[Centrioles can replicate in cultured cells in the absence of a nucleus]

Cytoplasts of cultured L fibroblasts, obtained by enucleation at the end of G1 of synchronized cells collected in mitosis, have usually two centrioles. Starting from 8 h after enucleation, the centrioles in all cytoplasts were seen replicating. The formed procentrioles had an average length of 0.2 micron and did not grow within the next 16 h. When the same synchronized L cells were treated from the end of G1 with actinomycin D, inhibiting more than 96% of RNA synthesis, procentrioles were not observed for about 16 h of incubation. It is concluded that centrioles in cultured cells could replicate in the absence of RNA synthesis, and that the nucleus may not only regulate the centriole replication, but also suppress this process.