Brain Development: Normal Processes and the Effects of Alcohol ...

FIGURE 2- 1 Diagra m o f the architectoni c an d cytokineti c compartment s i n
the developing mammalian brain . The ventricula r surface is to the lef t and th e
piai surface to the right. A. Four cytoarchitectonic compartments can be recognized
o n th e basi s o f cytologica l criteri a (Boulder Committee, 1970 ; Smart ,
1976): the ventricular zone (VZ, or the ependymal layer), subventricular zone
(SZ, o r the subependyma l layer) , the intermediat e zon e (IZ , o r th e externa l
sagittal stratum), and three differentiating fields—a subplate (SP), cortical plate
(CP), and marginal zone (MZ). Cells in the VZ are organized a s a pseudostratified
columna r epithelium , wherea s the S Z and SP/CP/M Z contain randoml y
oriented, nonepithelial cells. The I Z consists predominantly of columnar arrays
of bipolar cells and growin g axons (black lines). The border s of the S Z and I Z
are ambiguous. The dashed lines indicate the approximate borders between th e
different compartments . B . Precursor cells can be classifie d int o two groups on
the basi s of their interkinetic nuclear migratory pattern: a pseudostratified ven -
tricular epithelium (PVE ) and a secondary proliferati ve population (SPP) . PVE
cells undergo interkineti c nuclea r migratio n (blac k arrows) such that nuclei of
cells in M phase of the cell cycle are located a t the ventricular surface and th e
nuclei o f cells i n S phase ar e farthes t fro m th e ventricula r surface. Nucle i of
cells in Gl an d G2 phase s are at intermediate distances . SP P cells do not undergo
interkinetic nuclear migration, and the nuclei of cells in the different cel l
cycle phases are scattered throughout the VZ and I Z (soli d black arrows). PVE
cells that leave the cell cycl e exit the VZ, migrate through th e S Z and IZ (broken,
curved arrows), and settle in the CP/MZ. SPP cells that exit the cell cycl e
also migrate to the CP/MZ. C. The spatial distribution of PVE, SPP , and CP/MZ
cells i s illustrated to sho w the overla p among th e proliferativ e and postmitoti c
populations. Th e PV E near the ventricular surface is a "pure" population; how -
ever, the S-phas e zone (wher e nuclei of cells undergoing S phase are located) of
the PV E overlap s with the SPP . The CP/M Z i s a population o f predominantly
postmitotic cell s near the piai surface (right-hand side of the figure); however, in
the SZ/IZ area, some postmitotic cell s mix with precursor cells of the SPP . Thus,
the architectonic and cytokinetic compartments show considerable overlap in the
developing nervous system. (Source: Modifie d from Bhide , 1996) .
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