Calmodulin and calbindin localization in retina from six vertebrate species

Abstract

Calmodulin is abundant in the central nervous system, including the retina. However, the localization of calmodulin in the retina has not been described in detail. We therefore decided to investigate calmodulin localization in retinae from six vertebrate species, by using immunohistochemical labeling with four different rabbit polyclonal antibodies against calmodulin. The localization of calbindin-D28k, another calcium-binding protein already well described in retina, was compared. We found that calmodulin distribution is more highly conserved among species, contrasting with calbindin variability. The most striking result emerging is that calmodulin could not be detected in photoreceptors although other layers are intensely calmodulin-immunoreactive, casting doubt about a direct role of calmodulin in phototransduction. Horizontal cells are weakly calmodulin-immunoreactive, bipolar cells are calmodulin-immunoreactive except in turtle retina, numerous amacrine and ganglion cells are labeled in all species, and the fiber layer is always labeled. These data demonstrate that, while the calmodulin distribution in retina is similar among vertebrate species, selective differences in localization can be detected not only among the same cell types in different species but also among different cell types in the same species. The results showing differences in calmodulin immunoreactivity among cell types also provide further evidence that calmodulin expression in eukaryotes is not constitutive, in the sense that not every cell expresses similar levels of calmodulin.

Differential Modification of Phosducin Protein in Degenerating rd1 Retina Is Associated with Constitutively Active Ca2+/Calmodulin Kinase II in Rod Outer Segments

“…Pochet et al (45) reported lack of immunoreactivity in mouse photoreceptors, which fits well with the very weak CaM signal in ONL and inner and outer segments in this study. On the other hand, CaM was detected in feline and bovine OS by ultrastructural immunostaining and biochemical methods, respectively (67,68).…”

Localization of Calcineurin in the Mature and Developing Retina

“…Therefore, calcineurin not only binds calcium but is regulated by a most representative Ca ϩϩ -binding protein, CaM. Among the Ca ϩϩ -binding proteins whose presence has been shown by immunohistochemistry in various retinal cells (ganglion and amacrine but, specifically, neither photoreceptor nor Müller cells) are CaM (Seto-Ohshima et al 1987;Pochet et al 1991), calbindin D-28k (Uesugi et al 1992), parvalbumin (Endo et al 1985), calretinin (Bastianelli et al 1995), and neurocalcin (Nakano et al 1992). Another Ca ϩϩ -binding protein, recoverin, is exceptional because it is located mainly in photoreceptor and bipolar cells (Korf et al 1992;Günhan-Agar et al 2000).…”

Calbindin in Cerebellar Purkinje Cells Is a Critical Determinant of the Precision of Motor Coordination

“…Because of the specificity of the generated conditional mutation, the former possibility is unlikely. Specifically, an alteration of the properties of retinal bipolar cells, which are known to express L7/pcp-2 and the Cre transgene used in this study (Barski et al, 2000), can be excluded, because calbindin is not expressed in these cells in mice (Celio, 1990;Pochet et al, 1991). These data show that absence of calbindin from cerebellar Purkinje cells affects eye (as well as limb) coordination and suggest that calbindin in these cells is important for differential regulation of calcium signals involved in processing of visual and vestibular information.…”