Detlev Arendt

..This is also reflected in the level of genes, making these groups ideally suited for developmental comparative studies...

..Our data thus support the view that an ancestral ground pattern of segmental identities existed in the trunk of the last common protostome ancestor that was lost or modified in protostomes lacking overt segmentation...

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..Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution...

..Also, they outline a minimum set of cell types and tissues that existed in the protostome-deuterostome ancestor...

..Our data indicate that this mediolateral architecture was present in the last common bilaterian ancestor and thus support a common origin of nervous system centralization in Bilateria...

..This way, different aspects of the molecular architecture of the urbilaterian nervous system are reconstructed and yield insight into the degree of centralization that was in place in the bilaterian ancestors...

..I propose that the retinal ganglion, amacrine and horizontal cells are evolutionary sister cell types that evolved from a common rhabdomeric photoreceptor cell precursor...

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..We propose that the underlying direct coupling of light sensing and ciliary locomotor control was a principal feature of the proto-eye and an important landmark in the evolution of animal eyes...

..We propose that pax6-, six1/2- and ath-positive larval eyes, as found in today's trochophora, were present already in Urbilateria...

..Based on these findings, we propose that convergent extension movements of the trunk neuroectoderm represent an ancestral feature of bilaterian development that triggered the separation of mouth and anus along the elongating trunk...

..These data indicate deep homology of pallium and mushroom bodies and date back the origin of higher brain centers to prebilaterian times...

..A report on the annual UK Evolutionary Developmental Biology meeting, Oxford, UK, 13 September 2004...

..Whole-mount reflection CLSM will thus greatly facilitate large-scale cellular resolution expression profiling in vertebrate and invertebrate model organisms...

..A comparison of coding exon sequences confirms the ancestral nature of Platynereis and human genes. Thus, the urbilaterian ancestor had complex, intron-rich genes that have been retained in Platynereis and human...

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..Availability: AQUA is implemented in Tcl/Tk and runs in command line on all platforms. The source code is available under the GNU GPL license. Source code, README and Supplementary data are available at http://www.bork.embl.de/Docu/AQUA...

..The most surprising outcome is that human genes seem to be closer to the bilaterian roots than previously assumed...

..4DXpress will be an invaluable tool for developmental as well as for computational biologists interested in gene regulation and evolution. 4DXpress is available at http://ani.embl.de/4DXpress...

..Notably, these structures also express different opsins, indicating that sea urchins possess an intricate molecular set-up to sense their environment...

..Here, a similar "molecular fingerprint" of cells is taken as indication of cross-bilaterian homology. This approach makes it possible to reconstruct the cell-type repertoire of the urbilaterian nervous system...

..Functional segregation of cell types in eye evolution also explains the emergence of more elaborate photosensory-motor axonal circuits, with interneurons relaying the visual information...

..abstract:..

..We propose a scenario for how the initial membrane patch gradually protruded to enhance exposure to the environment, then started to move, and finally compartmentalised to render receptor signalling and ciliary beating more efficient...

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..In agreement with similarities in segment ontogeny and morphological organization in arthropods and annelids, we interpret our results as molecular evidence of a segmented ancestor of protostomes...

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..These data suggest altogether that these functions are ancestral to protostomes...