Proneural transcription factors Dlx2 and Pax6 are altered in adult SVZ neural precursor cells following striatal cell loss

Dynamic transcriptome analysis of Bombyx mori embryonic development

Bombyx mori has been extensively studied but the gene expression control of its embryonic development is unclear. In this study, we performed transcriptome profiling of six stages of B. mori embryonic development using RNA sequencing (RNA-seq). A total of 12 894 transcripts were obtained from the embryos. Of these, 12 456 transcripts were shared among the six stages, namely, fertilized egg, blastoderm, germ-band, organogenesis, reversal period, and youth period stages. There were 111, 48, 41, 54, 77, and 107 transcripts specifically expressed during the six stages, respectively. By analyzing weighted gene correlation networks and differently expressed genes, we found that during embryonic development, many genes related to DNA replication, transcription, protein synthesis, and epigenetic modifications were upregulated in the early embryos. Genes of cuticle proteins, chitin synthesis-related proteins, and neuropeptides were more abundant in the late embryos. Although pathways of juvenile hormone and the ecdysteroid 20-hydroxyecdysone, and transcription factors were expressed throughout the embryonic development stages, more regulatory pathways were highly expressed around the organogenesis stage, suggesting more gene expression for organogenesis. The results of RNA-seq were confirmed by quantitative real-time polymerase chain reaction of 16 genes of different pathways. Nucleic acid methylation and seven sites in histone H3 modifications were confirmed by dot blot and western blot. This study increases the understanding of the molecular mechanisms of the embryonic developmental process and information on the regulation of B. mori development.

Human Cerebral Organoid Implantation Alleviated the Neurological Deficits of Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) causes a high rate of mortality and disability, and its treatment is still limited. Loss of neurons in damaged area is hardly rescued by relative molecular therapies. Based on its disease characteristics, we transplanted human embryonic stem cell- (hESC-) derived cerebral organoids in the brain lesions of controlled cortical impact- (CCI-) modeled severe combined immunodeficient (SCID) mice. Grafted organoids survived and differentiated in CCI-induced lesion pools in mouse cortical tissue. Implanted cerebral organoids differentiated into various types of neuronal cells, extended long projections, and showed spontaneous action, as indicated by electromyographic activity in the grafts. Induced vascularization and reduced glial scar were also found after organoid implantation, suggesting grafting could improve local situation and promote neural repair. More importantly, the CCI mice's spatial learning and memory improved after organoid grafting. These findings suggest that cerebral organoid implanted in lesion sites differentiates into cortical neurons, forms long projections, and reverses deficits in spatial learning and memory, a potential therapeutic avenue for TBI.

Cell Replacement Therapy for Huntington's Disease

Huntington's disease (HD) is an inherited neurodegenerative disorder which is characterised by a triad of highly debilitating motor, cognitive, and psychiatric symptoms. While cell death occurs in many brain regions, GABAergic medium spiny neurons (MSNs) in the striatum experience preferential and extensive degeneration. Unlike most neurodegenerative disorders, HD is caused by a single genetic mutation resulting in a CAG repeat expansion and the production of a mutant Huntingtin protein (mHTT). Despite identifying the mutation causative of HD in 1993, there are currently no disease-modifying treatments for HD. One potential strategy for the treatment of HD is the development of cell-based therapies. Cell-based therapies aim to restore neuronal circuitry and function by replacing lost neurons, as well as providing neurotropic support to prevent further degeneration. In order to successfully restore basal ganglia functioning in HD, cell-based therapies would need to reconstitute the complex signalling network disrupted by extensive MSN degeneration. This chapter will discuss the potential use of foetal tissue grafts, pluripotent stem cells, neural stem cells, and somatic cell reprogramming to develop cell-based therapies for treating HD.

Regional Immunoreactivity of Pax6 in the Neurogenic Zone After Chronic Prenatal Hypoxia

BACKGROUND/AIM

Neurogenesis is a complex process to generate new neurons from neural progenitor cells. Neural progenitor cells are observed in two principal neurogenic regions of the forebrain, the subventricular zone and the subgranular zone of the hippocampal dentate gyrus. The cerebral cortex also plays a role as the neurogenic zone under hypoxic conditions. Hypoxia has many effects on neurogenesis, but the effect of chronic prenatal hypoxia on paired box 6 (Pax6), a protein that plays an important role in neurogenesis, has not been studied in vivo. In the present study, we used a rat model to evaluate the effect of hypoxia on Pax6 immunoreactivity.

MATERIALS AND METHODS

Hypoxia status was induced by unilateral uterine-artery ligation in pregnant rats. The fetuses were obtained from the uterine horn on the twenty-first day of pregnancy and immunohistochemistry of the fetal brain was examined regarding anti-hypoxia-induced factor 1α and Pax6 antibody.

RESULTS

The density of HIF1α-IR cells in the hypoxia group was greater than the density of HIF1α-IR cells in the control group in the subventricular zone, subgranular zone, and cerebral cortex. The density of Pax6-IR cells in the hypoxic group was higher in both the subventricular zone and the subgranular zone than in the control group. However, the density of Pax6-IR cells in the cerebral cortex was lower in fetuses that experienced hypoxia than in control fetuses.

CONCLUSION

These results suggest that Pax6 immunoreactivity showed diverse patterns in the neurogenic zone after prenatal hypoxia and Pax6 has important effects on neurogenesis.

Endogenous Brain Repair: Overriding intrinsic lineage determinates through injury-induced micro-environmental signals

Adult human neurogenesis has generated excitement over the last 2 decades with the idea that endogenous adult stem cells could act as a potential cell source for brain repair after injury. Indeed, many forms of experimentally induced brain injury including stroke and excitotoxic lesioning can promote proliferation from the subventricular zone and mobilise neuroblasts and oligodendrocyte progenitor cells to migrate through brain parenchyma to damaged regions. However the failure of neuroblasts to mature into appropriate neuronal subtypes for cell replacement has been an issue. Recent work by our group and others has indicated that micro-environmental signals released from areas of cell loss may be able to override intrinsic gene expression lineages and covert neuroblasts into oligodendrocyte progenitor cells. This commentary will discuss the enhanced fate plasticity of both adult neural progenitors and parenchymal NG2 cells after injury, and the importance of understanding brain-injury induced micro-environmental signals in the quest toward promoting endogenous regeneration after injury.

The Effect of Pro-Neurogenic Gene Expression on Adult Subventricular Zone Precursor Cell Recruitment and Fate Determination After Excitotoxic Brain Injury

Despite the presence of on-going neurogenesis in the adult mammalian brain, neurons are generally not replaced after injury. Using a rodent model of excitotoxic cell loss and retroviral (RV) lineage tracing, we previously demonstrated transient recruitment of precursor cells from the subventricular zone (SVZ) into the lesioned striatum. In the current study we determined that these cells included migratory neuroblasts and oligodendrocyte precursor cells (OPC), with the predominant response from glial cells. We attempted to override this glial response by ectopic expression of the pro-neurogenic genes Pax6 or Dlx2 in the adult rat SVZ following quinolinic acid lesioning. RV-Dlx2 over-expression stimulated repair at a previously non-neurogenic time point by enhancing neuroblast recruitment and the percentage of cells that retained a neuronal fate within the lesioned area, compared to RV-GFP controls. RV-Pax6 expression was unsuccessful at inhibiting glial fate and intriguingly, increased OPC cell numbers with no change in neuronal recruitment. These findings suggest that gene choice is important when attempting to augment endogenous repair as the lesioned environment can overcome pro-neurogenic gene expression. Dlx2 over-expression however was able to partially overcome an anti-neuronal environment and therefore is a promising candidate for further study of striatal regeneration.

Redirection of doublecortin-positive cell migration by over-expression of the chemokines MCP-1, MIP-1α and GRO-α in the adult rat brain

Inflammation-induced chemoattraction plays a major role in adult subventricular zone (SVZ)-derived precursor cell migration following neural cell loss, in particular through the release of chemokines by activated microglia and macrophages. We previously demonstrated that monocyte chemotactic protein-1 (MCP-1) (chemokine (c-c motif) ligand (CCL)2), macrophage inflammatory protein-1α (MIP-1α) (CCL3) and growth regulatory protein-α (GRO-α) (chemokine (c-x-c motif) ligand (CXCL)1) are up-regulated following neural cell loss in the adult striatum and act as potent chemoattractants for SVZ-derived precursor cells in vitro. Based on these observations, the current study aimed to examine the individual effect of MCP-1, MIP-1α and GRO-α on the migration of adult SVZ-derived neural precursor cells in vivo. To address this without the confounding effects of injury-induced chemotactic cues, adeno-associated viral (AAV)2-mediated in vivo gene transfer was used to ectopically express either MCP-1, MIP-1α or GRO-α, or the control red fluorescent protein (RFP) in the normal adult rat striatum. The extent of doublecortin (Dcx)-positive cell recruitment from the SVZ into the striatal parenchyma was then determined at 4 and 8weeks following AAV2 injection. Ectopic expression either of MCP-1 or MIP-1α in the normal adult rat brain significantly increased the number of Dcx-positive cells and the extent of their migration into the striatum at both 4 and 8weeks after vector injection but did not promote either precursor cell proliferation or neural differentiation. In contrast, while over-expression of GRO-α 4weeks after vector injection induced a significant increase in Dcx-positive cell migration compared to control, this effect was reduced to control levels by 8weeks post injection. Further, direct comparison between MCP-1, MIP-1α and GRO-α at both 4 and 8weeks post vector injection indicated that GRO-α may have a reduced effect in inducing Dcx-positive cell migration when compared to MCP-1. Combined, these results confirm that over-expression of the chemokines MCP-1, MIP-1α and GRO-α can override cues directing precursor cell migration along the rostral migratory stream (RMS) and provides a mechanism by which neural precursor cell migration can be redirected into a non-neurogenic region. Differences in the migratory effect observed between individual chemokine may be due to ligand-binding affinity and/or receptor expression on SVZ-derived precursor cells.

Rapid transgene expression in multiple precursor cell types of adult rat subventricular zone mediated by adeno-associated type 1 vectors

The adult rat brain subventricular zone (SVZ) contains proliferative precursors that migrate to the olfactory bulb (OB) and differentiate into mature neurons. Recruitment of precursors constitutes a potential avenue for brain repair. We have investigated the kinetics and cellular specificity of transgene expression mediated by AAV2/1 vectors (i.e., adeno-associated virus type 2 pseudotyped with AAV1 capsid) in the SVZ. Self-complementary (sc) and single-stranded (ss) AAV2/1 vectors mediated efficient GFP expression, respectively, at 17 and 24 hr postinjection. Transgene expression was efficient in all the rapidly proliferating cells types, that is, Mash1(+) precursors (30% of the GFP(+) cells), Dlx2(+) neuronal progenitors (55%), Olig2(+) oligodendrocyte progenitors (35%), and doublecortin-positive (Dcx(+)) migrating cells (40%), but not in the slowly proliferating glial fibrillary acidic protein-positive (GFAP(+)) neural stem cell pool (5%). Because cell cycle arrest by wild-type and recombinant AAV has been described in primary cultures, we examined SVZ proliferative activity after vector injection. Indeed, cell proliferation was reduced immediately after vector injection but was normal after 1 month. In contrast, migration and differentiation of GFP(+) precursors were unaltered. Indeed, the proportion of Dcx(+) cells was similar in the injected and contralateral hemispheres. Furthermore, 1 month after vector injection into the SVZ, GFP(+) cells, found, as expected, in the OB granular cell layer, were mature GABAergic neurons. In conclusion, the rapid and efficient transgene expression in SVZ neural precursors mediated by scAAV2/1 vectors underlines their potential usefulness for brain repair via recruitment of immature cells. The observed transient precursor proliferation inhibition, not affecting their migration and differentiation, will likely not compromise this strategy.

Neural stem cells: mechanisms and modeling

In the adult brain, neural stem cells have been found in two major niches: the dentate gyrus and the subventricular zone [corrected]. Neurons derived from these stem cells contribute to learning, memory, and the autonomous repair of the brain under pathological conditions. Hence, the physiology of adult neural stem cells has become a significant component of research on synaptic plasticity and neuronal disorders. In addition, the recently developed induced pluripotent stem cell technique provides a powerful tool for researchers engaged in the pathological and pharmacological study of neuronal disorders. In this review, we briefly summarize the research progress in neural stem cells in the adult brain and in the neuropathological application of the induced pluripotent stem cell technique.