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MBE Advance Access published online on April 27, 2005
Molecular Biology and Evolution, doi:10.1093/molbev/msi158
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© The Author 2005. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org
Accepted February 25, 2005

Research Article

Analysis of the Reticulon Gene Family Demonstrates the Absence of the Neurite Growth Inhibitor Nogo-A in Fish

Heike Diekmann 1 1, Michael Klinger 1 1, Thomas Oertle 2, Dietmar Heinz 1, Hans-Martin Pogoda 3, Martin E. Schwab 2, and Claudia A.O. Stuermer 1*

1 Department of Biology, University of Konstanz, 78457 Konstanz, Germany
2 Brain Research Institute, University of Zurich, and Department of Biology, Swiss Federal Institute of Technology Zurich, 8057 Zurich, Switzerland
3 Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA

* To whom correspondence should be addressed.
Claudia A.O. Stuermer, E-mail: Claudia.Stuermer{at}uni-konstanz.de


  Abstract

Reticulons (RTN) are a family of evolutionary conserved proteins with four RTN paralogs (RTN1, RTN2, RTN3, RTN4) present in land vertebrates. While the exact functions of RTN1 - RTN3 are unknown, mammalian RTN4-A/Nogo-A was shown to inhibit the regeneration of severed axons in the mammalian central nervous system (CNS). This inhibitory function is exerted via two distinct regions, one within the Nogo-A specific N-terminus and the other in the conserved reticulon homology domain (RHD). In contrast to mammals, fish are capable of CNS axon regeneration. We performed detailed analyses of the fish rtn gene family to determine whether this regeneration ability correlates with the absence of the neurite growth inhibitory protein Nogo-A. Seven rtn genes were identified in zebrafish, six in pufferfish and 30 in 8 additional fish species. Phylogenetic and syntenic relationships indicate that the identified fish rtn genes are orthologs of mammalian RTN1, RTN2, RTN3 and RTN4 and that several paralogous fish genes (e.g. rtn4 and rtn6) resulted from genome duplication events early in actinopterygian evolution. Accordingly, sequences homologous to the conserved RTN4/Nogo RHD are present in two fish genes, rtn4 and rtn6. However, sequences comparable to the first ~1000 aa of mammalian Nogo-A including a major neurite growth inhbitory region are absent in zebrafish. This result is in accordance with functional data showing that axon growth inhibitory molecules are less prominent in fish oligodendrocytes and CNS myelin compared to mammals.

Keywords: Danio rerio; Reticulon; Nogo; RTN4; gene duplication; conserved synteny.

1both authors contributed equally


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