Conserved protein motifs and structural organization of a fish gene homologous to mammalian apolipoprotein E

Abstract

Apolipoprotein E (apoE) plays a central role in lipid metabolism from its ability to interact with lipoprotein receptors. Besides its role in cardiovascular diseases, apoE polymorphism contributes to susceptibility to neurodegenerative diseases, such as Alzheimer's disease. The statistical significance of the combined match scores obtained after apoE motif-based protein sequence database searches, the structural features of the deduced protein, and the phylogenetic analysis, support the evidence that a homologue to mammalian apoE can be found in teleost fish. Isolation and characterization of the first nonmammalian APOE revealed that the zebrafish gene spans 2555/2692 bp instead of 3597 bp in human and has the same splice junctions and exon/intron organization as found in mammals, except that there is an additional intron that splits the last exon (exon 4) into two exons (exons 4 and 5). Enlargement of APOE size in the mammalian lineage occurs mainly by Alu repeats insertion. The additional intron found in zebrafish gene was also identified at the same splicing site in trout APOE and is located in the corresponding linker region following the conserved low density lipoprotein receptor binding domain. Primer extension and reverse transcriptase PCR (RT-PCR) assays demonstrated that two transcription start sites are located 26 and 28 bp upstream of the first intron and 22 or 24 bp downstream from a canonical TATA box. Sequence inspection of the 5 H -flanking region upstream of the TATA box revealed potential regulatory DNA elements. These results will serve as a basis for comparative studies on transcriptional and posttranscriptional mechanisms of APOE regulation in vertebrates.

Zebrafish Acetylcholinesterase Is Encoded by a Single Gene Localized on Linkage Group 7

“…In both teleosts, insertion takes place at the same position in ache exon 2 at position 415; in Danio it is located between consensus 5Ј-TG/GT-3Ј nucleotides usually found at exon junctions. This suggests that the insertion may be the result of an intron capture as recently described in zebrafish apolipoprotein E gene (45). When compared with the Torpedo ache gene, an insertion also occurred in exon 2 at position 318 in tetrapod ache genes.…”

Isolation and characterization of some novel genes of the apolipoprotein A-I family in Japanese eel, Anguilla japonica

“…In mammals, a group of nine exchangeable and soluble apolipoproteins including apoC-I, apoC-II, apoC-III, apoC-IV, apoA-I, apoA-II, apoA-IV, apoA-V, and apoE is associated with plasma lipoproteins and the structural organization of these genes is thoroughly understood [2,43,44]. Some fish apolipoproteins have been reported to have non-lipidmediated activities such as antimicrobial functions and innate immunity [11][12][13] but the structural organization of apolipoprotein genes in fish is currently limited to a very few studies [4,42]. The genetic information of fish apolipoproteins is expected to contribute not only to a better understanding of apolipoprotein evolution, but to lipid metabolism and physiology in fish lineages.…”

“…cDNAs encoding the major apolipoproteins, apoA-I, apoA-II-like, and 28kDa-1, have previously been isolated from the liver of Japanese eel [21,28,40], whereas information on apoE which participates in the regulation of plasma cholesterol and lipid metabolism has been confined to zebrafish [41], rainbow trout [42], and pufferfish [4] among non-mammalian vertebrates. This situation let us isolate apoE cDNA in Japanese eel, but an alternative apolipoprotein cDNA, an apoA-I isoform (apoIA-I), was amplified by the PCR reaction using a set of oligonucleotides corresponding to zebrafish and rainbow trout apoE.…”

Molecular cloning and expression characterization of ApoC-I in the orange-spotted grouper

“…However, little information about apolipoproteins has been obtained in lower vertebrates (Paolucci et al 1998). Only a few fish apolipoprotein genes had been reported, such as zebrafish (Danio rerio) and eel (Anguilla japonica) ApoA-I (Babin et al 1997;Kondo et al 2001), rainbow trout (Oncorhynchus mykiss) ApoC-II (Shen et al 2000), zebrafish and rainbow trout ApoE (Babin et al 1997;Durliat et al 2000), and eel, pufferfish (Takifugu rubripes) and orange-spotted grouper Apo-14 (Kondo et al 2001(Kondo et al , 2005Zhou et al 2005). Only ApoE, ApoA-I, and Apo-14 have been investigated for their developmental expression patterns (Babin et al 1997;Poupard et al 2000;Zhou et al 2005).…”