Fig. 3.

Time-lapse multiphoton laser scanning microscopy, using slice cultures of E12.5 telencephalon, of cells in the VZ showing Tis21-driven GFP expression. Shown are examples of cells dividing at the apical surface (a and b) or in the basal region (c and d), and their progeny (HR-rendering mode). (a-d) bl, basal boundary of VZ (note that, at later stages of the time-lapse, this boundary shifts upwards in the panels shown due to growth of the VZ); ap, apical surface, which runs horizontally across the bottom of each panel as indicated; open arrows, mother cell; arrowheads and arrows, daughter cells. The time of observation is indicated in min at the bottom of each panel. The square panels underneath a, c, and d show the mitoses at higher magnification and with enhanced fluorescent signal; the two white triangles at the margins indicate the initial position of the daughter cell nuclei (parallel, oblique, or perpendicular to ventricular surface). [Scale bar above top right panel in a, 20 μm (rectangular panels) and 10 μm (square panels).] (a) The elongated mother cell nucleus migrates toward the apical surface (0-110 min); the cell rounds up for mitosis (110-120 min); the initial position of the daughter cell nuclei is parallel to the ventricular surface (130 min), followed by their rotation (130-150 min); the daughter cell nuclei migrate separately in the basal direction (150-220 min); the leading nucleus then turns around (220 min), migrating apically toward (220-240 min), and then basally together with (240-290 min) the trailing one; and finally separates from the latter to migrate to and beyond the basal boundary of the VZ (290-530 min, note basal boundary at 380 min), followed by the trailing nucleus, which eventually reaches this boundary (290-650 min, note the shift in basal boundary from 380 min to 650 min). (b) The mother cell nucleus migrates toward the apical surface (0-10 min); the cell rounds up for mitosis (30 min) and apparently generates an apical and a basal daughter cell, which remain in close proximity to each other (40-70 min) and of which the apical one (arrows) was tracked; the apical daughter cell nucleus migrates to the basal side of the VZ (120-320 min), pauses there (320-400 min), and migrates rapidly back to the apical surface (400-430 min) followed by mitosis (430 min, arrows with asterisks). (c) The nucleus of the mother cell pauses in the basal half of the VZ, with subtle basal-apical-basal movement (0-270 min), the cell divides in the basal region of the VZ (270-300 min) with the initial position of the daughter cell nuclei being perpendicular to the ventricular surface (280 min), and both daughter cell nuclei migrate together basally into the adjacent neuronal layer (300-510 min). Note that the long axis of the ellipsoid daughter cell nuclei loses the strict radial orientation, which it shows while migrating in the VZ (arrowheads, 300-420 min; arrows, 300-450 min), upon entering the neuronal layer (arrowheads, 430-460 min; arrows, 470-490 min). (d) The nucleus of the mother cell migrates in the apical direction but does not divide (0-300 min), turns around and pauses (300-430 min), the cell divides in the basal region of the VZ (470-500 min) with an initial position of the daughter cell nuclei parallel to the ventricular surface (490 min), and the daughter cell nuclei migrate as a couple basally toward the neuronal layers (500-620 min), with one of them entering it before the end of the time-lapse (arrow, 620 min).