Terminates signal transduction at the neuromuscular junction by rapid hydrolysis of the acetylcholine released into the synaptic cleft. acetylcholine + H2O = acetate + choline + H(+) Dimers and collagen-tailed forms, in which catalytic tetramers are associated with anchoring proteins that attach them to the basal lamina or to cell membranes. In the collagen-tailed forms, subunits are associated with a specific collagen, COLQ, which triggers the formation of isoform T tetramers from dimers. First detected in the trunk, in discrete regions of paraxial mesodermal segmental plate at 12 h of devel-opment (6-somite stage). In older embryos a weak diffused staining is found, even in unsegmented presomitic mesoderm. Expression, probably located in myoblasts, proceeds in a rostro-caudal sequence according to the state of differentiation of the somites. Initial narrow staining progressively enlarged in the differentiating somite. At all stages, the ventral part of anterior somites showed more intense staining than the dorsal part. In the posterior brain expression and activity appear after 14 h. At 24h, detected in all primary neurons in the brain. Expression in cranial ganglia can be detected in whole embryo until about 36h. Expressed also in a sensory system in anterior and posteriorlateral line ganglia as seen in the embryo at 24h. In addition the heart shows strong expression from its early morphogenesis. No other isoforms exist. This protein corresponds to the T isoform in other species. Belongs to the type-B carboxylesterase/lipase family.