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 thi s lateral cell movement are currently unknown. We have used a model of neur ite outgrowth combined with cell movement to investigate the hypothesis tha t lateral cell movement is guided by dendritic interactions. We have assume d that cells repel each other in proportion to the degree of dendritic over lap between neighbouring cells. Our results first show that small cell move ments are sufficient to transform random cell distributions into regular mo saics, and that all cells within the population move. When dendritic fields are allowed to grow, the model produces regular mosaics across all cell de nsities tested. We also find that the model can produce constant coverage o f visual space over varying cell densities. However, if dendritic field siz es are fixed, mosaic regularity is proportional to the cell density and den dritic field size. Our model suggests that dendritic mechanisms may therefo re provide sufficient information for rearrangement of cells into regular m osaics. We conclude by mentioning possible future experiments that might su ggest whether dendritic interactions are adaptive or fixed during mosaic fo rmation.