THE EXPRESSION OF THE C-ELEGANS LABIAL-LIKE HOX GENE CEH-13 DURING EARLY EMBRYOGENESIS RELIES ON CELL FATE AND ON ANTEROPOSTERIOR CELL POLARITY

Clusters of homeobox-containing HOM-C/hox genes determine the morpholo gy of animal body plans and body parts and are thought to mediate posi tional information. Here, we describe the onset of embryonic expressio n of ceh-13, the Caenorhabditis elegans orthologue of the Drosophila l abial gene, which is the earliest gene of the C. elegans Hox gene clus ter to be activated in C. elegans development. At the beginning of gas trulation, ceh-13 is asymmetrically expressed in posterior daughters o f anteroposterior divisions, first in the posterior daughter of the in testinal precursor cell E and then in all posterior daughters of the A B descendants ABxxx. In this paper, we present evidence that supports position-independent activation of ceh-13 during early C. elegans embr yogenesis, which integrates cell fate determinants and cell polarity c ues. Our findings imply that mechanisms other than cell-extrinsic ante roposterior positional signals play an important role in the activatio n and regulation of the C. elegans Hox gene ceh-13.