In vitro culture of single cells facilitates biological studies by deconvoluting complications from cell population heterogeneity. However, there is still a lack of simple yet high-throughput methods to perform single cell culture experiments. In this paper, we report the development and application of a microfluidic device with a dual-well (DW) design concept for high-yield single-cell loading (~77%) in large microwells (285 and 485 μm in diameter) which allowed for cell spreading, proliferation and differentiation. The increased single-cell loading yield is achieved by using sets of small microwells termed “capture-wells” and big microwells termed “culture-wells” according to their utilities for single-cell capture and culture, respectively. This novel device architecture allows the size of the “culture” microwells to be flexibly adjusted without affecting the single-cell loading efficiency making it useful for cell culture applications as demonstrated by our experiments of KT98 mouse neural stem cell differentiation, A549 and MDA-MB-435 cancer cell proliferation, and single-cell colony formation assay with A549 cells in this paper.

Fibroblast growth factor 1 (FGF1) has been shown to maintain proliferation and self‐renewal capacities of neural stem/progenitor cells (NSPCs) in vitro. We have previously identified FGF1B as the major transcript of FGF1 gene expressed exclusively in brain areas that are known to be abundant for NSPCs in vivo. The 540‐bp (−540 to +31) sequence upstream of the 1B transcription start site (F1B) is sufficient to drive the expression of a heterologous luciferase reporter in cultured cells. In this study, we report a direct genetic and functional approach to isolate F1B(+) NSPCs using green fluorescent protein (GFP) reporter gene under the control of human F1B promoter. The F1B‐GFP reporter could facilitate the isolation of NSPCs with self‐renewal and multipotent capacities from human glioblastoma tissues, developing or adult mouse brains by fluorescence‐activated cell sorting. Future work elucidating the mechanisms that control FGF1B expression will help to identify new NSPC‐related genes. Developmental Dynamics 238:302–314, 2009.

Fibroblast growth factor 1 (FGF1) has been suggested to have an important role in cell growth, proliferation, and neurogenesis. Human FGF1 gene 1B promoter (−540 to +31)-driven green fluorescence (F1BGFP) has been shown to monitor endogenous FGF1 expression. F1BGFP could also be used to isolate neural stem/progenitor cells from embryonic, neonatal, and adult mouse brains or to isolate glioblastoma stem cells (GBM-SCs) from human glioblastoma tissues. Here, we present evidence that transcription factor RFX1 could bind the 18-bp cis-elements (−484 to −467) of the F1B promoter, modulate F1BGFP expression and endogenous FGF1 expression, and further regulate the maintenance of GBM-SCs. These observations were substantiated by using yeast one-hybrid assay, electrophoretic mobility shift assay, chromatin immunoprecipitation assay, gain- and loss-of-function assays, and neurosphere assays. Overexpression of RFX1 was shown to down-regulate FGF-1B mRNA expression and neurosphere formation in human glioblastoma cells, whereas RNA interference knockdown of RFX1 demonstrated the opposite effects. Our findings provide insight into FGF1 gene regulation and suggest that the roles of FGF1 and RFX1 in the maintenance of GBM-SCs. RFX1 may negatively regulate the self-renewal of GBM-SCs through modulating FGF-1B and FGF1 expression levels by binding the 18-bp cis-elements of the F1B promoter.

RBM4 participates in cell differentiation by regulating tissue-specific alternative pre-mRNA splicing. RBM4 also has been implicated in neurogenesis in the mouse embryonic brain. Using mouse embryonal carcinoma P19 cells as a neural differentiation model, we observed a temporal correlation between RBM4 expression and a change in splicing isoforms of Numb, a cell-fate determination gene. Knockdown of RBM4 affected the inclusion/exclusion of exons 3 and 9 of Numb in P19 cells. RBM4-deficient embryonic mouse brain also exhibited aberrant splicing of Numb pre-mRNA. Using a splicing reporter minigene assay, we demonstrated that RBM4 promoted exon 3 inclusion and exon 9 exclusion. Moreover, we found that RBM4 depletion reduced the expression of the proneural gene Mash1, and such reduction was reversed by an RBM4-induced Numb isoform containing exon 3 but lacking exon 9. Accordingly, induction of ectopic RBM4 expression in neuronal progenitor cells increased Mash1 expression and promoted cell differentiation. Finally, we found that RBM4 was also essential for neurite outgrowth from cortical neurons in vitro. Neurite outgrowth defects of RBM4-depleted neurons were rescued by RBM4-induced exon 9-lacking Numb isoforms. Therefore, our findings indicate that RBM4 modulates exon selection of Numb to generate isoforms that promote neuronal cell differentiation and neurite outgrowth.

Valproic acid (VPA) is the primary mood‐stabilizing drug to exert neuroprotective effects and to treat bipolar disorder in clinic. Fibroblast growth factor 1 (FGF1) has been shown to regulate cell proliferation, cell division, and neurogenesis. Human FGF1 gene 1B promoter (−540 to +31)‐driven green fluorescence (F1BGFP) has been shown to recapitulate endogenous FGF1 gene expression and facilitates the isolation of neural stem/progenitor cells (NSPCs) from developing and adult mouse brains. In this study, we provide several lines of evidence to demonstrate the underlying mechanisms of VPA in activating FGF‐1B promoter activity: (i) VPA significantly increased the FGF‐1B mRNA expression and the percentage of F1BGFP(+) cells; (ii) the increase of F1BGFP expression by VPA involves changes of regulatory factor X (RFX) 1‐3 transcriptional complexes and the increase of histone H3 acetylation on the 18‐bp cis‐element of FGF‐1B promoter; (iii) treatments of other histone deacetylases (HDAC) inhibitors, sodium butyrate and trichostatin A, significantly increased the expression levels of FGF‐1B, RFX2, and RFX3 transcripts; (iv) treatments of glycogen synthase kinase 3 (GSK‐3) inhibitor, lithium, or GSK‐3 siRNAs also significantly activated FGF‐1B promoter; (v) VPA specifically enhanced neuronal differentiation in F1BGFP(+) embryonic stem cells and NSPCs rather than GFP(−) cells. This study suggested, for the first time, that VPA activates human FGF1 gene promoter through inhibiting HDAC and GSK‐3 activities.