GTPase tethering membranes through formation of trans-homooligomers and mediating homotypic fusion of endoplasmic reticulum membranes. Functions in endoplasmic reticulum tubular network biogenesis. May also regulate microtubule polymerization and Golgi biogenesis. Required for dopaminergic neurons survival and the growth of muscles and synapses at neuromuscular junctions. Homooligomer; trans-homooligomer between proteins on adjacent membranes. Interacts with spas; interaction may regulate microtubule dynamics. Colocalizes with microtubules (PubMed:19341724). Ubiquitously expressed. Expression levels are high during embryonic development. Expressed within neuropil regions of the brain and ventral nerve cord in larval CNS and larval body-wall muscles (at protein level). The gene is essential with only a few escapers. Flies display a short life span and are sensitive to mechanical shocks. Following bumping they undergo muscle spasm, followed by paralysis, delayed spasm and finally recovery. The sensitivity to shocks increases with age. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.