Long-term proliferation of mouse thymic epithelial cells in culture

Long-term culture of porcine bladder epithelial cells

Epithelial cells from normal pig bladders proliferated when cocultured with lethally irradiated feeder cells of the LA7 rat mammary tumor line. When the bladder cells and feeders were plated together at a confluent density, the bladder cells proliferated as the feeder cells died, resulting in a confluent culture of bladder cells. The bladder cells were successfully subcultured by plating with freshly irradiated LA7 feeder cells. In this way, bladder cells from five pigs were carried to confluency in passages 1, 4, 7, 7, and 13, amounting to at least 6, 18, 24, 26, and 45 doublings in culture, respectively, and none showed signs of slowed proliferation at the time of culture termination. Fibroblasts never became a prominent feature of these cultures, and their frequency was determined to be about 26 fibroblasts per 10(5) cells in passage 9. Pig bladder cells in 0.5% serum doubled in number in slightly over 3 d, whereas cells in 5.0% serum doubled in about 6 d. In fresh medium without feeder cells only minimal proliferation of bladder cells occurred. In LA7-conditioned medium the bladder cell numbers decreased, leading to the conclusion that the stimulus from LA7 cells is mechanically or physically transmitted. The bladder cells reacted with antibodies to keratins 7 and 18 but not to keratin 14 or vimentin. Tight junctions, visualized with an antibody to the ZO1 protein, connected all the cells to their neighbors. Most cells in passage 9 carried the diploid chromosome number of 38.

Gap-junctional communication between feeder cells and recipient normal epithelial cells correlates with growth stimulation

LA7 rat mammary tumor cells stimulate the proliferation, in culture, of three normal epithelial cell types, namely mouse mammary, rat mammary, and mouse thymic cells. Gap-junctional communication between LA7 feeders and mouse mammary cells was demonstrated by microinjection of lucifer yellow, which traveled from LA7 to the surrounding mouse mammary cells. The amount of 3H-uridine exchange between feeder and recipient mouse mammary, rat mammary, and mouse thymus cells correlated with the growth rate induced by the feeders. Cells of the Madin Darby canine kidney (MDCK) line, which do not appreciably stimulate mouse mammary cell growth when used as feeder cells, also exchange little 3H-uridine with them. Expression of connexins Cx43, 32, and 26 was studied in all these cell lines and strains by immunocytochemistry. Mouse mammary cells expressed Cx26, and a few mouse thymic cells expressed Cx32. LA7, mouse mammary, mouse thymic, and rat mammary cells all expressed easily detectable amounts of the gap-junction protein Cx43, in contrast to MDCK cells, which expressed only a hint of the protein. These results suggest that gap junctions composed of Cx43 are those by which the normal epithelial cells communicate with the LA feeders. Thus, the ability of feeder cells to stimulate proliferation in recipients correlates with the expression of Cx43 in both members of the feeder/recipient pair and the capacity to form functional gap junctions between these cells.

Feeder cells impart a growth stimulus to recipient epithelial cells by direct contact

Mouse mammary epithelial cells have been shown to proliferate when cultured in the same vessel with lethally irradiated cells of the LA7 rat mammary tumor line. Presented here are experiments that indicate that the LA7 feeder cells stimulate growth of the normal mouse mammary cells by a mechanism that involves direct contact between the two cell types. It is possible that the LA7 feeder cells stimulate proliferation by secretion of a labile growth factor, by secretion of a soluble growth factor in such low concentrations that dilution by travel over a distance makes it less effective, that the stimulus is transduced directly through membrane receptors on the recipient epithelial cells, or that a growth message is sent through gap junctions between cells. This feeder cell system is proposed as an in vitro model for epithelial wound healing.

Cultured proliferating rat mammary epithelial cells

Normal epithelial cells from the rat mammary gland proliferated in culture when plated with lethally irradiated cells of the LA7 rat mammary tumor line. Proliferation of the normal rat cells occurred as the LA7 cells slowly died from the radiation. By labeling the cultures with 3H-thymidine it was determined that most of the proliferating rat cells were those adjacent to the LA7 feeder cells. The epithelial cells from the primary culture proliferated after subsequent passages if the cells were plated at each subculture with newly irradiated LA7 cells. If the cells were plated at a ratio of approximately 1:8 rat:LA7 a confluent layer of normal rat cells covered the plastic substrate after 6 to 7 wk. The cells have so far been carried up through Passage 7, which amounted to approximately 19 doublings in cell number, and still proliferate vigorously. The growth medium for this culture system was Dulbecco's modified Eagle's medium:Ham's F12 1:1 supplemented with fetal bovine serum, insulin, and antibiotics. The presence in the cells of keratin, desmosomes, and cell junctions attested to their epithelial origin. The cultures were composed of cells with diploid or near diploid chromosome numbers. Samples of the cultured cells were implanted into the cleared fat pads of nude mice. Most of the implants from Passage 2 formed normal mammary ductal structures, but the incidence of outgrowths decreased significantly with later passages until no outgrowths resulted from the implantation of cells from Passage 5. The one unusual, feeder-independent cell line that arose from a primary culture seemed to be immortal in culture, contained a hyperdiploid chromosome complement, and formed abnormal structures when implanted into cleared fat pads.

Establishment of functional epithelial cell lines from a rat thymoma and a rat thymus

Seven clonal epithelial cell lines from a thymoma of an (ACI/NMs x BUF/Mna)F1 rat and seven clonal epithelial cell lines from an ACI/NMs rat thymus were established in a medium containing 1 microM dexamethasone (DM) and were characterized cytologically. Long-term treatment of DM stabilized the epithelial nature of these epithelial cells irreversibly. The established cell lines showed a polygonal shape, were positively stained with antikeratin antiserum and had tonofilaments and desmosomes. Species of their keratin peptides were the same as those of normal thymic epithelial cells in primary cultures. The cell lines were positively stained with Th-4 monoclonal antibody which preferentially stains the medullary epithelial cells of the thymus, but not with Th-3 which preferentially stains the subcapsular and cortical epithelial cells of the thymus. The cells from the rat thymoma were much larger than those from the normal thymus, as reflected in their primary cultures. No transformed phenotypes, such as high growth rate, high saturation density, anchorage independency, low serum dependency and so on, were found in the cell lines from the thymoma as in the cell lines from the normal thymus by in vitro assays. DNA synthesis of the thymic lymphocytes was stimulated by culturing with a line of rat thymoma with no lectins. Thymic lymphocytes strongly bound on the cell lines from the thymoma and changed the shape of the cells. These cell lines may be useful to investigate the mechanism of thymomagenesis and the interactions between epithelial cells and thymocytes in the rat thymoma.

Short-term cultivation of murine thymic epithelial cells in a serum-free medium

Thymic epithelial cells were grown in defined medium without unknown serum factors and without concurrent growth of other cell types. Thymic tissue was obtained from 1- to 4-wk-old mice, disaggregated, and incubated in a mixture of collagenase-dispase-DNAse. The resulting organoids were seeded on collagen-coated flasks. The culture medium consisted of DME-F12 with low or high concentration of Ca2+ supplemented with insulin, epidermal growth factor, cholera toxin, hydrocortisone, and transferrin. Under these conditions, explants attached to the substrate within 2 d, and expanding epithelioid monolayer islets emerged from the organoids during the following days. [3H]Thymidine incorporation revealed a growth fraction of the cells close to 5%. By omitting either epidermal growth factor, insulin, or cholera toxin from the medium, pronounced reduction in sizes of islets and in [3H]thymidine incorporation was found. Throughout the culture period, the islets appeared as continuous sheets of polygonal cells. The epithelial nature of the expanding cell islets was confirmed by demonstration of cytokeratins and of desmosomes. Ultrastructural evaluation of early cultures revealed clusters of epithelial cells intermixed with lymphocytes, and late cultures showed a typical pattern of stratified keratinizing epithelium. However, squamous metaplasia was avoided by the use of low Ca2+ medium, which also proved essential for cell transfer. MHC class II antigen was detected on the majority of the cultured cells, and culture supernatants contained co-mitogenic activity for thymocytes and GM-colony stimulating activity.

A cloned rat thymic epithelial cell line established from serum-free selective culture

A serum-free system has been developed for selective growth and long-term culture of rat thymic epithelial cells. The growth media is a modification of McKeehan's WAJC 404, plus insulin, cholera toxin, dexamethasone, and epidermal growth factor. Cultures have been continuously passaged and maintained for over 6 mo., and a cloned cell line, TEA3A1, has been established. These cells are epithelial, judging by morphology and ultrastructure, and are positive for A2B5 and thymosin alpha 1 markers for thymic endocrine cells.