Inhibition of ornithine decarboxylase induces embryonal carcinoma cell differentiation

Murine embryonal carcinoma cells can be induced to differentiate in vitro by various physical and chemical means. We report here that inhibition of ornithine decarboxylase activity with a specific enzyme-activated inhibitor, alpha-difluoromethylornithine, can induce differentiation in embryonal carcinoma cells. The differentiated phenotype can be distinguished from undifferentiated embryonal carcinoma cells by altered cellular morphology, biochemical and cell surface antigenic properties. These results suggest that alterations in the levels of cellular polyamines may play a role in embryonal carcinoma cell differentiation.     

alpha-Difluoromethylornithine induces differentiation of a human embryonal carcinoma cell line in vitro

Human embryonal carcinoma cells could serve as a useful model system for analysis of early human development. A limited number of human embryonal carcinoma cell lines have been generated from in vivo tumors. We report here that alpha-difluoromethylornithine, a specific enzyme-activated inhibitor of ornithine decarboxylase activity, can induce differentiation in human embryonal carcinoma cells. The differentiated phenotype could be distinguished from undifferentiated cells by altered cellular morphology, biochemical and cell surface antigenic properties. These results suggest that alterations in the intracellular levels of polyamines may play a role in human embryonal carcinoma cell differentiation, and possibly human embryogenesis.     

Lack of expression of differentiation in mouse teratoma-fibroblast somatic cell hybrids

Somatic cell hybrids between multipotent mouse teratoma cells and mouse fibroblasts were established and isolated. The hybrid cells possess one chromosome set of each parental type and express major histocompatibility antigens of both strains of mice from which the parental cells were derived. Upon inoculation into F1 mice, hybrid cells produced tumors which were typical fibrosarcomas as were the tumors produced by the fibroblastic parental cell line. None of the well differentiated tissue types characteristic of the teratoma parent cell tumors were expressed in the hybrid tumors. The hybrid tumors possessed the majority of the chromosomes of the two parental cells; however, the modal numbers were slightly reduced in comparison with those of the cell populations inoculated. The possible role of ‘genic balance’ in phenotypic expression of cell hybrids is discussed.     

Retinoic acid induces neuronal differentiation of a cloned human embryonal carcinoma cell line in vitro

The human embryonal carcinoma cell lines $\text{NT2}\text{D1}$ and $\text{NT2}\text{B9}$, clonally derived from Tera-2, differentiate extensively in vitro when exposed to retinoic acid. This differentiation is marked by the appearance of several morphologically distinct cell types and by changes in cell surface phenotype, particularly by the disappearance of stage-specific embryonic antigen-3 (SSEA-3), which is characteristically expressed by human EC cells. Among the differentiated cells are neurons, which form clusters interconnected by extended networks of axon bundles, and which express tetanus toxin receptors and neurofilament proteins. These observations constitute the first instance of extensive somatic differentiation of a clonal human EC cell line in vitro.     

Reprogramming of ovine adult fibroblasts to pluripotency via drug-inducible expression of defined factors

Reprogramming of somatic cells in the enucleated egg made Dolly, the sheep, the first successfully cloned mammal in 1996. However, the mechanism of sheep somatic cell reprogramming has not yet been addressed. Moreover, sheep embryonic stem (ES) cells are still not available, which limits the generation of precise gene-modified sheep. In this study, we report that sheep somatic cells can be directly reprogrammed to induced pluripotent stem (iPS) cells using defined factors (Oct4, Sox2, c-Myc, Klf4, Nanog, Lin28, SV40 large T and hTERT). Our observations indicated that somatic cells from sheep are more difficult to reprogram than somatic cells from other species, in which iPS cells have been reported. We demonstrated that sheep iPS cells express ES cell markers, including alkaline phosphatase, Oct4, Nanog, Sox2, Rex1, stage-specific embryonic antigen-1, TRA-1-60, TRA-1-81 and E-cadherin. Sheep iPS cells exhibited normal karyotypes and were able to differentiate into all three germ layers both in vitro and in teratomas. Our study may help to reveal the mechanism of somatic cell reprogramming in sheep and provide a platform to explore the culture conditions for sheep ES cells. Moreover, sheep iPS cells may be directly used to generate precise gene-modified sheep.     

Transglutaminase activity and embryonal carcinoma cell differentiation

Murine embryonal carcinoma (EC) cells induced to differentiate by retinoic acid (RA) modulate transglutaminase (TGase) activity shortly after exposure to the inducer. Compounds that inhibit TGase enzyme activity in vitro can successfully block RA induced EC cell differentiation in culture. These observations suggest that TGase may play a role in mediating RA induced EC cell differentiation.     

Enhanced expression of alkaline phosphatase in hybrids between neuroblastoma and embryonal carcinoma

Three independent hybrid cell lines were isolated from the fusion of clonal lines of embryonal carcinoma and neuroblastoma. A series of subclones was subsequently derived from the original hybrid clones. In early hybrid generations all hybrid lines showed enhancement of alkaline phosphatase activity, expressing 2--8 times the activity of the teratoma parental line. The overexpression of APase appears to take place in the stationary phase of the growth cycle. Segregation for very high levels of APase activity was observed among subclones of one hybrid line. Specific activities of the segregants ranged from 0.1 to 133. Results of heat denaturation studies are consistent with the hypothesis that it is the embryonal carcinoma APase that is being expressed in the hybrids.     

Smooth muscle actin expression during P19 embryonal carcinoma differentiation in cell culture

P19 embryonal carcinoma (EC) cells can be induced in vitro to differentiate into cells resembling those normally formed in the embryo. Among these cell types is one whose morphology is fibroblast-like. Using indirect immunofluorescence and Western blot analysis with antibodies directed against various isoforms of actin, many of these fibroblast-like cells were found to express smooth muscle actin isoforms. Northern blot analysis of RNA indicated the presence of a smooth muscle-specific isoform of myosin heavy-chain mRNA in immortal lines of these fibroblast-like cells. These results suggest that these fibroblast-like cells resemble fetal myofibroblastic or myoepithelial cells, which have a wide distribution during embryonic development.     

Dominance and independent segregation of metabolic cooperation-competence and pluripotency in an embryonal carcinoma cell hybrid

We report the isolation of a fusion hybrid, PR3, from a pluripotent embryonal carcinoma (EC) cell line, PSA4, which is metabolic cooperation-competent, and an EC line R5/3OA which has a reduced capacity for metabolic cooperation and a restricted developmental capacity. PR3 resembles its pluripotent parent PSA4 in its capacity for gap-junction-mediated transfer of uridine nucleotides and in its pluripotency both in embryoid bodies in vitro and in tumors in vivo. This enabled the relationship between pluripotency and metabolic cooperation to be examined by the selection of segregant lines. Cooperation-deficient lines were isolated from a thioguanine-resistant intermediate line (PR3Tg12) using "Kiss of Death" selection. A novel method was devised for the selection of differentiation-deficient segregants using feeder cell-conditioned medium which partially inhibits in vitro differentiation. It was found that communication-competence and in vitro pluripotency segregated independently, demonstrating that the loss of developmental capacity in R5/3OA cannot be attributed to its communication-deficiency.     

Reprogramming cell differentiation in the absence of DNA synthesis

We examined whether the activation of muscle gene expression in nonmuscle cells required DNA synthesis. Human fibroblasts from amniotic fluid and fetal lung were fused with differentiated mouse muscle cells in the presence or absence of the DNA synthesis inhibitor, cytosine arabinoside. In the stable heterokaryons formed, the human contractile enzyme, MM-creatine kinase (CK), and the cell surface antigen, 5.1H11, were detected in comparable amounts regardless of whether DNA synthesis had occurred. A single cell analysis revealed that the efficiency of gene activation was high and that DNA synthetic activity was not affected by the ratio of muscle to nonmuscle nuclei in the heterokaryons. In addition, muscle gene expression was not restricted to the G1 phase of the cell cycle. We conclude that cell differentiation can be reprogrammed in heterokaryons regardless of cell cycle phase and in the absence of detectable DNA synthesis.     

Reprogramming of sheep fibroblasts into pluripotency under a drug-inducible expression of mouse-derived defined factors

Animal embryonic stem cells (ESCs) provide powerful tool for studies of early embryonic development, gene targeting, cloning, and regenerative medicine. However, the majority of attempts to establish ESC lines from large animals, especially ungulate mammals have failed. Recently, another type of pluripotent stem cells, known as induced pluripotent stem cells (iPSCs), have been successfully generated from mouse, human, monkey, rat and pig. In this study we show sheep fibroblasts can be reprogrammed to pluripotency by defined factors using a drug-inducible system. Sheep iPSCs derived in this fashion have a normal karyotype, exhibit morphological features similar to those of human ESCs and express AP, Oct4, Sox2, Nanog and the cell surface marker SSEA-4. Pluripotency of these cells was further confirmed by embryoid body (EB) and teratoma formation assays which generated derivatives of all three germ layers. Our results also show that the substitution of knockout serum replacement (KSR) with fetal bovine serum in culture improves the reprogramming efficiency of sheep iPSCs. Generation of sheep iPSCs places sheep on the front lines of large animal preclinical trials and experiments involving modification of animal genomes.     

Two specific markers for neural differentiation of embryonal carcinoma cells

Two multipotential embryonal carcinoma (EC) cell lines, 1003 and 1009, can be induced to form preferentially neural derivatives in vitro. Synthesis of specific proteins during neural differentiation was followed by two-dimensional gel electrophoresis. The comparison of protein patterns obtained with neural and non-neural derivatives of these EC cell lines indicates that two changes are specific for the neural pathway: (i) the appearance of a new beta-tubulin isoform and (ii) the accumulation of the brain isozyme of creatine phosphokinase already present in small amounts in EC stem cells. These changes were found to take place early in the course of differentiation and to occur even when neurite outgrowth was prevented.