Timely neurogenesis enables increased nuclear packing order during neuronal lamination

Abstract

The coordination of cell proliferation, migration, and differentiation is crucial for organogenesis in many tissues, including the central nervous system and other organs that arise from pseudostratified epithelia (PSE). PSE feature densely packed elongated epithelial cells, with nuclei positioned along the apicobasal cell axis in a cell cycle-dependent manner. Also, PSE serve as organ precursors in diverse developmental contexts across evolution. While the role of nuclear movements in PSE has been extensively studied, less is known about whether and how their nuclear packing arrangements and changes of packing state influence tissue morphogenesis. To address this, we analyzed nuclear shapes, sizes and neighborhood statistics by segmenting nuclei in 3D and over development in zebrafish retinal neuroepithelia (RNE). We find that in PSE nuclei exhibit orientational, nematic-like order but remain positionally disordered. This pattern is conserved in other, less packed, neuroepithelia, like the hindbrain, suggesting that nematic-like order is a hallmark of pseudostratification. Our analysis during retinal development also revealed that nuclear packing density increases, approaching theoretical packing limits for disordered monodisperse ellipsoids at stages when the tissue transitions to a laminated neuronal structure. As neurogenesis progresses, nuclear shapes are remodeled, enabling the RNE to shift to a crystalline, ordered structure, while maintaining orientational alignment. Failure to initiate neurogenesis results in severe tissue deformations due to increased buckling instability. Our results thus show an instance where nuclear shape and nuclear positioning and their changes are essential for proper retinal morphogenesis, a phenomenon most likely also found in other tissue arrangements.