Cloning and expression of the engrailed.a gene of the barnacle Sacculina carcini

Cirripedia (barnacles) constitute a crustacean monophyletic taxon which is very well defined by several synapomorphies. In particular, all cirripedes are composed of six thoracic segments, but are devoid of any complete abdom inal segment. This body plan is preserved in the adult in non-parasitic gro ups, while the parasitic rhizocephalan cirripedes completely lose arthropod ian segmentation at the adult stage. These traits make them a particularly favourable model for studying the formation and maintenance of segmental id entity. For the above reasons, it seemed worthwhile to look at the segmenta tion gene engrailed in a cirripede. A complete engrailed.a cDNA was isolate d from larvae of the rhizocephalan cirripede Sacculina carcini. Its express ion was monitored during larval development by use of the monoclonal antibo dy MAb4D9 directed against the Drosophila homologous proteins. The Sacculin a engrailed.a gene is expressed during the second and third larval stages i n stripes within a posterior area corresponding to the presumptive trunk se gments. Surprisingly, these stripes appear in a posterior to anterior seque nce. Six engrailed.a stripes characterize the thoracic segments of the cirr ipedean ground plan.