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

Abstract

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 abdominal segment. This body plan is preserved in the adult in non-parasitic groups, while the parasitic rhizocephalan cirripedes completely lose arthropodian segmentation at the adult stage. These traits make them a particularly favourable model for studying the formation and maintenance of segmental identity. For the above reasons, it seemed worthwhile to look at the segmentation gene engrailed in a cirripede. A complete engrailed.a cDNA was isolated from larvae of the rhizocephalan cirripede Sacculina carcini. Its expression was monitored during larval development by use of the monoclonal antibody MAb4D9 directed against the Drosophila homologous proteins. The Sacculina engrailed.a gene is expressed during the second and third larval stages in stripes within a posterior area corresponding to the presumptive trunk segments. Surprisingly, these stripes appear in a posterior to anterior sequence. Six engrailed.a stripes characterize the thoracic segments of the cirripedean ground plan.

The Articulata hypothesis ? or what is a segment?

“…Segmentation genes: It has been shown for numerous representatives of all major euarthropod groups that the segment polarity gene engrailed is expressed in transverse stripes in the ectoderm of the posterior portion of forming segments (Patel et al 1989a, b;Scholtz & Dohle 1996;Damen et al 1998;Peterson et al 1998;Telford & Thomas 1998;Queinnec et al 1999;Arthur 2002;Hughes & Kaufman 2002b). In addition, there is a secondary, neuronal engrailed expression in the ganglion anlagen showing a highly similar pattern in crustaceans and insects (Patel et al 1989a, b;Scholtz 1995;Harzsch et al 1998;Duman-Scheel & Patel 1999) (Fig.…”

Heterospecific transgenesis in Drosophila suggests that engrailed.a is regulated by POU proteins in the crustacean Sacculina carcini

“…We have studied the engrailed genes of barnacle crustaceans in order to understand the peculiar segmentation of these organisms (Gibert et al 1997(Gibert et al , 2000Queinnec et al 1999). The cloning of these genes provides an interesting tool to investigate engrailed regulation in a non-insect arthropod.…”

Synchronism of naupliar development of Sacculina carcini Thompson, 1836 (Pancrustacea, Rhizocephala) revealed by precise monitoring

“…Furthermore, the durations of naupliar instars are identical between broods obtained from different specimens. Synchronous larval development has been proposed for Rhizocephala [8,46], but to our knowledge, has never been previously demonstrated until this work.…”