Cortical progenitor biology: key features mediating proliferation versus differentiation

Genes and Mechanisms Involved in the Generation and Amplification of Basal Radial Glial Cells

The development of the cerebral cortex relies on different types of progenitor cell. Among them, the recently described basal radial glial cell (bRG) is suggested to be of critical importance for the development of the brain in gyrencephalic species. These cells are highly numerous in primate and ferret brains, compared to lissencephalic species such as the mouse in which they are few in number. Their somata are located in basal subventricular zones in gyrencephalic brains and they generally possess a basal process extending to the pial surface. They sometimes also have an apical process directed toward the ventricular surface, similar to apical radial glial cells (aRGs) from which they are derived, and whose somata are found more apically in the ventricular zone. bRGs share similarities with aRGs in terms of gene expression (SOX2, PAX6, and NESTIN), whilst also expressing a range of more specific genes (such as HOPX). In primate brains, bRGs can divide multiple times, self-renewing and/or generating intermediate progenitors and neurons. They display a highly specific cytokinesis behavior termed mitotic somal translocation. We focus here on recently identified molecular mechanisms associated with the generation and amplification of bRGs, including bRG-like cells in the rodent. These include signaling pathways such as the FGF-MAPK cascade, SHH, PTEN/AKT, PDGF pathways, and proteins such as INSM, GPSM2, ASPM, TRNP1, ARHGAP11B, PAX6, and HIF1α. A number of these proteins were identified through transcriptome comparisons in human aRGs vs. bRGs, and validated by modifying their activities or expression levels in the mouse. This latter experiment often revealed enhanced bRG-like cell production, even in some cases generating folds (gyri) on the surface of the mouse cortex. We compare the features of the identified cells and methods used to characterize them in each model. These important data converge to indicate pathways essential for the production and expansion of bRGs, which may help us understand cortical development in health and disease.

The neuroanatomy of Eml1 knockout mice, a model of subcortical heterotopia

The cerebral cortex is a highly organized structure responsible for advanced cognitive functions. Its development relies on a series of steps including neural progenitor cell proliferation, neuronal migration, axonal outgrowth and brain wiring. Disruption of these steps leads to cortical malformations, often associated with intellectual disability and epilepsy. We have generated a new resource to shed further light on subcortical heterotopia, a malformation characterized by abnormal neuronal position. We describe here the generation and characterization of a knockout (KO) mouse model for Eml1, a microtubule-associated protein showing mutations in human ribbon-like subcortical heterotopia. As previously reported for a spontaneous mouse mutant showing a mutation in Eml1, we observe severe cortical heterotopia in the KO. We also observe abnormal progenitor cells in early corticogenesis, likely to be the origin of the defects. EML1 KO mice on the C57BL/6N genetic background also appear to present a wider phenotype than the original mouse mutant, showing additional brain anomalies, such as corpus callosum abnormalities. We compare the anatomy of male and female mice and also study heterozygote animals. This new resource will help unravel roles for Eml1 in brain development and tissue architecture, as well as the mechanisms leading to severe subcortical heterotopia.

Zeb1 is important for proper cleavage plane orientation of dividing progenitors and neuronal migration in the mouse neocortex

During neocortical development, there are two important events, including expansion of the neural progenitor pool through symmetric divisions, and generation of neurons via asymmetrical divisions that lead to a serial process of neuronal polarization, migration, and layer-type specific phenotype acquisition. The mechanisms underlying these processes remain poorly elucidated. Here, we show that the transcription factor Zeb1 regulates the orientation of the cleavage plane of dividing neural progenitors, neuronal polarity, and migration. Upon Zeb1 removal, the cleavage plane of mitotic neural progenitors fails to orientate vertically, resulting in random orientation and premature neuronal differentiation. Consequently, these extra number of precociously produced neurons migrate aberrantly to the upper layer. Mechanistically, we show that Zeb1 suppresses Pak3, a p21-activated serine/threonine protein kinase, through formation of a functional repressing complex together with methyltransferase PRMT5 and Pak3. Our results reveal that Zeb1 plays an essential role in neocortical development and may provide insights into the mechanisms responsible for cortical developmental diseases.

Cortical Development and Brain Malformations: Insights From the Differential Regulation of Early Events of DNA Replication

During the development of the cortex distinct populations of Neural Stem Cells (NSCs) are defined by differences in their cell cycle duration, self-renewal capacity and transcriptional profile. A key difference across the distinct populations of NSCs is the length of G1 phase, where the licensing of the DNA replication origins takes place by the assembly of a pre-replicative complex. Licensing of DNA replication is a process that is adapted accordingly to the cell cycle length of NSCs to secure the timed duplication of the genome. Moreover, DNA replication should be efficiently coordinated with ongoing transcription for the prevention of conflicts that would impede the progression of both processes, compromising the normal course of development. In the present review we discuss how the differential regulation of the licensing and initiation of DNA replication in different cortical NSCs populations is integrated with the properties of these stem cells populations. Moreover, we examine the implication of the initial steps of DNA replication in the pathogenetic mechanisms of neurodevelopmental defects and Zika virus-related microcephaly, highlighting the significance of the differential regulation of DNA replication during brain development.

Knockdown of anti-silencing function 1B histone chaperone induces cell apoptosis via repressing PI3K/Akt pathway in prostate cancer

Prostate cancer (PCa) is one of the most common malignancies among males worldwide. Anti-silencing function 1B histone chaperone (ASF1B) has been reported to be involved in PCa. The present study aimed to investigate the role and molecular mechanism of ASF1B in PCa. Data of genes were obtained from The Cancer Genome Atlas data- base. The core gene was identified using the DAVID website. Cell viability and colony formation were detected using a cell counting kit-8 assay and crystal violet staining, respectively. Cell cycle distribution and apoptosis were assessed using flow cytometry analysis. The corresponding factors were analyzed by reverse transcription-quantitative polymerase chain reaction and western blotting. It was demonstrated that ASF1B was highly expressed in the PCa tissues and cells compared with the non-PCa tissues and cells, respectively. While siRNA-ASF1B significantly reduced the viability and colony formation, it promoted apoptosis, G1 phase cell cycle arrest of LNCap as well as C4-2 cells. siRNA-ASF1B was revealed to significantly reduce the level of B-cell lymphoma-2 and cyclin D1, and enhance the expression levels of p53, caspase-3 and Bcl-2 associated X protein. Furthermore, the phosphorylation levels of phosphatidylinositol 3 kinase (PI3K) and protein kinase B (Akt) were significantly decreased in the siRNA-ASF1B group compared with the mock group. In summary, the present study demonstrated that silencing of ASF1B suppressed the proliferation, and promoted apoptosis and cell cycle arrest of PCa cells. Inhibition of the PI3K/Akt signaling pathway was pertinent to the role of si-ASF1B. This phenomenon suggests that the downregulation of ASF1B may aid in inhibiting the progression of PCa.