In situ analysis of cultured Potorous cells. I. DNA synthesis and mitotic dynamics in bi- and multinucleate cells.

Abstract

The rat-kangaroo (Potorous tridactylis) cell line Pt-Kl was analyzed in situ after continuous labeling with H3-thymidine for 4–12 hours. Both DNA synthesis and early stages of mitosis were found to be incompletely synchronous in bi- and multinucleate cells. Chromosomal complements, however, catched up with each other so that the trigger of anaphase affected all chromosomes simultaneously. In these cells mitosis was usually multipolar and occasionally bipolar. Both S and mitosis were of longer duration than in mononucleate cells. Apparently, each nucleus enters mitosis with its own mitotic centers and interactions and coordinations among chromosomes and centers lead to the formation of spindle connections between related and unrelated poles, thus giving rise to a multipolar spindle which is a functional unit. Chromosomes from different nuclear origins do not mix with each other on the common bi- or multipolar equatorial plate. In binucleate cells undergoing quadripolar mitosis, each chromosomal complement was usually oriented on two adjacent arms of the X-shaped equatorial plate. The four daughter nuclei thus represented two parental and two recombinant types. The labeling patterns of recombinant nuclei indicated that chromosomes maintain their positions during the transition from anaphase to interphase. The implications of the present findings were discussed in relation to other related phenomena such as somatic segregation, chromosome behavior in hybrid cells, origin of haploid and triploid cells in diploid cell populations, depolyploidization, spatial relationships among chromosomes in bi- and multipolar spindles, and the orderly arrangement of interphase chromatin.