Figure 4.

Segregation of progenitor cells and neurons in the MGE OSVZ. (a) Pronounced type I clustering in PCW13 horizontal section. Magnified images of boxed area show streaks of progenitor cells that extended from ISVZ into OSVZ and were devoid of nuclei at their core (DAPI⁻). C, caudal; R, rostral. (b) Dense bundles of radial glial fibers formed the core of type I MGE progenitor cell clusters. SOX2⁺ progenitors clustered around apparent fascicles of nestin⁺ fibers. The structure of the neurovasculature (marked by collagen IV) was unrelated, although points of intersection were observed. (c) Type II clustering of progenitor cells in PCW14 frontal sections. Left, superior ganglionic eminences from a relatively caudal location; boxed OSVZ area is magnified in panel 1. Progenitors (SOX2⁺, ASCL1⁺) and non-progenitor cells (NKX2-1 only) segregated into broad, elongated streaks in the MGE OSVZ, oriented toward the LGE. Nestin signal was diffusely distributed throughout type II progenitor clusters (panel 2 from an adjacent section). (d) Type II clusters may be formed as neurons coalesce into migratory streams out of the MGE. Cells in the SOX2⁻ clusters expressed DCX, a marker of migrating neurons.