CORRECT HOX GENE-EXPRESSION ESTABLISHED INDEPENDENTLY OF POSITION IN CAENORHABDITIS-ELEGANS

THE Hox genes are expressed in a conserved sequence of spatial domains along the anteroposterior (A/P) body axes of many organisms(1). In Dr osophila, position-specific signals located along the A/P axis establi sh the pattern of Hox gene expression(2-4). In the nematode Caenorhabd itis elegans, it is not known how the pattern of Hox gene expression i s established, C. elegans uses lineal control mechanisms and local cel l interactions to specify early blastomere identities(5,6). However, m any cells expressing the same Hox gene are unrelated by lineage, sugge sting that, as in Drosophila, domains of Hox gene expression may be de fined by cell-extrinsic A/P positional signals. To test this, we have investigated whether posterior mesodermal and ectodermal cells will ex press their normal posterior Hox gene when they are mispositioned in t he anterior. Surprisingly, we find that correct Hox gene expression do es not depend on cell position, but is highly correlated with cell lin eage, Thus, although the most striking feature of Hox gene expression is its positional specificity, in C. elegans the pattern is achieved, at least in part, by a lineage-specific control system that operates w ithout regard to A/P position.