Tissue shape and the force generation mechanisms of apical nuclear migration are likely linked by the distinct actomyosin distribution in straight and basally constricted tissues. (A) Retinal tissue morphology in control and laminin α-1 morphant (laminin α-1 Mo) embryos, injected with different amounts of morpholino. (B) Representative time series of retinal cell morphology and actin distribution during apical migration in laminin α-1 morphant embryos, injected with different amounts of morpholino (shown is the maximum projection of all z planes in the 3D stack; Video 10). mKate2-PCNA labels nuclei (gray), and GFP-UtrophinCH labels actin (lookup table indicates minimal and maximal GFP-UtrophinCH signal values). Scale bars: 10 µm (A), 5 µm (B). (C) Schematic summary of suggested links between tissue shape and mechanisms of apical nuclear migration. Straight and basally constricted tissues show different distributions of actomyosin. In straight tissues, actomyosin is evenly distributed along the lateral sides of cells. An enrichment of actomyosin is observed basolaterally in basally constricted tissues. A basal actomyosin network that pushes the nucleus to the apical side could thus only be formed in cells of basally constricted but not straight tissues.