Transient neurites of retinal horizontal cells exhibit columnar tiling via homotypic interactions

Sensory neurons with common function are often non-randomly arranged and form dendritic territories that exhibit little overlap or tiling. Repulsive homotypic interactions underlie such patterns in cell organization in invertebrate neurons. In mammalian retinal horizontal cells, however, it is unclear how dendro-dendritic repulsive interactions can produce a non-random distribution of cells and their spatial territories because mature horizontal cell dendrites overlap substantially. By imaging developing mouse horizontal cells, we found that upon reaching their final laminar positions, these cells transiently elaborate vertical neurites that form non-overlapping columnar territories. Targeted cell ablation revealed that the vertical neurites engage in homotypic interactions resulting in tiling of neighboring cells prior to establishment of their dendritic fields. This developmental tiling of transient neurites correlates with the emergence of a non-random distribution of the cells, and could represent a mechanism that organizes neighbor relationships and territories of neurons of the same type before circuit assembly.