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Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.04.041 Byline: Kristin Tessmar-Raible (1), Florian Raible (1)(2), Foteini Christodoulou (1), Keren Guy (1), Martina Rembold (1), Harald Hausen (3), Detlev Arendt (1) Keywords: DEVBIO; EVO_ECOL; RNA Abstract: Neurosecretory control centers form part of the forebrain in many animal phyla, including vertebrates, insects, and annelids. The evolutionary origin of these centers is largely unknown. To identify conserved, and thus phylogenetically ancient, components of neurosecretory brain centers, we characterize and compare neurons that express the prohormone vasotocin (vasopressin/oxytocin)-neurophysin in the developing forebrain of the annelid Platynereis dumerilii and of the zebrafish. These neurons express the same tissue-restricted microRNA, miR-7, and conserved, cell-type-specific combinations of transcription factors (nk2.1, rx, and otp) that specify their identity, as evidenced by the specific requirement of zebrafish rx3 for vasotocin-neurophysin expression. MiR-7 also labels another shared population of neurons containing RFamides. Since the vasotocinergic and RFamidergic neurons appear to be directly sensory in annelid and fish, we propose that cell types with dual sensory-neurosecretory properties were the starting point for the evolution of neurosecretory brain centers in Bilateria. Author Affiliation: (1) Developmental Biology Unit, European Molecular Biology Laboratory, MeyerhofstraAe 1, D-69012 Heidelberg, Germany (2) Computational Biology Unit, European Molecular Biology Laboratory, MeyerhofstraAe 1, D-69012 Heidelberg, Germany (3) Institut fur Biologie, FU Berlin, Konigin-Luisen-StraAe 1-3, D-14195 Berlin, Germany Article History: Received 3 August 2006; Revised 12 January 2007; Accepted 26 April 2007 Article Note: (miscellaneous) Published: June 28, 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.08.070 Byline: Florian Raible (a)(b), Kristin Tessmar-Raible (b), Enrique Arboleda (c), Tobias Kaller (b)(d), Peer Bork (a), Detlev Arendt (b), Maria I. Arnone (c) Keywords: Sea urchin; Rhodopsin-type G-protein-coupled receptor (GPCR); Opsin; Surreal-GPCR; Gene cluster; Chemosensation; Olfaction; Pedicellariae, Tube feet Abstract: Rhodopsin-type G-protein-coupled receptors (GPCRs) contribute the majority of sensory receptors in vertebrates. With 979 members, they form the largest GPCR family in the sequenced sea urchin genome, constituting more than 3% of all predicted genes. The sea urchin genome encodes at least six Opsin proteins. Of these, one rhabdomeric, one ciliary and two G.sub.o-type Opsins can be assigned to ancient bilaterian Opsin subfamilies. Moreover, we identified four greatly expanded subfamilies of rhodopsin-type GPCRs that we call sea urchin specific rapidly expanded lineages of GPCRs (surreal-GPCRs). Our analysis of two of these groups revealed genomic clustering and single-exon gene structures similar to the most expanded group of vertebrate rhodopsin-type GPCRs, the olfactory receptors. We hypothesize that these genes arose by rapid duplication in the echinoid lineage and act as chemosensory receptors of the animal. In support of this, group B surreal-GPCRs are most prominently expressed in distinct classes of pedicellariae and tube feet of the adult sea urchin, structures that have previously been shown to react to chemical stimuli and to harbor sensory neurons in echinoderms. Notably, these structures also express different opsins, indicating that sea urchins possess an intricate molecular set-up to sense their environment. Author Affiliation: (a) Computational Unit, EMBL, 69117 Heidelberg, Germany (b) Developmental Unit, EMBL, 69117 Heidelberg, Germany (c) Stazione Zoologica Anton Dohrn, 80121 Napoli, Italy (d) FU Berlin, Institut fur Biologie, Chemie, Pharmazie, Zoologie, Evolution und Systematik der Tiere, 14195 Berlin, Germany Article History: Received 7 June 2006; Revised 28 August 2006; Accepted 30 August 2006