The zebrafish guanylate cyclase type 3 (zGC3) is specifically expressed in cone cells. A specifc antibody directed against zGC3 revealed expression at the protein level at 3.5 dpf in outer and inner retinal layers, which increased in intensity between 3.5 and 7 dpf. This expression pattern differed from sections of the adult retina showing strong immunostaining in outer segments of double cones and short single cones, less intense immunoreactivity in long single cones, but no staining in the inner retina. Although transcription and protein expression levels of zGC3 are similar to that of the cyclase regulator guanylate cyclase-activating protein 3 (zGCAP3), we surprisingly found that zGCAP3 is present in a 28-fold molar excess over zGC3 in zebrafish retinae. Further, zGCAP3 was an efficient regulator of guanylate cyclases activity in native zebrafish retinal membrane preparations. Therefore, we investigated the physiological function of zGCAP3 by two different behavioral assays. Using the morpholino antisense technique, we knocked down expression of zGCAP3 and recorded the optokinetic and optomotor responses of morphants, control morphants, and wild type fish at 5–6 dpf. No significant differences in behavioral responses among wild type, morphants and control morphants were found, indicating that a loss of zGCAP3 has no consequences in primary visual processing in the larval retina despite its prominent expression pattern. Its physiological function is therefore compensated by other zGCAP isoforms.
R？tscho N, Scholten A, Koch KW (2009) Expression profiles of three novel sensory guanylate cyclases and guanylate cyclase-activating proteins in the zebrafish retina. Biochim Biopyhs Acta 1793: 1110–1114.
Rinner O, Makhankov YV, Biehlmaier O, Neuhauss SCF (2005) Knockdown of cone-specific kinase GRK7 in larval zebrafish leads to impaired cone response recovery and delayed dark adaptation. Neuron 47: 231–42.
Vogalis F, Shiraki T, Kojima D, Wada Y, Nishiwaki Y, Jarvinen JLP, Sugiyama J, Kawakami K, Masai I, Kawamura S, Fukada Y, Lamb TD (2011) Ectopic expression of cone-specific G-protein-coupled receptor kinase GRK7 in zebrafish rods leads to lower photosensitivity and altered responses. J. Physiol. 589: 2321–2348.
Imanishi Y, Yang L, Sokal I, Filipek S, Palczewski K, Baehr W (2004) Diversity of guanylate cyclase-activating proteins (GCAPS) in teleost fish: characterization of three novel GCAPs (GCAP4, GCAP5, GCAP7) from zebrafish (Danio rerio) and prediction of eight GCAPs (GCAP1-8) in pufferfish (Fugu rubripes). J Mol Evol 59: 2204–217.
Kretschmer F, Hein A, Kretzberg J (2011) Virtual experimental arena for behavioral experiments on small vertebrates. IEEE Proceedings of the 4th International Congress on Image and Signal Processing (CISP) vol 1: 441–445.
Brockerhoff SE, Rieke F, Matthews HR, Taylor MR, Kennedy B, Ankoudinova I, Niemi GA, Tucker CL, Xiao M, Cilluffo MC, Fain GL, Hurley JB (2003) Light stimulates a transducin-independent increase of cytoplasmic Ca2+ and suppression of current in cones from the zebrafish mutant nof. J Neurosci 23: 470–480.