells as well as constitutive cells in various organs have been demonstrated to be Thy-1+, their origin and function are not certain. To assess these issues, two experimental protocols were established. First, grafts of whole skin from AKR mice were placed orthotopically on (AKD2)F1 recipients. Immigration of recipient-derived cells into graft epidermis was assessed histologically by fluorescence microscopy employing monoclonal anti-Thy-1.2 and anti-I-Ad antibodies. Second, bone marrow chimeras were established in AKR recipients after lethal irradiation and reconstitution with cells from (AKD2)F1 donors. In the first protocol, dendritic I-Ad+ LCs of donor origin infiltrated each graft to normal densities within 2 weeks. Thy-1.2+ cells also immigrated into the same grafts, but at much slower rates. In the second protocol, bone marrow-derived Thy-1.2+ cells populated normal skin epidermis slowly over several months, with densities reaching 70/mm2. We conclude that some, if not all, Thy-1+ cells in normal murine epidermis are derived from bone marrow precursors, that their infiltration rates differ substantially from those of LCs, and that those factors which govern immigration rates into adult skin derive from the skin itself rather than from the systemic availability of their precursors. We suggest that the function of Thy-1+ epidermal cells will therefore reside among those usually ascribed to recirculating hematogenous cells, including the possibility that they may down-regulate immunizing signals that emerge from skin.

Thy-1+ dendritic cells in murine epidermis are bone marrow-derived

Thy-1+, Ly-5+ dendritic cells have recently been described as a resident cell population in murine epidermis, but their ontogeny and function are unknown. We therefore investigated the origin and turnover of epidermal Thy-1+ cells utilizing chimeric mice. Lethally x-irradiated AKR/J (Thy-1.1+) and AKR/Cum (Thy-1.2+) mice were reconstituted with allogeneic bone marrow cells with or without thymocytes from congenic AKR/Cum or AKR/J mice, respectively. The density of residual indigenous Thy-1.1+ cells in AKR/J chimeras and Thy-1.2+ cells in AKR/Cum chimeras was substantially reduced following x-irradiation, as determined by immunofluorescence staining of epidermal sheets. Epidermal repopulation by allogeneic Thy-1+ dendritic epidermal cells was first observed at 5 weeks in AKR/J chimeras and at 7 weeks in AKR/Cum chimeras and progressed slowly. Repopulation was not enhanced by increasing the number of allogeneic bone marrow cells injected from 2 X 10(7) to 10(8) cells or by the addition of 8 X 10(7) allogeneic thymocytes to the donor inoculate. Epidermal repopulation by allogeneic Thy-1.2+ cells was not seen in AKR/J mice reconstituted with syngeneic bone marrow cells and allogeneic Thy-1.2+ AKR/Cum thymocytes. Taken together, these results indicate that Thy-1+ dendritic epidermal cells are derived from the bone marrow and suggest that they are not related to conventional peripheral T-lymphocytes.

Thy-1 antigen-bearing dendritic cells populate murine epidermis

Two distinct cell populations, melanocytes and Langerhans cells (LC), have been recognized previously to possess dendritic configuration in normal mammalian epidermis. Employing immunofluorescence microscopy with monoclonal antibodies against Thy-1.2 antigen to identify cells in whole mounts of murine epidermis, we have identified a third dendritic cell population which differs from both LC and melanocytes. Thy-1 antigen-bearing (Thy-1+) epidermal cells are primarily dendritic, although round and angular forms may be found. They are distributed relatively evenly across skin surfaces, although densities vary greatly from site to site and from strain to strain. Densities were highest in ear epidermis from the pigmented strain B10.A (580 cells/mm2), a value approaching that of epidermal LC, and were lowest in ear epidermis from the albino strain BALB/c (5 cells/mm2). Thy-1+ epidermal cells possess neither Ia antigens nor substantial amounts of melanin, and their surface distributions are disparate from those of both LC and mature melanocytes. We propose that at least some of these cells are T lymphocytes whose malignant counterparts account for cutaneous T-cell lymphomas.

Expression of Thy-1 antigen by murine epidermal cells

We report on the occurrence of a cell population within the murine epidermis which, by both morphologic and surface property criteria, is distinct from all other epidermal cell types known so far. These previously unrecognized cells are evenly distributed within the epidermis, display a primarily dendritic shape, exhibit a lobulated nucleus, contain large amounts of vimentin type intermediate-sized filaments, but lack desmosomes, melanosomes, Merkel cell granules, and Birbeck granules. As opposed to melanocytes, these cells fail to display tyrosinase activity. Surface marker analysis reveals these cells to uniformly express the Thy-1 antigen and to lack I-A and I-E/C antigen specificities. A major portion of these Thy-1-bearing cells are reactive with a monoclonal antibody to the Ly-5 determinant whereas attempts to demonstrate Lyt-1,2,3 antigens consistently yield negative results. These findings strongly suggest that Thy-1+ epidermal cells originate from the bone marrow; however, their precise relationship to distinct members of the hemopoietic differentiation pathway remains to be established.

Topographical arrangement of basement membrane proteins in lactating rat mammary gland: comparison of the distribution of type IV collagen, laminin, fibronectin, and Thy-1 at the ultrastructural level

The topographical distribution of type IV collagen, laminin, fibronectin, and the thymocyte differentiation antigen Thy-1 in the basement membrane of the lactating rat mammary gland was investigated. Small cubes of tissue, which had not been subjected to prior fixation or freezing, were incubated with monospecific or monoclonal antibodies to these proteins, and the antibodies were located by an indirect immunoperoxidase staining technique and observed in the electron microscope. The lamina densa stained uniformly with antibodies to type IV collagen and laminin. In addition, both laminin and type IV collagen were present in semiperiodic clusters that traversed the lamina lucida from the cell surface to the lamina densa. Fibronectin was present only in the semiperiodic clusters and not elsewhere in the basement membrane. These clusters were irregularly spaced along the cell surface and heterogeneous in size. It remains to be determined if these three proteins are present in the same clusters. Thy-1 was largely present on the lamina densa and not on the lamina lucida. The Thy-1 staining of the lamina densa occurred in discrete maxima and minima. These maxima occurred in regions adjacent to Thy-1-bearing stromal cells. Thus, the topographical distribution of proteins within a basement membrane varies in a nonrandom manner, and local factors can modify this distribution. We suggest that this topographical variability may play a role in cell recognition and signalling processes that occur across the basement membrane.

Epithelial cell types and their evolution in the rat mammary gland determined by immunological markers

We have used immunological reagents for characterizing epithelial cell types in the adult rat mammary gland. Some were sera against purified proteins; others were monoclonal antibodies to mammary cells. On the basis of marker distribution we have identified 10 different cell types. We have established the developmental connection between these types by adopting the principle that cells displaying the same markers are directly related to each other. The results concur with those previously obtained by studying the growth response of mammary cells to the hormonal changes of the estrus cycle.

Thy-1 cDNA sequence suggests a novel regulatory mechanism

Thy-1 was originally defined in mice as a cell-surface alloantigen of thymus and brain with two allelic forms, Thy-1.1 and Thy-1.2 (ref. 1). Subsequently, the Thy-1.1 alloantigenic determinant was identified in rats. In both species, Thy-1 is present in large amounts on thymus and brain cells and in smaller quantities on fibroblasts, epidermal cells, mammary glands and immature skeletal muscle. In many of these tissues the level of Thy-1 expression changes dramatically during cell differentiation. The molecules expressing the Thy-1 antigenic determinant have been isolated from rat and mouse brain cells and have been shown to have a molecular weight of 17,500 (ref. 8). One-third of the Thy-1 molecule is carbohydrate and the remainder is a polypeptide of 111 amino acids whose sequence has been fully determined. We report here the isolation and characterization of a cDNA clone encoding the rat thymus Thy-1 antigen but find that the DNA sequence ends prematurely at a position corresponding to amino acid 103. It appears to be a complete transcript, however, as the last codon is followed directly by a poly(A) tract.

Isolation and characterization of a serially cultivated, neoplastic, epithelial cell line from the N-nitrosomethylurea induced rat mammary adenocarcinoma

A new in vitro model for human breast cancer is described. Derived from an N-nitrosomethylurea (NMU) induced rat mammary adenocarcinoma, this serially cultivated cell line has been demonstrated, by a variety of criteria, to be an authentic neoplastic, rat mammary epithelial cell line. The criteria used include morphological and growth characteristics; the presence of specific cell surface antigens; steroid hormone receptors; hormone responsiveness; casein production; karyotype and isoenzyme profile analysis; anchorage independent growth and oncogenicity. Inasmuch as the NMU cell line possesses high concentrations of glucocorticoid and androgen receptors, it may provide a useful model for study of the action of these hormones in human breast cancer. In addition, the NMU line may serve as a valuable in vitro model in which to assess the effects of a variety of endogenous and exogenous agents known to influence mammary tumor growth in vivo, including drugs, nutrients, and growth factors.

Thy-1 determinants are present on many murine hematopoietic cells other than T cells

The development of a highly amplified immunofluorescence assay and the availability of monoclonal anti-Thy-1 antibodies have provided the methodology to reexamine the presence of Thy-1 antigen on murine lymphohematopoietic cells. The representation of this antigen is not, as previously believed, restricted to the T cell compartment of these cells. It is present on a significant number of mouse bone marrow cells (25-30%), including, as in the rat, multipotential stem cells, prothymocytes and some B cell precursors. Eosinophils and some immature myeloid cells are also antigen-positive.

Rat brain Thy-1 glycoprotein. The amino acid sequence, disulphide bonds and an unusual hydrophobic region

The full sequence of the Thy-1 membrane glycoprotein of rat brain is reported. The sequence was determined from tryptic and V-8 proteinase peptides and consisted of 111 amino acids. The amino terminus was blocked and consisted of a pyroglutamic acid residue. The molecule contained two disulphide bonds, namely Cys-9--Cys-111 and Cys-19--Cys-85. Three N-linked amino sugars were located at Asn-23, Asn-74 and Asn-98. In each case the sequence on the C-terminal side of the attachment point was Asn-Xaa-Thr as would be expected for N-linkage. The C-terminal peptides were unusual, in that they were either obtained in a highly aggregated form, or could only be purified after binding to Brij 96 micelles. Thus they appeared to have hydrophobic properties, yet did not contain any extended sequence of hydrophobic amino acids. Other unusual features of the C-terminal peptides were the presence of unidentified ninhydrin-positive material and of glucosamine and galactosamine. The C-terminal residue has not been directly identified but Cys-111 is the last conventional amino acid. It is suggested that the hydrophobic properties of the C-terminal peptides may be due to the linkage of lipid. The sequence of the Thy-1 glycoprotein showed homologies with immunoglobulin domains. This relationship is examined in detail in the paper following [Cohen et al. (1981) Biochem. J. 193, 000--000].

Generation of fibroblast-like cells from cloned epithelial mammary cells in vitro: a possible new cell type

We have isolated clonal cell lines from a nitrosomethylurea-induced mammary tumor in Wistar--Furth rats. The epithelial-like cells of these lines give rise to fibroblast-like cells. A study of several markers showed that the epithelial-like cells are similar to epithelial mammary cells. The fibroblastic cells, however, were similar to stromal cells, except for the production of collagen IV. The events occurring in these cultures are identical to those observed in previously isolated mammary cultures [Bennett, D. C., Peachey, L. A., Durbin, H. & Rudland, P. S. (1976) Cell 15, 283--298], suggesting their generality. The fibroblast-like cells generated in culture may be a hitherto unrecognized type of mammary cell.

Differentiation and morphogenesis of mammary cells in vitro

Cells of a mammary cell line isolated from a DMBA-induced rat mammary carcinoma undergo differentiation in vitro. A reversible differentiation leads to the formation of two types of microstructure (domes and ridges); this paper is concerned with the mechanism of dome formation. This differentiation is initiated by inducers, some of which are generated in the cultures and act locally; their effect is strongly dependent on cell concentration and requires hydrocortisone. There are, in addition, exogenous inducers as well as inhibitors. In the pathway to dome formation important roles are played by cAMP (probably both intracellular and extracellular), the organization of the cytoskeleton, and the Thy-1 antigen. The pathway and the significance of the phenomenon for mammary gland development are discussed.

Isolation and characterization of the thymus-brain antigen (analogous to thy-1 antigen) from human brain

1. The human thymus-brain antigen, which corresponds to the murine (mouse or rat) Thy-1 antigen complex, was isolated from brain after solubilization in deoxycholate by gel-permeation chromatography, wheat-germ-lectin affinity chromatography and ion-exchange chromatography. 2. The isolated antigen is a glycoprotein displaying an apparent molecular weight of 26 000-29 000 in sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 3. No antigen activity was found with the lipid fraction from human brain. 4. The protein has a tendency for spontaneous self-association (dimerization), leading to aggregates resistant to dissociating and reducing agents on prolonged storage. 5. The antigen is microheterogeneous with respect to size, charge (approximate isoelectric points of the monomer 7.7, 7.0 and 6.5) and to lectin-binding affinity. 6. The antigen can be reconstituted to protein-lipid vesicles. The antigen activity of solubilized antigen is strongly increased by reconstitution and that of membranes decreased by solubilization with detergent.

Hidden Thy-1 antigen in a subpopulation of mouse bone marrow cells

Immunofluorescence and cytolysis studies using antisera against the xeno- and alloantigenic components of the Thy-1 molecule have shown that in adult mouse bone marrow more cells bear the xeno than the alloantigen. Allo+ cells form a subset of a larger, xeno+ population. Xeno+ allo- 'prothymocytes' can be induced to express the alloantigen in vitro; this could result from the unmasking of cryptic antigen, the presence of which is demonstrated, rather than de novo antigen synthesis. Some xeno+ allo- cells are involved in splenic haemopoiesis, either as a subpopulation of precursors, or as accessory helper cells.

Association of thy-1 cell surface differentiation antigen with certain connective tissues in vivo

The cell surface differentiation antigen, Thy-1, has been demonstrated by immunofluorescence to be associated with some collagen-based connective tissue. In the rat, the basement membrane of kidney collecting tubules of certain blood vessels, reticulin of the lamina propria, loose connective tissue in the dermis, and collagen fibres within certain nerve cell tumours, bear the antigen. Other, apparently similar, connective tissue (especially that of muscle and liver) lacked Thy-1. In the mouse, only the connective tissue of the skin was found to bear the antigen. The possible origin of this extracellular Thy-1, and its implications for the function of the molecule, are discussed.

Role of Thy-1 antigen in the in vitro differentiation of a rat mammary cell line

A line of rat mammary cells, LA7, undergoes differentiation into domes or ridges or projections under partial medium control. Immunofluorescent studies show that at the time of dome formation the LA7 cultures express the Thy-1 antigen at the borders between cells. Exposure of the cultures to certain monoclonal anti-Thy-1.1 sera prevents formation of new domes and causes disappearance of preexisting ones; antisera to whole cells produce no visible effect. Cultures exposed to anti-Thy-1 sera at effective concentrations of antibody against domes show morphological changes and ridge formation. It seems that the specific interactions of these antisera with the Thy-1 antigen redirects the differentiation program of the cells.

Differentiation of a rat mammary cell line in vitro

We have studied the development of fusiform (probably related to myoepithelial) cells in Rama 25 cultures [Bennett, D. C. Peachey, L. A., Durbin, H. & Rudland, P. S. (1978) Cell 15, 283--298]; we show that they are generated from special differentiated structures (projections) that contain a rapidly differentiating cell type (F-precursor cells). Clonal sublines isolated from projections develop in several directions under both environmental and genetic control. Some types of differentiation are reversible; others are irreversible. The various cell occurring in vitro may correspond to specific cell types in vivo.