碱性成纤维生长因子和表皮生长因子对脊髓神经干细胞增殖与分化的影响

目的观察碱性成纤维生长因子(bFGF)和表皮生长因子(EGF)对胚胎脊髓神经干细胞(NSC)增殖与分化的影响。方法从14 d胚胎大鼠的脊髓组织中分离培养脊髓NSC,并随机分为3组:EGF组、bFGF组和bFGF+EGF组。通过光镜观察不同时间点各组脊髓NSC克隆细胞团数量及直径大小,并采用免疫荧光染色检测各组脊髓NSC向神经元和星形胶质细胞分化的情况。结果①EGF组培养1、3、7 d后NSC克隆细胞团数量和直径均少于bFGF和bFGF+EGF组,差异有统计学意义(P0.05)。而bFGF+EGF组仅在培养1 d时克隆细胞团数量多于bFGF组,在培养3、7 d时差异无统计学意义。②EGF组分化细胞中神经元比例显著少于bFGF和bFGF+EGF组,星形胶质细胞数量明显大于bFGF和bFGF+EGF组,差异有统计学意义(P0.05)。而bFGF和bFGF+EGF组组间差异无统计学意义。结论 EGF对脊髓NSC克隆形成有一定作用,而bFGF能较好地促进克隆细胞团的形成及生长,两者联合应用在培养早期可显著促进克隆细胞团形成。EGF可诱导脊髓NSC更多分化为星形胶质细胞,而bFGF则可促进脊髓NSC向神经元分化。     

大鼠胚胎神经干细胞的体外培养及鉴定

目的探讨大鼠胚胎神经干细胞（NSC）的体外培养和诱导分化的条件和特点。方法从孕14～16d的大鼠胚胎脑皮质中分离NSC，在表皮生长因子、碱性成纤维生长因子和B27联合作用下使其稳定增殖，并用10％的胎牛血清诱导其贴壁分化，应用免疫荧光染色方法行巢蛋白（Nestin）、神经元特异性烯醇化酶（NSE）、胶质纤维酸性蛋白（GFAP）、Gale-C免疫荧光染色，对NSC及其分化的细胞进行鉴定。结果体外培养的NSC增殖成神经干细胞球并传代，鉴定为Nestin染色阳性细胞，并可诱导分化为神经元细胞（NSE染色阳性细胞）、星形胶质细胞（GFAP染色阳性细胞）和少突胶质细胞（Gale-C染色阳性细胞）。结论采用无血清培养基中加入特定生长因子的培养技术，可培养出在体外稳定增殖并有多向分化潜能的大鼠胚胎NSC。     

表皮生长因子对胎鼠纹状体神经干细胞的作用

目的：研究表皮生长因子（EGF）对胎鼠纹状体神经干细胞分裂增殖及分化的诱导作用。方法：应用EGF促使体外培养中的胎鼠神经干细胞分裂增殖并诱导其分化,随后使用透射电子显微镜及免疫组化方法研究干细胞的生物学特性。结果：胎鼠纹状体存在多潜能神经干细胞,EGF可以促使胎鼠纹状体神经干细胞分裂,并使其分化产生一定比例的神经元及胶质细胞。结论：EGF作为外源性信号因子作用于胎鼠纹状体神经干细胞的相应受体,对其分裂分化可产生重要作用。     

人小龄胚胎神经干细胞的分离培养、扩增及鉴定

目的 探索人胚胎神经干细胞的体外分离培养条件，从而在体外大量扩增神经干细胞；并观察神经干细胞增殖、分化的特点。方法 从人胚胎脑分离神经干细胞，部分细胞冻存，另一部分细胞进行体外培养。采用无血清培养液，加入表皮生长因子(EGF)和碱性成纤维细胞生长因子(bFGF)刺激细胞增殖，进行体外扩增、传代培养。采用免疫荧光法鉴定神经干细胞和分化的神经元及胶质细胞。结果 从人胚胎脑分离的细胞在含有EGF和bFGF的无血清培养液中能形成大量的神经干细胞球，这些神经干细胞球可在体外扩增及传代培养。免疫荧光法鉴定神经干细胞球中大部分为神经上皮干细胞蛋白(nestin)表达阳性细胞。贴壁后可以分化出神经元特异性烯醇化酶(NSE)、胶质纤维酸性蛋白(GFAP)表达阳性的细胞。经冻存后的胎脑细胞也能培养出具有同样特征的神经干细胞。结论 在含有EGF和bFGF的无血清培养液中，从人胚胎脑能分离培养出神经干细胞，并能在体外大量扩增。这为人类神经干细胞的进一步研究和应用提供了材料。     

PDGF对人神经干细胞分化和甲状腺激素受体表达的影响

目的　探讨血小板衍生生长因子 (platelet-derived growth factor,PDGF)在神经干细胞 (neural stem cell,NSC)定向分化中的作用 ,以及 PDGF在 NSC分化过程中对甲状腺激素受体 (thyroid hormone receptors,TRs)表达的调控。方法　用免疫细胞化学方法鉴定分化后的细胞类型 ,分别用 RT-PCR半定量法、ELISA法检测不同诱导条件下 NSC分化前后 TR-α1 、TR-α2 、TR-β1 在转录与蛋白表达水平上的变化。结果　 PDGF诱导分化后神经丝蛋白 (neurofilament protein,NF)细胞约占 80 % ;TR-α1 、TR-α2 、TR-β1 m RNA表达水平分别比 1 0 % (体积分数 )胎牛血清诱导分化组上调约 40 %、3 0 %、1 0 % (P<0 .0 5 )。TR-α、TR-β蛋白质表达趋势为 NSC>PDGF诱导分化组 >血清诱导分化组 (P <0 .0 5 )。结论　 PDGF能引发 NSC向神经元分化 ,同时在转录与蛋白表达水平上调 NSC分化后 TR各亚型的表达 ,增强甲状腺激素对中枢神经系统发育的调控作用。     

慢病毒载体VP22-EGFP的构建及其对大鼠神经干细胞转染及表达的研究

目的 研究VP22穿梭蛋白对神经干细胞(neural stem cell,NSC)转染效率的影响.方法 通过酶切质粒pUL49ep获得VP22片段后克隆到含有增强型绿色荧光蛋白(enhanced greenfluorescent protein,EGFP)的慢病毒(Lentivirus)pHIV-EGFP质粒载体上,并采用PCR及基因测序技术对VP22基因进行鉴定.病毒包装采用三质粒系统共转染293T细胞后感染经体外原代培养、扩增的SD大鼠胎脑NSC,荧光显微镜下观察EGFP在NSC中的表达,流式细胞仪检测EGFP的表达,PCR检测基因组中VP22-EGFP基因的表达,MTT法测定转染前后单纯NSC、含有EGFP及含有VP22-EGFP的NSC的增殖活性.结果 PCR和DNA测序证实,外源基因VP22成功插入到质粒载体pHIV-EGFP的骨架结构中的启动子CMV和EGFP序列之间;荧光显微镜下均见有绿色荧光蛋白的表达;流式细胞仪测定结果:Lentivirus-EGFP及Lentivirus-VP22-EGFP转染的NSC的EGFP的表达率分别为(23.1±1.8)%及(34.9±2.9)%(P<0.01);PCR结果显示VP22整合入NSC的基因组DNA中;MTT结果显示转染前后单纯NSC、含有EGFP及含有VP22-EGFP的NSC的细胞生长曲线无明显改变.结论 VP22能够提高慢病毒对NSC的转染效率,且不影响其生长特性.表明VP22作为一种短链蛋白可以与编码的治疗基因形成融合蛋白增强基因治疗的疗效,在基因修饰的工程化干细胞中具有良好应用前景.     

甲基-β-环糊精干扰脂质微区影响脑胶质瘤细胞系C6侵袭和迁移的体外研究

目的观察甲基-β-环糊精(MβCD)破坏脂质微区结构对经体外培养的大鼠脑胶质瘤细胞系C6细胞侵袭和迁移能力的影响。方法采用MβCD(5mmol/L)破坏经体外培养的大鼠脑胶质瘤细胞系C6细胞膜脂质微区,通过Transwell细胞侵袭和迁移实验检测细胞侵袭性和迁移能力;Western blotting检测细胞膜脂质微区结构蛋白Caveolin-1和膜受体表皮生长因子受体表达水平的变化。结果干扰组大鼠脑胶质瘤细胞系C6细胞Caveolin-1和表皮生长因子受体表达水平明显低于对照组(P=0.000,0.001)。对照组大鼠脑胶质瘤细胞系C6细胞穿过聚碳酸酯微膜数目为(54.00±9.59)个/视野,干扰组为(23.94±5.56)个/视野,两组比较差异有统计学意义(P=0.000)。对照组大鼠脑胶质瘤细胞系C6细胞迁移至空白端的细胞数目为(134.00±9.68)个/视野,干扰组为(88.00±6.22)个/视野,两组比较差异有统计学意义(P=0.000)。结论甲基-β-环糊精破坏脂质微区结构后可降低经体外培养的大鼠脑胶质瘤细胞系C6细胞的侵袭性和迁移能力,其机制可能与降低Caveolin-1和表皮生长因子受体等多种膜蛋白和受体表达水平有关。     

脊髓来源神经干细胞分离培养及向雪旺氏细胞的诱导分化

目的 探讨新生大鼠脊髓来源神经干细胞(NSCs)的分离培养及在体外一定条件下向周围神经雪旺氏细胞分化的可行性. 方法 分离新生大鼠的脊髓组织,在含有B27(终浓度1%)、碱性成纤维细胞生长因子(bFGF)和表皮生长因子(EGF)(终浓度均为20 μg/L)培养基中分离培养出NSCs.用复合诱导因子(10%FBS+5 μmol/L血小板凝集抑制剂+10 ng/mL bFGF+5 ng/mE血小板源性生长因子)在体外诱导NSCs分化为雪旺氏细胞.免疫荧光细胞化学方法[一抗为p75、S-100、神经胶质纤维酸性蛋白(GFAP)]鉴定体外诱导分化结果.结果 培养的新生大鼠脊髓组织细胞nestin染色表达阳性;分离培养的大鼠脊髓来源NSCs经诱导分化后形态类似雪旺氏细胞,免疫荧光细胞化学方法显示诱导后细胞表达雪旺氏细胞的表面标志,GFAP、S-100和P75表达阳性.结论 新生大鼠脊髓来源NSCs可以在体外诱导分化为雪旺氏细胞.     

多细胞因子诱导成年鼠骨髓基质细胞向神经细胞分化的实验研究

目的观察大鼠骨髓基质细胞(rBMSCs)的生长特点及诱导条件下分化成神经细胞的能力,并对其机制进行初步探讨。方法以密度梯度离心分离骨髓基质细胞,在神经干细胞培养液中培养,采用四唑盐(MTT)法观察在培养液中添加碱性成纤维细胞生长因子(bFGF)、表皮生长因子(EGF)对BMSCs增殖的影响;观察添加脑源性神经生长因子(BDNF)、神经生长因子(NGF)和维甲酸(RA)对rBMSCs的诱导分化情况;采用免疫组织化学法(ABC)检测诱导后的细胞表达神经元特异性烯醇化酶(NSE)、神经元核蛋白(NeuN)和胶质原性纤维酸性蛋白抗体(GFAP)等特异性标志物的情况;以流式细胞分选确定神经元的比例。结果bFGF和EGF能在体外促进rBMSCs增殖,BDNF、NGF和RA能诱导rBMSCs来源的神经干细胞(NSCs)表达NSE、GFAP等特异性标志物。结论EGF、bFGF、BDNF、NGF、RA及适宜的培养液可使rBMSCs定向转化为NSCs,获得足够的目的细胞,进而分化为神经元样和神经胶质样细胞。     

经枕大池移植神经干细胞治疗重型颅脑损伤大鼠的实验研究

目的探讨胎脑皮质来源的神经干细胞(NSC)用于重型颅脑损伤模型大鼠的治疗作用。方法用电子颅脑损伤仪制备重型颅脑损伤大鼠模型(n=46),随即分为神经干细胞治疗组(NSC组,n=23)和对照组(DMEM/F12组,n=23)。将胎鼠皮质来源的NSC经体外培养、扩增后用BrdU标记,经枕大池移植到模型大鼠的脑脊液中,于移植后24h,3d,7d,14d,21d,28d对大鼠进行改良神经功能缺损评分(mNSS)的评估。对照组用相同体积的DMEM/F12代替NSC,mNSS评估时间和方法同NSC组。4w后NSC组取5只大鼠脑组织行免疫组化法染色检测BrdU表达。结果 NSC组大鼠在移植后第7d、14d、21d和24d,其mNSS评分与DMEM/F12组相比,均有显著性差异。对脑组织行BrdU免疫荧光染色,发现移植后第4w脑损伤灶及周围脑组织中有BrdU阳性细胞的表达。结论经枕大池移植后,NSC可在大鼠脑组织内存活、增殖,并能促进脑损伤大鼠神经功能的恢复。     

Total saponins of Panax ginseng effects on proliferation and differentiation of human embryonic neural stem cells and in a Parkinson's disease mouse model

BACKGROUND:Total saponins of Panax ginseng(TSPG) exhibits neuroprotection against Parkinson's disease in the substantia nigra. OBJECTIVE:To investigate the effects of TSPG on human embryonic neural stem cells(NSCs) proliferation and differentiation into dopaminergic neurons using in vitro studies,and to observe NSC differentiation in a mouse model of Parkinson's disease,as well as behavioral changes before and after transplantation. DESIGN,TIME AND SETTING:In vitro neural cell biology trial and in vivo r...     

Zuckerkandl's organ improves long-term survival and function of neural stem cell derived dopaminergic neurons in Parkinsonian rats

Transplantation of neural stem cells (NSC) derived dopamine (DA) neurons has emerged as an alternative approach to fetal neural cell transplantation in Parkinson's disease (PD). However, similar to fetal neural cell, survival of these neurons following transplantation is also limited due to limited striatal reinnervation (graft with dense neuronal core), limited host-graft interaction, poor axonal outgrowth, lack of continuous neurotrophic factors supply and principally an absence of cell adhesion molecules mediated appropriate developmental cues. In the present study, an attempt has been made to increase survival and function of NSC derived DA neurons, by co-grafting with Zuckerkandl's organ (a paraneural organ that expresses neurotrophic factors as well as cell adhesion molecules); to provide continuous NTF support and developmental cues to transplanted DA neurons in the rat model of PD. 24 weeks post transplantation, a significant number of surviving functional NSC derived DA neurons were observed in the co-transplanted group as evident by an increase in the number of tyrosine hydroxylase immunoreactive (TH-IR) neurons, TH-IR fiber density, TH-mRNA expression and TH-protein level at the transplantation site (striatum). Significant behavioral recovery (amphetamine induced stereotypy and locomotor activity) and neurochemical recovery (DA-D2 receptor binding and DA and DOPAC levels at the transplant site) were also observed in the NSC+ZKO co-transplanted group as compared to the NSC or ZKO alone transplanted group. In vivo results were further substantiated by in vitro studies, which suggest that ZKO increases the NSC derived DA neuronal survival, differentiation, DA release and neurite outgrowth as well as protects against 6-OHDA toxicity in co-culture condition. The present study suggests that long-term and continuous NTF support provided by ZKO to the transplanted NSC derived DA neurons, helped in their better survival, axonal arborization and integration with host cells, leading to long-term functional restoration in the rat model of PD.     

Nogo-6受体基因沉默神经干细胞立体定向移植治疗重型脑损伤

Inhibition of neurite growth, which is mediated by the Nogo-66 receptor (NgR), affects nerve regeneration following neural stem cell (NSC) transplantation. The present study utilized RNA interference to silence NgR gene expression in NSCs, which were subsequently transplanted into rats with traumatic brain injury. Following transplantation of NSCs transfected with small interfering RNA, typical neural cell-like morphology was detected in injured brain tissues, and was accompanied by absence of brain tissue cavity, increased growth-associated protein 43 mRNA and protein expression, and improved neurological function compared with NSC transplantation alone. Results demonstrated that NSC transplantation with silenced NgR gene promoted functional recovery following brain injury.     

Quiescent neural cells regain multipotent stem cell characteristics influenced by adult neural stem cells in co-culture

The source of cells participating in central nervous system (CNS) tissue repair and regeneration is poorly defined. One possible source is quiescent neural cells that can persist in CNS in the form of dormant progenitors or highly specialized cell types. Under appropriate conditions, these quiescent cells may be capable of re-entering the mitotic cell cycle and contributing to the stem cell pool. The aim of this study was to determine whether in vitro differentiated neural stem cells (NSC) can regain their multipotent-like stem cell characteristics in co-culture with NSC. To this end, we induced neural differentiation by plating NSC, derived from the periventricular subependymal zone (SEZ) of ROSA26 transgenic mice in Neurobasal A/B27 medium in the absence of bFGF. Under these conditions, NSC differentiated into neurons, glia, and oligodendrocytes. While the level of Nestin expression was downregulated, persistence of dormant progenitors could not be ruled out. However, further addition of bFGF or bFGF/EGF with conditioned medium derived from adult NSC did not induce any noticeable cell proliferation. In another experiment, differentiated neural cells were cultured with adult NSC, isolated from the hippocampus of Balb/c mice, in the presence bFGF. This resulted in proliferating colonies of ROSA26 derived cells that mimicked NSC in their morphology, growth kinetics, and expressed NSC marker proteins. The average nuclear area and DAPI fluorescence intensity of these cells were similar to that of NSC grown alone. We conclude that reactivation of quiescent neural cells can be initiated by NSC-associated short-range cues but not by cell fusion.     

人胚脑与脊髓神经干细胞体外生物学特性的差异

目的:探讨人胚脑源性神经干细胞和脊髓源性神经干细胞的体外培养和分化的差异。方法:从人胚脑组织和脊髓组织中分离培养神经干细胞,分为EGF组、bFGF组、EGF±bFGF组,在连续传代过程中观察并比较神经干细胞体外培养特性的差异:用血清诱导神经干细胞分化,观察其分化状况的不同。结果:从人胚脑组织分离的细胞在bFGF 单独存在时无法形成神经球,在EGF或EGF±bFGF存在时形成大量具有连续增殖能力的神经球;从人胚脊髓组织分离的细胞在EGF单独存在时无法形成神经球,在bFGF单独存在时只形成少量神经球,在EGF±bFGF存在时形成大量具有连续增殖能力的神经球。同样在EGF±bFGF存在的情况下,脑源性于细胞的增殖速度较快。经血清诱导后,脑组织来源的干细胞分化为NSE阳性细胞数明显多于脊髓组织来源的干细胞,二者之间的差异具有显著性(P<0．05)。结论:脑源性和脊髓源性神经干细胞在生长和分化方面有明显差别:脑源性神经干细胞可在bFGF或EGF士bFGF存在的情况下长期传代,而脊髓源性神经干细胞只能在EGF±bFGF存在的情况下长期传代,脑源性干细胞的增殖能力明显高于脊髓源性干细胞;脑源性干细胞较脊髓源性干细胞更易分化为神经元。     

人脑胶质瘤的表皮生长因子基因表达

采用Ｎｏｒｔｈｅｒｎ杂交和斑点杂交的方法检测了５０例胶质瘤、４个恶性胶质瘤体外细胞系和７例正常脑组织表皮生长因子（ＥＧＦ）ｍＲＮＡ表达水平。结果显示：上述组织或细胞都可表达５．０ｋｂ的ＥＧＦｍＲＮＡ片断，高恶度胶质瘤较低恶度胶质瘤和正常脑组织ＥＧＦｍＲＮＡ表达水平增高，低恶度胶质瘤与正常脑组织的表达无显著差异。在５０例胶质瘤中２９例（５８％）ＥＧＦｍＲＮＡ过表达，其中多见于恶性胶质瘤，ＥＧＦｍＲＮＡ表达与肿瘤的分级呈正相关。提示胶质瘤可以合成ＥＧＦ，在胶质瘤的发生发展过程中，ＥＧＦ参与或促进了其恶性进展。     

Comparison between epidermal growth factor, transforming growth factor-alpha and EGF receptor levels in regions of adult rat brain.

Examination of adult rat brain regions by specific radioimmunoassays revealed a widespread distribution of transforming growth factor-alpha (TGF-alpha), but not epidermal growth factor (EGF), the peptide that had previously been reported to be present in rodent brain. Polyadenylated RNA samples from the different regions of rat brain were analyzed by Northern blot to identify mRNA species encoding precursor proteins for EGF (preproEGF), TGF-alpha (preproTGF-alpha), and the EGF/TGF-alpha receptor. The results indicate that TGF-alpha is the most abundant ligand for the EGF/TGF-alpha receptor in most parts of the brain analyzed. Message for preproEGF was only detectable after prolonged autoradiographic exposure; levels of preproEGF mRNA were between two and three orders of magnitude lower in brain than those expressed in control tissue (kidney), and one to two orders of magnitude lower than preproTGF-alpha mRNA levels in all brain regions. These results were confirmed by analysis of mRNA by RT/PCR, and support the hypothesis that expression of preproEGF mRNA in the brain is limited to smaller discrete areas, whereas preproTGF-alpha gene expression is almost ubiquitous.     

Unique expression and localization of aquaporin-4 and aquaporin-9 in murine and human neural stem cells and in their glial progeny

Aquaporins (AQP) are water channel proteins that play important roles in the regulation of water homeostasis in physiological and pathological conditions. AQP4 and AQP9, the main aquaporin subtypes in the brain, are expressed in the adult forebrain subventricular zone (SVZ), where neural stem cells (NSCs) reside, but little is known about their expression and role in the NSC population, either in vivo or in vitro. Also, no reports are available on the presence of these proteins in human NSCs. We performed a detailed molecular and phenotypical characterization of different AQPs, and particularly AQP4 and AQP9, in murine and human NSC cultures at predetermined stages of differentiation. We demonstrated that AQP4 and AQP9 are expressed in adult murine SVZ-derived NSCs (ANSCs) and that their levels of expression and cellular localization are differentially regulated upon ANSC differentiation into neurons and glia. AQP4 (but not AQP9) is expressed in human NSCs and their progeny. The presence of AQP4 and AQP9 in different subsets of ANSC-derived glial cells and in different cellular compartments suggests different roles of the two proteins in these cells, indicating that ANSC-derived astrocytes might maintain in vitro the heterogeneity that characterize the astrocyte-like cell populations in the SVZ in vivo. The development of therapeutic strategies based on modulation of AQP function relies on a better knowledge of the functional role of these channels in brain cells. We provide a reliable and standardized in vitro experimental model to perform functional studies as well as toxicological and pharmacological screenings.     

Adult cerebrospinal fluid inhibits neurogenesis but facilitates gliogenesis from fetal rat neural stem cells

Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Administration of NSCs into the cerebrospinal fluid (CSF) offers a nontraumatic transplantation method into the brain. However, cell survival and intraparenchymal migration of the transplants are limited. Furthermore, CSF was recently reported to be an important milieu for controlling stem cell processes in the brain. We studied the effects of adult human leptomeningeal CSF on the behavior of fetal rat NSCs. CSF increased survival of NSCs compared with standard culture media during stem cell maintenance and differentiation. The presence of CSF enhanced NSC differentiation, leading to a faster loss of self‐renewal capacity and faster and stronger neurite outgrowth. Some of these effects (mainly cell survival, neurite brancing) were blocked by addition of the bone morphogenic protein (BMP) inhibitor noggin. After differentiation in CSF, significantly fewer MAP2ab⁺ neurons were found, but there were more GFAP⁺ astroglia compared with standard media. By RT‐PCR analysis, we determined a decrease of mRNA of the NSC marker gene Nestin but an increase of Gfap mRNA during differentiation up to 72 hr in CSF compared with standard media. Our data demonstrate that adult human leptomeningeal CSF enhances cell survival of fetal rat NSCs during proliferation and differentiation. Furthermore, CSF provides a stimulus for gliogenesis but inhibits neurogenesis from fetal NSCs. Our data suggest that CSF contains factors such as BMPs regulating NSC behavior, and we hypothesize that fast differentiation of NSCs in CSF leads to a rapid loss of migration capacity of intrathecally transplanted NSCs. © 2009 Wiley‐Liss, Inc.     

Roles of insulin and transferrin in neural progenitor survival and proliferation

Multipotent neural progenitor cells or neural stem cells (NSC) can be propagated in vitro from a variety of sources and have great potential for neural repair. Although it is well known that NSC divide in response to basic fibroblast growth factor (FGF-2) and epidermal growth factor (EGF), cofactors necessary for survival and maintenance of a multipotent potential are still a matter of debate. In the current study, we examined the requirements for NSC proliferation and survival in vitro using the neurosphere culture system. Apotransferrin (TF), along with EGF and FGF-2, was sufficient for the formation of primary neurospheres derived from embryonic rat cortices. The addition of low concentrations of insulin or insulin-like growth factor-1 (IGF-1) enhanced neurosphere size and number and was necessary for continued passaging. Both insulin and IGF-1 acted at low concentrations, suggesting that their effects were mediated by their cognate receptors, both of which were expressed by neurosphere cultures. Sphere-forming progenitors survived for long periods in culture without EGF or FGF-2 when either insulin or IGF-1 was added to the media. Cell cycle analysis determined that surviving progenitors were relatively quiescent during the period without mitogens. Upon the reintroduction of EGF and FGF-2, surviving progenitors gave rise to new spheres that produced largely glial-restricted progeny compared with sister cultures. These data indicate that the neurogenic potential of NSC may be intimately linked to a continuous exposure to mitogens.