Connexin36 localization to pinealocytes in the pineal gland of mouse and rat

Abstract

Several cell types in the pineal gland are known to establish intercellular gap junctions, but the connexin constituents of those junctions have not been fully characterized. Specifically, the expression of connexin36 (Cx36) protein and mRNA has been examined in the pineal, but the identity of cells that produce Cx36 and that form Cx36-containing gap junctions has not been determined. We used immunofluorescence and freeze fracture replica immunogold labelling (FRIL) of Cx36 to investigate the cellular and subcellular localization of Cx36 in the pineal gland of adult mouse and rat. Immunofluorescence labelling of Cx36 was visualized exclusively as puncta or short immunopositive strands that were distributed throughout the pineal, and which were absent in pineal sections from Cx36 null mice. By double immunofluorescence labelling, Cx36 was localized to tryptophan hydroxylase-positive and 5-hydroxytryptamine-positive pinealocyte cell bodies and their large initial processes, including at intersections of those processes and at sites displaying a confluence of processes. Labelling for the cell junction marker zonula occludens-1 (ZO-1) either overlapped or was closely associated with labelling for Cx36. Pinealocytes thus form Cx36-containing gap junctions that also incorporate the scaffolding protein ZO-1. FRIL revealed labelling of Cx36 at ultrastructurally-defined gap junctions between pinealocytes, most of which was at gap junctions having reticular, ribbon or string configurations. The results suggest that the endocrine functions of pinealocytes and their secretion of melatonin is supported by their intercellular communication via Cx36-containing gap junctions, which may now be tested by the use of Cx36 null mice.

Gap junctions coordinate the propagation of glycogenolysis induced by norepinephrine in the pineal gland

“…Various studies have demonstrated the presence of GJs between pinealocytes (Wolfe 1965;Taugner et al 1981;Saez et al 1991), between astrocytes (Saez et al 1991;Berthoud and Saez 1993) and between pinealocytes and astrocytes (Cieciura and Krakowski 1991). In the rat pineal gland, Cx43 and Cx26 have been identified in GJs formed between astrocytes and pinealocytes, respectively (Saez et al 1991), but also Cx36 has been identified in pinealocytes (Belluardo et al 2000;Wang et al 2017). Nonetheless, the metabolic role of the functional coupling between pinealocytes and astrocytes have not been reported.…”