Amplification of neural stem cell proliferation by intermediate progenitor cells in Drosophila brain development

Background

Expression of correct neurotransmitters is crucial for normal nervous system function. How neurotransmitter expression is regulated is not well-understood; however, previous studies provide evidence that both environmental signals and intrinsic differentiation programs are involved. One environmental signal known to regulate neurotransmitter expression in vertebrate motoneurons is Hepatocyte growth factor, which acts through the Met receptor tyrosine kinase and also affects other aspects of motoneuron differentiation, including axonal extension. Here we test the role of Met in development of motoneurons in embryonic zebrafish.

Results

We found that met is expressed in all early developing, individually identified primary motoneurons and in at least some later developing secondary motoneurons. We used morpholino antisense oligonucleotides to knock down Met function and found that Met has distinct roles in primary and secondary motoneurons. Most secondary motoneurons were absent from met morpholino-injected embryos, suggesting that Met is required for their formation. We used chemical inhibitors to test several downstream pathways activated by Met and found that secondary motoneuron development may depend on the p38 and/or Akt pathways. In contrast, primary motoneurons were present in met morpholino-injected embryos. However, a significant fraction of them had truncated axons. Surprisingly, some CaPs in met morpholino antisense oligonucleotide (MO)-injected embryos developed a hybrid morphology in which they had both a peripheral axon innervating muscle and an interneuron-like axon within the spinal cord. In addition, in met MO-injected embryos primary motoneurons co-expressed mRNA encoding Choline acetyltransferase, the synthetic enzyme for their normal neurotransmitter, acetylcholine, and mRNA encoding Glutamate decarboxylase 1, the synthetic enzyme for GABA, a neurotransmitter never normally found in these motoneurons, but found in several types of interneurons. Our inhibitor studies suggest that Met function in primary motoneurons may be mediated through the MEK1/2 pathway.

Conclusion

We provide evidence that Met is necessary for normal development of zebrafish primary and secondary motoneurons. Despite their many similarities, our results show that these two motoneuron subtypes have different requirements for Met function during development, and raise the possibility that Met may act through different intracellular signaling cascades in primary and secondary motoneurons. Surprisingly, although met is not expressed in primary motoneurons until many hours after they have extended axons to and innervated their muscle targets, Met knockdown causes some of these cells to develop a hybrid phenotype in which they co-expressed motoneuron and interneuron neurotransmitters and have both peripheral and central axons.     

Isolation and characterization of neural stem/progenitor cells from post-stroke cerebral cortex in mice

The CNS has the potential to marshal strong reparative mechanisms, including activation of endogenous neurogenesis, after a brain injury such as stroke. However, the response of neural stem/progenitor cells to stroke is poorly understood. Recently, neural stem/progenitor cells have been identified in the cerebral cortex, as well as previously recognized regions such as the subventricular or subgranular zones of the hippocampus, suggesting that a contribution of cortex-derived neural stem/progenitor cells may repair ischemic lesions of the cerebral cortex. In the present study, using a highly reproducible murine model of cortical infarction, we have found nestin-positive cells in the post-stroke cerebral cortex, but not in the non-ischemic cortex. Cells obtained from the ischemic core of the post-stroke cerebral cortex formed neurosphere-like cell clusters expressing nestin; such cells had the capacity for self-renewal and differentiated into electrophysiologically functional neurons, astrocytes and myelin-producing oligodendrocytes. Nestin-positive cells from the stroke-affected cortex migrated into the peri-infarct area and differentiated into glial cells in vivo . Although we could not detect differentiation of nestin-positive cells into neurons in vivo , our current observations indicate that endogenous neural stem/progenitors with the potential to become neurons can develop within post-stroke cerebral cortex.     

Contribution of intermediate progenitor cells to cortical histogenesis

The mammalian cerebral cortex is the most cellularly complex structure in the animal kingdom. Almost all cortical neurons are produced during a limited embryonic period by cortical progenitor cells in a proliferative region that surrounds the ventricular system of the developing brain. The proliferative region comprises 2 distinct zones, the ventricular zone, which is a neuroepithelial layer directly adjacent to the ventricular lumen, and the subventricular zone, which is positioned superficial to the ventricular zone. Recent advances in molecular and cell biology have made possible the study of specific cell populations, and 2 cortical progenitor cell types, radial glial cells in the ventricular zone and intermediate progenitor cells in the subventricular zone, have been shown to generate neurons in the embryonic cerebral cortex. These findings have refined our understanding of cortical neurogenesis, with implications for understanding the causes of neurodevelopmental disorders and for their potential treatment.     

Stage‐specific requirement for cyclin D1 in glial progenitor cells of the cerebral cortex

Despite the vast abundance of glial progenitor cells in the mouse brain parenchyma, little is known about the molecular mechanisms driving their proliferation in the adult. Here we unravel a critical role of the G1 cell cycle regulator cyclin D1 in controlling cell division of glial cells in the cortical grey matter. We detect cyclin D1 expression in Olig2‐immunopositive (Olig2+) oligodendrocyte progenitor cells, as well as in Iba1+ microglia and S100β+ astrocytes in cortices of 3‐month‐old mice. Analysis of cyclin D1‐deficient mice reveals a cell and stage‐specific molecular control of cell cycle progression in the various glial lineages. While proliferation of fast dividing Olig2+ cells at early postnatal stages becomes gradually dependent on cyclin D1, this particular G1 regulator is strictly required for the slow divisions of Olig2+/NG2+ oligodendrocyte progenitors in the adult cerebral cortex. Further, we find that the population of mature oligodendrocytes is markedly reduced in the absence of cyclin D1, leading to a significant decrease in the number of myelinated axons in both the prefrontal cortex and the corpus callosum of 8‐month‐old mutant mice. In contrast, the pool of Iba1+ cells is diminished already at postnatal day 3 in the absence of cyclin D1, while the number of S100β+ astrocytes remains unchanged in the mutant. GLIA 2014;62:829–839     

Injury‐induced neural stem/progenitor cells in post‐stroke human cerebral cortex

Increasing evidence points to accelerated neurogenesis after stroke, and support of such endogenous neurogenesis has been shown to improve stroke outcome in experimental animal models. The present study analyses post‐stroke cerebral cortex after cardiogenic embolism in autoptic human brain. Induction of nestin‐ and musashi‐1‐positive cells, potential neural stem/progenitor cells, was observed at the site of ischemic lesions from day 1 after stroke. These two cell populations were present at distinct locations and displayed different temporal profiles of marker expression. However, no surviving differentiated mature neural cells were observed by 90 days after stroke in the previously ischemic region. Consistent with recent reports of neurogenesis in the cerebral cortex after induction of stroke in rodent models, the present current data indicate the presence of a regional regenerative response in human cerebral cortex. Furthermore, observations underline the potential importance of supporting survival and differentiation of endogenous neural stem/progenitor cells in post‐stroke human brain.     

Effects of prenatal progesterone on the development of pyramidal cells in rat cerebral cortex

Pregnant rats received daily injections of 6 or 40 mg/kg progesterone or vehicle only from days 1 to 16 of gestation. The morphology of pyramidal cells in the parietal cortex of the offspring on days 5 and 25 was assessed after staining by the Golgi technique. At postnatal day 5 the cells from both progesterone groups showed a 16% increase in branching of basal dendrites but no change in dendritic spread or cell diameter. At day 25 the number of spines in the apical dendrites of layer IV and V cells were increased 24% in the low-dose group and 36% in the high-dose group. Moreover, the high-dose group showed a significant increase in brain weight on day 25. The amplitude and latency of the cortical evoked potentials on day 5 were not altered by the progesterone treatment. We conclude that progesteone can influence cortical cell morphology but there was no evidence for modification of developing somatosensory pathways.     

1000/内皮祖细胞与缺血性脑卒中

背景：内皮祖细胞不仅能够早期预测血管损伤的程度,而且具有修复损伤的内皮细胞、促进新生血管形成管腔结构、参与神经再生的功能。内皮细胞移植已逐渐应用于血管相关性疾病的治疗。目的：文章综述了内皮祖细胞的生物学特性及在缺血性脑卒中领域的最新研究进展,为其临床应用提供理论支持。方法：以“endothelial progenitor cells; ischemic infarction;”为检索词检索Medline、HighWire Press数据库(2000-01/2009-12)。纳入与血管新生、内皮和神经再生密切相关的研究,排除内容陈旧、重复性及缺乏可信度文章。 结果与结论：计算机初检得到126篇文献,根据纳入排除标准,对其中28篇文献进行分析。内皮祖细胞具有修复损伤的内皮细胞、延缓动脉粥样硬化进展、促进缺血组织新生血管形成等功能,它参与缺血性脑卒中后血管新生,防治支架术后血栓形成及再狭窄,预测脑缺血的发生及预后,在防治缺血性脑卒中方面具有广泛的应用前景。关键词：内皮祖细胞;缺血性脑卒中;血管新生;内皮再生;神经再生;综述文献     

Morphometric study of human cerebral cortex development

Morphometric studies of immature cerebral cortex in humans show developmental changes extending up to the time of adolescence. Growth of dendrites and of synaptic connections occurs during infancy and early childhood. Excess synaptic connections are eliminated during later childhood years. The exuberant connections that occur during infancy may form the anatomical substrate for neural plasticity and for certain types of early learning.     

Role of glial cells in cerebral ischemia

Despite intense efforts at the bench and at the bedside, few therapeutic strategies exist to combat the consequences of cerebral ischemia. Traditionally, a "neurocentric" view has dominated research in this field. Evidence is now accumulating that glial cells, in particular astrocytes, play an active and important role in the pathophysiology of cerebral ischemia. Brain energetics, water and ion homeostasis, inflammation, trophic factor production, vascular regulation, neuroneogenesis, and vasculogenesis, among others, are all under the control of glial cells. As a consequence, glial cells have been identified as promising targets for novel therapeutic approaches in brain protection. This review aims at dissecting possible protective as well as destructive roles of astrocytes (and other glial cells) in cerebral ischemia. By emphasizing open issues in this field, we hope to stimulate further research into this relatively unexplored aspect of brain pathophysiology.     

Hippocampal progenitor cells express nestin following cerebral ischemia in rats

This study addresses whether hippocampal progenitor cells express nestin following cerebral ischemia in rats. Cell counts within the hippocampal hilus were significantly greater following severe (eight-vessel occlusion) ischemia than following intermediate (four-vessel occlusion) ischemia (1527+/-87/mm2 vs. 918+/-71/mm2). Bromedeoxyuridine-positive cell counts were significantly higher with severe ischemia than with intermediate ischemia or in sham-operated animals, respectively (368+/-45, 43+/-14 and 7+/-1/mm2). In the eight-vessel occlusion group, 47+/-8/mm2 bromedeoxyuridine-labeled cells expressed nestin, significantly higher than in the four-vessel occlusion group and sham-operated animals (1+/-1 and 1+/-0/mm2, P<0.01 vs. eight-vessel occlusion, respectively). Confocal microscopy verified that a subset of the bromedeoxyuridine-positive cells expressed nestin. In conclusion, severe ischemia elicits nestin expression in hippocampal progenitor cells in rats.     

Distinct development of the cerebral cortex in platypus and echidna

Both lineages of the modern monotremes have distinctive features in the cerebral cortex, but the developmental mechanisms that produce such different adult cortical architecture remain unknown. Similarly, nothing is known about the differences and/or similarities between monotreme and therian cortical development. We have used material from the Hill embryological collection to try to answer key questions concerning cortical development in monotremes. Our findings indicate that gyrencephaly begins to emerge in the echidna brain shortly before birth (crown-rump length 12.5 mm), whereas the cortex of the platypus remains lissencephalic throughout development. The cortices of both monotremes are very immature at the time of hatching, much like that seen in marsupials, and both have a subventricular zone (SubV) within both the striatum and pallium during post-hatching development. It is particularly striking that in the platypus, this region has an extension from the palliostriatal angle beneath the developing trigeminoreceptive part of the somatosensory cortex of the lateral cortex. The putative SubV beneath the trigeminal part of S1 appears to accommodate at least two distinct types of cell and many mitotic figures and (particularly in the platypus) appears to be traversed by large numbers of thalamocortical axons as these grow in. The association with putative thalamocortical fibres suggests that this region may also serve functions similar to the subplate zone of Eutheria. These findings suggest that cortical development in each monotreme follows distinct paths from at least the time of birth, consistent with a long period of independent and divergent cortical evolution.     

The growth and development of microvasculature in human cerebral cortex

Sections of the occipital cortex from 31 fetuses, infants and children, ranging in age from 15 weeks gestation to ten years postnatal, were stained to demonstrate alkaline phosphatase activity in intracortical vessels. At 15 weeks gestation intracortical positively staining vessels, assumed to be arterial precursors, were radially oriented, originating from leptomeningeal arteries. Most radial vessels coursed through the cerebral cortex without branching to vascularize the subcortical tissue. By 20 weeks gestation horizontal branches arose from radial vessels, most frequently in the lower half of the cortex. Occasionally, recurrent collaterals ascended from these horizontal branches to more superficial cortex. From 20-27 weeks gestation, the number of horizontal branches and recurrent collaterals increased in the lower half of the cortex, horizontal branches appeared in the upper half. From 27 weeks to term, shorter radial vessels, terminating in the more superficial cortical laminae increased in number. After birth a network of fine vessels, presumable precursors of capillaries, increased, particularly vascular layer 3 (neuronal lamina IV and Va). The number of radially oriented vessels per mm2 of pial surface (NA) decreased throughout development, with the most dramatic decrease occurring prenatally. In five cases of trisomy values of NA decreased less rapidly than in the normal.