Lens metabolic cooperation: a study of mouse lens transport and permeability visualized with freeze-substitution autoradiography and electron microscopy.

Abstract

Transport of metabolites is demonstrated between compartments of the adult mouse lens by freeze-substitution autoradiography . In vivo patterns of lysine incorporation are compared with in vitro patterns of lysine, glucose, uridine, and deoxyglucose incorporation . Intracellular and extracellular distributions of tritiated metabolites are determined by comparison of transported substrates with the nontransported molecules of similar molecular size : mannitol and sucrose. The permeability of the lens intercellular spaces is probed with Procion Yellow at the level of fluorescence microscopy, and with horseradish peroxidase at the electron microscope level . Freeze-fracture electron microscopy reveals gap junctions between epithelial cells, between lens fibers, and between epithelial cells and lens fibers . Zonulae occludentes (tight junctions) are not routinely observed between epithelial cells in the mouse. This latter result is subject to species variation, however, since zonulae occludentes are abundant between chicken epithelial cells. The permeability results suggest that the lens cells are capable of metabolic cooperation, mediated by an extensive gap junction network.

Lengsin expression and function during zebrafish lens formation

“…The localization of EGFP in the transgenic lenses indicates the reporter protein diffuses throughout the fiber cell mass. This expression pattern suggests the zebrafish lens possesses syncitial properties similar to that demonstrated for chick and mouse (Kaiser and Maurice, 1964;Goodenough et al, 1980;Goodenough, 1992). Alternatively, the GFP may simply persist in the lens center and increase in concentration over time as fiber cells mature and lose water.…”

Molecular cloning and functional characterization of chick lens fiber connexin 45.6.

“…Posteriorly, the fibers in the center of the lens, because they have neither blood supply nor organelles, are uniquely dependent on communication with cells at the lens surface. Lens fibers have been shown to be joined into a functional syncytium (Duncan, 1969;Eisenberg and Rae, 1976;Rae, 1979;Mathias et al, 1981;Rae, 1985, 1989) mediated by gap junctions between adjacent fibers, which permit ions (Phillipson et al, 1975;Rae, 1979;Rae and Stacey, 1979) and small transported metabolites (Goodenough et al, 1980) as well as dyes (Schuetze and Goodenough, 1982;Miller and Goodenough, 1986) to diffuse between adjacent cells. The lens has three different cellular interfaces: epithelium/epithelium, fiber/fiber, and epithelium/fiber.…”

“…These channels permit small metabolites, second messengers, and ions to pass from cell to cell (Bennett and Goodenough, 1978;Goodenough et al, 1980) and may play important roles in cellular signaling and growth regulation. These channels are formed by members of a family of proteins known as connexins, which contain highly conserved membrane spanning and extracellular regions, whereas cytoplasmic regions are unique (Zimmer et al, 1987;Goodenough et al, 1988;Hertzberg et al, 1988;Milks et al, 1988;Yancey et al, 1989;Beyer et al, 1990).…”

Development of a macromolecular diffusion pathway in the lens

“…Rather, small molecules are thought to enter the surface cells and diffuse from cell to cell into the core of the lens. This view of the lens, in which the metabolism of the mature lens fibers is sustained via communication with cells at the periphery, has been termed 'metabolic cooperation' (Goodenough et al, 1980).…”