SAD-1 phosphorylation of SYD-2 at 3 sites controls phase separation and active zone assembly.

(A) HSN synapse formation phenotypes visualized with Airyscan superresolution imaging of endogenous fluorescent tags in the indicated mutants. Scale bars, 5 μm. (B) Quantification of HSN intensities in (A). ****, p n > 20 for each genotype. (D) FRAP of mScarlet-SYD-2 phosphomutants at embryonic nerve ring synapses to measure dynamics. Wild-type SYD-2 is present in dynamic phase-separated condensates, while certain phosphomutants inhibit condensate formation. Scale bars, 5 μm. (E) Quantification of FRAP in (D). Underlying data is available in S1 Data. FRAP, fluorescence recovery after photobleaching; HSN, hermaphrodite-specific neuron.