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

Manipulation of OCT4 Levels in Human Embryonic Stem Cells Results in Induction of Differential Cell Types

To fully understand self-renewal and pluripotency and their regulation in human embryonic stem cells (hESCs), it is necessary to generate genetically modified cells and analyze the consequences of elevated and reduced expression of genes. Genes expressed in hESCs using plasmid vectors, however, are subject to silencing. Moreover, hESCs have a low plating efficiency when dissociated to single cells, making creation of subcloned lines inefficient. In addition to overexpression experiments, it is important to perform loss-of-function studies, which can be achieved rapidly using RNA interference (RNAi). We report stable long-term expression of enhanced green fluorescent protein (eGFP) in hESCs using a lentiviral vector, and establishment of an eGFP-expressing subline (RG6) using manual dissection. To demonstrate the efficacy of RNAi in hESCs, an RNAi expression vector was used to achieve reduced expression of eGFP in hESCs. To evaluate the role of OCT4 in the regulation of hESC self-renewal and differentiation, a vector expressing a hairpin RNA targeting endogenous expression of OCT4 was constructed. In a novel experiment in hESCs, the OCT4 cDNA sequence was cloned into an expression vector to allow for the transient upregulation of OCT4 in hESCs. The ability to manipulate levels of OCT4 above and below enodogenous levels allows the determination of OCT4 function in hESCs. Specifically, reduced expression of OCT4 in hESCs promoted upregulation of markers indicative of mesoderm and endoderm differentiation, and elevated levels of OCT4 in hESCs promoted upregulation of markers indicative of endoderm derivatives. Thus, both upregulation and downregulation of Oct4 in hESCs results in differentiation, but with patterns distinct from parallel experiments in mice.

Establishment of a new embryonic stem cell line derived from C57BL/6 mouse expressing EGFP ubiquitously

Transgenic mice ubiquitously expressing enhanced green fluorescent protein (EGFP) are useful as marker lines in chimera experiments. We established a new embryonic stem (ES) cell line (named B6G-2) from a C57BL/6 blastocyst showing ubiquitous EGFP expression. Undifferentiated B6G-2 cells showed strong green fluorescence and mRNAs of pluripotent marker genes. B6G-2 cells were transferred into a C57BL/6 blastocyst to generate a germline chimera, the progeny of which inherited ubiquitous EGFP expression. Mice derived completely from B6G-2 cells were also developed from the ES cells; these were tetraploid chimeras. The established B6G-2 cells were shown to be pluripotent and to be capable of differentiating into cells of all lineages. Thus, the new ES cell line expressing EGFP ubiquitously is useful for basic research in the field of regenerative medicine. The B6G-2 cell line is freely available from the BioResource Center, RIKEN Tsukuba Institute (http://www.brc.riken.jp/lab/cell/english/).

Multipotential hemopoietic cell lines isolated from stem cell cultures infected with Friend virus complex (MuLV + F-SFFV) show presence of MuLV but not F-SFFV

The only factor-dependent or factor-independent hemopoietic murine stem cell lines which can be permanently maintained in vitro are cell lines which originate from bone marrow cultures of congenic mice differing in the Fv-2 locus infected with Friend spleen focus forming virus (F-SFFV) in conjunction with either Rauscher or Friend helper virus (R-MuLV or F-MuLV). We determined the viral state of these cells by restriction enzyme analysis, measurement of SFFV and MuLV related RNA, immunoprecipitation analysis of viral related proteins and biological activity to test whether integration and expression of R-MuLV or F-SFFV are obligatory. All stem cell lines (SUT, JUT, 416B) showed expression of MuLV coded proteins or virus but SFFV was not found in these cell lines. A two-fold difference of RNA hybridizing with SFFV-specific cDNAs observed in stem cells of Fv-2rr and of Fv-2ss genotype is in agreement with data published earlier.

The use of cloned gene probes to study differentiation in teratocarcinomas

The molecular control of early embryonic gene expression can be studied in teratocarcinoma derived cell lines. Several genes known to be regulated during in vitro differentiation have been cloned and used to measure mRNA levels. In all cases studied there is good agreement between protein levels and mRNA levels, strongly implying transcriptional regulation. Two non-exclusive hypotheses have been proposed to explain transcriptional control: methylation of DNA and the interactive effects of cis-acting enhancer sequences and trans-acting proteins. Experiments with oncoviruses suggest both mechanisms may play a role.