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 in 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 Sβ or early G~2~βphase of the cell cycle, and that embryonic lens cells retain the capacity to divide, even after acquiring large amounts of tissueβspecific structural proteins.