Elevated synaptic vesicle fusion with impaired activity-dependent neurotransmission in a genomic ferlinopathy model

Ferlins are a family of Ca2+/phospholipid-binding C2 domain transmembrane proteins (e.g. Myoferlin, Dysferlin, Otoferlin) mutated in multiple heritable human disease conditions. The unifying function of all Ferlins is Ca2+-dependent vesicle fusion, with roles in muscle formation, membrane repair, and neurotransmission.

Drosophila has one well-conserved Ferlin, misfire (mfr), which provides the opportunity to test global Ferlin function via single gene manipulation. We find misfire null mutants form and maintain normal muscles with elevated muscle function. Consistently, we find misfire expressed in motor neurons with loss-of-function elevating synaptic vesicle fusion.

Basal neurotransmission is normal at the glutamatergic neuromuscular junction (NMJ) model synapse, but misfire null mutants exhibit progressive synaptic depression with accumulating failures during high-frequency stimulation. We discover that experience-dependent neurotransmission potentiation from chronic neuronal activity elevation is eliminated in the absence of misfire function. These findings suggest neuronal presynaptic vesicle regulation may be the ancestral Ferlin role, similar to Otoferlin function in humans and mouse disease models.

Taken together, these results show that misfire modulates synaptic vesicle fusion during neurotransmission and mediates activity-dependent changes in both signaling fidelity and synaptic strength. We are grateful to the Bloomington Drosophila Stock Center (BDSC; Indiana University, Bloomington, IN, USA) for essential genetic stocks, and to the Developmental Studies Hybridoma Bank (DSHB; University of Iowa, Iowa City, IA, USA) for essential antibodies. The misfire mutants were a kind gift from Dr.

Barbara Wakimoto (Department of Biology and Center for Developmental Biology, University of Washington, Seattle, WA, USA). We finally wish to thank Broadie Lab members for much insightful input on this study. This work was supported by National Institute of Health grant R01NS131557 to K.B.

Imaging was performed in part through the use of the Vanderbilt Cell Imaging Shared Resource (supported by NIH grants CA68485, DK58404, and EY08126). Medical Scientist Training Program, Vanderbilt University and Medical Center, Nashville, TN, 37235-1634, USA Vanderbilt Brain Institute, Vanderbilt University and Medical Center, Nashville, TN, 37235-1634, USA Ericka J. Randazzo, Emma Rushton & Kendal Broadie Departments of Biological Sciences, Cell and Developmental Biology, and Pharmacology, Vanderbilt University and Medical Center, Nashville, TN, 37235-1634, USA Kennedy Center for Research On Human Development, Vanderbilt University and Medical Center, Nashville, TN, 37235-1634, USA The authors declare no competing interests.