Cell Fate Determination by Transcription Factors.

Transcription factors fulfill a key role in the formation and maintenance of different cell-types during development. It is known that transcription factors largely dissociate from chromosomes during mitosis. We found, previously, that mitosis is also a time when somatic nuclei can be far more easily reprogrammed after nuclear transfer than the nuclei of interphase cells. We refer to this as a mitotic advantage. Here, the rate of exchange of a transcription factor on its designated DNA-binding site is discussed. It is proposed that the Xenopus oocyte could serve as an experimental system in which the duration of binding site occupancy could be usefully analyzed. In particular, the Xenopus oocyte has several characteristics which make it possible to determine accurately the concentration and duration of transcription factor binding. It is proposed that the concentration and time are the key variables which govern the action of transcription factors when they activate genes needed for cell lineage determination.