Two Guanylate Cyclase Activating Proteins in Medaka Retina
Hanayo Honkawa, Osamu Hisatomi*, Yoshihiro Kishida and Fumio Tokunaga
Interdisciplinary Information Science in press
Guanylate cyclase activating protein (GCAP1 and 2) is a Ca2+-sensitive regulator of the retinal membrane guanylate cyclases (GCs). In mammalian retina, GCAP1 is localized in cones and GCAP2 is present in rods, cones and other retinal cells. Here we isolated two kinds of cDNAs encoding putative medaka GCAPs (OlGCAP1 and OlGCAP2). Sequence analysis and characterization of recombinant proteins indicate that OlGCAP1 and 2 are closely related to mammalian GCAP1 and 2, respectively, and that OlGCAP1 and 2 appear to regulate GCs in a manner similar to that of mammalian GCAPs. However, in situ hybridization and immunocytochemistry suggest that both OlGCAP1 and 2 coexist mainly in rods, and that OlGCAP1, but not OlGCAP2, is present in the inner nuclear layer and ganglion cell layer, indicating that localization of these medaka GCAPs is totally different from that of mammalian GCAPs. The Ca2+-feedback system in vertebrate retinal phototransduction may be evolved in the expression of GCs and GCAPs in photoreceptors.
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