Lack of ventricular contact and apical markers in mitotic basal progenitors.

Heterozygous Tis21-nucGFP embryos were analyzed, with or without in utero electroporation of either mRFP or membrane GFP at E12.5 followed by expression for 24 h as indicated. Analysis of mitotic BPs in the dorsal telencephalon was carried out by two-photon video microscopy of slice cultures (membrane GFP) or by confocal microscopy of 20-µm fixed cryosections of intrinsic mRFP fluorescence or double immunofluorescence for MPM-2 and either prominin-1 (Prom1), megalin or ZO-1 as indicated. The latter data are from three littermate embryos, each immunostained for each marker on at least 5 cryosections. Mitotic BPs were scored for the absence (–) or presence (+) of Tis21-nucGFP fluorescence, mRFP–, GFP– or MPM-2–stained apical processes contacting the ventricle or processes extending apically and basally from the cell body, and polarized immunoreactivity of apical markers. Note that any apical and basal extensions from the cell body did not exceed one cell body diameter in length. Asterisks indicate prominin-1 immunoreactivity over the cell body due to extracellular particles known to be present within the neuroepithelium [44], [45]; n.d., not determined.