Double-segment defining role of even-skipped homologs along the evolution of insect pattern formation.

Recent studies on insect patterning suggest that the genetic hierarchy may be roughly conserved in phylogenetically divergent species, but pair-rule genes may not function identically in all insects. In order to understand potential evolutionary changes in the role of the pair-rule genes, a Bombyx even-skipped homolog was cloned and its expression pattern during early embryogenesis studied. Eight stripes of Bombyx even-skipped were progressively expressed in an antero-posterior order. Later, these stripes disappeared anteriorly. Under this detection system, Bombyx even-skipped stripes clearly do not resolve into the corresponding secondary stripes, an obvious difference from Drosophila and Tribolium. These results suggest that Bombyx even-skipped may serve a double-segment defining role and may determine the odd-numbered engrailed stripes.