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SUMMARY:Fitting pieces and further puzzles - What 'nobody' can tell about 
 the evolution of arthropod neurogenesis - Georg Brenneis\, Humboldt Univer
 sity Berlin\, Germany
DTSTART:20120523T120000Z
DTEND:20120523T130000Z
UID:TALK37721@talks.cam.ac.uk
CONTACT:Vera Hunnekuhl
DESCRIPTION:Fitting pieces and further puzzles - What 'nobody' can tell ab
 out the evolution of arthropod neurogenesis\n\nPycnogonida (sea spiders or
  ‘nobodies’) are a group of bizarre marine arthropods being now genera
 lly considered as basal-most chelicerate branch or alternatively even disc
 ussed as earliest extant offshoot from the euarthropod lineage. Given this
  interesting position\, investigation of pycnogonid development promises t
 o contribute important data for the unravelling of arthropod evolution. Du
 ring the last two decades\, new data on early neurogenesis in different ar
 thropod lineages has led to a vivid discussion about the evolution of arth
 ropod nervous system development. However\, a re-investigation of sea spid
 er neurogenesis is still lacking. We studied early neurogenesis in Pseudop
 allene sp.\, a pycnogonid with prolonged embryonic development. It is char
 acterised by immigration of cells and cell clusters lacking mitotic activi
 ty\, similar to euchelicerates and myriapods. In contrast to the latter tw
 o lineages\, only part of the immigrating cell groups can be shown to aris
 e in a stereotyped arrangement\, which is potentially due to spatial restr
 ictions of the neuroectoderm. Intriguingly\, big flask-shaped cells with h
 igh mitotic activity are encountered in paired neuroectodermal invaginatio
 ns during later embryonic development. These cells represent morphological
 ly distinct neural precursor cells\, a feature unknown for all euchelicera
 tes investigated so far and only tentatively discussed for some myriapod r
 epresentatives. In terms of cell size\, position and proliferation activit
 y\, the pycnogonid neural precursors show some correspondences to tetracon
 ate neuroblasts. However\, for the assessment of more detailed similaritie
 s or differences cell lineage studies and gene expression data are indispe
 nsable. During postembryonic development\, the neural precursor cells deta
 ch from the ectoderm and form small segmental clusters on the ventral side
  of the growing ganglion anlagen. A persisting connection between ganglia 
 and ventral cell clusters via ‘cell-streams’\, coupled to mitosis patt
 erns and ganglion cell counts indicates the clusters to act as source for 
 additional neuronal cell material during postembryonic life. The ‘cluste
 r/cell-stream/ganglion’ composition shows structural similarities to the
  life-long active neurogenic niche in the olfactory system of some crustac
 eans. A similar function of the pycnogonid ventral clusters is discussed.
LOCATION:Part II Lecture Theatre\, Department of Zoology
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