Cadm1 expression has been shown to influence epithelial cell morphology,
35 and, in neural tissue, Cadm1 plays a role in regulating growth cone morphology.
36 To determine what role Cadm1 might play in lens cell morphogenesis, we examined the detailed three-dimensional structure of individual cells in the lens epithelium and the fiber cell population. Immunofluorescence images suggested that the highest levels of Cadm1 in the lens were found in the basolateral membranes of the epithelial cells (
Fig. 6A). Living epithelial cells were imaged in intact lens tissue by crossing wild-type or
Cadm1-null animals with a mouse strain (
TgN(GFPU)5Nagy) in which GFP was expressed spontaneously by scattered cells in the lens epithelium. Side-by-side comparisons of wild-type and
Cadm1-null epithelia failed to reveal any qualitative difference in epithelial morphologies between the two genotypes (
Figs. 8A,
8B). In each case, epithelial cells had structurally complex basolateral membranes and relatively simple, polygonal, apical membranes. The GFP labeling technique was not suitable for visualizing lens fiber cell morphology because GFP is not well retained by expressing lens fiber cells.
37 Therefore, to visualize fiber cell morphology, we microdissected individual fiber cells from the lens and stained them with an antibody against MIP, an abundant lens membrane protein. Image stacks of wild-type or
Cadm1-null fiber cells were deconvolved and volume rendered. A gallery of representative cells from each genotype is shown in
Figure 8C. Previous scanning electron microscopy studies have revealed that fiber cells in the cortex of the mouse lens follow an undulating, sinusoidal course.
38 We confirmed this observation for wild-type lens fiber cells (
Fig. 8C, right). However, the three-dimensional morphology of
Cadm1-null fiber cells differed significantly from that of wild-type cells. Namely, in the
Cadm1-null fiber cells, the undulations were irregular in period and exaggerated in amplitude (
Fig. 8C, left). Thus, Cadm1 plays an indispensable role in establishing and maintaining the characteristic three-dimensional architecture of the lens fiber cells.