MSc Student
Supervisor: Georg Brenneis

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna

Abstract

Pycnogonida (sea spiders) is a group of bizarre marine arthropods, which are widely accepted as a member of the Chelicerata (true spiders, scorpions and kin), in which they represent the sister group of all remaining extant taxa (termed Euchelicerata). Interestingly, the development of the nervous system, i.e. neurogenesis, in pycnogonids differs from that of other chelicerates in that it appears to feature large neural stem cells (NSCs) which show high mitotic activity as well as a morphologically asymmetric mode of division. These cells show many similarities with neuroblasts (NBs), a well-characterized type of neural stem cell driving neurogenesis in the Pancrustacea (crustaceans + Hexapoda). Neuroblasts also divide asymmetrically resulting in one daughter cell retaining NB identity while the other assumes the identity of a so-called ganglion mother cell (GMC), which in turn divides typically only once and symmetrically, producing two post-mitotic neurons/glial cells. In pycnogonids, similar cells, which are morphologically smaller than the NSCs and divide symmetrically, have previously been described and termed intermediate neural precursor (INP).
However, these morphological cell type descriptions in pycnogonids are insufficient to make any informed assumptions about whether they are homologous to the neurogenic cell types of pancrustaceans. With gene expression studies addressing pycnogonid neurogenesis being so far completely lacking, this study aims to provide first insights into the transcriptional profiles of pycnogonid NSCs and INPs, to enable their comparison to the pancrustacean NBs and GMCs. To this end, the expression of a set of conserved candidate genes, which are involved in arthropod neurogenesis is studied with hybridization chain reaction fluorescent in-situ hybridization (HCR-FISH) in combination with cytoskeletal and nuclear staining.