Polycomb-group genes and hematopoiesis

Although long-range chromatin organization during cell differentiation has not yet been determined, considerable evidence suggests that regulation of the chromatin structure may play a crucial part in transcriptional regulati on. Drosophila genetics has introduced a unique system that can maintain ge nes in the on or off state after the initial gene expression decision has b een established. This maintenance system is known to be mediated through th e trithorax-group (trxG) and Polycomb-group (PcG) genes. The products from these 2 genes individually form multimeric complexes in the chromatin. The trxG genes are known to maintain the transcriptionally active states of the chromatin, and the PcG genes are thought to maintain the repressive states . The function of the PcG genes is defined in terms of anteroposterior patt erning not only in Drosophila but also in mammals, whereas mammalian PcG ge nes have additional functions in higher order biological functions. All PcG gene-deficient mice have provided evidence that these genes play a crucial role in hematopoiesis These findings should help shed new light on the rol es of the chromatin regulatory system in hematopoiesis. Int J Hematol. 2000 ;72:165-172. (C) 2000 The Japanese Society of Hematology.