Striatal neuron differentiation from neurosphere-expanded progenitors depends on Gsh2 expression

Quantitative approach to numbers and sizes: Generation of primary neurospheres from the dorsal lateral ganglionic eminence of late embryonic mice

Background: The neurosphere assay is a powerful in vitro tool to investigate neural stem cells in the dorsal lateral ventricle (dLGE). In the dLGE, metrics of sizes and numbers of neurospheres generated using this assay has not been completely characterized. The objective of this protocol is to provide a stepwise method from a single isolation that predicts the average number of neurospheres generated and to estimate an approximation of its sizes after several days in vitro. The advantage of this protocol is that no expensive and specialized equipment is needed for tissue isolation. Estimates about the numbers and sizes of neurospheres will provide investigators with quantitative data to advise on how much starting dLGE tissue is required to generate the appropriate number of spheres for the implementation of downstream applications, including immunocytochemistry, self-renewal and differentiation assays.

Methods: Our method is based on a simple dissection technique, where tissue surrounding the dorsal lateral ventricle from a single mouse embryo is trimmed away to enrich for neural stem cell and progenitor populations. Following this dissection, tissue is mechanically dissociated by trituration. Cells are then cultured in media containing epidermal growth factor and other supplements to generate healthy primary neurospheres.

Results: Using this approach, we found reproducible number of primary neurospheres after 7 days in vitro (DIV). Furthermore, we observed that this method yields an average range of neurospheres sizes greater than 50 μm, but less than 100 μm after 7 DIV. Lastly, using an anti-GFAP antibody, we show that these neurospheres can be stained, confirming their use in future immunocytochemistry studies.

Conclusions: Future use of this protocol provides metrics on the generation of primary neurospheres that will be useful for further advances in the area of stem cell biology.

Growth hormone (GH) is a survival rather than a proliferative factor for embryonic striatal neural precursor cells

OBJECTIVE

A possible role of GH during central nervous system (CNS) development has been suggested by the presence of this hormone and its receptor in brain areas before its production by the pituitary gland. Although several effects have been reported for GH, the specific role of this hormone during CNS development remains unclear. Here, we examined the effect of GH on proliferation, survival and neurosphere formation in primary cultures of striatal tissue from 14-day-old (E14) mouse embryos.

DESIGN

GH receptor gene expression was confirmed by RT-PCR. Primary cultures of embryonic striatal cells were treated with different doses of GH in serum free media, then the number of neurospheres was determined. To examine the GH effect on proliferation and survival of the striatal primary cultures, bromodeoxyuridine (BrdU) and TUNEL immunoreactivity was conducted.

RESULTS

In the presence of the epidermal growth factor (EGF), GH increased the formation of neurospheres, with a maximal response at 10 ng/ml, higher doses were inhibitory. In absence of EGF, GH failed to stimulate neurosphere formation. Proliferation rate in the primary striatal cultures was inhibited by 24 or 48 h incubation with GH. However, in the absence of EGF, GH increased BrdU incorporation. GH treatment decreases the rate of apoptosis of nestin and GFAP positive cells in the primary striatal cultures, enhancing neurosphere formation.

CONCLUSIONS

Our in vitro data demonstrate that GH plays a survival role on the original population of embryonic striatal cells, improving Neural Precursor Cells (NPCs) expansion. We suggest that this GH action could be predominant during striatal neurodevelopment.

GABAergic neurons from mouse embryonic stem cells possess functional properties of striatal neurons in vitro, and develop into striatal neurons in vivo in a mouse model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease where GABAergic medium spiny neurons (MSNs) in the striatum degenerate. Embryonic stem cell-derived neural transplantation may provide an appropriate therapy for HD. Here we aimed to develop a suitable protocol to obtain a high percentage of functional GABAergic neurons from mouse embryonic stem cells (mESCs), and then tested their differentiation potential in vivo. The monolayer method was compared with the embryoid body and five stage method for its efficiency in generating GABAergic neurons from mESCs. All three methods yielded a similar percentage of GABAergic neurons from mESCs. Monolayer method-derived GABAergic neurons expressed the MSN marker dopamine- and cyclic AMP-regulated phosphoprotein (DARPP32). The pluripotent stem cell population could be eliminated in vitro by treating cells with puromycin and retinoic acid. Using patch-clamp recordings, the functional properties of GABAergic neurons derived from mESCs were compared to GABAergic neurons derived from primary lateral ganglionic eminence. Both types of neurons showed active membrane properties (voltage-gated Na(+) and K(+) currents, Na(+)-dependent action potentials, and spontaneous postsynaptic currents) and possessed functional glutamatergic receptors and transporters. mESC-derived neural progenitors were transplanted into a mouse model of HD. Grafted cells differentiated to mature neurons expressing glutamate decarboxylase, dopamine type 1 receptors, and DARPP32. Also, neural precursors and dividing populations were found in the grafts. In summary, mESCs are able to differentiate efficiently into functional GABAergic neurons using defined in vitro conditions, and these survive and differentiate following grafting to a mouse model of HD.

The homeobox gene Gsx2 regulates the self-renewal and differentiation of neural stem cells and the cell fate of postnatal progenitors

The Genetic screened homeobox 2 (Gsx2) transcription factor is required for the development of olfactory bulb (OB) and striatal neurons, and for the regional specification of the embryonic telencephalon. Although Gsx2 is expressed abundantly by progenitor cells in the ventral telencephalon, its precise function in the generation of neurons from neural stem cells (NSCs) is not clear. Similarly, the role of Gsx2 in regulating the self-renewal and multipotentiality of NSCs has been little explored. Using retroviral vectors to express Gsx2, we have studied the effect of Gsx2 on the growth of NSCs isolated from the OB and ganglionic eminences (GE), as well as its influence on the proliferation and cell fate of progenitors in the postnatal mouse OB. Expression of Gsx2 reduces proliferation and the self-renewal capacity of NSCs, without significantly affecting cell death. Furthermore, Gsx2 overexpression decreases the differentiation of NSCs into neurons and glia, and it maintains the cells that do not differentiate as cycling progenitors. These effects were stronger in GESCs than in OBSCs, indicating that the actions of Gsx2 are cell-dependent. In vivo, Gsx2 produces a decrease in the number of Pax6+ cells and doublecortin+ neuroblasts, and an increase in Olig2+ cells. In summary, our findings show that Gsx2 inhibits the ability of NSCs to proliferate and self-renew, as well as the capacity of NSC-derived progenitors to differentiate, suggesting that this transcription factor regulates the quiescent and undifferentiated state of NSCs and progenitors. Furthermore, our data indicate that Gsx2 negatively regulates neurogenesis from postnatal progenitor cells.

Impairment of developmental stem cell-mediated striatal neurogenesis and pluripotency genes in a knock-in model of Huntington's disease

The pathogenesis of Huntington's disease (HD) remains elusive. The identification of increasingly early pathophysiological abnormalities in HD suggests the possibility that impairments of striatal medium spiny neuron (MSN) specification and maturation may underlie the etiology of HD. In fact, we demonstrate that HD knock-in (Hdh-Q111) mice exhibited delayed acquisition of early striatal cytoarchitecture with aberrant expression of progressive markers of MSN neurogenesis (Islet1, DARPP-32, mGluR1, and NeuN). Hdh-Q111 striatal progenitors also displayed delayed cell cycle exit between E13.5-15.5 (BrdU birth-dating) and an enhanced fraction of abnormal cycling cells in association with expansion of the pool of intermediate progenitors and over expression of the core pluripotency (PP) factor, Sox2. Clonal analysis further revealed that Hdh-Q111 neural stem cells (NSCs) displayed: impaired lineage restriction, reduced proliferative potential, enhanced late-stage self-renewal, and deregulated MSN subtype specification. Further, our analysis revealed that in addition to Sox2, the core PP factor, Nanog is expressed within the striatal generative and mantle regions, and in Hdh-Q111 embryos the fraction of Nanog-expressing MSN precursors was substantially increased. Moreover, compared to Hdh-Q18 embryos, the Hdh-Q111 striatal anlagen exhibited significantly higher levels of the essential PP cofactor, Stat3. These findings suggest that Sox2 and Nanog may play roles during a selective window of embryonic brain maturation, and alterations of these factors may, in part, be responsible for mediating the aberrant program of Hdh-Q111 striatal MSN specification and maturation. We propose that these HD-associated developmental abnormalities might compromise neuronal homeostasis and subsequently render MSNs more vulnerable to late life stressors.

Fetal striatum- and ventral mesencephalon-derived expanded neurospheres rescue dopaminergic neurons in vitro and the nigro-striatal system in vivo

The pathogenesis of Parkinson's disease (PD) involves ongoing apoptotic loss of dopaminergic neurons in the substantia nigra pars compacta. Local delivery of the trophic factors can rescue dopaminergic neurons and halt the progression of PD. In this study we show that fetal E11 striatum-derived neurospheres and E14.5 ventral mesencephalon (VM) -derived neurospheres (NS E11 and NSvm, respectively) are a source of factors that rescue dopaminergic neurons. First, long-term expanded NS E11 and NSvm rescued primary dopaminergic neurons from serum-deprivation induced apoptosis and promoted survival of dopaminergic neurons for 14 days in vitro and this effect was due to soluble contact-independent factor/s. Second, green fluorescent protein-expressing NS E11 and NSvm grafted into the midbrain of mice with unilateral 6-hydroxydopamine-induced Parkinsonism resulted in partial rescue of the nigro-striatal system and improvement of the hypo-dopaminergic behavioral deficit. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that intact NS E11 and NSvm expressed fibroblast growth factor-2, brain-derived neurotrophic factor (BDNF), pleiotrophin, neurotrophin-3, but not glial cell line-derived neurotrophic factor (GDNF). GDNF expression was also undetectable in vivo in grafted NS E11 and NSvm suggesting that NS-derived factor/s other than GDNF mediated the rescue of nigral dopaminergic neurons. Identification of NS-derived soluble factor(s) may lead to development of novel neuroprotective therapies for PD. An unexpected observation of the present study was the detection of the ectopic host-derived tyrosine hydroxylase (TH) -expressing cells in sham-grafted mice and NS E11- and NSvm -grafted mice. We speculate that injury-derived signals (such as inflammatory cytokines that are commonly released during transplantation) induce TH expression in susceptible cells.

Genetic modification does not affect the stemness of neural stem cells in nestin promoter-GFP transgenic mice

Because nestin promoter-GFP mice have frequently been used in neural stem cell (NSC) research, it is essential to prove that there is no alteration in the stemness of NSCs derived from this transgenic model for the interpretation and validity of the data. We compared the stemness of NSCs derived from transgenic mice expressing GFP driven by the nestin enhancer with those from wild-type (C57BL/6) mice with respect to the general gene expression profile, expression of neural stem cell markers as nestin and Sox2, and responsiveness to neurotrophins (BDNF, PDGF-BB, and NT-3). The gene expression profile analysis showed that the coefficient of correlation between the two groups was very high (r=0.9865) in the total genes. We found that 23 genes were either up- or down-regulated more than two-fold in the NSCs from the transgenic mice (p<0.05), without any obvious functional relatedness among them. Likewise, there was no difference between the two mouse groups in the expression of nestin or Sox2, the ability to form neurospheres and the neuronal differentiation of NSCs by neurotrophins. Taken together, the self-renewal and neuronal differentiation ability of NSCs from the transgenic mice showed the great similarity to those from wild-type mice. Such information will be useful when the properties of NSCs are evaluated following genetic modification in such a nestin-GFP Tg model.

Generation of GABAergic and dopaminergic interneurons from endogenous embryonic olfactory bulb precursor cells

During the embryonic period, many olfactory bulb (OB) interneurons arise in the lateral ganglionic eminence (LGE) from precursor cells expressing Dlx2, Gsh2 and Er81 transcription factors. Whether GABAergic and dopaminergic interneurons are also generated within the embryonic OB has not been studied thoroughly. In contrast to abundant Dlx2 and Gsh2 expression in ganglionic eminences (GE), Dlx2 and Gsh2 proteins are not expressed in the E12.5-13.5 mouse OB, whereas the telencephalic pallial domain marker Pax6 is abundant. We found GABAergic and dopaminergic neurons originating from dividing precursor cells in E13.5 OB and in short-term dissociated cultures prepared from the rostral half of E13.5 OB. In OB cultures, 22% of neurons were GAD+, of which 53% were Dlx2+, whereas none expressed Gsh2. By contrast, 70% of GAD+ cells in GE cultures were Dlx2+ and 16% expressed Gsh2. In E13.5 OB slices transplanted with EGFP-labeled E13.5 OB precursor cells, 31.7% of EGFP+ cells differentiated to GABAergic neurons. OB and LGE precursors transplanted into early postnatal OB migrated and differentiated in distinct patterns. Transplanted OB precursors gave rise to interneurons with dendritic spines in close proximity to synaptophysin-positive boutons. Interneurons were also abundant in differentiating OB neural stem cell cultures; the neurons responded to the neurotrophin Bdnf and expressed presynaptic proteins. In vivo, the Bdnf receptor TrkB colocalized with synaptic proteins at the glomeruli. These findings suggest that, in addition to receiving interneurons from the LGE, the embryonic OB contains molecularly distinct local precursor cells that generate mature GABAergic and dopaminergic neurons.

Efficient transduction of neurons using Ross River glycoprotein-pseudotyped lentiviral vectors

Lentiviral vectors are promising tools for CNS gene transfer since they efficiently transduce the cells of the nervous system in vivo. In this study, we have investigated the transduction efficiency of lentiviral vectors pseudotyped with Ross River virus glycoprotein (RRV-G) (RRV-G-pseudotyped lentiviral vectors (RRV-LV)). The RRV is an alphavirus with an extremely broad host range, including the cells of the central nervous system. Previous studies have shown that lentiviral vectors can be efficiently pseudotyped with this envelope protein and have demonstrated promising features of such vectors, including the possibility to establish stable producer cell lines. After injection of RRV-LV expressing green fluorescent protein into different structures in the rat brain we found efficient transduction of both neurons and glial cells. By using two cell-type-specific promoters, neuron-specific enolase and human glial fibrillary acidic protein, we demonstrated cell-specific transgene expression in the desired cell type. Ross River virus glycoprotein-pseudotyped lentiviral vectors also transduced human neural progenitor cells in vitro, showing that receptors for the RRV-G are present on human neural cells.

Alterations in cellular phenotypes differentiating from embryonic rat brain neurosphere cultures by immunoselection of neuronal progenitors

The neurosphere culture system is widely used to expand neural stem/progenitor cells in vitro and to provide a source of cells for transplantation approaches to CNS disorders. This study describes the populations of neurones, astrocytes and oligodendrocytes which differentiated from embryonic day (E) 14 rat cortical and striatal tissue grown as neurosphere cultures over three passages. The percentages of cells that adopted neuronal phenotypes decreased with passage, astrocytic percentages increased and oligodendrocytic percentages remained constant. In the second part of this study, immunomagnetic separation was used to positively select neuronal progenitor cells from E14 rat cortical and striatal tissue using an antibody, 2F7, which recognises an epitope on the cell surface of pre- and post-mitotic neurones. These immunomagnetically selected cells were grown as neurosphere cultures over three passages and gave rise to significantly different percentages of neurones, astrocytes and oligodendrocytes than those found in the baseline study. In particular, the percentage of neurones arising from the second and third passages was significantly higher following immunoselection. This indicates that neuronal progenitor cells can be isolated using immunomagnetic separation and then expanded using the neurosphere culture system, to generate enriched populations of neurones that can be used in CNS repair.

Cerebellum- and forebrain-derived stem cells possess intrinsic regional character

The existence of stem cells in the adult nervous system is well recognized; however, the potential of these cells is still widely debated. We demonstrate that neural stem cells exist within the embryonic and adult cerebellum. Comparing the potential of neural stem cells derived from the forebrain and cerebellum, we find that progeny derived from each of these brain regions retain regional character in vitro as well as after homotopic transplantation. However, when ectopically transplanted, neurosphere-derived cells from either region are largely unable to generate neurons. With regard specifically to embryonic and adult cerebellar stem cells, we observe that they are able to give rise to neurons that resemble different select classes of cerebellar subclasses when grafted into the perinatal host cerebellum. Most notably, upon transplantation to the perinatal cerebellum, cerebellar stem cells from all ages are able to acquire the position and mature electrophysiological properties of cerebellar granule cells.