title: The genome of the early chordate Ciona intestinalis encodes only five cytoplasmic intermediate filament proteins including a single type I and type II keratin and a unique IF-annexin fusion protein.
abstract: We screened the recently established draft genome of the early chordate Ciona intestinalis for genes encoding cytoplasmic intermediate filament (IF) proteins. The draft of the tunicate/urochordate genome contains only the five genes (IF-A, IF-B, IF-C, IF-D and IF-F) previously established by cDNA cloning. Three of these IF proteins (IF-D, IF-C, IF-A) were shown to be orthologs of vertebrate IF subfamilies I to III while two proteins (IF-B, IF-F) seemed tunicate specific. This is now firmly established for protein IF-F since the genomic data show that it arises as a fusion protein with a C-terminal annexin domain, a feature not found before in the very large collection of metazoan IF proteins. The results also confirm the previous proposal that urochordates lack orthologs of vertebrate type IV IF proteins. We discuss the striking increase of IF complexity from 5 tunicate to 65 human genes during chordate evolution. Thus the tunicate has a single keratin pair, which is expressed in the epidermis, while the human genome has at least 25 genes each for keratins I and keratins II. Finally there are four normal Ciona annexin genes in addition to the gene encoding the IF-annexin fusion proteins (IF-F).
authors.affiliation: Department of Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Goettingen, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Karabinos
authors.forename: Alexander
authors.initials: A
authors.lastname: Zimek
authors.forename: Klaus
authors.initials: K
authors.lastname: Weber
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017302:Annexins / Q000235:genetics*; D001483:Base Sequence; D002938:Ciona intestinalis / Q000235:genetics*; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D016678:Genome; D007381:Intermediate Filament Proteins / Q000235:genetics*; D007382:Intermediate Filaments / Q000235:genetics*; D007633:Keratins / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D010802:Phylogeny; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D017302:Annexins; D018076:DNA, Complementary; D007381:Intermediate Filament Proteins; D007633:Keratins