Rescue of Rod Synapses by Induction of Ca(v) Alpha 1F in the Mature Ca(v)1.4 Knock-Out Mouse Retina

PURPOSE: Ca(v)1.4 is a voltage-gated calcium channel clustered at the presynaptic active zones of photoreceptors. Ca(v)1.4 functions in communication by mediating the Ca(2+) influx that triggers neurotransmitter release. It also aids in development since rod ribbon synapses do not form in Ca(v)1.4 knock-out mice. Here we used a rescue strategy to investigate the ability of Ca(v)1.4 to trigger synaptogenesis in both immature and mature mouse rods. METHODS: In vivo electroporation was used to transiently express Ca(v) α(1F) or tamoxifen-inducible Ca(v) α(1F) in a subset of Ca(v)1.4 knock-out mouse rods. Synaptogenesis was assayed using morphologic markers and a vision-guided water maze. RESULTS: We found that introduction of Ca(v) α(1F) to knock-out terminals rescued synaptic development as indicated by PSD-95 expression and elongated ribbons. When expression of Ca(v) α(1F) was induced in mature animals, we again found restoration of PSD-95 and elongated ribbons. However, the induced expression of Ca(v) α(1F) led to diffuse distribution of Ca(v) α(1F) in the terminal instead of being clustered beneath the ribbon. Approximately a quarter of treated animals passed the water maze test, suggesting the rescue of retinal signaling in these mice. CONCLUSIONS: These data confirm that Ca(v) α(1F) expression is necessary for rod synaptic terminal development and demonstrate that rescue is robust even in adult animals with late stages of synaptic disease. The degree of rod synaptic plasticity seen here should be sufficient to support future vision-restoring treatments such as gene or cell replacement that will require photoreceptor synaptic rewiring.