synaptotagmin Mutants Reveal Essential Functions for the C2B Domain in Ca2+-Triggered Fusion and Recycling of Synaptic Vesicles In Vivo

J. Troy Littleton; Jihong Bai; Bimal Vyas; Radhika Desai; Andrew E. Baltus; Martin B. Garment; Stanley D. Carlson; Barry Ganetzky; Edwin R. Chapman

doi:10.1523/JNEUROSCI.21-05-01421.2001

Fig. 5.

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Ultrastructural analysis of stimulated synapses in C2B mutants. Ultrastructural defects in control cn(A), AD3 cn/T11 cn(B), and AD1 cn/T41 cn(C) photoreceptor synapses were examined by driving photoreceptors with constant light stimulation for 10 min, followed by rapid fixation. Both AD1 andAD3 mutants lack the on–off transients measured during ERG recordings in the retina (shown on the right), demonstrating that synaptic transmission is disrupted at these photoreceptor synapses. AD1 mutants show a decrease in the overall number of synaptic vesicles, whereas AD3synapses do not show a depletion of synaptic vesicles, but rather a defect in the ability of docked synaptic vesicles to fuse. Quantification of vesicles per photoreceptor synapse for each of the genotypes was: AD1 cn/T41 cn, 25 ± 14 SD;AD1 cn/T7 cn, 27 ± 20 SD; AD3 cn/T11 cn, 88 ± 28 SD; cn controls, 96 ± 37 SD. Quantification of vesicles per T-bar for each of the genotypes was:AD1 cn/T41 cn, 1.4 ± 0.9 SD; AD1 cn/T7 cn, 1.9 ± 0.9 SD; AD3 cn/T11 cn, 2.6 ± 1.4 SD; cn controls, 2.3 ± 0.9 SD.