title: Expression of segment polarity genes in brachiopods supports a non-segmental ancestral role of engrailed for bilaterians.
abstract: The diverse and complex developmental mechanisms of segmentation have been more thoroughly studied in arthropods, vertebrates and annelids-distantly related animals considered to be segmented. Far less is known about the role of "segmentation genes" in organisms that lack a segmented body. Here we investigate the expression of the arthropod segment polarity genes engrailed, wnt1 and hedgehog in the development of brachiopods-marine invertebrates without a subdivided trunk but closely related to the segmented annelids. We found that a stripe of engrailed expression demarcates the ectodermal boundary that delimits the anterior region of Terebratalia transversa and Novocrania anomala embryos. In T. transversa, this engrailed domain is abutted by a stripe of wnt1 expression in a pattern similar to the parasegment boundaries of insects-except for the expression of hedgehog, which is restricted to endodermal tissues of the brachiopod embryos. We found that pax6 and pax2/5/8, putative regulators of engrailed, also demarcate the anterior boundary in the two species, indicating these genes might be involved in the anterior patterning of brachiopod larvae. In a comparative phylogenetic context, these findings suggest that bilaterians might share an ancestral, non-segmental domain of engrailed expression during early embryogenesis.
authors: Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5006 Bergen, Norway.
authors: Bruno C
authors: BC
authors: Vellutini
authors: Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5006 Bergen, Norway.
authors: Andreas
authors: A
authors: Hejnol
mesh_terms: D000818:Animals; D060829:Arthropod Proteins / Q000235:genetics; D001181:Arthropods / Q000145:classification / Q000196:embryology / Q000235:genetics*; D019521:Body Patterning / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism*; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics; D007814:Larva / Q000235:genetics; D010802:Phylogeny; D014157:Transcription Factors / Q000235:genetics; D051155:Wnt1 Protein / Q000235:genetics
chemical_list: D060829:Arthropod Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; D051155:Wnt1 Protein