Potential Existence of Stem Cells With Multiple Differentiation Abilities to Three Different Germ Lineages in Mouse Neurospheres

Isolation and characterization of neural stem cells from fetal canine spinal cord

Neurogenesis in adult mammals occurs mainly in the subventricular and subgranular areas of the brain, but there are also reports of its occurrence in the spinal cord. In a study on rats, neural stem cells and neuroprogenitor cells could be obtained through primary spinal cord culture, but there are no studies on these cells in canine species, to date. Dogs represent an appropriate animal model for studies on neurogenesis and neurological disorders. In addition, they are animals of great affective value, and the therapeutic use of neural stem cells can represent a breakthrough in regenerative veterinary medicine. Therefore, this study aimed to determine a protocol for the isolation, culture, and characterization of neural and neuroprogenitor stem cells derived from the spinal cord of canine fetuses. The cells were isolated from spinal cord fragments and cultured in serum-free culture medium supplemented with EGF and FGF-2 growth factors. These cells were observed daily by optical microscopy to analyze their morphological characteristics. From the third day in vitro, it was possible to observe translucent cell groupings, similar to the neurospheres, which approximately ranged from 50 µm to 200 µm at seven days in vitro. Throughout the culture period, the neurospheres developed ribbons in their periphery that migrated and communicated with other neurospheres. RT-PCR revealed that the cells expressed the characteristic genes SOX2, NESTIN, and GFAP. In addition to gene expression, the cells were phenotypically marked in the immunofluorescence assay for the proteins Nestin, GFAP, and β-tubulin III, characterizing them as neurospheres. Our results suggest that the spinal cord may be a source of neural stem cells and neural progenitor cells in canine fetuses. These cells may be an interesting option for neurogenesis and neuroregenerative therapy studies.

Psychiatry in a Dish: Stem Cells and Brain Organoids Modeling Autism Spectrum Disorders

Autism spectrum disorders are a group of pervasive neurodevelopmental conditions with heterogeneous etiology, characterized by deficits in social cognition, communication, and behavioral flexibility. Despite an increasing scientific effort to find the pathophysiological explanations for the disease, the neurobiological links remain unclear. A large amount of evidence suggests that pathological processes taking place in early embryonic neurodevelopment might be responsible for later manifestation of autistic symptoms. This dysfunctional development includes altered maturation/differentiation processes, disturbances in cell-cell communication, and an unbalanced ratio between certain neuronal populations. All those processes are highly dependent on the interconnectivity and three-dimensional organizations of the brain. Moreover, in order to gain a deeper understanding of the complex neurobiology of autism spectrum disorders, valid disease models are pivotal. Induced pluripotent stem cells could potentially help to elucidate the complex mechanisms of the disease and lead to the development of more effective individualized treatment. The induced pluripotent stem cells approach allows comparison between the development of various cellular phenotypes generated from cell lines of patients and healthy individuals. A newly advanced organoid technology makes it possible to create three-dimensional in vitro models of brain development and structural interconnectivity, based on induced pluripotent stem cells derived from the respective individuals. The biggest challenge for modeling psychiatric diseases in vitro is finding and establishing the link between cellular and molecular findings with the clinical symptoms, and this review aims to give an overview over the feasibility and applicability of this new tissue engineering tool in psychiatry.

SOX2 and OCT4 mRNA-expressing cells, detected by molecular beacons, localize to the center of neurospheres during differentiation

Neurospheres are used as in vitro assay to measure the properties of neural stem cells. To investigate the molecular and phenotypic heterogeneity of neurospheres, molecular beacons (MBs) targeted against the stem cell markers OCT4 and SOX2 were designed, and synthesized with a 2'-O-methyl RNA backbone. OCT4 and SOX2 MBs were transfected into human embryonic mesencephalon derived cells, which spontaneously form neurospheres when grown on poly-L-ornitine/fibronectin matrix and medium complemented with bFGF. OCT4 and SOX2 gene expression were tracked in individual cell using the MBs. Quantitative image analysis every day for seven days showed that the OCT4 and SOX2 mRNA-expressing cells clustered in the centre of the neurospheres cultured in differentiation medium. By contrast, cells at the periphery of the differentiating spheres developed neurite outgrowths and expressed the tyrosine hydroxylase protein, indicating terminal differentiation. Neurospheres cultured in growth medium contained OCT4 and SOX2-positive cells distributed throughout the entire sphere, and no differentiating neurones. Gene expression of SOX2 and OCT4 mRNA detected by MBs correlated well with gene and protein expression measured by qRT-PCR and immunostaining, respectively. These experimental data support the theoretical model that stem cells cluster in the centre of neurospheres, and demonstrate the use of MBs for the spatial localization of specific gene-expressing cells within heterogeneous cell populations.

Isolation of multilineage progenitors from mouse brain

Stem cells are unique cell populations with the ability to undergo self-renewal and differentiation. These cells have been identified in a wide range of tissues and possess varied differentiation potentials. Tissue-specific stem cells have typically been thought to have limited differentiation capabilities. We show here that fibroblast-like cells isolated from mouse brain possess cross-germ layer differentiation abilities. These cells were found to express typical mesenchymal stem cell markers (CD44, CD29, and CD105) and were able to be passaged more than 50 times. When treated under defined conditions, the brain-derived cells were able to generate many different cell types including adipocytes, osteocytes, astrocytes, neurons, and even hepatocyte-like cells. The hepatocyte-like cells not only expressed liver cell-specific markers, but also exhibited the capacity for glycogen storage and low-density lipoprotein uptake. These results demonstrate the existence of cells in the brain with three-germ-layer differentiation potential.

Expression analysis of pluripotency-associated genes in human fetal cortical and striatal neural stem cells during differentiation

In the field of developmental biology, there is compelling evidence for a network of activity of pluripotency and stem-associated genes comprising of Oct4, Nanog and nestin. During neurogenesis, the choice between enhancement versus suppression of transcriptional modulation of these identified genes determines the balance between self-renewal neural stem cells (NSC) and immature neuronal phenotypes. By using immunocytochemistry and RT-PCR techniques, our study aims to address the question whether and to what extent mRNA and protein profiles are expressed in human fetal neurospheres obtained from cortical and striatal brain regions, both in expansion (undifferentiated cells) and differentiation conditions monitored after 1 and 4 weeks in vitro culturing. Our results clearly demonstrate the sustained presence of opposite signals: strong downregulation of Oct4 and Nanog genes in cortical differentiating cells and significant up-regulation for nestin gene both in cortical and striatal differentiating cells. Notably, by immunostaining techniques, Oct4 and Nanog protein expression have indicated the presence of both nuclear and cytoplasmic content followed by their rapid turnover (immediately after 1 week). Moreover, during the differentiation process, dissociated neurospheres displayed unexpected number of nestin positive cells accompanied by a constant level of staining intensity. In conclusion, the present study provides new insights into brain region related features in terms of Oct4, Nanog and nestin expression both at cellular and molecular level.

Metabolic flexibility and cell hierarchy in metastatic cancer

Cancer is characterized by disturbed homeostasis of self-renewing cell populations, and their ability to seed and grow in multiple microenvironments. This overarching cellular property of metastatic cancer emerges from the contentious cancer stem cell hypothesis that underpins the more generic hallmarks of cancer (Hanahan and Weinberg, 2000) and its subsequent add-ons. An additional characteristic, metabolic flexibility, is related to concepts developed by Warburg and to subsequent work by mid 20th century biochemists who elucidated the bioenergetic workings of mitochondria. Metabolic flexibility may circumvent limitations inherent in the increasingly popular but erroneous view that aerobic glycolysis is a universal property of cancer cells. Cancer research in the second half of the 20th century was largely the domain of geneticists and molecular biologists using reductionist approaches. Integrated approaches that address cancer cell hierarchy and complexity, and how cancer cells adapt their metabolism according to their changing environment are now beginning to emerge, and these approaches promise to address the poor mortality statistics of metastatic cancer.

Dynamic methylation and expression of Oct4 in early neural stem cells

Neural stem cells are a multipotent population of tissue-specific stem cells with a broad but limited differentiation potential. However, recent studies have shown that over-expression of the pluripotency gene, Oct4, alone is sufficient to initiate a process by which these can form 'induced pluripotent stem cells' (iPS cells) with the same broad potential as embryonic stem cells. This led us to examine the expression of Oct4 in endogenous neural stem cells, as data regarding its expression in neural stem cells in vivo are contradictory and incomplete. In this study we have therefore analysed the expression of Oct4 and other genes associated with pluripotency throughout development of the mouse CNS and in neural stem cells grown in vitro. We find that Oct4 is still expressed in the CNS by E8.5, but that this expression declines rapidly until it is undetectable by E15.5. This decline is coincident with the gradual methylation of the Oct4 promoter and proximal enhancer. Immunostaining suggests that the Oct4 protein is predominantly cytoplasmic in location. We also found that neural stem cells from all ages expressed the pluripotency associated genes, Sox2, c-Myc, Klf4 and Nanog. These data provide an explanation for the varying behaviour of cells from the early neuroepithelium at different stages of development. The expression of these genes also provides an indication of why Oct4 alone is sufficient to induce iPS formation in neural stem cells at later stages.