No abstract

The time of initial synthesis and the subsequent localization of the crystallins in the embryonic mouse lens were studied with antisera to adult mouse lens using the indirect fluorescent antibody technique. Fluorescence was first detected in a few centrally located cells of deeply invaginated lens rudiments (10.75 to 11 days of gestation), after a prolonged period of contact between presumptive lens and presumptive retina. The reaction usually was restricted to the basal cytoplasm of these cells. During formation of the lens vesicle in 11 to 11.5 day embryos a gradually increasing fraction of lens cells began to display fluorescence, throughout their cytoplasm. At the time of closure of the vesicle the reaction had spread throughout the posterior wall. After fiber elongation became distinct, the cells of the anterior lens epithelium began to fluoresce (11.5 days). All cells of the lens rudiment were uniformly fluorescent in 12 day embryos and i n all subsequent prenatal stages. Reactions were never observed outside the lens. We concluded that the mouse crystallins are tissue specific proteins and that their production begins at a relatively late stage of lens morphogenesis.When cells first showed fluorescence, they always had an elongated shape and their nuclei were in a basal position, close to the optic cup. A few hours later dividing cells became positive. Taking into account earlier found relations between cell shape and cell cycle phase, these observations may indicate that crystallin synthesis is initiated in the late S-or early G1-phase of the cell cycle, and that embryonic lens cells retain the capacity to divide, even after acquiring large amounts of tissue-specific structural proteins.

Development and regression of the conjunctival papillae have been examined with both light and electron microscopy. The fibrous strands which extend from the papillae to the mesenchyme of the pre-ossicular plate have been identified as collagen. Furthermore, the initial deposition of collagen fibrils has been shown to occur within channels between cells of the basal epithelium during stages 2 and 3. Bundles of collagen fibrils extend continuously from the uppermost portions of the cavity of the papilla to the mesenchyme of the condensing pre-ossicular plate during stage 5.Degeneration is localized in a small area of the papilla during stages 3 and 4 but spreads throughout the mass during stage 5. Late in stage 5 , necrotic epithelial cells are sloughed into the cavity of the papilla from its basal layer. These findings are discussed in relation to earlier light microscopic and experimental studies which have shown the papillae to be required for the subsequent development of the scleral ossicles in the subjacent mesenchyme.

The role of cell proliferation in the formation of scleral ectomesenchymal condensations underlying the conjunctival papillae was examined with in vivo tritiated thymidine labelling in chick embryos ranging in age from 8 days 0 h to 10 days 12 h. Percentages of labelled nuclei were determined in both ectomesenchyme and the deeper fibrous sclera for short-term and continuous tritiated thymidine incubations. During formation of the ectomesenchymal condensations the percentages of labelled nuclei were consistently higher within the condensations than in corresponding non-condensing ectomesenchyme between papillae. The consistent differences of labelling percentages observed within the condensing versus noncondensing ectomesenchyme were not found in the fibrous sclera at any stage. All areas of both the ectomesenchyme and fibrous sclera showed decreases in the percentages of labelled nuclei from 8 days Oh to 10 days 12h, although the decline in the ectomesenchymal condensations beneath papillae occurred more slowly than in areas between papillae. The data suggest that the conjunctival papillae directly influence the proliferation in the subjacent condensing ectomesenchyme but have no effect on the ectomesenchyme between papillae or any region of the deeper fibrous sclera. The observations of this investigation are discussed in relation to other studies of the development of the pre-ossicular mesenchyme.