Abstract
Abstract: :
Purpose: Previous studies on embryonic lenses have suggested that elongation of primary fiber cells is driven directly by volume increase. To test whether a similar mechanism operates during the elongation of secondary fiber cells, we examined the length/volume relation of cells at various stages of differentiation in the adult mouse lens. Methods: Lenses were obtained from a strain of mice (TgN(GFPU)5Nagy) carrying a GFP transgene. The expression of GFP in the lens was sporadic, resulting in the labeling of individual cells in the lens epithelium and cortex. High resolution confocal microscopy was used in conjunction with deconvolution and volume rendering techniques to examine the three–dimensional structure of individual GFP–expressing cells. Results: Cells in the central epithelium had an unexpectedly irregular appearance when imaged in three dimensions. This was shown not to be due to the presence of GFP. The basolateral membrane had a particularly complex structure. Lamellipodia– and filopodia–like processes extended from the cell body. These membrane projections allowed non–neighboring cells to be in direct contact. Lateral projections were absent from epithelial cells located immediately anterior to the lens equator. In cells of this region, the basal membrane was reorganized into a motile structure, with filopodia extending from its leading edge. Cell volume measurements in the epithelium and outer cortex indicated that during the initial stage of elongation (in which cells increased in length by approximately fifteen fold) cell volume increased only modestly (2–3 fold). Elongation thus reflected a change in cell shape rather than cell volume. Conclusions: During secondary fiber cell formation, length and volume do not increase proportionately. Therefore, osmotic volume increase is unlikely to be the driving force behind secondary fiber cell elongation. The data suggest that the mechanism of cell elongation may differ fundamentally between primary and secondary fiber cells.
Keywords: imaging/image analysis: non–clinical • microscopy: confocal/tunneling • cell membrane/membrane specializations