Fig. 7

Foxg1 mediates cell cohesion in an Fgf-dependent manner.

(A) Schematic of the overexpression-cell-transplantation-bead-implantation assay to test for an Fgf-dependent effect of foxg1 on cell cohesion by monitoring lateral cell spreading in live embryos. (B–D) Live images of horizontal cell spreading at sphere (0 h postimplantation [p.i.], top), bud (6 h postimplantation, middle), and 15ss (12 h postimplantation, bottom) from a representative clone overexpressing foxg1cherry in the presence of a PBS control bead (B), a clone overexpressing foxg1cherry in the presence of an Fgf8 bead (C), and a clone overexpressing cherry in the presence of an Fgf8 bead (D). Left: memGFP image (confocal z-projection), right: clone outline (green line), derived from memGFP image, superimposed with a bright-field (BF) image, showing bead localization (white circle). Dotted outlines: neural tube border. Insets in lower panels show cell morphology (bright-field image superimposed with a single confocal section of memGFP). Open arrowheads in (B): abnormal cells not included in tracking the clone outline. White arrowheads in (B): autonomous clustering of foxg1-overexpressing cells in the olfactory placode, head mesenchyme, and telencephalon. Scale bar: 50 μm. (E) Quantification of lateral cell spreading relative to the site of bead implantation. The maximal cell distance (d_max, blue) and the minimal distance from the bead surface (d_min, red) was measured (on projected z-stacks) and the median distance (d_med, green) calculated on the basis of d_max and d_min for four representative clones at sphere, bud, and 15ss. Radial plots of average d_max, d_min, and d_med values (in micrometers) at sphere, bud, and 15ss, (n = 4/stage) for foxg1cherry overexpression in the presence of a PBS control bead (top axis), foxg1cherry overexpression in the presence of an Fgf8 bead (right axis), and cherry overexpression in the presence of an Fgf8 bead (left axis). p-Values for 15ss stage derived by a paired, two-tailed t-test. (F) Line plots of single d_max values (in micrometers) over time (sphere, bud, 15ss) for four representative clones overexpressing foxg1cherry in the presence of a PBS control bead (red), overexpressing foxg1cherry in the presence of a Fgf8 bead (blue), and overexpressing cherry in the presence of a Fgf8 bead (green). Brackets indicate d_max value range at 15ss.