CONSERVATION OF WINGLESS PATTERNING FUNCTIONS IN THE SHORT-GERM EMBRYOS OF TRIBOLIUM-CASTANEUM

DURING embryogenesis, all insects reach a conserved, or phylotypic, st age at which all future segments are present1,2. Different insects, ho wever, arrive at this stage by overtly different pathways. In the long -germ insect Drosophila melanogaster, segmentation of the entire embry o occurs nearly simultaneosly and results from the action of a cascade of transcriptional regulatory factors that operate in the acellular e nvironment of the syncytial blastoderm3,4. In short-germ insects, segm entation occurs in an anterior-to-posterior sequence, within a cellula r environment1, and might then be dependent on intercellular signallin g5,6. To compare the molecular mechanisms of segmentation, we have iso lated 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 cell s immediately anterior to cells expressing the engrailed gene, and its later restriction to a ventral sector of the developing appendages.