Developmental and gene expression patterns during neurogenesis in basal branching Annelida
Systematics and Morphology (Zoology)
Final Report Abstract
Annelida possess a huge variety of morphological adaptations and therefore discussions concerning the characteristics of the last common annelid ancestor were difficult. Thanks to transcriptomic and phylogenomic analyses this picture has changed and several annelid families could be placed at the base of the annelid radiation to provide a framework for further investigations. Due to the lack of knowledge, main goal of the project was the investigation of morphological and developmental characteristics of early branching annelid taxa to unravel the evolution of organ systems within Annelida and Spiralia. With main focus on neural characteristics, comprehensive analyses including molecular as well as morphological approaches such as immunohistochemistry or in situ hybridization were carried out at the “SARS - International Centre for Marine Molecular Biology”. Summarizing, the neural development of early branching annelids such as Oweniidae and Magelonidae reveals many aspects well-known from other taxa. Thus, the early presence of adult precursors, a prominent apical organ formed by flask-shaped perikarya, early development of circumesophageal connectives interconnecting apical and trunk nervous system, and the serially arranged clusters of somata in the ventral nerve cord in addition with serial lateral nerves at least in early juveniles, are highly comparable features among annelids and Spiralia. Notably, the lack of apical serotonergic somata in larval oweniids or the absence of a ring-nerve underlying the prototroch in magelonids seem to be features restricted to Palaeoannelida and therefore illustrate the future potential of developmental studies dealing with these so far neglected annelid taxa. Furthermore, investigations of the adult nervous system within deeper branching annelids refute the traditional subepidermal ladder-like median ventral nerve cord as ancestral and instead reconstruct a non-ganglionated intraepidermal ventral cord as the ancestral state for annelids. This also reveals a further disparity of the annelid ventral cord to that of arthropods and vertebrates, and perhaps a greater resemblance to other Spiralia. Further on, comprehensive data on glial cells in annelids and other taxa indicate an early evolution of radial glial cells in Bilateria and suggest an important role of this cell type in nervous systems throughout Nephrozoa. The comparative data provide important and hitherto missing insights into the evolution of bilaterian radial glial cells and thus nervous systems in general. In summary, the comparative results of this DFG-funded project highlight the great potential of developmental studies in deeper branching annelid taxa, refute the traditional ladder-like nervous system as ancestral state for Annelida and unravel the early evolution of radial glial cells in Bilateria. The outcome of this project hereby provides fundamental and hitherto lacking insights into the evolution of nervous systems in Annelida and Bilateria in general.
Publications
- (2017) Early evolution of radial glial cells in Bilateria. Proceedings. Biological sciences 284 (1859)
Helm, Conrad; Karl, Anett; Beckers, Patrick; Kaul-Strehlow, Sabrina; Ulbricht, Elke; Kourtesis, Ioannis; Kuhrt, Heidrun; Hausen, Harald; Bartolomaeus, Thomas; Reichenbach, Andreas; Bleidorn, Christoph
(See online at https://doi.org/10.1098/rspb.2017.0743) - (2015): Annelida. In: Evolutionary Developmental Biology of Invertebrates 2, 1. Edition, Chapter: 9, Publisher: Springer-Verlag Wien, Editors: Andreas Wanninger, pp.193-230
Bleidorn C., Helm C., Weigert A. & Aquado M.T.
- (2016): Owenia fusiformis – a basally branching annelid suitable for studying ancestral features of annelid neural development. BMC Evolutionary Biology 16: 129
Helm C., Vöcking O., Kourtesis I. & Hausen H.
(See online at https://doi.org/10.1186/s12862-016-0690-4) - (2017): Comparative analyses of glycerotoxin expression unveil a novel structural organization of the bloodworm venom system. BMC Evolutionary Biology 17: 64
Richter S., Helm C., Meunier F.A., Hering L., Campbell L.I., Drukewitz S.H., Undheim E.A.B., Jenner R.A., Schiavo G. & Bleidorn C.
(See online at https://doi.org/10.1186/s12862-017-0904-4)
