Nuclear crowding and nonlinear diffusion during interkinetic nuclear migration in the zebrafish retina

Abstract

An important question in early neural development is the origin of stochastic nuclear movement between apical and basal surfaces of neuroepithelia during interkinetic nuclear migration. Tracking of nuclear subpopulations has shown evidence of diffusion - mean squared displacements growing linearly in time - and suggested crowding from cell division at the apical surface drives basalward motion. Yet, this hypothesis has not yet been tested, and the forces involved not quantified. We employ long-term, rapid light-sheet and two-photon imaging of early zebrafish retinogenesis to track entire populations of nuclei within the tissue. The time-varying concentration profiles show clear evidence of crowding as nuclei reach close-packing and are quantitatively described by a nonlinear diffusion model. Considerations of nuclear motion constrained inside the enveloping cell membrane show that concentration-dependent stochastic forces inside cells, compatible in magnitude to those found in cytoskeletal transport, can explain the observed magnitude of the diffusion constant.

Fish primary embryonic pluripotent cells assemble into retinal tissue mirroring in vivo early eye development

“…This behavior changed at about 34 hpa, when GFP-positive cells showed directed migration – non-linear growth of mean squared displacement – with an estimated speed of 0.413–0.479 μm/min resulting in the morphogenesis of the OV-like structures by 40 hpa ( Figure 5a,b ; Video 5 ). A similar transition from linear to nonlinear diffusion, due to increasing density of nuclear packing, was recently demonstrated in vivo in the growing retina of 24 hpf zebrafish ( Azizi et al, 2020 ). Directionality analysis of single cell tracks ( Figure 5c ) showed that 51% of the Rx3 -expressing cells were moving from the center to the periphery (outward) of the organoid and contributed to the formation of the OV (see dark blue, red, orange, and yellow tracks in Figure 5a ).…”

Fish primary embryonic stem cells self-assemble into retinal tissue mirroringin vivoearly eye development

“…This behavior changed at about 34 hpa, when GFP-positive cells showed directed migrationnon-linear growth of mean squared displacementwith an estimated speed of 0.413-0.479 m/min resulting in the morphogenesis of the optic vesicle-like structures by 40hpa(Figure 4g, h; Video 4). A similar transition from linear to nonlinear diffusion, due to increasing density of nuclear packing, was recently demonstrated in vivo in the growing retina of 24 hpf zebrafish(Azizi et al, 2020). Directionality analysis of single cell tracks(Figure 4i)…”

Cephalopod Retinal Development Shows Vertebrate-like Mechanisms of Neurogenesis

“…It may also be that the physics and dynamics of pseudostratified epithelia is better at accommodating increased proliferation or provides an organizational scaffold for the differentiating network of neurons. It will be interesting to apply new fluid dynamics approaches used to study vertebrate neurogenesis to the cell biology of this similar tissue (Azizi et al, 2020) . Ultimately, the evidence we have generated in cephalopods suggest that vertebrate-like cell behaviors during neurogenesis is not exclusive to the deuterostome lineage, and with greater sampling we may better understand the evolutionary changes that contribute to the diversity and complexity we see.…”