FREQUENIN - A NOVEL CALCIUM-BINDING PROTEIN THAT MODULATES SYNAPTIC EFFICACY IN THE DROSOPHILA NERVOUS-SYSTEM

The T(X;Y)V7 rearrangement in Drosophila has originally been recognize d as a Shaker-like mutant because of its behavioral and electrophysiol ogical phenotype. The gene whose expression is altered by the V7 rearr angement has been characterized. It encodes a novel Ca2+-binding prote in named frequenin, which is related to recoverin and visinin. In vitr o, the frequenin protein functions like recoverin as a Ca2+-sensitive guanylyl cyclase activator. Anti-frequenin antibodies stain the centra l and peripheral nervous system in Drosophila embryos and in larval an d adult tissue sections. Frequenin appears to be particularly enriched in synapses, such as the motor nerve endings at neuromuscular junctio ns. Neuromuscular junctions of transgenic flies, which overexpress fre quenin upon heat shock, exhibit an extraordinarily enhanced, frequency -dependent facilitation of neurotransmitter release, with properties i dentical to those observed in V7 junctions. We propose that frequenin represents a new element for the Ca2+-dependent modulation of synaptic efficacy.