Lateral cell movement driven by dendritic interactions is sufficient to form retinal mosaics

The formation of retinal mosaics is thought to involve lateral movement of retinal cells from their clonal column of origin. The forces underlying this lateral cell movement are currently unknown. We have used a model of neurite outgrowth combined with cell movement to investigate the hypothesis that lateral cell movement is guided by dendritic interactions. We have assumed that cells repel each other in proportion to the degree of dendritic overlap between neighbouring cells. Our results first show that small cell movements are sufficient to transform random cell distributions into regular mosaics, and that all cells within the population move. When dendritic fields are allowed to grow, the model produces regular mosaics across all cell densities tested. We also find that the model can produce constant coverage of visual space over varying cell densities. However, if dendritic field sizes are fixed, mosaic regularity is proportional to the cell density and dendritic field size. Our model suggests that dendritic mechanisms may therefore provide sufficient information for rearrangement of cells into regular mosaics. We conclude by mentioning possible future experiments that might suggest whether dendritic interactions are adaptive or fixed during mosaic formation.