ULTRASTRUCTURAL STUDY OF THE PROCESS OF ROSETTE FORMATION BY DISSOCIATED NEURAL RETINAL CELLS IN STATIONARY CULTURE

Well orientated two-dimensional rosettes were produced in stationary cultures of dissociated neural retinal cells of 5 1/2-day-old chick embryos. Observations by electron microscopy were made on aggregates at the different steps in the process leading to rosette formation. Though all of the dissociated neural retinal cells showed a clear morphological polarity, primary cell-to-cell adhesion occurred at random with respect to the cellular polarity. A special junction of the zonula adhaerens type was found at the contact area between the "mitochondria-containing portions" or their neighboring regions of both adjoining cells. During stationary culturing, the contact area between the cells gradually increased. Where the "mitochondria-containing portions" of adjoining cells were brought into contact with each other, junctions of zonula adhaerens type were formed between them. In this way, a radial arrangement of all the cells within an aggregate was established, leading to the formation of the fundamental structures of rosettes.