mTOR signaling regulates the morphology and migration of outer radial glia in developing human cortex

Outer radial glial (oRG) cells are a population of neural stem cells prevalent in the developing human cortex that contribute to its cellular diversity and evolutionary expansion. The mammalian Target of Rapamycin (mTOR) signaling pathway is active in human oRG cells. Mutations in mTOR pathway genes are linked to a variety of neurodevelopmental disorders and malformations of cortical development. We find that dysregulation of mTOR signaling specifically affects oRG cells, but not other progenitor types, by changing the actin cytoskeleton through the activity of the GTPase, CDC42. These effects change oRG cellular morphology, migration, and mitotic behavior. Thus, mTOR signaling can regulate the architecture of the developing human cortex by maintaining the cytoskeletal organization of oRG cells and the radial glia scaffold. Our study provides insight into how mTOR dysregulation may contribute to neurodevelopmental disease.

Modeling of dynamic mosaicism on ring chromosomes in human fibroblasts and IPSCS

Митотическая нестабильность кольцевых хромосом может приводить к появлению клеточных клонов с различной генетической структурой. В качестве модели нестабильности кольцевых хромосом в митозе мы использовали фибробласты от пациентов с r(8), r(13), r(18) и r(22) и полученные из них индуцированные плюрипотентные стволовые клетки (ИПСК). Линии ИПСК с r(22) имели относительно стабильный кариотип на протяжении десятков (до 60) пассажей и сохраняли неизменную структуру кольцевой хромосомы. Кариотип линий ИПСК с r(8) и r(18) на ранних пассажах стабильный, планируется его изучение на поздних пассажах. Наибольшее разнообразие кариотипа выявлено в линиях ИПСК с r(13), в которых наблюдали различные перестройки и выраженную клеточную гетерогенность. Определение факторов, влияющих на митотическую стабильность кольцевых хромосом, может иметь значение для консультирования пациентов. Mitotic instability of ring chromosomes can lead to the appearance of cell clones with different genetic structure. IPSCs from fibroblasts of patients with r(8), r(13), r(18), and r(22) were used as a model of ring chromosomes mitotic behavior. Karyotypes of iPSC lines with r(8) and r(18) have so far been evaluated only in the early passages, lines with r(22) have maintained a relatively stable karyotype up to 60 passages. The occurrence of rearrangements and cellular heterogeneity was found characteristic for r(13) iPSCs. The determination of factors affecting the ring chromosomes mitotic stability would be beneficial for the patient’s prognosis.

The actin cytoskeleton governs apical mitosis and daughter cell dispersion in intestinal epithelia

Cell proliferation is critical for maintaining the absorptive, protective and regenerative functions of the small intestine throughout adulthood. Interphase nuclei are positioned near the basal surface of the intestinal epithelium, but during mitosis, chromosomes are located apically. The molecular basis for apical-basal DNA positioning and its consequences for tissue homeostasis are poorly understood. Here, we image and pharmacologically perturb these behaviors in live murine intestinal organoids. We find that apical and basal DNA movements occur as a result of mitosis-coupled actin rearrangements that alter the basolateral shape of dividing cells, while the apical cell surface remains confined by cell-cell contacts that persist throughout mitosis. Strikingly, these polarized shape changes allow neighboring cells to insert between nascent daughters, intermingling cells of different lineages. In summary, polarized rearrangements of the actin cytoskeleton govern the mitotic behavior of intestinal epithelial cells and lead to interspersion of cell lineages.

The CENP-S complex is essential for the stable assembly of outer kinetochore structure

The constitutive centromere-associated network (CCAN) proteins are central to kinetochore assembly. To define the molecular architecture of this critical kinetochore network, we sought to determine the full complement of CCAN components and to define their relationships. This work identified a centromere protein S (CENP-S)–containing subcomplex that includes the new constitutive kinetochore protein CENP-X. Both CENP-S– and CENP-X–deficient chicken DT40 cells are viable but show abnormal mitotic behavior based on live cell analysis. Human HeLa cells depleted for CENP-X also showed mitotic errors. The kinetochore localization of CENP-S and -X is abolished in CENP-T– or CENP-K–deficient cells, but reciprocal experiments using CENP-S–deficient cells did not reveal defects in the localization of CCAN components. However, CENP-S– and CENP-X–deficient cells show a significant reduction in the size of the kinetochore outer plate. In addition, we found that intrakinetochore distance was increased in CENP-S– and CENP-X–deficient cells. These results suggest that the CENP-S complex is essential for the stable assembly of the outer kinetochore.

Topical Review: Neuronal Migration in Cortical Development

Cortical formation in the developing brain is a highly complicated process involving neuronal production (through symmetric or asymmetric cell division) interaction of radial glia with neuronal migration, and multiple modes of neuronal migration. It has been convincingly demonstrated by numerous studies that radial glial cells are neural stem cells. However, the processes by which neurons arise from radial glia and migrate to their final destinations in vivo are not yet fully understood. Recent studies using time-lapse imaging of neuronal migration are giving investigators an increasingly more detailed understanding of the mitotic behavior of radial glia and the migrating behavior of their daughter cells. In this review, we describe recent progress in elucidating neuronal migration in brain formation and how neuronal migration is disturbed by mutations in genes that control this process. ( J Child Neurol 2005;20:274—279).