Figure 1: Topographic organization of dendritic growth patterns.

(a) Schematic summarizing the age-related dorsoventral organization of motoneurons in the spinal cord of zebrafish larvae. The youngest motoneurons are located in ventral spinal cord with older motoneurons occupying progressively more dorsal locations. This organization correlates with a gradient in the recruitment of motoneurons such that the youngest motoneurons are recruited most often, during movements of all speeds, whereas the older, more powerful dorsal motoneurons are recruited less frequently at only high speeds. (b) Images of motoneuron dendrites labelled with mGFP at 2 and 4 dpf. Right panel shows a motoneuron co-expressing PSD-95 (post synaptic density 95) tagged with GFP to mark glutamatergic synapses and a membrane-targeted Cherry (mMCherry) to highlight the dendritic arbour. Arrows point to filopodia-like structures without PSD-95 puncta. (c) Growth of motoneurons between 4 and 6 days. Left panel shows an overlay of the dendritic arbour of an individual motoneuron at 4 (green) and 6 days (red). Middle panel shows the relationship between the dendritic length added between 4 and 6 days and the dorsoventral position of the motoneuron. Right panel shows the dendritic growth between 4 and 6 days as a percentage of the total dendritic length at 4 days. Scale bar, 5 μm in b,c.