[The fine structure of the zonular fibre of the rat. Development andaging changes]

Development of actin polygonal arrays in rabbit lens epithelial cells

In searching for a clue to the role of actin filament bundles organized into polygonal arrays, or geodomes, in lens epithelial cells, we examined several physical events occurring in the young rabbit lens which may initiate their formation. We used NZW rabbits between the ages of 24 days gestation and 50 days postnatal. Data were obtained from TEM, SEM and fluorescence microscopy. Parameters measured were lens weights, apical surface areas of cells in epithelial whole mounts, epithelial cell thickness, and timing of eyelid opening, breakdown of the tunica vasculosa lentis (TVL) and formation of the ciliary zonules; these findings were correlated with the first signs of development of the arrays. Polygonal arrays formed slowly beginning at one to two days after birth, and with advancing time these thickened and made more numerous connections with the lateral plasma membranes. Development of the arrays was not correlated with onset of vision or disappearance of the TVL or a sudden increase in cell area, since these events occur postnatally at about 9-10 days, nor with the development of zonular fibers since these are already in place at 24 days of gestation. Only lens weights showed a dramatic increase between 24 days gestation and birth. It is surmised that the expanding lens mass may be involved in some way in signaling the organization of actin filaments into geodomes.

An ultrastructural study of complex carbohydrates in the posterior chamber and vitreous base of the mouse

The fibrillar and mucoid extracellular matrix of the posterior chamber and vitreous base was studied in the mouse by electron microscopy using fixation and staining methods that demonstrated complex carbohydrates. These methods, including block-staining with Alcian Blue, allowed globular and filamentous hyaluronic acid, finely filamentous oligosaccharides, laminated glycolipids or lipophilic glycoproteins and stellate proteoglycan monomers to be identified tentatively. There was much less globular hyaluronic acid along the basement membrane of the peripheral retina and ciliary body than has been observed in the posterior fundus. A finely filamentous network on the basement membrane interconnected with a similar network covering individual collagen fibrils, zonules and meridional fibrillar laminae as well as with a branching fibrillar network that was seen in the posterior chamber and vitreous base. This interconnected system of fibrillar proteins and complex carbohydrates was also connected to the anterior hyaloid membrane. The infoldings of the ciliary epithelium contained stellate densities with characteristics of proteoglycan monomers similar to those reported in the matrix of cartilage. The complex carbohydrates of the posterior chamber and vitreous base are of several types known to affect protein function, provide water binding and assist in mechanical stability.

Microfibrils, elastic anchoring components of the extracellular matrix, are associated with fibronectin in the zonule of Zinn and aorta

Microfibrils are striated tubules that play a role in the formation of elastin fibers by providing a scaffold upon which newly synthesized elastin is deposited. Ultrastructural and staining studies also demonstrate microfibrils that terminate where elastin is sparse or absent in basal laminae, plasma membranes, and the collagenous matrix. The most striking accumulation of microfibrils is found in the zonule of Zinn, the transparent and elastic suspensory ligament of the lens, which contains no elastin. Application of immunocytochemical staining with a peroxidase-antiperoxidase (PAP) procedure demonstrates that fibronectin is associated with the microfibrils of the zonule and aorta. Aggregates of microfibrils are identical to oxytalan ('acid enduring') fibers that have been described in peridontal membranes and other sites subject to mechanical stress and they can be found in sites as disparate as the rabbit zonule, rat hepatic stroma and human cardiac papillary muscle, indicating that microfibrils are a widely distributed connective tissue element with a function that extends beyond elastogenesis; their association with fibronectin and localization suggests that they serve as an elastic anchoring component of the extracellular matrix.

The organization of tissues of the eye by different collagen types

Bovine cornea, sclera, iris, ciliary body, choroid, zonular fibers, lens capsule, lens nucleus, vitreous body, and retina were investigated for collagen content and type. Cornea, sclera, iris, ciliary body, choroid, lens capsule, and vitreous body contain hydroxyproline, whereas in zonular fibers, lens nucleus, and retina no hydroxyproline was detectable. Preparative isolation of collagen was achieved by digestion of the different eye tissues with pepsin. The pepsin-solubilized collagen was separated by differential salt precipitation into different collagen types. The polyacrylamide gel electrophoresis of the pepsin-solubilized collagens revealed type I collagen in cornea, sclera, iris, ciliary body, and choroid. As well as type I collagen, type III collagen was isolated from cornea, sclera, and uveal tissues. The identification of types I and III collagen was supported by the CNBr-derived peptides of these collagens. Lens capsule collagen consisted mainly of type IV collagen. Zonular fibers contained no hydroxyproline but when examined by polyacrylamide gel electrophoresis, a band migrating in the alpha-position of collagen was observed. Polyacrylamide gel electrophoresis of both the pepsin-solubilized component and the CNBr-derived peptides of vitreous body protein showed no relation to any of the four common collagen types.

Electron microscopic studies on zonule. Its origin and fibroblast

Rabbit fetuses (14, 16, 17, 18, 20, 22, and 24 days in utero) were examined with an electron microscope, and the following results were obtained: 1. At the equatorial region of the lens, developing endothelium of the tunica vasculosa lentis was very similar in morphology to typical fibroblast. 2. Much debris of amorphous material was observed around the endothelium and fibroblast, but in general, zonule-like fine fibrils were seen near the former, whereas short collagen fibrils were observed around the latter amid amorphous material. 3. Topographically, fibroblasts lay apart from the lens equator, and few fibroblasts migrated into the posterior portion. 4. From the above data it was postulated that debris around the tunica vasculosa lentis in the vicinity of the lens equator was presumably the precursor of zonular fibrils and that fibroblasts had almost no relation to zonular formation.

[The proof of two distinct types of collagen in the fibrils of the vitreous body and zonula fibers (author's transl)]

Vitreous body fibrils and zonula fibers are analyzed by disc-electrophoresis. In both tissues the presence of collagen is established. The disc-electrophoresis patterns of vitreous body fibrils and zonula fibers show that a different type of collagen is present in each tissue. The absence of the alpha 2-chain indicates that the tissues investigated contain no type I collagen but types consisting of three identical alpha-chains.

[On scanning electron microscpy to the anterior part of the eye with special regard to the coruse of zonula Zinnii (author's transl)]

Three areas in which zonular fibers of Zinn enter were demonstrated with the aid of scanning electron microscopy. 1. The area, which applied to the edge of the lens. 2. The area of Pars plicata corporis ciliaris. 3. The area of Pars plana. The connection of zonuar fibers with limited membran of vitreous body was presented too.

[The course of zonular fiber. A further electronenmicroscopic study (author's transl)]

Zonular fibers could be shown between the basement membrane of the pigmented epithelium of pars plana and the elastic tissue of Bruch's membrane. A connection of zonular fibrils between the unpigmented epithelium and the basement membrane of pigmented epithelium of the pars plana could not be observed. It is possible to discuss two independent courses of zonular fibers.

[The course of zonular fibers in the area of pars plicata corporis cilaris pars plana, ora serrata and retina. Eectron microsocpic study]

The course of zonular fibers in the area of pars plicata corporis ciliaris could be shown down to the pigmented epithelial layer and its basement membrane. S ingle fibrils enter in a connection with the plasma membrane in allinvestigated parts. Fibrils could be observed in the cytoplasm of the ora serrata. For the other areas (pars plicata corporis ciliaris, parsplana) this can be suggested too.

Electron microscopic studies on zonular fibers. II. Changes of the zonular fibers after the treatment with collagenase, alpha-chymotrypsin and hyaluronidase

Adult rabbit zonular fibers maintained in their native condition were treated with collagenase, alpha-chymotrypsin and hyaluronidase, and were observed with the electron microscope. The results obtained were as follows: 1. Collagenase digested the lens capsule, but not the zonular fibers. 2. Long time collagenase action obscured the cell membrane of the lens epithelium and the basal lamina of the ciliary epithelium. 3. Washing with 0.9% NaCl increased the collagenase action on the lens capsule. 4. Alpha-chymotrypsin digested the zonular fibers and the zonular lemalla, but not the lens capsule and the basal lamina of the ciliary epithelium. 5, Hyaluronidase only slightly changed the lens capsule. 6. The vitreous fibers were digested by collagenase, but not by alpha-chymotrypsin or hyaluronidase. Thes results together with the review of recent literature indicate that the zonular fiber has a nature close to that of the microfibril of elastic fiber.

[Identification of zonula fiber protein by disc-electrophoresis (author's transl)]

By our investigations we found identity of collagen and zonula fibers protein. In Disk-electrophoresis both the zonula fibers ans the fibers of the vitreous show the alpha-component only. Therefore it is likely that these proteins are closely related.