Some Observations on Nuclear Budding and Nuclear Extrusions in a Chinese Hamster Cell Culture

Extensive nuclear budding was observed with the light microscope in living and fixed cells of a long-term, aneuploid culture derived from a Chinese hamster embryo. Nuclear buds developed during interphase and resembled miniature nuclei, containing chromatin threads, nuclear sap, and, often, nucleoli and chromocenters. One to 3 buds might be present on a single, otherwise normal nucleus. Some buds burst at their tips and released a clear substance forming a well-marked vacuole in the surrounding cytoplasm. Occasionally nucleolar or chromocentral bodies were also released into the cytoplasm. Nuclear protrusions were constricted at the base and sometimes separated completely from the parent nucleus. Bursting nuclear buds and accompanying cytoplasmic vacuoles were also observed in some micronuclei formed during the development of restitution nuclei from colchicine-metaphase chromosomes. One to 3 particular chromosomes may be specifically involved in the budding. Consideration is given to whether micronuclei, formed from the pinching off of nuclear buds, contain chromosomal fragments or one (or more) intact chromosomes. Further, the probability that nuclear budding and associated processes can be normal occurrences in tumor and nontumor cells alike is discussed.