Somatic cell hybrids between Friend erythroleukemia cells and mouse hepatoma cells

Activation and repression of a beta-globin gene in cell hybrids is accompanied by a shift in its temporal replication

To investigate whether a switch in the transcriptional activity of a gene is associated with a change in the timing of replication during the S phase, we examined the replication timing of the beta-globin genes in two different types of somatic cell hybrids. In mouse hepatoma (Hepa 1a) x mouse erythroleukemia (MEL) hybrid cells, the beta-globin gene from the MEL parent is transcriptionally inactivated and is later replicating than in the parental MEL cell line. In human fibroblast (GM3552) x MEL hybrid cells, the human beta-globin gene is transcriptionally activated, and all of the sequences within the human beta-globin domain (200 kilobases) we have examined appear to be earlier replicating than those in the parental fibroblast cell line. The chromatin configuration of the activated human beta-globin domain in the hybrids is relatively more sensitive to nucleases than that in the fibroblasts. Furthermore, major nuclease-hypersensitive sites that were absent in the chromatin flanking the distal 5' region of the human beta-globin gene cluster in the parental fibroblast cell line are present in the transcriptionally activated domain in the hybrid cell line. These results suggest that timing of replication of globin genes has been altered in these hybrid cells and thus is not fixed during the process of differentiation.

Activation and repression of a beta-globin gene in cell hybrids is accompanied by a shift in its temporal replication

To investigate whether a switch in the transcriptional activity of a gene is associated with a change in the timing of replication during the S phase, we examined the replication timing of the beta-globin genes in two different types of somatic cell hybrids. In mouse hepatoma (Hepa 1a) x mouse erythroleukemia (MEL) hybrid cells, the beta-globin gene from the MEL parent is transcriptionally inactivated and is later replicating than in the parental MEL cell line. In human fibroblast (GM3552) x MEL hybrid cells, the human beta-globin gene is transcriptionally activated, and all of the sequences within the human beta-globin domain (200 kilobases) we have examined appear to be earlier replicating than those in the parental fibroblast cell line. The chromatin configuration of the activated human beta-globin domain in the hybrids is relatively more sensitive to nucleases than that in the fibroblasts. Furthermore, major nuclease-hypersensitive sites that were absent in the chromatin flanking the distal 5' region of the human beta-globin gene cluster in the parental fibroblast cell line are present in the transcriptionally activated domain in the hybrid cell line. These results suggest that timing of replication of globin genes has been altered in these hybrid cells and thus is not fixed during the process of differentiation.

Rapid reprogramming of globin gene expression in transient heterokaryons

Interspecific heterokaryons were formed by fusing adult mouse erythroleukemia (MEL) cells and human embryonic/fetal erythroid (K562) cells with each other, or with a variety of mouse and human nonerythroid cell types. Analysis of total cellular RNA isolated 24 hr after fusion revealed that normally inactive globin genes can be activated in these "transient" heterokaryons, in which the nuclei do not fuse. In general, the types of globin genes expressed in the donor erythroid cell are activated in the nucleus of the recipient cell. Therefore, erythroid cells contain transacting regulatory factors that are capable of activating the expression of globin genes in a stage- and tissue-specific manner. These observations also indicate that globin genes are not irreversibly repressed in differentiated cells and that their expression can be rapidly reprogrammed in the presence of the appropriate regulatory factors.

Trans acting regulation of beta globin gene expression in erythroleukemia (K562) cells

K562 cells are induced by hemin to produce gamma and epsilon globin but not beta globin, although the beta globin gene is intact, and when isolated is expressed in a transient expression assay (1, 2). We have previously shown that an epsilon globin gene transferred into K562 cells is expressed and inducible (3). In this paper, we report the stable transfer of a sickle or betaS globin gene into K562 cells. Thirty-six different transformed lines were tested; 24 of 36 lines contained an intact betaS globin gene. However, using S1 nuclease, Dot blot, and Northern blotting analyses, none of these lines showed beta globin mRNA expression. These results indicate that trans acting factors are responsible for the lack of expression of the beta globin gene in K562 cells.

Time course of arrest of immunoglobulin expression in heterokaryons and early hybrids of human lymphoma cells and mouse fibroblasts. A study of transcriptional and translational events

Early events in arrest of immunoglobulin expression were investigated at the levels of both translation and transcription in heterokaryons and early hybrids between human Daudi lymphoma cells and mouse cl. 1D cells. Large populations of 1s: 1s hybrids, isolated by fluorescence-activated cell sorting (FACS) a few hours after fusion, were grown for up to 5 days. A survey at the light-microscopical level of peroxidase-antiperoxidase-immunostained cell populations showed that arrest of expression of IgM heavy chain (mu) occurred in up to 98% of the cells. Furthermore, quantitation of mu chain contents, by using an ELISA technique, suggested that synthesis of IgM was blocked shortly after fusion. The levels of cytoplasmic mRNA specific for mu and kappa chains, respectively, decreased at rates similar to those induced in unfused Daudi cells by treatment with actinomycin D. It is concluded that arrest of immunoglobulin expression in these hybrids occurs immediately or very shortly after fusion by mechanisms that affect the levels of their cytoplasmic mRNAs.

Cell cycle regulation of mouse H3 histone mRNA metabolism

The mechanisms responsible for the periodic accumulation and decay of histone mRNA in the mammalian cell cycle were investigated in mouse erythroleukemia cells, using a cloned mouse H3 histone gene probe that hybridizes with most or all H3 transcripts. Exponentially growing cells were fractionated into cell cycle-specific stages by centrifugal elutriation, a method for purifying cells at each stage of the cycle without the use of treatments that arrest growth. Measurements of H3 histone mRNA content throughout the cell cycle show that the mRNA accumulates gradually during S phase, achieving its highest value in mid-S phase when DNA synthesis is maximal. The mRNA content then decreases as cells approach G2. These results demonstrate that the periodic synthesis of histones during S phase is due to changes in the steady-state level of histone mRNA. They are consistent with the conventional view in which histone synthesis is regulated coordinately with DNA synthesis in the cell cycle. The periodic accumulation and decay of H3 histone mRNA appear to be controlled primarily by changes in the rate of appearance of newly synthesized mRNA in the cytoplasm, determined by pulse-labeling whole cells with [3H]uridine. Measurements of H3 mRNA turnover by pulse-chase experiments with cells in S and G2 did not provide evidence for changes in the cytoplasmic stability of the mRNA during the period of its decay in late S and G2. Furthermore, transcription measurements carried out by brief pulse-labeling in vivo and by in vitro transcription in isolated nuclei indicate that the rate of H3 gene transcription changes to a much smaller extent than the steady-state levels of the mRNA or the appearance of newly synthesized mRNA in the cytoplasm. The results suggest that post-transcriptional processes make an important contribution to the periodic accumulation and decay of histone mRNA and that these processes may operate within the nucleus.

Synergistic enzyme induction by glucocorticoids and cyclic AMP observed in glioma x hepatoma cell hybrids but not in their parents

Enzyme induction by hydrocortisone (HC) and dibutyryl cyclic AMP (dbcAMP) was studied in C6 rat glioma cells, FU5AH rat hepatoma cells, and five C6 x FU5AH hybrids. Hormone responsive enzymes from both parental lines were studied, including: tyrosine aminotransferase (TAT), alanine aminotransferase (AAT), glycerol phosphate dehydrogenase (GPDH), lactate dehydrogenase (LDH), and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP). There was no overall dominance of one parental phenotype over the other in expression of uninduced or induced enzyme activity after fusion, and the hybrids possessed some enzymatic properties characteristic of both parents. GPDH was induced by dbcAMP in all five hybrids, and TAT was induced by dbcAMP in four of the hybrids, although neither of these enzymes were induced by dbcAMP in the parents. Furthermore, synergistic induction of these enzymes by HC and dbcAMP was observed in the hybrids but not in the parents. These hybrids provide a model system to study hormone interaction in enzyme induction.

Cell cycle regulation of mouse H3 histone mRNA metabolism

The mechanisms responsible for the periodic accumulation and decay of histone mRNA in the mammalian cell cycle were investigated in mouse erythroleukemia cells, using a cloned mouse H3 histone gene probe that hybridizes with most or all H3 transcripts. Exponentially growing cells were fractionated into cell cycle-specific stages by centrifugal elutriation, a method for purifying cells at each stage of the cycle without the use of treatments that arrest growth. Measurements of H3 histone mRNA content throughout the cell cycle show that the mRNA accumulates gradually during S phase, achieving its highest value in mid-S phase when DNA synthesis is maximal. The mRNA content then decreases as cells approach G2. These results demonstrate that the periodic synthesis of histones during S phase is due to changes in the steady-state level of histone mRNA. They are consistent with the conventional view in which histone synthesis is regulated coordinately with DNA synthesis in the cell cycle. The periodic accumulation and decay of H3 histone mRNA appear to be controlled primarily by changes in the rate of appearance of newly synthesized mRNA in the cytoplasm, determined by pulse-labeling whole cells with [3H]uridine. Measurements of H3 mRNA turnover by pulse-chase experiments with cells in S and G2 did not provide evidence for changes in the cytoplasmic stability of the mRNA during the period of its decay in late S and G2. Furthermore, transcription measurements carried out by brief pulse-labeling in vivo and by in vitro transcription in isolated nuclei indicate that the rate of H3 gene transcription changes to a much smaller extent than the steady-state levels of the mRNA or the appearance of newly synthesized mRNA in the cytoplasm. The results suggest that post-transcriptional processes make an important contribution to the periodic accumulation and decay of histone mRNA and that these processes may operate within the nucleus.

Introduction of purified genes into mammalian cells

There are a number of methods to introduce genes into mammalian cells. These include cell hybridization, chromosome-mediated and DNA-mediated gene transfer. DNA-mediated transfer can be achieved by direct microinjection methods or by indirect methods. The DNA enters the nucleus and is expressed in a high proportion of cells transiently. The DNA then becomes integrated into host cell DNA at random sites resulting in more stably expressing transformants. A number of genes for which selection systems exist can be introduced into mammalian cells. Nonselectable genes can also be introduced into cells by either ligating them to a selectable gene or by mixing them with carrier DNA and a selectable gene. If an amplifiable gene sequence is introduced into cells, it and other genes in its proximity can be coamplified. Amplification of the genes can also be achieved by the use of appropriate viral vectors and recipient cells. The foreign genes are expressed in the recipient cells if they contain the appropriate recognition signals for initiation and termination of transcription. Transfection systems are thus permitting identification of DNA sequences which have a regulatory role in gene expression. The identification of transcriptional signal sequences has formed the basis for construction of appropriate molecules which would permit expression of genes which cannot normally be expressed in mammalian cells (e.g., bacterial genes). The foreign genes are not only expressed in the recipient cells but they can also be subject to regulation in the appropriate environment. This observation is paving the way for identification of regulatory sequences. The foreign DNA sequences integrated into the host genome can be recovered by a variety of methods. Such methods permit isolation of genes which code for a selectable gene product.

Spontaneous, in vitro, malignant transformation of a basophil/mast cell line

It has recently become possible to grow basophil/mast cells in vitro for extended periods of time. Normally, these cultures remain fully dependent upon the presence of an adequate supply of growth factor(s) and the cells express several basophil/mast cell differentiated traits. We report here a case of spontaneous, in vitro, malignant transformation of such a basophil/mast cell line. The transformed cells no longer require the addition of growth factor(s) for continuous proliferation in vitro, and they have become highly tumorigenic in vivo. In contrast, when compared to their untransformed counterparts, they display the same set of differentiated traits, characteristic of immature basophil/mast cells. Thus, the data support the hypothesis that cell transformation results from a decreased sensitivity of precursor cells toward normal growth regulators but does not affect significantly the expression of differentiated functions.

Introduction and expression of a fetal human globin gene in mouse fibroblasts

An 8.5-kilobase segment of cloned human DNA including the complete G gamma-globin gene was introduced into LMTK- cells by the calcium phosphate precipitation method in the presence or absence of carrier DNA. Transfectants containing one or more copies of intact G gamma-globin genes were obtained either by ligation of the human DNA segment to a plasmid containing the herpes simplex virus thymidine kinase gene or by nonligated cotransfer. The integrity of the integrated gamma-globin gene was established by Southern blotting experiments. Expression of the herpes simplex virus thymidine kinase and human gamma-globin genes was evaluated by Northern blotting and solution hybridization. Of 23 transfectants analyzed, 21 produced a 9S gamma-globin RNA migrating like authentic gamma-globin mRNA on denaturing agarose gels. The gamma-globin RNA is polyadenylated and present in the cytoplasm of the transfected cells; it accumulates to a level 10 times that of thymidine kinase mRNA, or about 5 to 50 molecules per transfected cell. By using plasmids in which the gamma-gene is inserted in either transcriptional orientation with respect to the thymidine kinase gene, it was possible to show that transcription occurred from the gamma-gene promoter.

Newly isolated Friend cell lines are blocked at the same stage of erythroid differentiation as established clones

Friend erythroleukemia cells, a widely used in vitro model of murine erythropoiesis, express prior to induction, a state of erythroid differentiation similar to that of the early erythroblast in vivo. To investigate whether this uniform and stable epigenetic state was the result of a selection in long-term culture for the corresponding cell type, 29 new cell lines were isolated from the hemopoietic organs of DBA/2 mice infected with Friend virus and were analyzed without delay for the expression of several erythroid traits. All the lines examined displayed levels of expression of the markers indistinguishable from those displayed by established Friend cell clones. Thus, newly isolated Friend cell lines appear to be blocked at essentially the same stage of erythroid differentiation as established clones. This indicates that the expression of several characteristic erythroid markers is remarkably stable in vitro and does not result from long-term selection. In contrast, the capacity of these cells to respond to chemical inducers varies considerably from clone to clone and with time in culture.

Molecular mechanism of extinction of liver-specific functions in mouse hepatoma x rat fibroblast hybrids: extinction of the albumin gene

Hybrids formed by the fusion of mouse hepatoma (BWTG3) and rat fibroblast (JF1) cells exhibit the extinction of mouse albumin and alpha-fetoprotein synthesis. Karyotype analyses suggest that all parental chromosomes are present in the hybrids. The extinction, therefore, of mouse hepatocyte genes is attributed to the inhibitory action of the rat genome. In these studies, we show that these hybrids possess and express the mouse beta-glucuronidase gene (which is encoded on the same chromosome as the mouse albumin and alpha-fetoprotein gene), and we present data of Southern blot analysis which demonstrate that such hybrids have indeed retained both mouse and rat albumin DNA sequences. In addition, using mouse albumin cDNA, we have shown by cDNA-RNA reassociation kinetics that albumin mRNA is virtually absent in these hybrids. We conclude from these studies that the extinction of albumin synthesis involves a mechanism which results in the loss of cytoplasmic albumin mRNA.

Introduction and expression of a fetal human globin gene in mouse fibroblasts

An 8.5-kilobase segment of cloned human DNA including the complete G gamma-globin gene was introduced into LMTK- cells by the calcium phosphate precipitation method in the presence or absence of carrier DNA. Transfectants containing one or more copies of intact G gamma-globin genes were obtained either by ligation of the human DNA segment to a plasmid containing the herpes simplex virus thymidine kinase gene or by nonligated cotransfer. The integrity of the integrated gamma-globin gene was established by Southern blotting experiments. Expression of the herpes simplex virus thymidine kinase and human gamma-globin genes was evaluated by Northern blotting and solution hybridization. Of 23 transfectants analyzed, 21 produced a 9S gamma-globin RNA migrating like authentic gamma-globin mRNA on denaturing agarose gels. The gamma-globin RNA is polyadenylated and present in the cytoplasm of the transfected cells; it accumulates to a level 10 times that of thymidine kinase mRNA, or about 5 to 50 molecules per transfected cell. By using plasmids in which the gamma-gene is inserted in either transcriptional orientation with respect to the thymidine kinase gene, it was possible to show that transcription occurred from the gamma-gene promoter.

Transcriptional control of the expression of mouse globin genes in myeloma x erythroleukemia cell hybrids

Fusions were made between thymidine kinase deficient (TK-) Friend Cells inducible for hemoglobin production, and immunoglobulin-producing, hypoxanthine-guanine phosphoribosyltransferase-deficient (HGPRT-) myeloma cells. Hybrids were selected in hypoxanthine-aminopterin-thymidine (HAT) and identified by isozyme analysis and chromosome counts. All hybrids resembled the myeloma cell line in mode of growth and were immunoglobulin secretors. All hybrids did not express hemoglobin and were uninducible for hemoglobin production with dimethyl sulfoxide (DMSO). Hybridization of genomic globin DNA probes with hybrid-derived nuclear and cytoplasmic mRNAs blotted to nitrocellulose filter indicated that lack of expression of the globin genes in the hybrids was due to lack of transcription.

Expression of the albumin gene in rat hepatoma cells and their dedifferentiated variants

Rat hepatoma clones whose cells do and do not produce albumin, as well as somatic hybrid between the two types of cells, have been examined for albumin mRNA. A direct proportionality between the rate of albumin production and the concentration of albumin mRNA sequences was found for all albumin-producing hepatoma and hybrid clones, indicating that rate of synthesis of the protein is determined by the concentration of its mRNA. Albumin-negative dedifferentiated variant and somatic hybrid cells contain fewer than one to five molecules of albumin mRNA per cell; the block in expression of the gene appears to be at the same (probably transcriptional) level in variants and their somatic hybrids.

Immunofluorescence analysis of the time-course of extinction, reexpression, and activation of albumin production in rat hepatoma-mouse fibroblast heterokaryons and hybrids

We have used a combination of a sensitive immunocytochemical stain for intracellular albumin, and Hoechst 33258 dye for identification of parental nuclei to investigate the time-course of extinction, reexpression, and activation of albumin production in fusion products of 1s (hyperdiploid) or 2s (hypertetradiploid) rat hepatoma cells with mouse fibroblasts (L cells or embryonic cells). In all combinations, the initial event is extinction of albumin production. Extinction occurs immediately after fusion when the mouse fibroblast is a normal embryonic (senescent?) cell. In the case of an L cell, rat albumin is synthesized and secreted during the first 12 h after fusion; no production of mouse albumin occurs. Thereafter, albumin production ceases. 8-12 d after fusion, young hybrid colonies are found to resume the synthesis of rat albumin (reexpression), and several days later the production of mouse albumin begins (activation). The patterns of reexpression and activation indicate (a) that chromosome loss is not necessary for either event to occur and (b) that the cells active in the synthesis of mouse albumin are a subpopulation of those cells already engaged in the production of rat albumin. We conclude that (a) extinction is mediated by diffusible factor(s) from the L-cell parent that act in the hepatoma nucleus to prevent the formation of new albumin messenger RNA; (b) reexpression and activation are gene dosage-dependent but extinction is not; and (c) previously active genes are more rapidly expressed than previously silent ones.

Inducibility of spleen focus-forming virus by BrdUrd is controlled by the differentiated state of the cell

All Friend cells--except thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21)-deficient mutants--are highly inducible for the release of biologically active spleen focus-forming virus (SFFV) after exposure to BrdUrd. We studied SFFV production in somatic cell hybrids made between Friend leukemia cells (FLC) and cells expressing various differentiation programs. High inducibility of SFFV and release of constitutive Friend virus (FV) and SFFV are eliminated in all hybrids in which the potential for erythroid differentiation is suppressed. FV release and its induction by BrdUrd are unchanged in hybrids that maintain the expression of erythroid differentiation.

Activation of human beta-globin genes from nonerythroid cells by fusion with murine erythroleukemia cells

A human beta-globin gene derived from an established human lymphoblast cell line was introduced into murine erythroleukemia (MEL) cells by cell fusion. The globin genes in MEL cells are inducible by dimethyl sulfoxide (Me2SO); induction leads to the accumulation of mouse globin mRNA and hemoglobin. Globin mRNA was not detected in the cytoplasm of the human lymphoblast cells, even at low levels, whether or not these cells were treated with Me2SO. In cell hybrids that had retained the lymphoblast-derived beta-globin gene, human beta-globin mRNA was induced by Me2SO. Poly(A)-containing 10S human beta-globin mRNA was detected in the cytoplasm of the hybrid cells. Karyologic and isozymic analyses of a series of hybrids and subclones showed that human beta-globin gene expression occurred only in hybrids that had retained human chromosome 11. Analysis of one hybrid bearing a deletion of both the beta-globin and lactate dehydrogenase A genes indicated that the beta-globin gene is located on the short arm of human chromosome 11. No other human chromosomes are required for human beta-globin gene expression in MEL cell hybrids. We conclude that the restricted expression of a globin gene in a human nonerythroid cell can be reversed. Furthermore, all components required for the transcription, processing, and transport to the cytoplasm of a human globin mRNA appear to be present in mouse erythroleukemia cells. Thus cell fusion with MEL cells provides a way to isolate permanent cell lines with functioning human globin genes. The technique should be useful for studying the biochemical basis for abnormal function of mutant globin genes, such as those present in individuals with the thalassemia syndromes.

Co-expression of differentiation markers in hybrids between Friend cells and lymphoid cells and the influence of the cell shape

We have studied the regulation of differentiation within the hemopoietic system by fusing mouse Friend cells (which can be induced to undergo red blood cell differentiation) to various mouse lymphomas and myelomas which express characteristic T and B lymphocytes surface antignes. Our results show that both erythroid and lymphoid differentiation markers can be co-expressed within the same cell. To determine whether this result applies to other differentiation states, we fused suspension Friend cells to three adherent fibroblast cell lines, and isolated both adherent and suspension hybrids. In fact, suspension hybrid clones were inducible for hemoglobin, whereas adherent clones were not. No obvious differences in overall chromosome balance were evident between the adherent and suspension hybrids. A similar correlation between suspension morphology and inducibility of hemoglobin was found in hybrids between suspension Friend cells and an adherent lymphoma line. These results show that different developmental programs can be co-expressed within the same hybrid cell; but the strongly adherent type of morphology is inconsistent with expression of the red blood cell phenotype, both in hybrid cells derived entirely from hemopoietic parental cells and in cells from widely different lineages.

X-linked control of globin mRNA and hemoglobin production in erythroleukemia-lymphoma cell hybrids

In somatic cell hybrids formed by the fusion of mouse erythroleukemic cells with cultured mouse lymphoma cells, retention of the X chromosome donated by the lymphoma parent is correlated with inhibition of hemoglobin accumulation in response to dimethyl sulfoxide. The inhibition of hemoglobin production was due to an inhibition of globin mRNA accumulation. Heme can partially overcome the effects of the lymphoma X chromosome and induce globin mRNA and hemoglobin accumulation in the dimethylsulfoxide-treated hybrid cells. The data suggests that the X chromosome contributed by the lymphoma cells inhibits hemoglobin production by inhibiting both inducible globin mRNA accumulation as well as inducible heme biosynthesis, most likely at a step after the formation of delta-aminolevulinic acid. The properties of erythroleukemia x lymphoma cell hybrids are compared with those of a series of erythroleukemia x bone marrow cell hybrids. The data indicate the possibility of multiply loci on the X chromosome capable of regulating the expression of erythroid characteristics.

Selective activation of human beta-but not gamma-globin gene in human fibroblast x mouse erythroleukaemia cell hybrids

The human alpha- and beta-globin genes have been activated in MEL X human fibroblast cell hybrids. However, even though the human gamma- and beta-globin genes are closely linked and were shown in these hybrid clones to be present in approximately equal numbers, no human gamma-globin mRNA was produced. Thus, the human beta- and gamma-globin genes in these cells are differentially regulated apparently by a positive regulatory factor(s) specific for individual globin genes.

Maintenance of hemoglobin inducibility in somatic cell hybrids of tetraploid (2S) mouse erythroleukemia cells with mouse or human fibroblasts

It has previously been reported that Friend mouse erythroleukemia (MEL) cells synthesize hemoglobin when exposed to 2% dimethylsulfoxide, and that hybrids between MEL cells and fibroblasts (or other nonerythroid cells) do not synthesize hemoglobin. We have been successful in obtaining hybrids (3/15) between MEL cells and mouse L-cell fibroblasts that maintain hemoglobin inducibility by preserving nonadherent cells after fusion. The proportion of hemoglobin inducible hybrids can be increased (8/11) by using a stable 2S (pseudotetraploid) MEL parent in addition to preserving nonadherent cells after fusion. All hybrids which were nonadherent were hemoglobin inducible, and all hybrids which were adherent were not. Five nonadherent hybrid clones were analyzed from fusions between a stable 2S MEL parent and a human fibroblast (WI-38, VA-2). All these clones were inducible for hemoglobin. It is concluded that gene dosage is effective in increasing the proportion of hemoglobin inducible hybrids, but hybrid morphology is the phenotype characteristic that correlates most closely with expression of hemoglobin inducibility.

Hemoglobin synthesis in cell hybrids formed between teratocarcinoma and Friend erythroleukemia cells

Viable hybrid cells have been isolated following fusion of Friend erythroleukemia cells and undifferentiated teratocarcinoma cells. The hybrids formed between near-diploid parental cells resembled Friend cells in the ability to grow in suspension and to synthesize hemoglobin in the presence of the chemical inducers dimethyl sulfoxide (DMSO) and ouabain. Erythropoietin (EPO) was effective in inducing hemoglobin synthesis in some of the hybrid cell lines. The hemoglobins synthesized by the hybrids were of the adult forms, but were quantitatively different from those hemoglobins synthesized by the parental Friend cells, suggesting that the fusion event modulated the expression of the hemoglobin chain genes.