Elimination of EVE protein by CALI in the short germ band insect Triboliumsuggests a conserved pair-rule function for even skipped

The question of the degree of evolutionary conservation of the pair-rule pa tterning mechanism known from Drosophila is still contentious. We have empl oyed chromophore-assisted laser inactivation (CALI) to inactivate the funct ion of the pair-rule gene even skipped (eve) in the short germ embryo of th e flour beetle Tribolium. We show that it is possible to generate pair-rule type phenocopies with defects in alternating segments. Interestingly, we f ind the defects in odd numbered segments and not in even numbered ones as i n Drosophila. However, this apparent discrepancy can be explained if one ta kes into account that the primary action of eve is at the level of parasegm ents and that different cuticular markers are used for defining the segment borders in the two species. In this light, we find that eve appears to be required for the formation of the anterior borders of the same odd numbered parasegments in both species. We conclude that the primary function of eve as a pair rule gene is conserved between the two species. (C) 1999 Elsevie r Science Ireland Ltd. All rights reserved.