Cortical pRLC modulation during mitotic progression. Medial single-section confocal images of first cell cycle S. purpuratus zygotes. All cells were identically fixed and stained with Sytox green to reveal nuclei (green) and an antibody to serine19 pRLC (lavender). Identical microscope settings were used throughout for pRLC, but laser intensity was adjusted for Sytox green to make different nuclear condensation states discernable. Lavender arrowheads indicate the polar cortex of the nascent daughter cells, where pRLC reaccumulates before abscission. The white arrowhead indicates pRLC-depleted surface flanking the pRLC-enriched furrow. Bar, 25 μm.