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General conclusions and perspectives for future research 27 General conclusions and perspectives for future research The results presented herein are the first developmental gene expression studies in Brachiopoda, as well as the first detailed comparative description of myogenesis and neurogenesis in brachiopod larvae based on antibody staining, confocal laserscanning microscopy, and 3D reconstruction software. This study shows that microanatomical data can yield new insights into the evolution and development of lesser known metazoan phyla such as Brachiopoda. It provides the first evidence of an apical organ in brachiopod larvae that comprises serotonergic flask-shaped cells, similar to those found in ectoprocts and spiralians. This result strongly suggests that such an apical organ constitutes a morphological apomorphy of Lophotrochozoa. Gene expression analyses of TtrNot imply an ancestral role of this gene in gastrulation and ectoderm specification in Brachiopoda. The function of Not in notochord formation in chordates and left/right determination in ambulacrarians and vertebrates might thus be co-opted in these deuterostome clades. Analysis of the TtrCdx gene expression suggests an ancestral role in gastrulation and the formation of posterior tissues in Brachiopoda as well as in Bilateria in general. Further studies should extend the database of brachiopod morphogenesis and gene expression patterns to more organ systems as well as to the third brachiopod subtaxon, Linguliformea. This would allow for a full representation of the phylum Brachiopoda with its three clades Craniiformea, Linguliformea, and Rhynchonelliformea and should allow significant inferences concerning gene function and organ system evolution within this lophophorate phylum. Such data would allow insights into the evolution of organ systems, and body plans in Brachiopoda. Additionally, investigation of gene expression patterns in Brachiopoda is needed in order to compare the function of genes, co-option, and ancestral gene functions among Brachiopoda and other animal phyla. An expressed sequence tags or genome-based approach would be the best choice in order to obtain the sequences of the whole range of developmental genes. Preferably, this should be done for one representative of each brachiopod clade. Morphological and molecular data together would facilitate the reconstruction of the evolution of organ systems in Brachiopoda once the phylogenetic position of Brachiopoda and its sister groups has been settled.
28 References References Abdelkhalek, H. B., Beckers, A., Schuster-Gossler, K., Pavlova, M. N., Burkhardt, H., Lickert, H., Rossant, J., Reinhardt, R., Schalkwyk, L. C., Müller, I., Herrmann, B. G., Ceolin, M., Rivera-Pomar, R., and Gossler, A. 2004. The mouse homeobox gene Not is required for caudal notochord development and affected by the truncate mutation. Genes Dev 18:1725- 1736. Anderson, D. 1973. Embryology and Phylogeny in Annelids and Arthropods. Oxford: Pergamon Press Ltd. Anderson, P. and Trapido-Rosenthal, H. 2009. Physiological and chemical analysis of neurotransmitter candidates at a fast excitatory synapse in the jellyfish Cyanea capillata (Cnidaria, Scyphozoa). Invert Neurosci 9:167-173. Arendt, D., Denes, A. S., Jékely, G., and Tessmar-Raible, K. 2008. The evolution of nervous system centralization. Philos Trans R Soc Lond B Biol Sci 363:1523-1528. Arendt, D. and Nübler-Jung, K. 1999. Comparison of early nerve cord development in insects and vertebrates. Development 126:2309-2325. Arendt, D., Technau, U., and Wittbrodt, J. 2001. Evolution of the bilaterian larval foregut. Nature 409:81-85. Ax, P. 2003. Multicellular animals: Order in nature - system made by man. Vol. III. Heidelberg: Springer. Balczarek, K. A., Lai, Z. C., and Kumar, S. 1997. Evolution of functional diversification of the paired box (Pax) DNA-binding domains. Mol Biol Evol 14:829-842. Benito-Gutiérrez, È. and Arendt, D. 2009. CNS evolution: New insight from the mud. Curr Biol 19:R640-R642. Blochmann, F. 1892a. Ueber die Anatomie und die verwandtschaftlichen Beziehungen der Brachiopoden. Arch. Freunde Naturgesch. Mecklenbg. 46:37-50. Blochmann, F. 1892b. Untersuchungen über den Bau der Brachiopoden. Jena: Gustav Fischer. Brinkmann, N. and Wanninger, A. 2008. Larval neurogenesis in Sabellaria alveolata reveals plasticity in polychaete neural patterning. Evol Dev 10:606-618. Brinkmann, N. and Wanninger, A. 2010. Integrative analysis of polychaete ontogeny: cell proliferation patterns and myogenesis in trochophore larvae of Sabellaria alveolata. Evol Dev 12:5-15.
Page 1 and 2: Comparative neurogenesis, muscle de
Page 3 and 4: 2 Principal supervisor Assoc. P
Page 5 and 6: 4 Preface This thesis presents
Page 7 and 8: 6 Abstract Brachiopods are a sm
Page 9 and 10: 8 Acknowledgements The endeavou
Page 11 and 12: 10 Introduction Nervous system Micr
Page 13 and 14: 12 Material and methods Material an
Page 15 and 16: 14 Material and methods purpuratus,
Page 17 and 18: 16 Results and discussion Results a
Page 19 and 20: 18 Results and discussion posterior
Page 21 and 22: 20 Results and discussion Myogenesi
Page 23 and 24: 22 Results and discussion Wanninger
Page 25 and 26: 24 Results and discussion Growth pa
Page 27: 26 Results and discussion argument
Page 31 and 32: 30 References priapulids and protos
Page 33 and 34: 32 References James, M. A., Ansell,
Page 35 and 36: 34 References regionalization, prol
Page 37 and 38: 36 References 211. Williams, A., Ca
Page 39 and 40: 38 Chapter II Frontiers in Zoology
Page 53 and 54: 52 Chapter III Chapter III Altenbur
Page 55 and 56: 54 Chapter III Altenburger and Wann
Page 63 and 64: 62 Chapter IV Chapter IV Altenburge
Page 65 and 66: 64 Submitted manuscript Chapter IV
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78 Submitted manuscript Chapter IV
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