Isolation of a germline-transmissible embryonic stem (ES) cell line from C3H/He mice

MicroRNA biomarkers for chemical hazard screening identified by RNA deep sequencing analysis in mouse embryonic stem cells

We investigated the responses of microRNAs (miRNAs) using mouse embryonic stem cells (mESCs) exposed to nine chemicals (bis(2-ethylhexyl)phthalate, p-cresol, p-dichlorobenzene, phenol, pyrocatecol, chloroform, tri-n-butyl phosphate, trichloroethylene, and benzene), which are listed as "Class I Designated Chemical Substances" from the Japan Pollutant Release and Transfer Register. Using deep sequencing analysis (RNA-seq), several miRNAs were identified that show a substantial response to general chemical toxicity (i.e., to these nine chemicals considered as a group) and several miRNA biomarkers that show a substantial and specific response to benzene. The functions of the identified miRNAs were investigated in accordance with Gene Ontology terms of their predicted target genes, indicating regulation of cellular processes. We compared the results with those for the long non-coding RNAs (ncRNAs) and mRNAs reported in our previous studies in addition to previously identified miRNAs that are either up- or down-regulated in response to the benzene as stimuli. We also observed that the changes in expression of miRNAs were smaller than those for long ncRNAs and mRNAs. Taken together the current and previous results revealed that toxic chemical stimuli regulate the expression of miRNAs. We believe that the use of miRNAs, including the thus identified miRNAs, as biomarkers contribute to predicting the potential toxicity of particular chemicals or identifying human individuals that have been exposed to chemical hazards.

Identification of RNA biomarkers for chemical safety screening in mouse embryonic stem cells using RNA deep sequencing analysis

Although it is not yet possible to replace in vivo animal testing completely, the need for a more efficient method for toxicity testing, such as an in vitro cell-based assay, has been widely acknowledged. Previous studies have focused on mRNAs as biomarkers; however, recent studies have revealed that non-coding RNAs (ncRNAs) are also efficient novel biomarkers for toxicity testing. Here, we used deep sequencing analysis (RNA-seq) to identify novel RNA biomarkers, including ncRNAs, that exhibited a substantial response to general chemical toxicity from nine chemicals, and to benzene toxicity specifically. The nine chemicals are listed in the Japan Pollutant Release and Transfer Register as class I designated chemical substances. We used undifferentiated mouse embryonic stem cells (mESCs) as a simplified cell-based toxicity assay. RNA-seq revealed that many mRNAs and ncRNAs responded substantially to the chemical compounds in mESCs. This finding indicates that ncRNAs can be used as novel RNA biomarkers for chemical safety screening.

Genome-wide gene expression analysis of mouse embryonic stem cells exposed to p-dichlorobenzene

Because of the limitations of whole animal testing approaches for toxicological assessment, new cell-based assay systems have been widely studied. In this study, we focused on two biological products for toxicological assessment: mouse embryonic stem cells (mESCs) and long noncoding RNAs (lncRNAs). mESCs possess the abilities of self-renewal and differentiation into multiple cell types. LlncRNAs are an important class of pervasive non-protein-coding transcripts involved in the molecular mechanisms associated with responses to chemicals. We exposed mESCs to p-dichlorobenzene (p-DCB) for 1 or 28 days (daily dose), extracted total RNA, and performed deep sequencing analyses. The genome-wide gene expression analysis indicated that mechanisms modulating proteins occurred following acute and chronic exposures, and mechanisms modulating genomic DNA occurred following chronic exposure. Moreover, our results indicate that three novel lncRNAs (Snora41, Gm19947, and Scarna3a) in mESCs respond to p-DCB exposure. We propose that these lncRNAs have the potential to be surrogate indicators of p-DCB responses in mESCs.

Dodecaploid H1 embryonic stem cells abolished pluripotency in L15F10 medium both with and without leukemia inhibitory factor

Two lines of dodecaploid H1 embryonic stem cells, 12H1 and 12H1(-) cells (mouse-originated cells), were established through polyploidization of two hexaploid H1 cells, 6H1 and 6H1(-) cells, which were cultured in L15F10 (7:3) medium with and without leukemia inhibitory factor (LIF), respectively. The G1, S, and G2/M phase fractions of 12H1 and 12H1(-) cells were almost the same as those of 6H1 and 6H1(-) cells, respectively, but the doubling time of cell proliferation was prolonged, suggesting that cell death occurred in 12H1 and 12H1(-)cells. The cell volumes of 12H1 and 12H1(-) cells were about double those of 6H1 and 6H1(-) cells, respectively. 12H1 and 12H1(-) cells showed near-negative activity of alkaline phosphatase and no ability to form teratocarcinomas in mouse abdomen, suggesting that 12H1 and 12H1(-) cells lost pluripotency. The DNA contents of 12H1 and 12H1(-) cells decayed in long-term culturing, suggesting that 12H1 and 12H1(-) cells were DNA-unstable. Possible explanations for the lost pluripotency and for the DNA decay in 12H1 and 12H1(-) cells are presented.

Effects of etoposide on the proliferation of hexaploid H1 (ES) cells

Etoposide is a specific inhibitor of topoisomerase II, which is an enzyme that enables double-stranded DNA to pass through another double-stranded DNA. Topoisomerase II is a major constituent of chromosome scaffold, existing at appreciable amounts in cells. To examine the effects of etoposide on the cell cycle, hexaploid H1 (ES) cells (6H1 cells) were used with diploid H1 (ES) cells (2H1 cells) as a control. Exponentially growing 2H1 and 6H1 cells were exposed to etoposide at various concentrations, and cultured for about 60 days in L15F10 medium with leukemia inhibitory factor. With a high concentration of etoposide (1 μM), the DNA histograms showed G(2)/M accumulation, suggesting that etoposide arrested the cell cycle at the G(2)/M phase. With a low concentration of etoposide (50 nM), the cell proliferation was suppressed with a doubling time of 98.4 h for 2H1 cells and 51.6 h for 6H1 cells, and without significant alteration in DNA histograms. Time-lapse videography revealed that 6H1 cells survived in the medium containing 50 nM etoposide had a cell cycle time of 18.8 h, which was equivalent to 19.2 h of the doubling time for the 6H1 cell population in drug-free medium, suggesting that a part of the cell population died and was excluded from the cell system. It was concluded that etoposide affected the cell cycle at a wide range of concentrations.

Pluripotency of a polyploid H1 (ES) cell system without leukaemia inhibitory factor

OBJECTIVES

Tetraploid cells are strictly biologically inhibited from composition of embryos; by the same token, only diploid cells compose embryos. However, the distinction between diploid and tetraploid cells in development has not been well explained. To examine pluripotency of polyploid ES cells, a polyploid embryonic stem (ES)-cell system was prepared.

MATERIALS AND METHODS

Diploid, tetraploid, pentaploid, hexaploid, octaploid and decaploid H1 (ES) cells (2H1, 4H1, 5H1, 6H1, 8H1 and 10H1 cells, respectively) were cultured for about 460 days in L15F10 medium without leukaemia inhibitory factor (LIF). The cells cultured under LIF-free conditions were denoted as 2H1(-), 4H1(-), 5H1(-), 6H1(-), 8H1(-) and 10H1(-) cells, respectively. Pluripotency and gene expression were examined.

RESULTS

Ploidy alteration of H1(-) cells was similar to that of H1 cells. The polyploid H1(-) cells showed positive activity of alkaline phosphatase, suggesting that they maintained pluripotency in vitro without LIF. The polyploid H1(-) cells formed teratocarcinomas in mouse abdomen, suggesting they could differentiate in mouse abdomen in vivo. 2H1, 4H1 and polyploid H1(-) cells expressed nanog, oct3/4 and sox2 genes, suggesting that they fulfilled the criteria of ES cells. Nanog gene was significantly over-expressed in 4H1 and polyploid H1(-) cells, suggesting that overexpression of nanog gene was a characteristic of polyploid H1 cells.

CONCLUSION

Polyploid H1 (ES) cells retained pluripotency in vitro, without LIF with nanog over-expression.

DNA-unstable decaploid mouse H1 (ES) cells established from DNA-stable pentaploid H1 (ES) cells polyploidized using demecolcine

OBJECTIVES

DNA content of diploid H1 (ES) cells (2H1 cells) has been shown to be stable in long-term culture; however, tetraploid and octaploid H1 (ES) cells (4H1 and 8H1 cells, respectively) were DNA-unstable. Pentaploid H1 (ES) cells (5H1 cells) established recently have been found to be DNA-stable; how, then is cell DNA stability determined? To discuss ploidy stability, decaploid H1 (ES) cells (10H1 cells) were established from 5H1 cells and examined for DNA stability.

MATERIALS AND METHODS

5H1 cells were polyploidized using demecolcine (DC) and 10H1 cells were obtained by one-cell cloning.

RESULTS

Number of chromosomes of 10H1 cells was 180 and durations of their G(1), S, and G(2)/M phases were 3, 7 and 6 h respectively. Volume of 10H1 cells was double that of 5H1 cells and morphology of 10H1 cells was flagstone-like in shape. 10H1 cells exhibited alkaline phosphatase activity and their DNA content decayed in 91 days of culture. 10H1 cells injected into mouse abdomen formed solid tumours that contained several kinds of differentiated cells with lower DNA content, suggesting that 10H1 cells were pluripotent and DNA-unstable. Loss of DNA stability was explained using a hypothesis concerning DNA structure of polyploid cells as DNA reconstructed through ploidy doubling was arranged in mirror symmetry in a new configuration.

CONCLUSION

In the pentaploid-decaploid transition of H1 cells, cell cycle parameters and pluripotency were retained, but morphology and DNA stability were altered.

Hexaploid H1 (ES) cells established from octaploid H1 cells are as DNA stable as pentaploid H1 cells

Hexaploid H1 (ES) cells (6H1 cells) were established from octaploid H1 cells (8H1 cells), as were pentaploid H1 cells (5H1 cells). 6H1 cells were compared with 5H1 cells. The number of chromosomes of 6H1 cells was 115, 20 more than the 95 of 5H1 cells. The durations of G(1), S, and G(2)/M phases of 6H1 cells were 3, 7, and 6 h, respectively, almost the same as those of 5H1 cells. The cell volume of 6H1 cells was equivalent that of 5H1 cells. The morphology of 6H1 cells was flattened circular cluster, different from the spherical cluster of 5H1 cells. 6H1 cells exhibited alkaline phosphatase activity as well as 5H1 cells. The DNA content of 6H1 cells was stable and maintained for 300 days of culturing, the same as that of 5H1 cells. The DNA stability of 6H1 cells was explained using a hypothesis concerning the DNA structure of polyploid cells because the asymmetric configuration of homologous chromosomes in 6H1 cells inhibited chromosome loss.

Different responses between diploid and tetraploid H1 embryonic stem cells appeared during long-term culturing in L15F10 medium without leukemia inhibitory factor

To examine the alteration in cellular characteristics of polyploid embryonic stem (ES) cells during long-term culturing without leukemia inhibitory factor (LIF), mouse diploid and tetraploid H-1 (ES) cells (2H1 and 4H1 cells, respectively) were cultured without LIF for approximately 5 months. 2H1 and 4H1 cells were adapted to the medium without LIF by decreasing the concentration for several passages, and they were denoted as 2H1(⁻) and 4H1(⁻) cells, respectively. DNA content of 4H1(⁻) cells decreased gradually in the early stage, increased abruptly in the second stage, and then was maintained for a long time. 4H1(⁻) cells exhibited longer doubling time and equivalent phase fraction compared with those of 2H1(⁻) cells. The G₁ phase fractions of 2H1(⁻) and 4H1(⁻) cells were increased compared with that of 2H1 cells. Cellular morphology and pluripotency were maintained in 4H1(⁻) cells but not in 2H1(⁻) cells. 2H1(⁻) cells showed a cell population consisting of several kinds of cells, and they lost alkaline phosphatase activity, suggesting that the cells had differentiated. 4H1(⁻) cells, however, exhibited alkaline phosphatase activity and formed teratocarcinoma in mouse abdomen, suggesting that the cells maintained their pluripotency in the medium without LIF.

DNA stable pentaploid H1 (ES) cells obtained from an octaploid cell induced from tetraploid cells polyploidized using demecolcine

Pentaploid H1 (ES) cells (5H1 cells) were accidentally obtained through one-cell cloning of octaploid H1 (ES) cells (8H1 cells) that were established from tetraploid H1 (ES) cells (4H1 cells) polyploidized using demecolcine. The number of chromosomes of 5H1 cells was 100, unlike the 40 of diploid H1 (ES) cells (2H1 cells), 80 of 4H1, and 160 of 8H1 cells. The durations of G(1), S, and G(2)/M phases of 5H1 cells were 3, 7, and 6 h, respectively, almost the same as those of 2H1, 4H1, and 8H1 cells. The cell volume of 5H1 cells was half of that of 8H1 cells, suggesting that 5H1 cells were created through abnormal cell divisions of 8H1 cells. The morphology of growing 5H1 cells was a spherical cluster similar to that of 2H1 cells and differing from the flagstone-like shape of 4H1 and 8H1 cells. Pentaploid solid tumors were formed from 5H1 cells after interperitoneal injection into the mouse abdomen, and they contained endodermal, mesodermal, and ectodermal cells as well as undifferentiated cells, suggesting both that the DNA content of 5H1 cells was retained during tumor formation and that the 5H1 cells were pluripotent. The DNA content of 5H1 cells was stable in long-term culturing as 2H1 cells, meaning that 5H1 and 2H1 cells shared similarities in DNA structure. The excellent stability of the DNA content of 5H1 cells was explained using a hypothesis for the DNA structure of polyploid cells because the pairing of homologous chromosomes in 5H1 cells is spatially forbidden.

Cell cycle, morphology and pluripotency of octaploid embryonic stem cells in comparison with those of tetraploid and diploid cells

To examine the alteration of cellular characteristics on ploidy transition of embryonic stem (ES) cells, octaploid cells (8H1 cells) were established from tetraploid H-1 (ES) cells, and compared with tetraploid and diploid H-1 (ES) cells (4H1 and 2H1 cells, respectively). The duration of G(1), S, and G(2)/M phases were essentially the same among 2H1, 4H1, and 8H1 cells, suggesting that cell cycle progression is conserved. The ratio of cell volume of 2H1, 4H1, and 8H1 cells was about 1 : 2 : 4, indicating that these polyploid cells were generated through cell cycle progression without cell division. The morphology of 8H1 cells was flagstone-like and flatter than that of 4H1 cells, and differed from the spindle-like shape of 2H1 cells, suggesting that transformation occurred during the ploidy transitions. Alkaline phosphatase activity was expressed equivalently in 2H1, 4H1, and 8H1 cells, and solid tumors that contained endodermal, mesodermal, and ectodermal cells were formed by 2H1, 4H1 or 8H1 cells after interperitoneal injection into the mouse abdomen, suggesting that pluripotency was preserved in the ploidy transition.

Mouse embryonic stem cells are not susceptible to cytomegalovirus but acquire susceptibility during differentiation

BACKGROUND

Cytomegalovirus (CMV) is the most significant infectious cause of congenital anomalies of the central nervous system caused by intrauterine infection in humans. The timing of infection and the susceptibility of cells in early gestational stages are not well understood. In this study we investigated the susceptibility of embryonic stem (ES) cells to CMV infection during differentiation.

METHODS

ES cell lines were established from transgenic mice integrated with the murine CMV (MCMV) immediate-early (IE) promoter connected with a reporter lacZ gene. The susceptibility of the ES cells was analyzed in terms of viral gene expression and viral replication after induction of differentiation.

RESULTS

ES cells were nonpermissive to MCMV infection in the undifferentiated state. Upon differentiation, permissive cells appeared approximately 2 weeks after the leukemia inhibitory factor was removed. Upon neural differentiation by retinoic acid (RA), glial cells showed specific susceptibility in terms of expression of the viral antigen. The MCMV IE promoter was not activated in ES cells from the transgenic mice. Activation of the IE promoter was detected approximately 2 weeks after induction of differentiation and observed predominantly in glial cells. Upon MCMV infection of the ES cells, viral infection was correlated with the activation of the IE promoter.

CONCLUSIONS

ES cells are nonpermissive to MCMV infection and acquire permissiveness about 2 weeks after induction of differentiation, especially in glial cells. Acquisition of permissiveness in differentiated ES cells may be associated with activation of the IE promoter.

ES cell line establishment

A method is described to establish mouse embryonic stem cell (ESC) lines from hybrid and inbred strains of mice. Attention is paid not only to the methodology for isolation and culture but also to the validation of freshly derived lines, in order to be maintained for prolonged time without significant differentiation or karyotype instability, and to provide reproducible germline transmission in chimaeric mice.

Alteration and preservation of cellular characteristics in long-term culture of tetraploid H-1 (ES) cells

To examine the alteration in cellular characteristics of polyploid ES cells during long-term culturing, tetraploid H-1 (ES) cells were continuously cultured for 180 days. Cellular DNA content of the tetraploid cells decreased and reached a plateau of 3.3 C, where C represents the complement of haploid chromosomes. The chromosome number also decreased, indicating that the DNA loss was induced by chromosome loss. Cell volume was maintained, suggesting that the DNA loss did not involve cytoplasmic loss. The cell cycle parameters were almost the same during the DNA decay process, indicating that cell cycle progression was independent of the quantity of homologous chromosomes. Hypotetraploid cells showed alkaline phosphatase activity and formed teratocarcinomas in mouse abdomens, suggesting that the pluripotent potential was maintained. Cellular morphology was also retained, suggesting that the gene expression specifying morphological characteristics was conserved. We conclude that these initial cellular characteristics of tetraploid H1 (ES) cells were preserved in long-term culture, irrespective of chromosome loss.

Mouse embryonic stem (ES) cell isolation

Building on the technology presented in earlier units of Chapter 23, this unit describes the basic method for the isolation of mouse embryonic (ES) stem cells. ES cells from wild-type mice may be used for the production of mouse mutants by homologous recombination and blastocyst-mediated transgenesis. ES cells from mutant mouse lines may be used in the analysis of mutant phenotypes.

Polyploidization of 2nH1 (ES) cells by K-252a and staurosporine

Mouse 2nH1 (ES) cells were examined for polyploidization using K-252a and staurosporine. Though 2nH1 cells were polyploidized by both K-252a and staurosporine, tetraploid cells, 4nH1K cells, were obtained only from cell populations exposed to K-252a. The probability of successful establishment of tetraploid cells was 2/9, suggesting that the highly polyploidized-tetraploid transition might occur infrequently. Cell cycle parameters of 4nH1K cells were almost the same as those of 2nH1 cells, suggesting that the rate of DNA synthesis was about twice that of the diploid cells. The cell volume of 4nH1K cells was about twice of that of diploid cells, indicating that 4nH1K cells contained about twice as much total intracellular material as 2nH1 cells. The morphology of the 4nH1K cells was flagstone-like, thus differing from that of the spindle-shaped 2nH1 cells, suggesting that morphological transformation occurred during the diploid-tetraploid transition. 4nH1K cells exhibited alkaline phosphatase activity and formed teratocarcinomas, implying that they were pluripotent. These characteristics of 4nH1K cells were similar to those of tetraploid 4nH1 cells that have been established through polyploidization by demecolcine, suggesting that 4nH1K and 4nH1 cells are similar irrespective of the different mechanisms of polyploidization.

Establishment of a tetraploid cell line from mouse H-1 (ES) cells highly polyploidized with demecolcine

OBJECTIVE

Establishment of tetraploid ES cells.

MATERIALS AND METHODS

Mouse H-1 (ES) cells were polyploidized by demecolcine and released from the drug.

RESULTS

A tetraploid cell line (4nH1 cells) was established from mouse H-1 (ES) cells (2nH1 cells) highly polyploidized by treatment with demecolcine. Cell cycle parameters of 4nH1 cells were almost the same as those of 2nH1 cells, suggesting that the rate of DNA synthesis was about twice that of the diploid cells. Mode of chromosome number of 4nH1 cells was 76, about twice that of 2nH1 cells. Cell volume of 4nH1 cells was about twice of that of diploid cells, indicating that 4nH1 cells contained about twice as much total intracellular material as 2nH1 cells. Morphology of the 4nH1 cells was flagstone-like, thus differing from that of the spindle-shaped 2nH1 cells, suggesting that the transformation had occurred during the diploid-tetraploid transition. 4nH1 cells exhibited alkaline phosphatase activity and formed teratocarcinomas, implying that they would be pluripotent.

CONCLUSION

A pluripotent tetraploid cell line (4nH1 cells) was established.

Mouse cloning with nucleus donor cells of different age and type

We have tested different cell types as sources for nucleus donors to determine differences in cloning efficiency. When donor nuclei were isolated from cumulus cells and injected into recipient oocytes from adult hybrid mice (B6D2F1 and B6C3F1), the success rate of cloning was 1.5-1.9%. When cumulus cell donor nuclei were isolated from adult inbred mice (C57BL/6, C3H/He, DBA/2, 129/SvJ, and 129/SvEvTac), reconstructed oocytes did not develop to full term or resulted in a very low success rate (0-0.3%) with the exception of 129 strains which yielded 0.7-1.4% live young. When fetal (13.5-15.5 dpc), ovarian, and testicular cells were used as nucleus donors, 2.2 and 1.0% of reconstructed oocytes developed into live offspring, respectively. When various types of adult somatic cells (fibroblasts, thymocytes, spleen cells, and macrophages) were used, oocytes receiving thymocyte nuclei never developed beyond implantation, whereas those receiving the nuclei of other cell types did. These results indicate that adult somatic cells are not necessarily inferior to younger cells (fetal and ES cells) in the context of mouse cloning. Although fetal cells are believed to have less genetic damage than adult somatic cells, the success rate of cloning using any cell types were very low. This may largely be due to technical problems and/or problems of genomic reprogramming by oocytes rather than the accumulation of mutational damage in adult somatic cells.