New Murine Homeoboxes: Structure, Chromosomal Assignment, and Differential Expression in Adult Erythropoiesis

The nucleotide sequence, chromosomal assignment, and preliminary transcriptional analysis of four murine homeoboxes is presented. Three of these are linked to the Hox-2 gene complex on chromosome 11, whereas the fourth, Hox-4, was assigned to mouse chromosome 12. A comparative analysis of homeobox sequences reveals that two of our sequences represent the previously described Hox-2.2 and Hox-2.3 loci, whereas a third, mhl9, could represent the predicted Hox-2.6 locus. Homeoboxes Hox-2.2 and Hox-2.3 are the cognates of two previously reported human homeoboxes that belong to a similar gene cluster on a closely related human chromosome (Chr 17), suggesting that homeoboxes may have been preserved as clusters during evolution. Moreover Hox-4, mhl9, and the previously described Hox-1.5 homeobox form a separate subgroup of mammalian homeoboxes (90–92% amino acid and nucleotide homology). All four homeoboxes are expressed in the mouse embryo. Of special interest is the expression of mhl9, a 4.2-kb transcript of which appears to be connected to the induced differentiation of Friend erythroleukemia cells.