Cell cycle parameters and patterns of nuclear movement in the neocortical proliferative zone of the fetal mouse

Abstract

Cytogenesis is the critical determinant of the total number of neurons that contribute to the formation of the cerebral cortex and the rate at which the cells are produced. Two distinct cell populations constitute the proliferative population, a pseudostratified ventricular epithelium (PVE) lying within the ventricular zone (VZ) at the margin of the ventricle, and a secondary proliferative population that is intermixed with the PVE within the VZ but also is distributed through the overlying subventricular and intermediate zones of the cerebral wall. The present analysis, based upon cumulative S-phase labeling of the proliferative cells with 5-bromo-2′-deoxyuridine, is principally concerned with the PVE of the gestational-day-14 (E14) murine cerebral wall. It has immediate but also more far reaching general objectives. The most immediate objective, essential to the design and interpretation of later experiments, is to provide estimates of critical parameters of cytogenesis for the PVE. The growth fraction is virtually 100%. The lengths of the overall cell cycle, S-, G2+M-m, and G1-phases are 15.1 hr, 3.8 hr, 2 hr, and 9.3 hr, respectively. The PVE is homogeneous with respect to cell cycle length. For methodological considerations, these estimates are more accurate than estimates of the same parameters obtained in earlier analyses based upon S-phase labeling with tritiated thymidine. It is particularly with respect to a shorter length of S-phase determined here that the present values are different from those obtained with thymidine. At a more innovative level, the temporal and spatial resolution of nuclear movement made possible by the methods developed here will allow, in a way not previously attempted, a fine-grained tracking of nuclear movement as cells execute the successive stages of the cell cycle or exit the cycle subsequent to mitosis. Such observations are pertinent to our understanding of the regulatory mechanisms of neocortical histogenesis and the cell biological mechanisms that govern the proliferative cycle of the ventricular epithelium itself. It is known that the velocity of nuclear movement in the PVE is maximum in G2 (fourfold increase from S- phase) and minimum in M and early G1.(ABSTRACT TRUNCATED AT 400 WORDS)

Coevolution of radial glial cells and the cerebral cortex

“…Although NECs retain contact with both apical and basal sides of the neural tube (facing the luminal space or the brain's surface, respectively), they always undergo mitosis at the apical side to then undergo interkinetic nuclear migration (INM) during the other phases of the cell cycle: during G1 they move their soma to the basal side, where they undergo S‐phase, and during G2 they move back down to the apical side to finally undergo mitosis (Takahashi et al, 1993). The dynamic movement of these cell bodies along the apical–basal axis of the neuroepithelium confers it a false appearance of stratification (pseudostratified; Bayer and Altman, 1991; Sidman and Rakic, 1973; Taverna et al, 2014).…”

Cdk6-Dependent Regulation of G1 Length Controls Adult Neurogenesis

“…The GF (representing the proportion of proliferating cells) was determined as the maximum LI value attained for each genotype. T C and T S were determined using (a) y-intercept ¼ GF Â T S /T C and (b) time to reach maximum LI ¼ T C À T S [18]. Mitotic cells were identified using antiphosphohistone H3 antibodies (mitotic marker).…”

“…Mitotic cells were identified using antiphosphohistone H3 antibodies (mitotic marker). The combined length of G 2 plus M phases (T G2þM ) was determined as the time required to label all mitotic (i.e., Ki-67 þ /phH3 þ ) cells with BrdU [18]. The length of G 1 phase (T G1 ) was computed using the equation T G1 ¼ T C À (T S þ T G2þM ), as shown previously [18].…”

“…As our data support an increased rate of precursor cell cycle exit in Cdk6 À/À neurogenic regions, we compared the length of G 1 in Cdk6-knockout and WT animals. To this aim, we performed cumulative S-phase labeling with BrdU [18,40] (Fig. 6A-6D).…”

Reduction of the Cell Cycle Length by Decreasing G1 Phase and Cell Cycle Reentry Expand Neuronal Progenitor Cells in the Subventricular Zone of Adult Rat after Stroke

“…During development, neocortex forms by the orderly migration and subsequent differentiation of neuronal precursors arising from the proliferating ventricular zone (VZ) (Takahashi et al, 1993;Caviness et al, 2003;Noctor et al, 2004). The VZ is replaced by an ependymal layer, while the subventricular zone (SVZ) persists in the adult rodent (Morshead et al, 1998).…”