The roles of laminin and fibronectin in the development of the lens capsule.

This study examines the distribution of laminin and fibronectin in the rat lens capsule during development. Both these extracellular matrix glycoproteins are localised in the interspace between presumptive lens and presumptive retina as well as in their basal laminae. The lens capsule arises from multilayering of the basal lamina of the lens cells. Immunofluorescence localises both laminin and fibronectin in the capsule at 16 days of embryonic development, although reactivity for fibronectin is much weaker than for laminin. In the 19 day embryo only laminin is detected. This indicates that during embryonic development fibronectin becomes a minor component of lens cell ECM and is not accumulated in the developing capsule. The roles of laminin and fibronectin in promoting cell migration during development were analysed in explant cultures. Lens epithelial explants from 16, 17 and 19 day old embryos and neonatal rats were grown on a laminin or fibronectin substratum. Lens cells from all ages of rats migrated on the laminin substratum, whereas lens cells progressively lost the ability to migrate on a fibronectin substratum as the age of the donor increased. This developmental loss of ability to migrate on fibronectin in vitro coincides with the developmental loss of fibronectin from the lens capsule in vivo. Therefore, we propose that whilst both laminin and fibronectin may be important for promoting migration of lens cells on their substratum at early stages of lens morphogenesis, during development laminin takes over as the key molecule that promotes migration on the capsule.

A morphometric analysis of the development of the rat lens capsule.

This study analysed patterns of growth of the lens capsule by measuring capsule thickness at 13, 16 and 19 days of embryonic development and 2, 21, 140 and 600 days of post-natal development. The major findings were that, at early stages of embryonic development, the posterior capsule was thicker than the anterior capsule. However, at later stages, the posterior capsule did not increase in thickness whereas the anterior capsule continued to thicken so that, by 2 days of post-natal development, the situation was reversed and the anterior capsule was significantly thicker than the posterior capsule. This trend continued and by 600 days post-natal development, the anterior capsule was 7.5 times thicker than the posterior capsule. In these older lenses the capsule tapered sharply in thickness from the anterior to the posterior equatorial region. These regional differences in thickness of the lens capsule, and the changes reported during development, may reflect changes in capsule production by epithelial and fibre cells as they differentiate.