The surface morphology of embryonic and adult chick lens‐fiber cells

Abstract

The surface morphology of lens fibers in embryonic and adult chicken lenses has been studied by scanning electron microscopy. As the elongating epithelial cells enter into a state of terminal differentiation they elaborate a number of cellular processes interconnecting neighboring fibers. The interlocking devices take the shapes of balls on a short stalk, tonguelike flaps, and fingerlike processes that fit into complementarily shaped sockets, imprints, and fingerprints, respectively, of adjoining fibers. Gap junctions comprising more than 50% of the fiber-cell membrane may serve as ultrastructural interlocking devices. The interlocking devices and gap junctions are probably necessary to maintain fiber order--a critical requirement for lens transparency. With increase maturation, the uniform morphology of the fibers and their interlocking devices is lost. The highly repetitive ordered alignment of young uniformly shaped fiber cells acts to minimize large-particle scatter. The results of this study show a progressive loss of uniform shape and order in chicken fibers of advanced maturity. This phenomenon of lens development may be the basis for the increase in light scattering seen in aged lenses of other species such as man.

Caspase Remodeling of the Spectrin Membrane Skeleton during Lens Development and Aging

“…In addition, membrane protrusions are not present in the day 7 embryonic lens but are first observed later in the day 10 embryonic lens; these membrane protrusions become more elaborate with age (42). Moreover, in the adult chicken lens, newly differentiated cortical fiber cells exhibit smooth profiles, whereas older fiber cells display numerous membrane protrusions (43). In support of a role for spectrin fragmentation in the development of membrane protrusions, antibodies, which recognize both full-length and fragments of ␣-spectrin stain protrusions of nuclear fiber cells (19) as well as blebs decorating differentiated lens cells in culture.…”

Electron microscopic observations of the crystalline lens

“…25), though the exact type of cytoskeletal elements cannot be ascertained from this technique. Polygonal domains of furrowed membrane without overlying microvilli are noted in middle age primate lens fibers, as well as in nuclear fibers of less long-lived mammals (e.g., bovine: Costello et al, 1985;Zampighi et al, 1982) and other vertebrates (chicken: Kuszak et al, 1980; and frog: Kuszak and Rae, 1982). Freeze-etch analysis of the most senescent fibers in primate lenses reveals that the ridges and microvilli of polygonal domains are characterized by square array membrane (Lo and Harding, 1984; Fig.…”

“…However, the lateral membrane interdigitations of fibers are more numerous, elaborate and regularly arrayed along fiber length than in any other epithelia. Scanning electron microscopy is unparalled as a method to optimally demonstrate the structure of fiber lateral interdigitations (Dickson and Crock, 1972;Farnsworth et al, 1974;Hansson, 1970;Harding, et al, 1976;Hollenberg et al, 1976;Kuszak and Rae, 1982;Kuszak et al, 1980Kuszak et al, , 1983Kuwabara, 1975;Nelson and Rafferty, 1976). There are two basic types of lateral membrane interdigitations between fibers that vary minimally in shape, size and periodic arrangement between species.…”

Development of lens sutures

“…1974; Kuszak et al, 1980;Kuszak and Rae, 1982;Kuszak et al, 1985;Rafferty, 1985;Kuszak et al, 1996;Kuszak and Costello, 2002). Lens formation begins as surface ectodermal cells, immediately overlying the developing optic vesicle, are induced to thicken and form the lens placode.…”

“…1, first row) (Duke-Elder, 1970;Kuszak et al, 1980;Willekens and Vrensen, 1985;Bassnett and Winzenburger, 2003). As fiber development and growth occurs circumferentially around the equator, fibers from opposite sides of avian and reptilian lenses become arranged end to end as pairs forming ellipses around the embryonic nucleus.…”