Die molekulare Evolution der Hämocyaninsuperfamilie der Arthropoden

In vielen Arthropoden wird Sauerstoff mittels des Kupferproteins Hämocyanin transportiert. In der vorliegenden Arbeit wurde das Hämocyanin einiger Vertreter der Arthropoden molekularbiologisch untersucht. Bei den Crustaceen (Homarus americanus und Palinurus elephas) konnten vier Untereinheiten isoliert werden, bei denen es sich um Hämocyanine des a-Typs handelt. Bei den Myriapoden (Chilopoda, Scutigera coleoptrata und Diplopoda, Spirostreptus spec.) konnten drei unterschiedliche Hämocyaninuntereinheiten gefunden werden. Erst seit einiger Zeit ist das Hämocyanin bei Myriapoden biochemisch charakterisiert und bei diesen Hämocyaninsequenzen handelt es sich um die ersten von Myriapoden. Bei den Onychophoren (Epiperipatus spec.) konnte ebenfalls erstmals ein Hämocyanin isoliert und sequenziert werden. Hierbei handelt es sich um den ersten Hinweis, dass Onychophoren über ein respiratorisches Protein verfügen. In einer phylogenetischen Analyse der Hämocyaninsequenzen konnte ein Stammbaum der Hämocyaninsuperfamilie erstellt werden. Innerhalb der Crustacea ordnen sich die verschiedenen Hämocyaninuntereinheiten in distinkten Ästen an. Die Hämocyanine der Myriapoda sind monophyletisch, wobei die Auftrennung in distinkte Untereinheiten bereits vor der Trennung der Chilopoden und Diplopoden erfolgte; die phylogenetische Stellung der Myriapoda kann anhand der Hämocyaninsequenzen nicht zuverlässig aufgelöst werden. Eine gemeinsame Anordnung mit den Hexapoda ('Tracheata'-Hypothese) kann jedoch mit hoher Sicherheit ausgeschlossen werden. Die Onychophora stehen im Arthropodenstammbaum an basaler Position und können somit als Proarthropoda angesprochen werden. Es konnte gezeigt werden, dass die Hämocyaninevolution der Arthropodenevolution entspricht.

Early steps in ventral nerve cord development in chelicerates and myriapods and formation of brain compartments in spiders

The central point of this work is the investigation of neurogenesis in chelicerates and myriapods. By comparing decisive mechanisms in neurogenesis in the four arthropod groups (Chelicerata, Crustacea, Insecta, Myriapoda) I was able to show which of these mechanisms are conserved and which developmental modules have diverged. Thereby two processes of embryonic development of the central nervous system were brought into focus. On the one hand I studied early neurogenesis in the ventral nerve cord of the spiders Cupiennius salei and Achaearanea tepidariorum and the millipede Glomeris marginata and on the other hand the development of the brain in Cupiennius salei.rnWhile the nervous system of insects and crustaceans is formed by the progeny of single neural stem cells (neuroblasts), in chelicerates and myriapods whole groups of cells adopt the neural cell fate and give rise to the ventral nerve cord after their invagination. The detailed comparison of the positions and the number of the neural precursor groups within the neuromeres in chelicerates and myriapods showed that the pattern is almost identical which suggests that the neural precursors groups in these arthropod groups are homologous. This pattern is also very similar to the neuroblast pattern in insects. This raises the question if the mechanisms that confer regional identity to the neural precursors is conserved in arthropods although the mode of neural precursor formation is different. The analysis of the functions and expression patterns of genes which are known to be involved in this mechanism in Drosophila melanogaster showed that neural patterning is highly conserved in arthropods. But I also discovered differences in early neurogenesis which reflect modifications and adaptations in the development of the nervous systems in the different arthropod groups.rnThe embryonic development of the brain in chelicerates which was investigated for the first time in this work shows similarities but also some modifications to insects. In vertebrates and arthropods the adult brain is composed of distinct centres with different functions. Investigating how these centres, which are organised in smaller compartments, develop during embryogenesis was part of this work. By tracing the morphogenetic movements and analysing marker gene expressions I could show the formation of the visual brain centres from the single-layered precheliceral neuroectoderm. The optic ganglia, the mushroom bodies and the arcuate body (central body) are formed by large invaginations in the peripheral precheliceral neuroectoderm. This epithelium itself contains neural precursor groups which are assigned to the respective centres and thereby build the three-dimensional optical centres. The single neural precursor groups are distinguishable during this process leading to the assumption that they carry positional information which might subdivide the individual brain centres into smaller functional compartments.rn