Coordinate HOX regulation in hematopoietic cells

Magli with co-workers [1991] have analyzed expression of the four human HOX loci in erythroleukemic, promyelocytic, and monocytic cell lines to investigate whether the physical organization of human Hox genes reflects a regulatory hierarchy involved in the differentiation process of hematopoetic cells. These results demonstrate that cells representing various stages of hematopoetic differentiation display differential pattern of Hox gene expression and that Hox genes are coordinately switched on or off in blocks that may include entire loci. The entire HOX-4 locus is silent in all lines analyzed and almost all HOX-2 genes are active in erythroleukemic cells and turned off in myeloid-restricted cells. In some instances, for example in the mouse embryonic CNS and prevertebral system, it has been found that corresponding genes within the groups are expressed in the same domains (Mouse homeo-genes within a subfamily, Hox-1.4, -2.6 and -5.1, display similar anteroposterior domains of expression in the embryo, but show stage- and tissue-dependent differences in their regulation.Gaunt et al., 1989. Chromosome assignment of the murine Hox-4.1 gene.Gaunt et al., 1989). This does not seem to be the case in the hematopoietic system, here Hox gene expression appears rather to be concerted within the individual loci. However, they observed that vertical group 5 seems to represent a boundary that defines genes 3' and 5' displaying different expression patterns.