Atsuyo Yamamoto

Visualization, direct isolation, and transplantation of midbrain dopaminergic neurons

To visualize and isolate live dopamine (DA)-producing neurons in the embryonic ventral mesencephalon, we generated transgenic mice expressing green fluorescent protein (GFP) under the control of the rat tyrosine hydroxylase gene promoter. In the transgenic mice, GFP expression was observed in the developing DA neurons containing tyrosine hydroxylase. The outgrowth and cue-dependent guidance of GFP-labeled axons was monitored in vitro with brain culture systems. To isolate DA neurons expressing GFP from brain tissue, cells with GFP fluorescence were sorted by fluorescence-activated cell sorting. More than 60% of the sorted GFP+ cells were positive for tyrosine hydroxylase, confirming that the population had been successfully enriched with DA neurons. The sorted GFP+ cells were transplanted into a rat model of Parkinsons disease. Some of these cells survived and innervated the host striatum, resulting in a recovery from Parkinsonian behavioral defects. This strategy for isolating an enriched population of DA neurons should be useful for cellular and molecular studies of these neurons and for clinical applications in the treatment of Parkinsons disease.

Evaluation of in vitro proliferative activity of human fetal neural stem/progenitor cells using indirect measurements of viable cells based on cellular metabolic activity

To scale up human neural stem/progenitor cell (NSPC) cultures for clinical use, we need to know how long these cells can live ex vivo without losing their ability to proliferate and differentiate; thus, a convenient method is needed to estimate the proliferative activity of human NSPCs grown in neurosphere cultures, as direct cell counting is laborious and potentially inaccurate. Here, we isolated NSPCs from human fetal forebrain and prepared neurosphere cultures. We determined the number of viable cells and estimated their proliferative activity in long‐term culture using two methods that measure viable cell numbers indirectly, based on their metabolic activity: the WST‐8 assay, in which a formazan dye is produced upon reduction of the water‐soluble tetrazolium salt WST‐8 by dehydrogenase activity, and the ATP assay, which measures the ATP content of the total cell plasma. We compared the results of these assays with the proliferative activity estimated by DNA synthesis using the 5‐bromo‐2′‐deoxyuridine incorporation assay. We found the numbers of viable human NSPCs to be directly proportional to the metabolic reaction products obtained in the WST‐8 and ATP assays. Both methods yielded identical cell growth curves, showing an exponentially proliferative phase and a change in the population doubling time in long‐term culture. They also showed that human NSPCs could be expanded for up to 200 days ex vivo without losing their ability to proliferate and differentiate. Our findings indicated that indirect measurements of viable cells based on metabolic activity, especially the ATP assay, are very effective and reproducible ways to determine the numbers of viable human NSPCs in intact neurospheres.

Direct isolation of committed neuronal progenitor cells from transgenic mice coexpressing spectrally distinct fluorescent proteins regulated by stage‐specific neural promoters

Many tissues arise from pluripotent stem cells through cell‐type specification and maturation. In the bone marrow, primitive stem cells generate all the different types of blood cells via the sequential differentiation of increasingly committed progenitor cells. Cell‐surface markers that clearly distinguish stem cells, restricted progenitors, and differentiated progeny have enabled researchers to isolate these cells and to study the regulatory mechanisms of hematopoiesis. Neuronal differentiation appears to involve similar mechanisms. However, neural progenitor cells that are restricted to a neuronal fate have not been characterized in vivo, because specific cell‐surface markers are not available. We have developed an alternative strategy to identify and isolate neuronal progenitor cells based on dual‐color fluorescent proteins. To identify and isolate directly progenitor cells from brain tissue without the need for either transfection or intervening cell culture, we established lines of transgenic mice bearing fluorescent transgenes regulated by neural promoters. One set of transgenic lines expressed enhanced yellow fluorescent protein (EYFP) in neuronal progenitor cells and neurons under the control of the Tα1 α‐tubulin promoter. Another line expressed enhanced green fluorescent protein (EGFP) in immature neural cells under the control of the enhancer/promoter elements of the nestin gene. By crossing these lines we obtained mice expressing both transgenes. To isolate neuronal progenitor cells directly from the developing brain, we used flow cytometry, selecting cells that expressed EGFP and EYFP simultaneously. We expect this strategy to provide valuable material with which to study the mechanisms of neurogenesis and to develop cell‐based therapies for neurological disorders. J. Neurosci. Res. 65:220–227, 2001.

Isolation and cellular properties of mesenchymal cells derived from the decidua of human term placenta

The clinical promise of cell-based therapies is generally recognized, and has driven an intense search for good cell sources. In this study, we isolated plastic-adherent cells from human term decidua vera, called decidua-derived-mesenchymal cells (DMCs), and compared their properties with those of bone marrow-derived-mesenchymal stem cells (BM-MSCs). The DMCs strongly expressed the mesenchymal cell marker vimentin, but not cytokeratin 19 or HLA-G, and had a high proliferative potential. That is, they exhibited a typical fibroblast-like morphology for over 30 population doublings. Cells phenotypically identical to the DMCs were identified in the decidua vera, and genotyping confirmed that the DMCs were derived from the maternal components of the fetal adnexa. Flow cytometry analysis showed that the expression pattern of CD antigens on the DMCs was almost identical to that on BM-MSCs, but some DMCs expressed the CD45 antigen, and over 50% of them also expressed anti-fibroblast antigen. In vitro, the DMCs showed good differentiation into chondrocytes and moderate differentiation into adipocytes, but scant evidence of osteogenesis, compared with the BM-MSCs. Gene expression analysis showed that, compared with BM-MSCs, the DMCs expressed higher levels of TWIST2 and RUNX2 (which are associated with early mesenchymal development and/or proliferative capacity), several matrix metalloproteinases (MMP1, 3, 10, and 12), and cytokines (BMP2 and TGFB2), and lower levels of MSX2, interleukin 26, and HGF. Although DMCs did not show the full multipotency of BM-MSCs, their higher proliferative ability indicates that their cultivation would require less maintenance. Furthermore, the use of DMCs avoids the ethical concerns associated with the use of embryonic tissues, because they are derived from the maternal portion of the placenta, which is otherwise discarded. Thus, the unique properties of DMCs give them several advantages for clinical use, making them an interesting and attractive alternative to MSCs for regenerative medicine.

Expression of Tubulin Beta II in Neural Stem/Progenitor Cells and Radial Fibers During Human Fetal Brain Development

Recent studies revealed that the “radial glia” in fetal rodent brains are dividing neuronal precursor cells. However, in fetal primate brains, this issue remains unclear, with previous reports indicating that radial glia are a specialized form of astroglia. To investigate the relationship between radial fibers (RFs) and neural stem/progenitor cells in the fetal human brain, we generated polyclonal antibodies to human nestin protein and developed a new mAb, KNY-379, by screening for antibodies that immunostained RFs on paraffin-embedded human fetal brain specimens (12 gestational weeks). The immunostaining for KNY-379 antigen and nestin was seen over the RFs in brains at 8 gestational weeks. Furthermore, KNY-379 antigen and nestin were also detected in human neural stem/progenitor cells in neurosphere cultures. At 12 to 15 gestational weeks, the KNY-379 immunostaining of RFs remained in the periventricular zone and the deep part of the intermediate zone, but it also appeared in outgrowing axons in the cortical plate, in the superficial portion of the intermediate zone, and in apical dendrites in the molecular layer. In the later stages of fetal development (18–40 gestational weeks), this antigen remained in the outgrowing axons and dendrites, but was no longer associated with RFs. Expression cloning and immunoblot analysis demonstrated the antigen to be tubulin beta II, which would thus be a good marker for studying RFs and neural stem/progenitor cells in the early developing human brain.

Musashi and seven in absentia downregulate Tramtrack through distinct mechanisms in Drosophila eye development.

We have examined the roles played by the Drosophila neural RNA-binding protein Musashi (MSI) in eye development. MSI expression was observed in the nuclei of all photoreceptor cells (R1-R8). Although a msi loss-of-function mutation resulted in only weak abnormalities in photoreceptor differentiation, we found that the msi eye phenotype was significantly enhanced in a seven in absentia (sina) background. sina is known to be involved in the degradation of the Tramtrack (TTK) protein, leading to the specification of the R7 fate. We demonstrated that MSI also functions to regulate TTK expression. The sina msi mutants showed significantly high ectopic expression of TTK69 and failure in the determination of the R1, R6, and R7 fates. Other photoreceptor cells also failed to differentiate with abnormalities occurring late in the differentiation process. These results suggest that MSI and SINA function redundantly to downregulate TTK in developing photoreceptor cells.

Expression of the Neural RNA-Binding Protein Musashi1 in Pediatric Brain Tumors

Musashi1 (MSI1) is an evolutionarily conserved RNA-binding protein, selectively expressed in neural stem cells (NSCs) and considered a versatile marker for normal NSCs and tumor cell diagnosis. Here, we examined MSI1 expression in primary pediatric brain tumors, medulloblastomas and ependymomas, by double immunostaining with lineage phenotypic markers (Lin). These tumors highly express MSI1 and are heterogeneous, containing both MSI1+/Lin– tumor cells in regions of relatively high cellularity and proliferative activity and MSI1+/Lin+ tumor cells in regions of lower cellularity. These findings suggest that MSI1 may be a useful marker for characterizing tumor heterogeneity and for examining in situ the analogy between normal NSCs and MSI1+ cells in pediatric brain tumors. This test could be easily applied to routine clinical diagnosis.

ABCB1 is predominantly expressed in human fetal neural stem/progenitor cells at an early development stage

ABCB1 is a human ABC transporter originally characterized by its ability to cause resistance to chemotherapy drugs in cancer cells, and later found to be functionally expressed in human neural stem/progenitor cells (NSPCs) in vitro. Here, we performed a detailed examination of ABCB1s expression on human NSPCs in vitro and in human fetal brain tissues, and analyzed the cellular properties of the human NSPCs expressing ABCB1. We confirmed that ABCB1 was expressed on the surface of human NSPCs, and its level correlated well with those of Nestin and CD133. The population of fluorescence‐activated cell sorter–sorted human NSPCs expressing high levels of ABCB1 showed enrichment of proliferating cells, higher expression of 246 genes (e.g., RGS6, IGFBP7, GFAP, TNC, Hes1), and lower expression of 71 genes (e.g., STMN2, DLX5, BASP1, DCX, CD24) compared with human NSPCs expressing low or no ABCB1. In situ, ABCB1 was selectively expressed in cells in the ventricular or subventricular regions of lateral ventricles that expressed Nestin in human development. These findings suggest that ABCB1 is predominantly expressed in immature human fetal NSPCs in vitro and at early developmental stages in vivo, and that it may be a useful marker for human NSPCs.

Feeder-Free Generation and Long-Term Culture of Human Induced Pluripotent Stem Cells Using Pericellular Matrix of Decidua Derived Mesenchymal Cells

Human ES cells (hESCs) and human induced pluripotent stem cells (hiPSCs) are usually generated and maintained on living feeder cells like mouse embryonic fibroblasts or on a cell-free substrate like Matrigel. For clinical applications, a quality-controlled, xenobiotic-free culture system is required to minimize risks from contaminating animal-derived pathogens and immunogens. We previously reported that the pericellular matrix of decidua-derived mesenchymal cells (PCM-DM) is an ideal human-derived substrate on which to maintain hiPSCs/hESCs. In this study, we examined whether PCM-DM could be used for the generation and long-term stable maintenance of hiPSCs. Decidua-derived mesenchymal cells (DMCs) were reprogrammed by the retroviral transduction of four factors (OCT4, SOX2, KLF4, c-MYC) and cultured on PCM-DM. The established hiPSC clones expressed alkaline phosphatase, hESC-specific genes and cell-surface markers, and differentiated into three germ layers in vitro and in vivo. At over 20 passages, the hiPSCs cultured on PCM-DM held the same cellular properties with genome integrity as those at early passages. Global gene expression analysis showed that the GDF3, FGF4, UTF1, and XIST expression levels varied during culture, and GATA6 was highly expressed under our culture conditions; however, these gene expressions did not affect the cells’ pluripotency. PCM-DM can be conveniently prepared from DMCs, which have a high proliferative potential. Our findings indicate that PCM-DM is a versatile and practical human-derived substrate that can be used for the feeder-cell-free generation and long-term stable maintenance of hiPSCs.

A method for efficiently generating neurospheres from human-induced pluripotent stem cells using microsphere arrays.

In vitro, human neural stem cells can be selectively expanded from fetal or adult neural tissues as neurospheres consisting of immature neural progenitor cells. Access to human neural tissues is limited, making it difficult to propagate and use primary neural stem or progenitor cells (NSPCs) from human neural tissues (hN-NSPCs). It was recently demonstrated that hN-NSPCs can be differentiated from either human embryonic stem cells (hESC-NSPCs) or human-induced pluripotent stem cells (hiPSC-NSPCs), and that hESC-NSPCs and hiPSC-NSPCs are adaptable, powerful substitutes for hN-NSPCs in both regenerative medicine and pharmacological or neurotoxicological assays. We here describe a new protocol to generate neurospheres consisting of hiPSC-NSPCs using microsphere arrays, the surface of which is modified with polyethylene glycol to render it nonadhesive to cells. Primary hiPSCs treated with noggin formed neurospheres on the microsphere arrays and could be stably propagated as free-floating spheroids. The hiPSC-NSPCs proliferating in these neurospheres were almost identical in phenotype to hN-NSPCs, in both cell-surface marker expression and their ability to differentiate into neuronal cells, although gene expression profiles showed that the hiPSC-NSPCs had higher neural and lower glial gene expression, along with mid-hindbrain-like regional specificity. This convenient propagation protocol can be used to evaluate the neurosphere-forming efficiency of hiPSC clones. This method will support the generation of neurospheres from hESCs and hiPSCs and contribute to the use of hESC-NSPCs and hiPSC-NSPCs in research.