Abstract
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.
Highlights
Visual excitation and adaptation in vertebrate cone cells is much less understood than in rod cells [1]
This expression pattern became more differentiated in the adult retina, where a strong staining was observed in the outer segments of double cones (DC) and short single cones (SSC) (Figure 3A and B)
We expected to find similar equal molar ratios of zebrafish guanylate cyclase type 3 (zGC3) to zGCAP3, since the intensity of photoreceptor staining by the anti-zGC3 antibody is comparable to our recent results we described for the immunolocalization of zGCAP3 in the adult zebrafish retina [9]
Summary
Visual excitation and adaptation in vertebrate cone cells is much less understood than in rod cells [1]. Allow discrimination of colors and are further able to maintain their responsiveness over 6–7 orders of magnitude of background light intensities. These remarkable performances require an efficient array of signaling molecules at the subcellular level. In recent years zebrafish has become a favorite model organism for the study of cone phototransduction [2]. The zebrafish retina is equipped with one type of rod cell and four types of cone cells: short single (UV-sensitive) cones, long single cones (blue-sensitive) and double cones (green- and red-sensitive). Light responses of double cones and UV-sensitive cones were measured by suctionpipette recording in response to illumination [3,4]
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