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Formation of calcified biominerals is widespread in marine animals and is often associated with important elements of their biology, such as support and protection. Serpulid polychaetes are relatively understudied examples of biomineralisation despite their prominence in many marine ecosystems. An investigation of calcification in the regenerating opercular plate of the serpulid polychaete Spirobranchus (formerly Pomatoceros) lamarcki was performed using optical microscopy, calcein labelling and powder diffraction analysis. Worms were collected between January 2012 and June 2013 from East Sands beach, St Andrews, Scotland (56.33°N, 2.78°W). The earliest visible signs of calcification were birefringent grains. Later-stage regenerates displayed a complex mixture of calcified structures including grains, round, smooth tiles, and larger tiles with a rugged appearance. The plate matures by the growth and eventual merging of tiles into a contiguous crust. Calcein pulse-chase experiments showed the progression of calcification from the centre towards the edge of the plate, and powder diffraction analysis of three regenerative stages revealed a major shift in mineralogy from a predominantly calcitic to a predominantly aragonitic composition. The mechanisms underlying the shift are currently unknown. These are the first mineralogical data comparing different developmental stages in a serpulid operculum and contribute to the understanding of biomineralisation in this group., Introduction Organisms with mineralised hard parts are cornerstones of many marine ecosystems. Biomineralisation occurs in phylogenetically diverse organisms and fulfils a wide variety of functions from skeletal support through defence [...]

Sponges are simple animals with few cell types, but their genomes paradoxically contain a wide variety of developmental transcription factors (1-4), including homeobox genes belonging to the Antennapedia (ANTP) class [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2008.11.027 Byline: Peter W. Osborne (a), Gerard Benoit (b), Vincent Laudet (b), Michael Schubert (b), David E.K. Ferrier (a) Keywords: Amphioxus; Retinoic acid; Gsx; Xlox; Cdx; ParaHox; Gene regulation; Evolution; Endoderm patterning Abstract: The ParaHox cluster is the evolutionary sister to the Hox cluster. Like the Hox cluster, the ParaHox cluster displays spatial and temporal regulation of the component genes along the anterior/posterior axis in a manner that correlates with the gene positions within the cluster (a feature called collinearity). The ParaHox cluster is however a simpler system to study because it is composed of only three genes. We provide a detailed analysis of the amphioxus ParaHox cluster and, for the first time in a single species, examine the regulation of the cluster in response to a single developmental signalling molecule, retinoic acid (RA). Embryos treated with either RA or RA antagonist display altered ParaHox gene expression: AmphiGsx expression shifts in the neural tube, and the endodermal boundary between AmphiXlox and AmphiCdx shifts its anterior/posterior position. We identified several putative retinoic acid response elements and in vitro assays suggest some may participate in RA regulation of the ParaHox genes. By comparison to vertebrate ParaHox gene regulation we explore the evolutionary implications. This work highlights how insights into the regulation and evolution of more complex vertebrate arrangements can be obtained through studies of a simpler, unduplicated amphioxus gene cluster. Author Affiliation: (a) Zoology Department, Oxford University, South Parks Road, Oxford, OX1 3PS, UK (b) Institut de Genomique Fonctionnelle de Lyon, Universite de Lyon, CNRS, INRA, Universite Claude Bernard Lyon 1, Ecole Normale Superieure de Lyon, 46 allee d'Italie, 69364 Lyon Cedex 07, France Article History: Received 2 October 2008; Revised 19 November 2008; Accepted 19 November 2008

Lancelets ('amphioxus') are the modern survivors of an ancient chordate lineage, with a fossil record dating back to the Cambrian period. Here we describe the structure and gene content of [...]

Evx genes are widely used in animal development. In vertebrates they are crucial in gastrulation, neurogenesis, appendage development and tailbud formation, whilst in protostomes they are involved in gastrulation and neurogenesis, as well as segmentation at least in Drosophila. We have cloned the Evx genes of amphioxus (Branchiostoma floridae), and analysed their expression to understand how the functions of Evx have evolved between invertebrates and vertebrates, and in particular at the origin of chordates and during their subsequent evolution. Amphioxus has two Evx genes (AmphiEvxA and AmphiEvxB) which are genomically linked. AmphiEvxA is prototypical to the vertebrate Evx1 and Evx2 genes with respect to its sequence and expression, whilst AmphiEvxB is very divergent. Mapping the expression of AmphiEvxA onto a phylogeny shows that a role in gastrulation, dorsal--ventral patterning and neurogenesis is probably retained throughout bilaterian animals. AmphiEvxA expression during tailbud development implies a role for Evx throughout the chordates in this process, whilst lack of expression at the homologous region to the vertebrate Midbrain-Hindbrain Boundary (MHB) is consistent with the elaboration of the full organiser properties of this region being a vertebrate innovation. Key Words: Amphioxus; Evx genes; chordates; gastrulation; neurogenesis; Midbrain--Hindbrain Boundary; tailbud development.

Examination of the Hox genes of the grasshopper, Schistocerca gregaria. S. gregaria homologues of Scr, abd-A, Abd-B and fiz hybridize to the same short chromosome; Minimum size of the grasshopper cluster; Grasshopper eve is not closely linked to Abd-B.