Molecular Biology and Evolution, Vol 13, 556-573, Copyright © 1996 by Society for Molecular Biology and Evolution
G Orti and A Meyer
The rate and pattern of DNA evolution of ependymin, a single-copy gene
coding for a highly expressed glycoprotein in the brain matrix of teleost
fishes, is characterized and its phylogenetic utility for fish systematics
is assessed. DNA sequences were determined from catfish, electric fish, and
characiforms and compared with published ependymin sequences from
cyprinids, salmon, pike, and herring. Among these groups, ependymin amino
acid sequences were highly divergent (up to 60% sequence difference), but
had surprisingly similar hydropathy profiles and invariant glycosylation
sites, suggesting that functional properties of the proteins are conserved.
Comparison of base composition at third codon positions and introns
revealed AT-rich introns and GC-rich third codon positions, suggesting that
the biased codon usage observed might not be due to mutational bias.
Phylogenetic information content of third codon positions was surprisingly
high and sufficient to recover the most basal nodes of the tree, in spite
of the observation that pairwise distances (at third codon positions) were
well above the presumed saturation level. This finding can be explained by
the high proportion of phylogenetically informative nonsynonymous changes
at third codon positions among these highly divergent proteins. Ependymin
DNA sequences have established the first molecular evidence for the
monophyly of a group containing salmonids and esociforms. In addition,
ependymin suggests a sister group relationship of electric fish
(Gymnotiformes) and Characiformes, constituting a significant departure
from currently accepted classifications. However, relationships among
characiform lineages were not completely resolved by ependymin sequences in
spite of seemingly appropriate levels of variation among taxa and
considerably low levels of homoplasy in the data (consistency index = 0.7).
If the diversification of Characiformes took place in an "explosive"
manner, over a relatively short period of time this pattern should also be
observed using other phylogenetic markers. Poor conservation of ependymin's
primary structure hinders the design of efficient primers for PCR that
could be used in wide-ranging fish systematic studies. However, alternative
methods like PCR amplification from cDNA used here should provide promising
comparative sequence data for the resolution of phylogenetic relationships
among other basal lineages of teleost fishes.
ORIGINAL ARTICLE
Molecular evolution of ependymin and the phylogenetic resolution of early divergences among euteleost fishes
Department of Genetics, University of Georgia, Athens 30602, USA. gorti@bscr.uga.ed
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  C. Li, G. Lu, and G. Orti Optimal Data Partitioning and a Test Case for Ray-Finned Fishes (Actinopterygii) Based on Ten Nuclear Loci Syst Biol, August 1, 2008; 57(4): 519 - 539. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-N. Volff, C. Körting, A. Meyer, and M. Schartl Evolution and Discontinuous Distribution of Rex3 Retrotransposons in Fish Mol. Biol. Evol., March 1, 2001; 18(3): 427 - 431. [Full Text]
|
|
|
|
|
|
D. L. Campbell, A. V. Z. Brower, and N. E. Pierce Molecular Evolution of the Wingless Gene and Its Implications for the Phylogenetic Placement of the Butterfly Family Riodinidae (Lepidoptera: Papilionoidea) Mol. Biol. Evol., May 1, 2000; 17(5): 684 - 696. [Abstract] [Full Text] [PDF]
|
|