The structural organization and protein composition of lens fiber junctions.
Open Access
- 1 June 1989
- journal article
- research article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 108 (6), 2255-2275
- https://doi.org/10.1083/jcb.108.6.2255
Abstract
The structural organization and protein composition of lens fiber junctions isolated from adult bovine and calf lenses were studied using combined electron microscopy, immunolocalization with monoclonal and polyclonal anti-MIP and anti-MP70 (two putative gap junction-forming proteins), and freeze-fracture and label-fracture methods. The major intrinsic protein of lens plasma membranes (MIP) was localized in single membranes and in an extensive network of junctions having flat and undulating surface topologies. In wavy junctions, polyclonal and monoclonal anti-MIPs labeled only the cytoplasmic surface of the convex membrane of the junction. Label-fracture experiments demonstrated that the convex membrane contained MIP arranged in tetragonal arrays 6-7 nm in unit cell dimension. The apposing concave membrane of the junction displayed fracture faces without intramembrane particles or pits. Therefore, wavy junctions are asymmetric structures composed of MIP crystals abutted against particle-free membranes. In thin junctions, anti-MIP labeled the cytoplasmic surfaces of both apposing membranes with varying degrees of asymmetry. In thin junctions, MIP was found organized in both small clusters and single membranes. These small clusters also abut against particle-free apposing membranes, probably in a staggered or checkerboard pattern. Thus, the structure of thin and wavy junctions differed only in the extent of crystallization of MIP, a property that can explain why this protein can produce two different antibody-labeling patterns. A conclusion of this study is that wavy and thin junctions do not contain coaxially aligned channels, and, in these junctions, MIP is unlikely to form gap junction-like channels. We suggest MIP may behave as an intercellular adhesion protein which can also act as a volume-regulating channel to collapse the lens extracellular space. Junctions constructed of MP70 have a wider overall thickness (18-20 nm) and are abundant in the cortical regions of the lens. A monoclonal antibody raised against this protein labeled these thicker junctions on the cytoplasmic surfaces of both apposing membranes. Thick junctions also contained isolated clusters of MIP inside the plaques of MP70. The role of thick junctions in lens physiology remains to be determined.This publication has 59 references indexed in Scilit:
- Connexin43: a protein from rat heart homologous to a gap junction protein from liver.The Journal of cell biology, 1987
- PROTEIN PROCESSING IN LENS INTERCELLULAR-JUNCTIONS - CLEAVAGE OF MP70 TO MP381987
- Immunolocalization of MP70 in lens fiber 16-17-nm intercellular junctions.The Journal of cell biology, 1987
- Gap junction structures after experimental alteration of junctional channel conductance.The Journal of cell biology, 1985
- Square arrays and their role in ridge formation in human lens fibersJournal of Ultrastructure Research, 1984
- Comparative analysis of the major polypeptides from liver gap junctions and lens fiber junctions.The Journal of cell biology, 1982
- The lens as a nonuniform spherical syncytiumBiophysical Journal, 1981
- Lens metabolic cooperation: a study of mouse lens transport and permeability visualized with freeze-substitution autoradiography and electron microscopy.The Journal of cell biology, 1980
- LENS GAP-JUNCTIONS - STRUCTURAL HYPOTHESIS FOR NON-REGULATED LOW-RESISTANCE INTER-CELLULAR PATHWAYS1979
- The maturation of the lens cell: a morphologic studyExperimental Eye Research, 1975