DURING embryogenesis, all insects reach a conserved, or phylotypic, stage at which all future segments are present1,2. Different insects, however, arrive at this stage by overtly different pathways. In the long-germ insect Drosophila melanogaster, segmentation of the entire embryo occurs nearly simultaneously and results from the action of a cascade of transcriptional regulatory factors that operate in the acellular environment of the syncytial blastoderm3,4. In short-germ insects, segmentation occurs in an anterior-to-posterior sequence, within a cellular environment1, and might then be dependent on intercellular signalling5,6. To compare the molecular mechanisms of segmentation, we have isolated a homologue of the Drosophila wingless gene, a mediator of cell-cell communications7-9, from the short-germ beetle Tribolium castaneum. The principal features of wingless expression patterns in Drosophila are conserved in Tribolium, including its early deployment in rostral and caudal domains in the blastoderm, its segmental iteration in cells immediately anterior to cells expressing the engrailed, gene and its later restriction to a ventral sector of the developing appendages.
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