Molecular analysis of ependymins from the cerebrospinal fluid of the orders clupeiformes and salmoniformes: no indication for the existence of an euteleost infradivision

Abstract

Ependymins represent the predominant protein constituents in the cerebrospinal fluid of many teleost fish and they are synthesized in meningeal fibroblasts. Here, we present the ependymin sequences from the herring (Clupea harengus) and the pike (Esox lucius). A comparison of ependymin homologous sequences from three different orders of teleost fish (Salmoniformes, Cypriniformes, and Clupeiformes) revealed the highest similarity between Clupeiformes and Cypriniformes. This result is unexpected because it does not reflect current systematics, in which Clupeiformes belong to a separate infradivision (Clupeomorpha) than Salmoniformes and Cypriniformes (Euteleostei). Furthermore, in Salmoniformes the evolutionary rate of ependymins seems to be accelerated mainly on the protein level. However, considering these inconstant rates, neither neighbor-joining trees nor DNA parsimony methods gave any indication that a separate euteleost infradivision exists.

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“…The most relevant were four cysteines within the molecule primary sequence at positions 45, 118, 188 and 232 (numbered according to the WebLogo; Figure 1). These residues have also been predicted by the Disulfind server [30,35] to participate in disulfide bond formation, pointing to a key role in protein folding and/or dimeric interactions and ultimately to the biological function of the Epds [2,4,36]. Two proteins (Ictalur_GS and Danio_Tj) were found to lack one of these Cys but this was probably due to sequencing errors on these ESTs.…”

Relationships of Lower Euteleostean Fishes

“…In subsequent work by Le (1991;Le et al, 1993) with a more extensive sample of teleosts, including Salmo, and longer 28S rRNA sequences, Esox was omitted. Muller-Schmidt et al (1993) analyzed the amino-acid sequence of ependymins of Esox, Oncorhynchus (two paralogous sequences), Clupea, and the cyprinids Carassius (two paralogous sequences), and Brachydanio. Their work, particularly their evidence for a clupeomorph/ostariophysan clade, is discussed by Lecointre and Nelson (this volume).…”

Calcium-Induced Conformational Transition of Trout Ependymins Monitored by Tryptophan Fluorescence

“…Fish ependymins are highly divergent [5-7]. The most conserved feature of piscine ependymins, other than the sequence F-E-E-G-V-x-Y-E/D-I/L-D between the two canonical N-glycosylation sites [6], is the presence of sialic acid residues in the N-linked sugar moiety [8]. As also shown for other extracellular proteins, e.g.…”

“…Soluble ependymins are the major protein constituents of the cerebrospinal fluid (CSF) of many teleost fish [5, 6, 18, 19]. Here they bind approximately 66% of the soluble Ca 2+ (for example, trout CSF contains about 2.7 mM soluble Ca 2+ ) [8].…”

“…Ependymins from this quasi-tetraploid species are encoded by two homologous genes. Both gene products contain a single tryptophan residue [5] which is strictly conserved in ependymin sequences of all species analyzed thus far [6, 7]. …”