Essential for tracheal development in embryos. Functions with the GTPase Rab39 and downstream of dnd, to regulate lumen fusion between previously separate tracheal branches (anastomosis). Essential component of secretory lysosome-related organelles (SLs) that are present in the tracheal fusion tip cells (FCs). Mediates intracellular fusion of the extending tracheal stalk cell lumen in the FCs by recruiting the SNARE complex component Syx1A to the SLs, this may then enable the SLs to interact with complementary SNAREs (such as Syb) present in the apical membrane of the FC-FC interface and the membranes of the separate tracheal stalk cells. May also function in the maturation and exocytosis of the SLs. Interacts with Cam. Expressed throughout the cytoplasm of embryonic tracheal cells, except in the tracheal fusion cells (FCs) where it localizes to discrete intracellular vesicles. These vesicles also accumulate Rab39 and display late-endosomal, lysosomal, and SNARE components (Syx1A), characteristics of lysosome-related organelles. Prior to contact between FCs the vesicles localize to the presumed fusion point and sometimes to the filopodia. On contact between FCs, the lysosomes accumulate and move along the cytoskeleton track in a dynein-dependent manner between the two apical domains, becoming densely packed around the interface between the fusion cells. Some of the puncta remain associated with the primary apical FC membrane. In stage 16-17 embryos, expressed in the epidermis, tracheal system, Malpighian tubules, boundary cells of the hindgut, muscles and dorsal vessel. Expressed in large puncta in the hemocytes. Expressed in the fusion cells of the tracheal branch tips (PubMed:27323327). Detected first in early pupae and has very high levels of expression in the adult head (PubMed:9813038). 'Staccato' means detached in Italian, referring to the unclosed gaps in the tracheal lumen of mutants. Belongs to the unc-13 family. Extended N-terminus.