« Spontaneous » Endoreduplication inChinese HamsterCell Cultures. I. Effect of Growth Conditions

Abstract

Experiments have been performed in order to study the spontaneous appearance of cells with diplochromosomes (endoreduplicated cells) in Chinese Hamster cultures. Endoreduplicated cells are present in sub-cultures (sub-M-cultures) prepared by trypsinising cultures (M cultures) in the plateau phase of growth. Two conditions are particularly important for the appearance of endoreduplicated cells: a change of medium 3 days before trypsinisation and the growth of the M-cultures in a closed atmosphere from that moment on. The maximum frequency of endoreduplicated cells occurs when the M-cultures are grown in bottles that have been stoppered also during the 6–9 days prior to the change of medium. In these conditions the frequency of endoreduplicated cells found in the sub-M-cultures 26–30 hours after trypsinisation varies around 8%. In the crowed M-cultures, which grow in closed atmospheres, the change of medium is followed by an unbalanced cell growth that leads to a greater protein content per cell. On the basis of these data a possible mechanism is proposed for the formation of the endoreduplicated cells. The possible similarities between the cell populations that we studied and the neoplasias are also discussed.