title: Localization of Cacna1s to ON bipolar dendritic tips requires mGluR6-related cascade elements.
abstract: OBJECTIVE
  L-type voltage gated calcium channels in retina localize primarily at the presynaptic active zones of photoreceptors and bipolar cells where they modulate glutamate release. However, the pore forming subunit Cacna1s of certain L-type channels is also expressed postsynaptically at the tips of ON bipolar cell dendrites where it colocalizes with mGluR6, but has an unknown function. At these dendritic tips, the components of the mGluR6 signaling cascade cluster together in a macromolecular complex, and each one's localization often depends on that of the others. Thus, we explored if Cacna1s is part of the mGluR6 complex.
  
  
  METHODS
  We determined Cacna1s expression by PCR using an ON bipolar library, by Western blotting, and by standard immunohistochemistry.
  
  
  RESULTS
  The PCR amplification confirmed expression of the transcript in ON bipolar cells, and Western blotting showed the expected bands. Immunostaining for Cacna1s was stronger in the dendritic tips of rod bipolar cells than in those of ON cone bipolar cells. This staining severely decreased in mice missing various mGluR6 cascade elements (Grm6(-/-), Gnao1(-/-), Gnb3(-/-), Gng13(-/-), and Trpm1(-/-)). During development, the ratio of the number of Cacna1s puncta to the number of presynaptic ribbons followed a sigmoidal pattern, rising rapidly from P13 to P17. The mGluR6 expression preceded that of Cacna1s and RGS11.
  
  
  CONCLUSIONS
  Our results show that the localization and stability of Cacna1s depend on the expression of mGluR6 and its cascade components, and they suggest that Cacna1s is part of the mGluR6 complex. We hypothesize that Cacna1s contributes to light adaptation by permeating calcium.
authors: Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Shanti R
authors: SR
authors: Tummala
authors: Adam
authors: A
authors: Neinstein
authors: Marie E
authors: ME
authors: Fina
authors: Anuradha
authors: A
authors: Dhingra
authors: Noga
authors: N
authors: Vardi
mesh_terms: D000818:Animals; D015153:Blotting, Western; D015220:Calcium Channels / Q000096:biosynthesis / Q000235:genetics*; D020746:Calcium Channels, L-Type; D004247:DNA / Q000235:genetics*; D003712:Dendrites / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000096:biosynthesis / Q000235:genetics*; D051245:Retinal Bipolar Cells / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: C529218:CACNA1S protein, mouse; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D018094:Receptors, Metabotropic Glutamate; C113897:metabotropic glutamate receptor 6; D004247:DNA
keywords: adaptation; mGluR6; retina; rod bipolar cell; signaling cascade