Theoretical Considerations of Genetic Regulation of Granulopoiesis

In a theoretical model describing the factoral hypotheses of granulopoietic control in terms of modern concepts of genetic regulation, the sequential nature of the differentiation process is explained as co-induction of operons or "gene clusters." The full derepression of the operator gene is possible in the presence of both a primary inducing "factor," and a "co-inducer" produced by the last structural gene in the preceding operon. The "coinducer" and "factor" act together to remove the repressor substance and to allow full functioning of the operon. When the inducer is removed or inactivated, feedback repression of earlier steps in the maturation sequence is noted. It is probable that this takes place at the translational level or during enzyme synthesis. Finally, the possibility exists that primary control of granulopoiesis occurs at the transcriptional or translational level. The presence of only two distinct factors ("maturation" and "release") would be prejudicial to translational control, but at present little evidence either supporting or refuting transcriptional control is available.