Isolation of cell lines from differentiating embryonal carcinoma cultures

DNA methylation specifies chromosomal localization of MeCP2

MeCP2 is a chromosomal protein that is concentrated in the centromeric heterochromatin of mouse cells. In vitro, the protein binds preferentially to DNA containing a single symmetrically methylated CpG. To find out whether the heterochromatic localization of MeCP2 depended on DNA methylation, we transiently expressed MeCP2-LacZ fusion proteins in cultured cells. Intact protein was targeted to heterochromatin in wild-type cells but was inefficiently localized in mutant cells with low levels of genomic DNA methylation. Deletions within MeCP2 showed that localization to heterochromatin required the 85-amino-acid methyl-CpG binding domain but not the remainder of the protein. Thus MeCP2 is a methyl-CpG-binding protein in vivo and is likely to be a major mediator of downstream consequences of DNA methylation.

A chondrogenic cell line derived from a differentiating culture of AT805 teratocarcinoma cells

A cell line, ATDC5, isolated from a differentiating culture of AT805 teratocarcinoma expressed a fibroblastic cell phenotype in a growing phase. With the addition of 10 micrograms/ml insulin to the medium, cells continued to grow even in a postconfluent phase, formed cartilage nodule-like cell aggregates, were stained with Alcian blue and produced cartilage-specific proteoglycan and type II collagen, typical marker molecules for chondrogenesis. Since ATDC5 cells also differentiated into unidentifiable pigmented cells, they are apparently composed of undetermined cells. ATDC5, therefore, provides a good model system with which to understand chondrogenic differentiation.

Clonal variants of differentiated P19 embryonal carcinoma cells exhibit epidermal growth factor receptor kinase activity

Differentiated clonal cell lines were isolated from pluripotent P19 embryonal carcinoma (EC) cells treated as aggregates with retinoic acid. Two were characterized in detail. The lines differ in morphology, proliferation rate, the production of plasminogen activator, and in their mitogenic response to insulin but both produce extracellular matrix proteins and can be serially passaged over extended periods, in contrast to differentiated derivatives of many other EC lines. Further, both lines have receptors for and respond mitogenically to epidermal growth factor (EGF). Endogenous phosphorylation of several proteins, including the EGF receptor (150 kDa) and a 38-kDa protein, is induced by EGF in membranes isolated from these cells. Preincubation of membranes with EGF renders them able to catalyze phosphorylation of tyrosine residues in exogenously added peptide substrates. High voltage electrophoresis confirmed the tyrosine specificity of the phosphorylation on the 150- and 38-kDa bands. By contrast, similar experiments in undifferentiated cells showed that intact P19 EC neither bind nor respond to EGF mitogenically and EGF induces no changes in phosphorylation in isolated membranes.

Lack of retrovirus gene expression in somatic cell hybrids of friend cells and teratocarcinoma cells with a teratocarcinoma phenotype

Two types of hybrids between cells with erythroid phenotype (Friend cells) and teratocarcinoma cells can be distinguished: cell hybrids with an erythroid phenotype, which release or can be induced to release large amounts of Friend spleen focus-forming virus (F-SFFV) on exposure to bromodeoxyuridine and cell hybrids with a teratocarcinoma phenotype, which do not release Friend virus and are not inducible for F-SFFV release. In this paper, we attempted to relate these differences to the expression of F-SFFV and Friend murine leukemia virus (F-MuLV) functions. Teratocarcinoma phenotype hybrids retained F-SFFV-and F-MuLV-related provirus sequences. They did not express F-SFFV- or F-MuLV-related RNA or proteins. The hybrids differentiated to endoderm-like cells on exposure to retinoic acid or hexamethylene-bis -acetamide. These cells, in contrast to the teratocarcinoma phenotype (uninduced) cells expressing SSEA-1-like antigens, did not express SSEA-1-like antigens; they formed typical, prekeratin-staining cytoskeletal structures and could be induced to release mouse interferon. The differentiating cells, but not the uninduced teratocarcinoma hybrids, were infected productively with F-MuLV or the F-MuLV--F-SFFV complex. They, however, did not express endogenous F-SFFV. Endogenous F-SFFV functions could not be rescued by infection with F-MuLV. Induction of teratocarcinoma hybrids with retinoic acid did not activate endogenous F-MuLV or F-SFFV transcription or protein synthesis. These data demonstrated two control mechanisms of Friend virus repression: one which acted trans during formation of the cell hybrids and was maintained only in teratocarcinoma phenotype cells and the other which acted cis and was still operative during induction of endodermal differentiation.

Lack of retrovirus gene expression in somatic cell hybrids of friend cells and teratocarcinoma cells with a teratocarcinoma phenotype

Two types of hybrids between cells with erythroid phenotype (Friend cells) and teratocarcinoma cells can be distinguished: cell hybrids with an erythroid phenotype, which release or can be induced to release large amounts of Friend spleen focus-forming virus (F-SFFV) on exposure to bromodeoxyuridine and cell hybrids with a teratocarcinoma phenotype, which do not release Friend virus and are not inducible for F-SFFV release. In this paper, we attempted to relate these differences to the expression of F-SFFV and Friend murine leukemia virus (F-MuLV) functions. Teratocarcinoma phenotype hybrids retained F-SFFV-and F-MuLV-related provirus sequences. They did not express F-SFFV- or F-MuLV-related RNA or proteins. The hybrids differentiated to endoderm-like cells on exposure to retinoic acid or hexamethylene-bis -acetamide. These cells, in contrast to the teratocarcinoma phenotype (uninduced) cells expressing SSEA-1-like antigens, did not express SSEA-1-like antigens; they formed typical, prekeratin-staining cytoskeletal structures and could be induced to release mouse interferon. The differentiating cells, but not the uninduced teratocarcinoma hybrids, were infected productively with F-MuLV or the F-MuLV--F-SFFV complex. They, however, did not express endogenous F-SFFV. Endogenous F-SFFV functions could not be rescued by infection with F-MuLV. Induction of teratocarcinoma hybrids with retinoic acid did not activate endogenous F-MuLV or F-SFFV transcription or protein synthesis. These data demonstrated two control mechanisms of Friend virus repression: one which acted trans during formation of the cell hybrids and was maintained only in teratocarcinoma phenotype cells and the other which acted cis and was still operative during induction of endodermal differentiation.