The correct establishment of either an axon or a dendrite is crucial for the normal wiring of a functional nervous system. As previously shown, the SAD serine-threonine kinases are required for such neuronal polarisation and also for the clustering of synaptic vesicles at neuromuscular junctions. Mei Zhen and colleagues now shed further light on how SAD functions in neuronal polarisation (see ). From a yeast two-hybrid screen in C. elegans,performed to isolate mediators of SAD-1 function, the authors identified Neurabin (NAB-1) and show that it physically interacts with SAD-1 in vivo and in vitro. Double sad-1 nab-1 mutants, they report, have polarity defects, in which synaptic vesicles cluster in both axons and dendrites. However, only nab-1 mutants have normal vesicle cluster morphology. The authors propose that NAB-1 acts as a scaffold for SAD-1, interacting with SAD-1 via PDZ domains. Mammalian neurabins are required for dendrite spine maturation, but whether they also have an earlier role in axon determination,as in C. elegans, remains to be determined.
