Individual nuclei in polykaryons can control cyclin distribution and DNA synthesis.

Nuclear patterns of cyclin (PCNA) distribution that subdivide S-phase (determined using PCNA autoantibodies specific for this protein) as well as [3H]thymidine incorporation followed by autoradiography have been used to determine the S-phase synchrony of homophasic polykaryons produced by polyethylene glycol (PEG)-induced fusion of populations of mitotic transformed human amnion cells (AMA) exhibiting the following average distribution of phases: prophase, 9%, metaphase, 60% (including early and late prometaphase), anaphase, 3.8%, telophase, 26.2% and interphase, 1%. Both synchronous and asynchronous polykaryons were generated from these fusions; the latter being frequently observed only amongst populations of multinucleated cells having three or more nuclei. These results are taken to imply that individual nuclei in these polykaryons can control cyclin distribution and DNA synthesis in spite of the fact that they share a common cytoplasm.