caa a22 4500 475767837 CHVBK 20180406123611.0 cr unu---uuuuu 170329e20000601xx s 000 0 eng 10.1007/s004270000073 doi (NATIONALLICENCE)springer-10.1007/s004270000073 Shimeld Sebastian M. School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, RG6 6AJ, UK E-mail: S.M.Shimeld@reading.ac.uk Tel.: +44-118-9875123 ext 7084, Fax: +44-118-9310180, GB aut An amphioxus netrin gene is expressed in midline structures during embryonic and larval development [Elektronische Daten] [Sebastian M. Shimeld] Abstract : Members of the netrin gene family have been identified in vertebrates, Drosophila and Caenorhabditis elegans and found to encode secreted molecules involved in axon guidance. Here I use the conserved function of netrins in triploblasts, coupled with the phylogenetic position of amphioxus (the closest living relative of the vertebrates), to investigate the evolution of an axon guidance cue in chordates. A single amphioxus netrin gene was isolated by PCR and cDNA library screening and named AmphiNetrin. The predicted AmphiNetrin protein showed high identity to other netrin family members but differed in that the third of three EGF repeats found in other netrins was absent. Molecular phylogene-tic analysis showed that despite the absent EGF repeat AmphiNetrin is most closely related to the vertebrate netrins. AmphiNetrin expression was identified in embryonic notochord and floor plate, a pattern similar to that of vertebrate netrin-1 expression. AmphiNetrin expression was also identified more widely in the posterior larval brain, and in the anterior extension of the notochord that underlies the anterior of the amphioxus brain. All of these areas of expression are correlated with developing axon trajectories: The floor plate with ventrally projecting somatic motor neurons and Rohde cell projections, the posterior brain with the ventral commissure and primary motor centre and the anterior extension of the notochord with ventrally projecting neurons associated with the median eye. Amphioxus is naturally cyclopaedic and also lacks the ventral brain cells that the induction of which results in the splitting of the vertebrate eye field and, when missing, result in cyclopaedia. These cells normally express netrins required for developing axon tracts in the brain, and the expression of AmphiNetrin in the anterior extension of the notochord underlying the brain may explain how amphioxus is able to maintain ventral guidance cues while lacking these cells. Springer-Verlag Berlin Heidelberg, 2000 Key words Netrin nationallicence Floor plate nationallicence Amphioxus nationallicence Axon guidance nationallicence Vertebrate evolution nationallicence https://doi.org/10.1007/s004270000073 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s004270000073 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Shimeld Sebastian M. School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, RG6 6AJ, UK E-mail: S.M.Shimeld@reading.ac.uk Tel.: +44-118-9875123 ext 7084, Fax: +44-118-9310180, GB aut Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer