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Abstract #3408 Published in IGR 4-2
Molecular profiling and cellular localization of connexin isoforms in the rat ciliary epithelium
Coffey KL; Krushinsky A; Green CR; Donaldson PJExperimental Eye Research 2002; 75: 9-21
The functionally distinct epithelial layers of the ciliary body act as a syncytium to produce the aqueous humor. Ultrastructural studies have shown that the pigmented (PE) and non-pigmented (NPE) cell layers of the ciliary epithelium are connected by gap junctions. However, the molecular composition of gap junctions both between and within the two cell layers has not been comprehensively studied. To address this issue, the authors performed an extensive molecular screening of connexin (Cx) expression patterns in ciliary epithelium of the rat. Initially, mRNA was extracted from rat ciliary bodies, reverse-transcribed, and subjected to two rounds of PCR using primer sets designed against each of the 14 Cx isoforms known to be expressed in the rat. This initial screening protocol amplified eight candidate Cx isoforms (Cxs 26, 31, 33, 37, 40, 43, 45 and 46). The Cx isoforms identified in this initial screen were then first assigned to the ciliary epithelium itself (Cxs 26, 31, 40 and 43) or structures outside the epithelium (Cxs 37, 40, and 45) using immunohistochemistry performed on ciliary body whole mounts. No convincing evidence for either Cx 33 or 46 labelling was found in the ciliary body. Then the four Cx isoforms localized to the epithelium were further localized to specific membrane domains within the epithelial cell layers by performing high resolution imaging of the antibody labelling patterns obtained in cryosections. This enabled Cx26 and 31 to be specifically localized to spatially different gap junctions between NPE cells. Cx31 labelled gap junctions associated with an extensive network of membrane interdigitations found between NPE cells at their basal surfaces. In contrast Cx26 labelling in NPE cells was restricted to the basolateral membranes of adjacent NPE cells. Cx40 and Cx43 were both localized to the PE-NPE interface where they formed discrete homomeric/homotypic gap junction plaques. No convincing evidence was found for antibody labelling between PE cells. Thus, it appears that intercellular communication, both within the NPE layer and between the PE and NPE cell layers, is mediated by gap junction channels that have distinctive permeability properties. In particular the results raise the possibility that the permeability of PE-NPE gap junctions can be modulated by changing the Cx43 : Cx40 expression ratio. Whether such a change in Cx expression ratios occurs and what effect it has on aqueous humor production and composition remains to be determined.
Dr. K.L. Coffey, Disciplines of Physiology, School of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
Classification:
2.9 Ciliary body (Part of: 2 Anatomical structures in glaucoma)
5 Experimental glaucoma; animal models
