Correlated scanning and transmission electron microscopy of developing lens vesicle in the chick.

Cells within the lens placode undergo transient surface modifications during the course of invagination. At stage 13, cellular apices bulge outward and display decreased surface diameters when compared to adjacent surface ectoderm. The lens vesicle is well invaginated by stage 14. An area of modified cells can be recognized ventral to the lens vesicle aperture. These cells present a smaller surface area and increased pleomorphism. Normal surface ectoderm extends to the dorsal and lateral edges of the aperture. The apical surfaces of cells which line the lumen of the lens vesicle display a complex topography such that individual cell boundaries are not easily distinguished. At stage 17, cellular processes which partially occlude the closing aperture of the lens vesicle may assist in reestablishing ectoderm over the newly formed lens. Preliminary results of cytochalasin B exposure on the invaginating lens vesicle suggest that the contractile action of microfilaments influences the complex cellular topography.