Localization of the paranodal protein Caspr in the mammalian retina

[摘要] Purpose: The retina has the demandingtask of encoding all aspects of the visual scene within the space ofone fixation period lasting only a few hundred milliseconds. Toaccomplish this feat, information is encoded in specialized parallelchannels and passed on to numerous central nuclei via the optic nerve.These parallel channels achieve specialization in at least three ways:the synaptic networks in which they participate, the neurotransmitterreceptors expressed and the types and locations of ion channels ortransporters used. Subcellular localization of receptors, channels andtransporters is made yet more complex in the retina by the double dutymany retinal processes serve. In the present work, we show that theprotein Caspr (Contactin Associated Protein), best known for itscritical role in the localization of voltage-gated ion channels at thenodes of Ranvier, is present in several types of retinal neuronsincluding amacrine, bipolar, horizontal, and ganglion cells. Methods: Using standard double labelimmunofluorescence protocols, we characterized the pattern of Casprexpression in the rodent retina. Results: Caspr labeling was observedthrough much of the retina, including horizontal, bipolar, amacrine,and ganglion cells. Among amacrine cells, Caspr was observed in AIIamacrine cells through co-localization with Parvalbumin and Disabled-1in rat and mouse retinas, respectively. An additional amacrine celltype containing Calretinin also co-localized with Caspr, but did notco-localize with choline-acetyltransferase. Nearly all cells in theganglion cell layer contain Caspr, including both displaced amacrineand ganglion cells. In the outer retina, Caspr was co-localized withPKC labeling in rod bipolar cell dendrites. In addition, Caspr labelingwas found inside syntaxin-4 'sandwiches' in the outer plexiform layer,most likely indicating its presence in cone bipolar cell dendrites.Finally, Caspr was co-localized in segments of horizontal celldendrites labeled with Calbindin-D28k. Conclusions: Caspr is best known for itsrole in organizing the localization of different voltage-gated ionchannels in and around nodes of Ranvier. As neuronal processes in theretina often play a dual role involving both input and output, it ispossible that the localization of Caspr in the retina will help usdecipher the way retinal cells localize ion channels in their processesto increase computational capacity.

[学科分类] 生物化学/生物物理