Cultured Rabbit Lens Research Articles

Pigmentation and enzymic inhibition by carbonyl compounds in the rabbit lens

When certain α-hydroxycarbonyl or dicarbonyl compounds were added to cultured rabbit lenses, changes occurred in enzymic activity, color and fluorescence. These changes resemble the decreased metabolism and the development of color and fluorescence that is seen in some aged human lenses. One representative compound, glycolaldehyde, inhibited activity of at least one enzyme (aldolase). When added to lysine, to muscle aldolase, to dialyzed lens homogenates or to intact cultured rabbit lenses, glycolaldehyde elicited u.v.-fluorescence and color, the latter ranging progressively from yellow to brown or even to black. Glycolaldehyde in solution with lysine at pH 8 formed a 1-1 adduct. Through subsequent reactions of the Maillard type there occurred further changes yielding a progression of color similar to that seen in glycolaldehyde-treated lenses or in colored human lenses. Other a-hydroxycarbonyl compounds or dicarbonyls which are inhibitory to metabolism in the lens (T. G. Scharff and O. L. Montgomery, Proc. Soc. exp. Biol. Med. 134, 658 1970) also probably underwent Maillard-type reactions with amino acids in solution to form similarly colored, fluorescent products with muscle aldolase, dialyzed lens homogenates or intact lenses. It is possible that colored Maillard-type complexes between unidentified carbonyl compounds and free or protein-incorporated amino acids may be involved in reduced metabolism and in color development in the aged human lens or other pigmented, aging tissues.

Effect of temperature on cell division in the cultured rabbit lens

Mitotic activity in the cultured rabbit lens is optimal between 34 and 37°C. Above 37°C there is a progressive cell lysis both in the central area and germinative zone of the lens epithelium. Mitotic duration at 35°C is 50–55 min whereas at 31°C it is approx. 100 min. Mitotic duration in vivo is approx. 43 min.

Possible Differentiation of Lens Fibers in Rabbit Lenses Maintained in Organ Culture

The adult ocular lens offers a unique system to study the process of cell division and/or differentiation. Mitosis is principally confined to the equatorial region of the lens and in the normal sequence of events the cells in this region divide, traverse the terminal cell cycle and differentiate, i.e., synthesize lens specific proteins. The cells which reside in the central epithelium are, on the other hand, blocked in the Go state but can be triggered to divide by culture in a medium which contains rabbit serum. Previous studies have defined the biochemical and morphological changes which precede and accompany DNA synthesis and mitosis in the cultured rabbit lens. This paper describes certain morphological changes which occur in the peripheral region of rabbit lenses which have been exposed to rabbit serum for 35 hours.

Characterization of macromolecular synthesis in the epithelium of cultured rabbit lenses

The chronological pattern of RNA, DNA, protein synthesis and mitosis has been characterized in the epithelial cells of cultured rabbit lenses. Increments in both RNA and protein synthesis (as reflected by the incorporation of tritiated uridine and tritiated protein hydrolysate) were detected by 7 hr of culture. These macromolecular changes precede and are essential for the initiation of DNA synthesis and mitosis, which commence at 24 and 35 hr, respectively. Lenses exposed to actinomycin D from 0–4 hr fail to enter either DNA synthesis or mitosis, and exhibit a reduced incorporation of tritiated uridine. At intervals beyond 18 hr, the antibiotic has little or no effect on the entrance of the cells into DNA synthesis. Continuous exposure to puromycin also inhibits both DNA synthesis and mitosis and brings about reduction in the increase in the incorporation of tritiated protein hydrolysate that normally accompanies the proliferative response. These macromolecular changes are correlated with recent observations on the fine structure of the cultured lens.

Changes in Tissue Organization which Precede the Onset of Cell Division in the Cultured Rabbit Lens

Mitosis in the adult lens is normally confined to a region of the epithelium referred to as the germinative zone. Cells of the central epithelium are normally devoid of proliferative activity but can be induced to undergo a parasynchronous burst of DNA synthesis and mitosis when cultured under suitable conditions. It would seem that the maintenance of the "blocked" mitotic state and the release of the cells from this state must have a basis in the overall organization of the tissue. If this is true, triggering of mitosis might be reflected in the initial fine structural changes which precede cell division in the cultured lens.

A chalone in the rabbit lens?

Studies on the rabbit lens have provided evidence for the existence of a protein which, in the presence of adrenaline, reversibly inhibits the mitotic activity of cultured rabbit lenses. This property is typical of a surface ectodermal chalone and it is possible therefore that the protein forms part of the mechanism which maintains the mitotic homeostasis of the tissue.