Abstracts - Deutsche Zoologische Gesellschaft

120 Developmental Biology PostersP DB.3 - ENDevelopment of nephridia in the polychaete Platynereis dumeriliiChristian Hasse, Wencke Reiher, Kathrin Sobjinski, Nicole Rebscher, Monika HasselSpezielle Zoologie und Evolution der Tiere, Fb. 17, Philipps-Universität MarburgNephridia are excretory organs invented at the base of bilateral symmetric animals. Morphologicalinvestigations showed that in polychaetes, the larval protonephridia are later on replaced bymetanephridia (1). The knowledge about their development is still fragmentary. In our study weanalysed formation of nephridia in embryonic, larval and adult stages of Platynereis dumerilii.Alkaline phosphatase (AlP) served as a marker. The first results suggest that during development 3morphologically and biochemically distinct types of nephridia form. These structures are also positivefor b-tubulin. AlP activity is first detectable in paired tubular structures lateral to the stomodaeumat 72 hrs of development (metatrochophora). In young worms containing 7 segments a pairof tubular structures between segments 1 and 2 is AlP-positive. In posterior segments, funnelled,segment-spanning tubular structures develop. In order to analyse if Platynereis nephridia containdistinct AlP isoforms, we used levamisol as a selective inhibitor. It inhibited AlP activity in theproximal but not in the distal part of the metanephridial tubule. Our study reveals complex morphologicalchanges during nephridiogenesis in Platynereis. Two different types of nephridia form– early, presumable protonephridia, and later, mature metanephridia. The presence of at least twodistinct AlP isoforms suggests functional specialisation between different regions of the tubule. (1)Bartolomaeus, T. Hydrobiologia 402: 21-37 (1999)P DB.4 - ENA presumptive germ plasm contains ß-Catenin RNA in the crustacean ParhyalehawaiensisJohanna Havemann, Matthias GerberdingMax-Planck-Institut für Entwicklungsbiologie, TübingenThe 8-cell stage of the amphipod crustacean Parhyale hawaiensis is set up of progenitor cells for allthree germ layers and the germ line. At this stage, the highly conserved ß-Catenin RNA localizes to asingle cell, the germ cell progenitor “g”. At the 1-cell stage, ß-Catenin RNA localizes to the cortex ina yolk-free cytoplasmic area, as ultrastructure analysis by transmission electron microscopy reveals.With the first division, the RNA is moved into the central cytoplasm of one daughter cell at the 2-cellstage. Until the 8-cell stage, RNA inheritance occurs asymmetrically to one cell. Subsequent cleavagessegregate it symmetrically to all daughter cells. During divisions, the RNA is attached to thecentrosome and its transport presumably occurs via cytoskeletal elements, but not actin. ß-Cateninprotein starts to be expressed zygotically at germ disc stage at day 1 and is clearly upregulated in thecytoplasm of the germ cells. Morpholino injections abolished protein expression, but did not exhibitany morphological phenotype. We suggest the presence of a germ plasm in the zygote of Parhyaleand continue functional analyses to identify possible roles of ß-Catenin during early crustaceandevelopment. Contrary to what has been described in other organisms such as Xenopus, zebrafish,Platynereis and nemerteans, ß-Catenin is not involved in axis establishment but restricted to thegerm line in early Parhyale embryogenesis.