Differential immunocytochemical localization of calretinin in the pineal gland of three mammalian species

Abstract

Calcium plays an important role for signal transduction in the mammalian pineal organ. The regulation of the intracellular concentration of free calcium probably involves calcium-binding proteins of the calmodulin superfamily. In the present study, we have investigated the expression of calretinin, one member of this superfamily, in the pineal organ of hamsters, gerbils and guinea-pigs by means of immunochemical and immunocytochemical analyses with a calretinin-specific antiserum. In immunoblots this antibody recognized a single protein band of approximately 29 kDa in the brain and pineal organ of all three mammalian species. Immunocytochemical investigations of serial semithin sections of plastic-embedded pineals revealed the constant occurrence of variable numbers of calretinin-positive cells throughout all glands. In order to identify the immunopositive cells precisely, adjacent sections were exposed to antibodies against various marker proteins of pineal cell types, i.e., synaptophysin, neuron-specific enolase, protein gene product 9.5, S-antigen, vimentin and S-100. By this approach, calretinin could be localized to vimentin-positive cells in the gerbil which are generally considered as interstitial glial cells. Likewise, calretinin-positive cells in the guinea-pig probably correspond to interstitial cells, taking into account their morphology and the lack of calretinin immunoreactivity in pinealocytes. The unusual expression of calretinin in astrocyte-like cells further supports the notion that pineal glial cells are endowed with peculiar properties. In contrast to gerbil and guinea-pig, a subpopulation of pinealocytes displayed calretinin immunoreactivity in the hamster. This finding adds to the hypothesis that in pinealocytes of some species calretinin plays a role in calcium-mediated signal transduction which eventually is linked to melatonin synthesis. Our results demonstrate that calretinin is a regular constituent of pineal glands in three mammalian species, but that its cellular localisation shows interspecific variation. This variation suggests that the protein is involved in diverse calcium-mediated functions in the mammalian pineal gland.

Expression of synaptic vesicle trafficking proteins in the developing rat pineal gland

“…The mesenchymal IF protein vimentin is an established marker of glial-like interstitial cells in the adult pineal organ (Schachner et al 1984;Løpez-Muñoz et al 1992;Redecker et al 1996a). We have now extended the current knowledge of pineal vimentin synthesis and distribution by demonstrating that, in contrast to the adult rat organ, this IF protein is expressed in virtually all pineal cells throughout the fetal stages investigated, and that it only becomes restricted to interstitial cells during the first two postnatal weeks.…”

Rodent pancreatic islet cells contain the calcium-binding proteins calcineurin and calretinin

“…Calretinin has also been detected in interstitial cells of the ovary and testis (Pohl et al 1992;Strauss et al 1994), in cells of the avian thymus (Kiraly and Celio 1993), in glial-like cells and pinealocytes of the pineal gland (Redecker et al 1996), and in a colon adenocarcinoma cell line (Gotzos et al 1992). Its expression in the endocrine pancreas has not yet been reported.…”

“…We used a polyclonal rabbit antibody against calretinin which has been raised against purified recombinant human calretinin and is known to react with tissues of several mammalian and non-mammalian species (Schwaller et al 1993;Weisenhorn et al 1994;Redecker et al 1996). The antiserum is specific for calretinin and does not cross-react with the closely related calbindin-D28k (Schwaller et al 1993).…”

Expression of postsynaptic density proteins of the ProSAP/Shank family in the thymus

“…Electrophoresis and immunoblotting of total tissue lysates was performed essentially as reported previously (Redecker et al 1996;Pabst and Redecker 1999). SDS-PAGE was carried out on 6% vertical mini slab gels (30-50 g protein/lane).…”