Gpc4 is necessary for the formation of long endodermal protrusions. (A and B) Snapshots from confocal time-lapse imaging performed on the indicated embryos (Video 1). White arrowheads, protrusions in the space between endodermal cells; yellow arrowheads, protrusions that link neighboring endodermal cells. (C–E) The total number of protrusions (C), the length of the protrusion (D), and the percentages of protrusions of different lengths (grouped into 3-µm bins; E) in each endodermal cell. The number of embryos, cells, and protrusions analyzed is indicated. Data are mean ± SEM. #, P > 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; unpaired Student's t test.