title: Synaptotagmin I regulates patterned spontaneous activity in the developing rat retina via calcium binding to the C2AB domains.
abstract: BACKGROUND
  In neonatal binocular animals, the developing retina displays patterned spontaneous activity termed retinal waves, which are initiated by a single class of interneurons (starburst amacrine cells, SACs) that release neurotransmitters. Although SACs are shown to regulate wave dynamics, little is known regarding how altering the proteins involved in neurotransmitter release may affect wave dynamics. Synaptotagmin (Syt) family harbors two Ca(2+)-binding domains (C2A and C2B) which serve as Ca(2+) sensors in neurotransmitter release. However, it remains unclear whether SACs express any specific Syt isoform mediating retinal waves. Moreover, it is unknown how Ca(2+) binding to C2A and C2B of Syt affects wave dynamics. Here, we investigated the expression of Syt I in the neonatal rat retina and examined the roles of C2A and C2B in regulating wave dynamics.
  
  
  RESULTS
  Immunostaining and confocal microscopy showed that Syt I was expressed in neonatal rat SACs and cholinergic synapses, consistent with its potential role as a Ca(2+) sensor mediating retinal waves. By combining a horizontal electroporation strategy with the SAC-specific promoter, we specifically expressed Syt I mutants with weakened Ca(2+)-binding ability in C2A or C2B in SACs. Subsequent live Ca(2+) imaging was used to monitor the effects of these molecular perturbations on wave-associated spontaneous Ca(2+) transients. We found that targeted expression of Syt I C2A or C2B mutants in SACs significantly reduced the frequency, duration, and amplitude of wave-associated Ca(2+) transients, suggesting that both C2 domains regulate wave temporal properties. In contrast, these C2 mutants had relatively minor effects on pairwise correlations over distance for wave-associated Ca(2+) transients.
  
  
  CONCLUSIONS
  Through Ca(2+) binding to C2A or C2B, the Ca(2+) sensor Syt I in SACs may regulate patterned spontaneous activity to shape network activity during development. Hence, modulating the releasing machinery in presynaptic neurons (SACs) alters wave dynamics.
authors.affiliation: Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.
authors.forename: Chung-Wei
authors.initials: CW
authors.lastname: Chiang
authors.forename: Yu-Chieh
authors.initials: YC
authors.lastname: Chen
authors.forename: Juu-Chin
authors.initials: JC
authors.lastname: Lu
authors.forename: Yu-Tien
authors.initials: YT
authors.lastname: Hsiao
authors.forename: Che-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Pin-Chien
authors.initials: PC
authors.lastname: Huang
authors.forename: Yu-Tzu
authors.initials: YT
authors.lastname: Chang
authors.forename: Payne Y
authors.initials: PY
authors.lastname: Chang
authors.forename: Chih-Tien
authors.initials: CT
authors.lastname: Wang
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D059329:Cholinergic Neurons / Q000378:metabolism; D005786:Gene Expression Regulation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D051381:Rats; D018091:Receptors, AMPA / Q000235:genetics / Q000378:metabolism; D012160:Retina / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology; D050863:Synaptotagmin I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018091:Receptors, AMPA; D050863:Synaptotagmin I; C104722:glutamate receptor ionotropic, AMPA 2; D002118:Calcium