Hung-Chih Kuo

Isolation and Characterization of Novel Rhesus Monkey Embryonic Stem Cell Lines

ESCs are important as research subjects since the mechanisms underlying cellular differentiation, expansion, and self‐renewal can be studied along with differentiated tissue development and regeneration in vitro. Furthermore, human ESCs hold promise for cell and tissue replacement approaches to treating human diseases. The rhesus monkey is a clinically relevant primate model that will likely be required to bring these clinical applications to fruition. Monkey ESCs share a number of properties with human ESCs, and their derivation and use are not affected by bioethical concerns. Here, we summarize our experience in the establishment of 18 ESC lines from rhesus monkey preimplantation embryos generated by the application of the assisted reproductive technologies. The newly derived monkey ESC lines were maintained in vitro without losing their chromosomal integrity, and they expressed markers previously reported present in human and monkey ESCs. We also describe initial efforts to compare the pluripotency of ESC lines by expression profiling, chimeric embryo formation, and in vitro‐directed differentiation into endodermal, mesodermal, and ectodermal lineages.

Oct-4 Expression in Pluripotent Cells of the Rhesus Monkey

Abstract The POU (Pit-Oct-Unc)-domain transcription factor, Oct-4, has become a useful marker of pluripotency in the mouse. It is found exclusively in mouse preimplantation-stage embryos after embryonic genome activation and is a characteristic of mouse embryonic stem (ES) cells, and its absence in knockout mice precludes inner cell mass (ICM) formation in blastocysts. Expression of Oct-4 has also been associated with pluripotency in primate cells. Here, we undertook a systematic study of Oct-4 expression in rhesus macaque preimplantation embryos produced by intracytoplasmic sperm injection and in ES cells before and after exposure to differentiating conditions in vitro. We also evaluated Oct-4 expression as a means of monitoring the extent of reprogramming following somatic cell nuclear transfer. Oct-4 was detected by reverse transcription-polymerase chain reaction and immunocytochemistry with a monoclonal antibody. Monkey pronuclear-stage zygotes and cleaving embryos up to the 8-cell stage showed no detectable Oct-4. Nuclear staining for Oct-4 first became obvious at the 16-cell stage, and a strong signal was observed in morula and compact morula stages. Both ICM and trophectodermal cell nuclei of monkey early blastocysts were positive for Oct-4. However, the signal was diminished in trophectodermal cells of expanded blastocysts, whereas expression remained high in ICM nuclei. Similar to the mouse, hatched monkey blastocysts showed strong Oct-4 expression in the ICM, with no detectable signal in the trophectoderm. Undifferentiated monkey ES cells derived from the ICM of in vitro-produced blastocysts expressed Oct-4, consistent with their pluripotent nature, whereas ES cell differentiation was associated with signal loss. Therefore, Oct-4 expression in the monkey, as in the mouse, provides a useful marker for pluripotency after activation of the embryonic genome. Finally, the observed lack or abnormal expression of Oct-4 in monkey nuclear transfer embryos suggests inadequate nuclear reprogramming.

Differentiation of Monkey Embryonic Stem Cells into Neural Lineages

Abstract Embryonic stem (ES) cells are self-renewing, pluripotent, and capable of differentiating into all of the cell types found in the adult body. Therefore, they have the potential to replace degenerated or damaged cells, including those in the central nervous system. For ES cell-based therapy to become a clinical reality, translational research involving nonhuman primates is essential. Here, we report monkey ES cell differentiation into embryoid bodies (EBs), neural progenitor cells (NPCs), and committed neural phenotypes. The ES cells were aggregated in hanging drops to form EBs. The EBs were then plated onto adhesive surfaces in a serum-free medium to form NPCs and expanded in serum-free medium containing fibroblast growth factor (FGF)-2 before neural differentiation was induced. Cells were characterized at each step by immunocytochemistry for the presence of specific markers. The majority of cells in complex/cystic EBs expressed antigens (α-fetal protein, cardiac troponin I, and vimentin) representative of all three embryonic germ layers. Greater than 70% of the expanded cell populations expressed antigenic markers (nestin and musashi1) for NPCs. After removal of FGF-2, approximately 70% of the NPCs differentiated into neuronal phenotypes expressing either microtubule-associated protein-2C (MAP2C) or neuronal nuclear antigen (NeuN), and approximately 28% differentiated into glial cell types expressing glial fibrillary acidic protein. Small populations of MAP2C/NeuN-positive cells also expressed tyrosine hydroxylase (∼4%) or choline acetyltransferase (∼13%). These results suggest that monkey ES cells spontaneously differentiate into cells of all three germ layers, can be induced and maintained as NPCs, and can be further differentiated into committed neural lineages, including putative neurons and glial cells.

Monozygotic Twinning in Rhesus Monkeys by Manipulation of In Vitro-Derived Embryos

Abstract The nonhuman primate is a relevant model for human disease that can be used for diverse biomedical investigations. The ability to propagate a founder animal by application of assisted reproductive technologies is pressing, but an even greater need in many studies is access to genetically identical animals. In an effort to create genetically identical monkeys, we evaluated two approaches to monozygotic twinning; blastomere separation, and blastocyst bisection. Embryos were produced by intracytoplasmic sperm injection of oocytes recovered following controlled ovarian stimulation. The quality of demiembryos produced in these efforts was evaluated by quantitating the efficiency of creating identical pairs for embryo transfer, by morphological assessment, by the allocation of cells to the inner cell mass (ICM) and trophectoderm (TE) in the blastocyst, and by the outcome of embryo transfer to synchronized host animals. Pairs were produced in high yield (85%–95%) by both twinning methods. Demiembryos resulting from blastomere separations at the 2- or 4-cell stage grew to blastocysts at the control frequency. Demiblastocysts contained, on average, half the number of cells of the intact controls while maintaining the same ICM:TE or ICM:total cell ratio. The equivalency of demiblastocysts within a set was also evaluated by differential cell counting. Embryo transfers of identical sets led to a 33% clinical pregnancy rate, with two twin pregnancies initiated. Neither pregnancy resulted in term birth of monozygotic twins, but our results are sufficiently encouraging to justify a large-scale twinning trial in the rhesus macaque.

Directed differentiation of rhesus monkey ES cells into pancreatic cell phenotypes

Embryonic stem cells (ES) can self-replicate and differentiate into all cell types including insulin-producing, beta-like cells and could, therefore, be used to treat diabetes mellitus. To date, results of stem cell differentiation into beta cells have been debated, largely due to difficulties in defining the identity of a beta cell. We have recently differentiated non-human primate (rhesus) embryonic stem (rES) cell lines into insulin producing, beta-like cells with the beta cell growth factor, Exendin-4 and using C-peptide as a phenotype marker. Cell development was characterized at each stage by gene and protein expression. Insulin, NKX6.1 and glucagon mRNA were expressed in stage 4 cells but not in early undifferentiated cells. We concluded that rES cells could be differentiated ex vivo to insulin producing cells. These differentiated rES cells could be used to develop a non-human primate model for evaluating cell therapy to treat diabetes. To facilitate the identification of beta-like cells and to track the cells post-transplantation, we have developed a marker gene construct: fusing the human insulin promoter (HIP) to the green fluorescent protein (GFP) gene. This construct was transfected into stage 3 rES derived cells and subsequent GFP expression was identified in C-peptide positive cells, thereby substantiating endogenous insulin production by rES derived cells. Using this GFP detection system, we will enrich our population of insulin producing rES derived cells and track these cells post-transplantation in the non-human primate model.

Serotonin neurons derived from rhesus monkey embryonic stem cells: similarities to CNS serotonin neurons

We sought an in vitro primate model for serotonin neurons. Rhesus monkey embryonic stem (ES) cell colonies were isolated and differentiated into embryoid bodies (EBs), then transferred to serum-free medium with 1% insulin-transferrin-selenium for 7 days to induce neural precursor cell (NPC) formation. NPCs were cultured in medium with 1% N-2 neural supplement and human fibroblast growth factor 2 (FGF2, 10 ng/ml) for 7 days to stimulate cell proliferation. Lastly, NPCs were dispersed into single cells and cultured without FGF2 for another 7 days to obtain terminal differentiation. Terminal cells were characterized for neuronal and serotonergic markers. Over 95% of the NPCs were immunopositive for nestin and Musashi1. Terminally differentiated cells appeared in both small and large morphologies. Most (>95%) of the mature cells (both small and large) were immunopositive for neuron-specific nuclear protein (NeuN), synaptophysin, microtubule-associated protein (MAP2C), Tau-1, neurofilament 160 (NF-160), beta-tubulin (TujIII), tryptophan hydroxylase (TPH), serotonin, the serotonin reuptake transporter (SERT), estrogen receptor-beta (ERbeta), and progestin receptor (PR), but not estrogen receptor-alpha (ERalpha). Less than 2-3% of cells were positive for tyrosine hydroxylase (TH). Reverse transcriptase polymerase chain reaction (RT-PCR) detected mRNA transcripts for TPH-1, TPH-2, SERT, 5-HT1A-autoreceptor, ERbeta, and PR in the differentiated population. A low level of expression of ERalpha mRNA was also detected. Quantitative RT-PCR indicated that the relative abundance of TPH-2 mRNA was greater than TPH-1 mRNA. Serotonin as measured by ELISA increased 3-fold in the mature stage compared to the selection and expansion stages. In summary, a remarkably high percentage of cells derived from monkey ES cells exhibited neuronal plus serotonergic markers as well as nuclear steroid receptors similar to primate CNS serotonin neurons, suggesting that these cells may serve as a useful primate model for serotonergic neurons.

Aberrant Genomic Imprinting in Rhesus Monkey Embryonic Stem Cells

Genomic imprinting involves modification of a gene or a chromosomal region that results in the differential expression of parental alleles. Disruption or inappropriate expression of imprinted genes is associated with several clinically significant syndromes and tumorigenesis in humans. Additionally, abnormal imprinting occurs in mouse embryonic stem cells (ESCs) and in clonally derived animals. Imprinted gene expression patterns in primate ESCs are largely unknown, despite the clinical potential of the latter in the cell‐based treatment of human disease. Because of the possible implications of abnormal gene expression to cell or tissue replacement therapies involving ESCs, we examined allele specific expression of four imprinted genes in the rhesus macaque. Genomic and complementary DNA from embryos and ESC lines containing useful single nucleotide polymorphisms were subjected to polymerase chain reaction–based amplification and sequence analysis. In blastocysts, NDN expression was variable indicating abnormal or incomplete imprinting whereas IGF2 and SNRPN were expressed exclusively from the paternal allele and H19 from the maternal allele as expected. In ESCs, both NDN and SNRPN were expressed from the paternal allele while IGF2 and H19 showed loss of imprinting and biallelic expression. In differentiated ESC progeny, these expression patterns were maintained. The implications of aberrant imprinted gene expression to ESC differentiation in vitro and on ESC‐derived cell function in vivo after transplantation are unknown.