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Proliferating neural stem cells and intermediate progenitors persist in the ventricular-subventricular zone (V-SVZ) of the adult mammalian brain. This extensive germinal layer in the walls of the lateral ventricles is the site of birth of different types of interneurons destined for the olfactory bulb. The cell cycle dynamics of stem cells (B1 cells), intermediate progenitors (C cells), and neuroblasts (A cells) in the V-SVZ and the number of times these cells divide remain unknown. Using whole mounts of the walls of the lateral ventricles of adult mice and three cell cycle analysis methods using thymidine analogs, we determined the proliferation dynamics of B1, C, and A cells in vivo. Achaete-scute complex homolog (Ascl)1(+) C cells were heterogeneous with a cell cycle length (T(C)) of 18-25 h and a long S phase length (T(S)) of 14-17 h. After C cells, Doublecortin(+) A cells were the second-most common dividing cell type in the V-SVZ and had a T(C) of 18 h and T(S) of 9 h. Human glial fibrillary acidic protein (hGFAP)::GFP(+) B1 cells had a surprisingly short Tc of 17-18 h and a T(S) of 4 h. Progenitor population analysis suggests that following the initial division of B1 cells, C cells divide three times and A cells once, possibly twice. These data provide essential information on the dynamics of adult progenitor cell proliferation in the V-SVZ and how large numbers of new neurons continue to be produced in the adult mammalian brain.

The article discusses the process of brain maturation in mammals, specifically focusing on the central nervous system (CNS). It explains that the CNS is built during embryogenesis by neural stem cells, and neuroblasts migrate to their final integration targets. The article emphasizes that postnatal and young ages are crucial for shaping the mature nervous system and allowing experiences to influence brain maturation. It also highlights the importance of understanding neuronal and brain maturation from various perspectives and the need for further research on interspecies differences and evolutionary implications. [Extracted from the article]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.02.037 Byline: Giovanna Ponti (a), Paolo Peretto (b), Luca Bonfanti (a)(c) Keywords: Development; Neurogenesis; Migration; Meninges; PSA-NCAM Abbreviations: SVZ, subventricular zone; PSA-NCAM, polysialylated neural cell adhesion molecule; BrdU, 5-bromo-2'-deoxyuridine; ML, molecular layer; GL, inner granular layer; EGL, external germinal layer; SPL, subpial layer; DCX, doublecortin; CNS, central nervous system Abstract: Protracted neurogenesis occurs at different postnatal stages in different brain locations, whereby leading to site-specific adult neurogenesis in some cases. No spontaneous genesis of neurons occurs in the cerebellum after the postnatal genesis of granule cells from the external germinal layer (EGL), a transitory actively proliferating zone which is thought to be exhausted before puberty. Here, we show the protracted genesis of newly generated neuronal precursors in the cerebellar cortex of young rabbits, persisting beyond puberty. Neuroblasts generated within an actively proliferating subpial layer thus extending the postnatal EGL are arranged to form thousands of tangential chains reminiscent of those responsible for cell migration in the forebrain subventricular zone. These subpial chains cover the whole cerebellar surface from the 2nd to the 5th month of life, then disappearing after puberty. In addition, we describe the appearance of similar groups of cells at the end of granule cell genesis in the mouse cerebellum, here limited to the short period of EGL exhaustion (4-5 days). These results show common features do exist in the postnatal reorganization of secondary germinal layers of brain and cerebellum at specific stages, parallel to differences in the slowing down of cerebellar neurogenesis among mammalian species. Author Affiliation: (a) Department of Veterinary Morphophysiology, University of Turin, Via Leonardo da Vinci 44, 10095 Grugliasco, Italy (b) Department of Animal and Human Biology, University of Turin, Via Accademia Albertina 13, 10153 Turin, Italy (c) Rita Levi Montalcini Center for Brain Repair, Italy Article History: Received 3 January 2006; Revised 20 February 2006; Accepted 22 February 2006