Biomedical Engineering Reference
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More recently, studies have also demonstrated that the SVZ progenitor
cells also directly produce oligodendrocytes (Menn et al. 2006). This work
suggests that type B cells can generate a subpopulation of transit-amplifying
type C cells that begin expressing Olig2. Cells derived from these primary
progenitors migrate orthogonal to the orientation of the chains of migrating
neuroblasts and invade the white matter to become local oligodendrocyte
progenitors (OPCs). These local OPCs act like displaced type C cells and
divide locally in the white matter to generate pre-myelinating and myelinating
oligodendrocytes.
Therefore, progenitor cells for both neuroblasts and OPCs in the SVZ of the
adult rodent brain correspond to type B cells, which have many characteristics
of astrocytes. The ventricular surface adjacent to the SVZ is largely covered
with multiciliated ependymal cells. Interestingly, recent work has shown that
type B cells have a thin apical process between ependymal cells that contacts the
ventricle, forming very small apical specializations with a short primary cilium
(Doetsch et al. 1997; Mirzadeh et al. 2008). The SVZ also contains blood
vessels, microglia, and a substantial extracellular matrix, thought to form the
substrate for its unique neurogenic niche (Mercier et al. 2002; Capela and
Temple 2006). The architecture of this specialized germinal zone allows for
extensive cell-cell interaction and the integration of signals from the ventricular
cerebrospinal fluid, the surrounding extracellular matrix, and local blood
vessels.
2 Unique Organization of the Human Subventricular Zone
The adult human SVZ also harbors a population of specialized astrocytes and a
small subpopulation of this cells proliferates in vivo and functions as adult
neural stem cells in vitro (Sanai et al. 2004). These human SVZ astrocytes form a
periventricular ribbon that is separated from the lateral ventricular lining by a
hypocellular 'gap' region. While there is no evidence of the massive human
neuroblast chain migration comparable to that which occurs in rodents or
primates (Lois et al. 1996; Kornack and Rakic 2001), a small population of
young neurons may still be generated in this region and some of these newborn
cells may migrate individually or in small groups to the olfactory bulb. Never-
theless, the magnitude and mechanism of neuronal proliferation and migration
in the adult human SVZ, as well as the persistence of human RMS, remains
controversial (Sanai et al. 2004, 2007; Curtis et al. 2007). Similarly, the sugges-
tion that an open olfactory ventricle, linking the anterior horn of the lateral
ventricle to the olfactory bulb, is not supported by previous work (Sanai et al.
2004; Bedard and Parent 2004; Humphrey 1940; Mueller et al. 2005; Muller and
O'Rahilly 1989; Nakashima et al. 1985).
Recently, the cellular composition and cytoarchitecture of the adult human
SVZ has been characterized in detail
(Quinones-Hinojosa et al. 2006),
