Ion concentrations, fluxes and electrical properties of the embryonic chicken lens

The molecular mechanisms underlying lens fiber elongation

Lens fiber cells are highly elongated cells with complex membrane morphologies that are critical for the transparency of the ocular lens. Investigations into the molecular mechanisms underlying lens fiber cell elongation were first reported in the 1960s, however, our understanding of the process is still poor nearly 50 years later. This review summarizes what is currently hypothesized about the regulation of lens fiber cell elongation along with the available experimental evidence, and how this information relates to what is known about the regulation of cell shape/elongation in other cell types, particularly neurons.

Morphometric analysis of fibre cell growth in the developing chicken lens

The optical characteristics of any lens are determined by its internal composition, size and shape. In the lens of the eye, the macroscopic form of the tissue reflects the arrangement and behaviour of its component cells. In the current study, we quantified changes in the morphology and organization of chicken lens fibre cells during embryonic development. Lens radii, fibre cell length, shape, cross-sectional aspect ratio, cross-sectional area, cross-sectional perimeter, and cell packing organization were measured from confocal and transmission electron micrographs using computer assisted image analysis. Derived values for cell surface area and volume were also calculated. Because of the radial symmetry of the avian lens, we were able to employ a novel coordinate system to track the fate of identified cohorts of cells at successive developmental stages. This allowed kinetic information, such as the rate of increase in length or volume, to be derived. By sampling identified cell populations (i.e. those located at a specific point on the lens radius) at regular intervals it was possible, for the first time, to reconstruct the life history of fibre cells buried within the cellular conglomerate of the lens. The measurements indicated that a surprising degree of structural remodeling occurs during fibre cell elongation and continues after extant cells have been buried by waves of newly differentiated fibres. Even in the anucleated cells of the lens core, the size and surface topology of the cells were altered continually during development. However, some aspects of fibre cell organization were established early in development and did not vary thereafter. For example, the packing arrangement of cells in the adult lens was traced to a cellular template established on the tenth day of embryonic development.

Optical dysfunction of the crystalline lens in aquaporin-0-deficient mice

Aquaporin-0 (AQP0), a water transport channel protein, is the major intrinsic protein (MIP) of lens fiber cell plasma membranes. Mice deficient in the gene for AQP0 (Aqp0, Mip) were generated from a library of gene trap embryo stem cells. Sequence analysis showed that the gene trap vector had inserted into the first exon of Aqp0, causing a null mutation as verified by RNA blotting and immunochemistry. At 3 wk of age (postnatal day 21), lenses from null mice (Aqp0(-/-)) contained polymorphic opacities, whereas lenses from heterozygous mice (Aqp0(+/-)) were transparent and did not develop frank opacities until approximately 24 wk of age. Osmotic water permeability values for Aqp0(+/-) and Aqp0(-/-) lenses were reduced to approximately 46% and approximately 20% of wild-type values, respectively, and the focusing power of Aqp0(+/-) lenses was significantly lower than that of wild type. These findings show that heterozygous loss of AQP0 is sufficient to trigger cataractogenesis in mice and suggest that this MIP is required for optimal focusing of the crystalline lens.