The stratified syncytium of the vertebrate lens

Abstract

The fusion of cells to generate syncytial tissues is a crucial event in the development of many organisms. In the lens of the vertebrate eye, proteins and other macromolecules diffuse from cell to cell via the large molecule diffusion pathway (LMDP). We used the tamoxifen-induced expression of GFP to investigate the nature and role of the LMDP in living, intact lenses. Our data indicate that the LMPD preferentially connects cells lying within a stratum of the lens cortex and that formation of the LMPD depends on the expression of Lim2, a claudin-like molecule. The conduits for intercellular protein exchange are most likely regions of partial cellular fusion, which are commonly observed in wild-type lenses but rare or absent in Lim2-deficient lenses. The observation that lens tissue constitutes a stratified syncytium has implications for the transparency, refractive function and pathophysiology of the tissue.

Connexin 46 (Cx46) Gap Junctions Provide a Pathway for the Delivery of Glutathione to the Lens Nucleus

“…Although it is possible that gap junctions may allow diffusion of the divalent ion to the periphery from the center because the coupling conductance of fiber cells is typically very high, other pathways for GSSG efflux/ breakdown might operate in the lens. Cell-cell diffusion of molecules in the lens may also be mediated by membrane fusions between adjacent fiber cells (39,40). Unlike gap junction channels, which exclude molecules above 1 kDa, membrane fusions can allow the diffusion of very large molecules such as green fluorescent protein (GFP) and Alexa 488 conjugated to dextran between adjacent cells (39,40).…”

“…Cell-cell diffusion of molecules in the lens may also be mediated by membrane fusions between adjacent fiber cells (39,40). Unlike gap junction channels, which exclude molecules above 1 kDa, membrane fusions can allow the diffusion of very large molecules such as green fluorescent protein (GFP) and Alexa 488 conjugated to dextran between adjacent cells (39,40). These fusions have been identified in adult lenses from several species, including humans and rodents, and require the presence of Lim2 (also known as MP20) (41).…”

Tropomodulin 1 Constrains Fiber Cell Geometry during Elongation and Maturation in the Lens Cortex

“…2C). Some of these small packing imperfections may be due to fiber cell fusions or to radial column branching during addition of new fiber cells during lens growth (Kuszak et al 2004;Shi et al 2009), but these events are unlikely to account for all of the small packing imperfections we observe. Instead, many packing imperfections are likely a consequence of the extremely flattened hexagonal shape of fiber cells, resulting in an inability to distinguish the two neighboring vertices at fiber cell short sides, owing to small distortions inherent to the cryosectioning process (Fig.…”

Biological glass: structural determinants of eye lens transparency

“…The three-dimensional morphology of the fibre cells is similarly complex and varies, depending on the location of the cell (figure 3c-i). [9]. GC, growth cone.…”