Distribution of CD133 reveals glioma stem cells self-renew through symmetric and asymmetric cell divisions.

Malignant gliomas contain a population of self-renewing tumorigenic stem-like cells; however, it remains unclear how these glioma stem cells (GSCs) self-renew or generate cellular diversity at the single-cell level. Asymmetric cell division is a proposed mechanism to maintain cancer stem cells, yet the modes of cell division that GSCs utilize remain undetermined. Here, we used single-cell analyses to evaluate the cell division behavior of GSCs. Lineage-tracing analysis revealed that the majority of GSCs were generated through expansive symmetric cell division and not through asymmetric cell division. The majority of differentiated progeny was generated through symmetric pro-commitment divisions under expansion conditions and in the absence of growth factors, occurred mainly through asymmetric cell divisions. Mitotic pair analysis detected asymmetric CD133 segregation and not any other GSC marker in a fraction of mitoses, some of which were associated with Numb asymmetry. Under growth factor withdrawal conditions, the proportion of asymmetric CD133 divisions increased, congruent with the increase in asymmetric cell divisions observed in the lineage-tracing studies. Using single-cell-based observation, we provide definitive evidence that GSCs are capable of different modes of cell division and that the generation of cellular diversity occurs mainly through symmetric cell division, not through asymmetric cell division.

Temporally and spatially regulated expression of a candidate G-protein-coupled receptor during cerebral cortical development.

Genes expressed in layer-specific patterns in the mammalian cerebral cortex may play a role in specifying the identity of different cortical layers. Using PCR-differential display, we identified a cDNA that encodes rCNL3, a gene cloned previously by sequence homology to G-protein-coupled receptors. rCNL3 is expressed predominantly in layers 2-4 of the young rat cortex and in the developing and adult striatum. Cortical expression of rCNL3 begins postnatally at P3 and continues at high levels until around P15, while striatal expression begins at E20 and continues through adulthood. rCNL3 expression is not detectable in the ventricular zone precursors that generate the neurons of layers 2-4. The expression pattern of rCNL3 in the developing cortex suggests that rCNL3 is not involved in the initial specification of laminar fate, but rather may be involved with later differentiation events within the superficial cortical layers.

Intrinsic polarity of mammalian neuroepithelial cells.

Progenitor cells in the mammalian forebrain can undergo either symmetric or asymmetric cell divisions by varying their cleavage orientation. In asymmetric divisions, cells distribute apically and basally localized proteins differentially to their daughters. Here we explore the intrinsic polarity of neuroepithelial cells in the developing telencephalon. Actin microfilaments are concentrated apically, forming beltlike structures that encircle spots of gamma-tubulin immunoreactivity. Staining for N-cadherin, beta-catenin, and the tyrosine kinase substrates pp120 and paxillin is also enriched at the lumenal surface, presumably due to the localization of these proteins at adherens junctions. Phosphotyrosine immunoreactivity is concentrated apically in rings, suggesting that adherens junctions are enriched for signaling molecules. In mitotic cells it appears that adherens junction proteins and phosphotyrosine immunoreactivity may be inherited either symmetrically or asymmetrically, depending on the cell's cleavage orientation during mitosis. The differential inheritance of junctional proteins may determine whether a daughter cell can respond to extrinsic signals after mitosis.

Postmitotic neurons migrate tangentially in the cortical ventricular zone.

Patterns of cell movement play a key role in the establishment of the brain's functional architecture during development. The migration of neuronal progenitor cells has been hypothesized to disperse clonally related cells among different areas of the developing cerebral cortex. To test this model, we explored the migratory patterns of cells in the proliferative zone of the intact cortex of the ferret. After focal injections of DiI, labeled cells migrated in all directions and over long distances within the ventricular and subventricular zones. These cells expressed the neuron-specific marker TuJ1 and did not incorporate BrdU after cumulative labeling. Our results reveal an extensive tangential dispersion of cortical cells mediated predominantly or exclusively by the non-radial migration of postmitotic neurons.

Cleavage orientation and the asymmetric inheritance of Notch1 immunoreactivity in mammalian neurogenesis.

Neurons in the mammalian central nervous system are generated from progenitor cells near the lumen of the neural tube. Time-lapse microscopy of dividing cells in slices of developing cerebral cortex reveals that cleavage orientation predicts the fates of daughter cells. Vertical cleavages produce behaviorally and morphologically identical daughters that resemble precursor cells; these symmetric divisions may serve to expand or maintain the progenitor pool. In contrast, horizontally dividing cells produce basal daughters that behave like young migratory neurons and apical daughters that remain within the proliferative zone. Notch1 immunoreactivity is distributed asymmetrically in mitotic cells, with Notch1 inherited selectively by the basal (neuronal) daughter of horizontal divisions. These results provide cellular and molecular evidence that cortical neurons are generated from asymmetric divisions.