Mitotic activity in the lens rudiment of the chicken embryo before and after the onset of crystallin synthesis : II. Immunofluorescence studies.

1. The fluorescent antibody method was used to study the first appearance of delta-crystallin in the lens rudiment of the chicken embryo, in relation to the cell cycle. At the beginning of lens invagination a few cells, with their nuclei in a basal position, displayed fluorescence. The percentage of cells with a positive reaction increased steadily, but it was not until invagination was well underway, about 3 hours after its start, that fluorescence was seen in dividing cells. It was concluded that in this system cell replication and synthesis of specific protein are not mutually exclusive. 2. Because the number of hours passing by before the appearance of fluorescent mitoses was about equal to the previously calculated duration of the G-2 phase of the cell cycle it follows that crystallin production becomes detectable in the late S- or early G-2 phase. Observations on the cellular shape, which is a function of cell cycle phase, at the time that cells first reacted with the fluorescent antibodies agree with this interpretation. 3. The suggestion is made that the inductive influence of the optic cup on the lens primordium may primarily be exerted during the DNA synthetic phase of the presumptive lens cells.