Enhanced production of neuroprogenitors, dopaminergic neurons, and identification of target genes by overexpression of sonic hedgehog in human embryonic stem cells.

Molecular and cellular signaling pathways are involved in the process of neural differentiation from human embryonic stem cells (hESC) to terminally differentiated neurons. The Sonic hedgehog (SHH) morphogen is required to direct the differentiation of hESC to several neural subtypes, for example, dopaminergic (DA) or motor neurons. However, the roles of SHH signaling and the pathway target genes that regulate the diversity of cellular responses arising from SHH activation during neurogenesis of hESC have yet to be elucidated. In this study, we report that overexpression of SHH in hESC promotes the derivation of neuroprogenitors (NP), increases proliferation of NP, and subsequently increases the yield of DA neurons. Next, gene expression changes resulting from the overexpression of SHH in hESC-derived NP were examined by genome-wide transcriptional profiling. Categorizing the differentially expressed genes according to the Gene Ontology biological processes showed that they are involved in numerous cellular processes, including neural development, NP proliferation, and neural specification. In silico GLI-binding sites analysis of the differentially expressed genes also identified a set of putative novel direct target genes of SHH in hESC-derived NP, which are involved in nervous system development. Electrophoretic mobility shift assays and promoter-luciferase assays confirmed that GLI1 binds to the promoter region and activates transcription of HEY2, a NOTCH signaling target gene. Taken together, our data provide evidence for the first time that there is cross-talk between the NOTCH and SHH signaling pathways in hESC-derived NP and also provide significant new insights into transcriptional targets in SHH-mediated neural differentiation of hESC.

Role of Sonic hedgehog signaling and the expression of its components in human embryonic stem cells.

Human embryonic stem cells (hESC) are characterized by their ability to self-renew and differentiate into all cell types of the body, making them a valuable resource for regenerative medicine. Yet, the molecular mechanisms by which hESC retain their capacity for self-renewal and differentiation remain unclear. The Hedgehog signaling pathway plays a pivotal role in organogenesis and differentiation during development, and is also involved in the proliferation and cell-fate specification of neural stem cells and neural crest stem cells. As there has been no detailed study of the Sonic hedgehog (SHH) signaling pathway in hESC, this study examines the expression and functional role of SHH during hESC self-renewal and differentiation. Here, we show the gene and protein expression of key components of the SHH signaling pathway in hESC and differentiated embryoid bodies. Despite the presence of functioning pathway components, SHH plays a minimal role in maintaining pluripotency and regulating proliferation of undifferentiated hESC. However, during differentiation with retinoic acid, a GLI-responsive luciferase assay and target genes PTCH1 and GLI1 expression reveal that the SHH signaling pathway is highly activated. Besides, addition of exogenous SHH to hESC differentiated as embryoid bodies increases the expression of neuroectodermal markers Nestin, SOX1, MAP2, MSI1, and MSX1, suggesting that SHH signaling is important during hESC differentiation toward the neuroectodermal lineage. Our findings provide a new insight in understanding the SHH signaling in hESC and the further development of hESC differentiation for regenerative medicine.

Generation of high-level stable transgene expressing human embryonic stem cell lines using Chinese hamster elongation factor-1 alpha promoter system.

The utilization of human embryonic stem cells (hESC) in regenerative medicine largely depends on the development of technologies that will allow efficient genetic manipulation of the cells in vitro. Although a few studies have described the transfection of hESC for generation of reporter lines stably expressing specific transgenes driven by different promoters, the optimal choice of promoter system for driving transgene in hESC has yet to be elucidated. We show for the first time that Chinese hamster elongation factor-1 alpha (CHEF1) promoter robustly drove reporter gene expression higher than the human elongation factor 1 alpha (hEF1 alpha), other constitutive Chinese hamster promoters, human cytomegalovirus (CMV) immediate early enhancer/promoter and SV40 promoters in hESC by quantitative analysis. We also successfully generated stably transfected hESC lines using this CHEF1 promoter system and demonstrated that they continued to express enhanced green fluorescent protein (EGFP) during prolonged undifferentiated proliferation, in differentiated embryoid bodies (EBs), and in teratomas without transgene silencing. By immunofluorescence staining and D ow cytometry analysis, the pluripotent markers, OCT-4, SSEA-4, and TRA-1-60, continued to be expressed in undifferentiated CHEF1-EGFP expressing hESC lines. When the stably transfected hESC were directed to differentiate into neural precursors in vitro, high-level EGFP expression was maintained and co-expression of neural markers, Nestin, and beta-tubulin III was observed. The morphology, karyotype, and telomerase activity of CHEF1-EGFP expressing hESC were normal after >50 continuous passages, and the cells retained the ability to differentiate into derivatives of the three germ layers in vitro as confirmed by RT-PCR analysis and immunocytochemical staining and in vivo teratoma formation. Therefore, stable CHEF1-EGFP hESC lines retained the capability for self-renewal and pluripotency. The novel CHEF1 promoter system described here enables high-level transgene expression in the stably transfected hESC. It may have signi, cant implication for uses in bioprocess development and future development of gene-modified hESC in tissue regeneration and transplantation applications.