title: The major adult alpha-globin gene of antarctic teleosts and its remnants in the hemoglobinless icefishes. Calibration of the mutational clock for nuclear genes.
abstract: The icefishes of the Southern Ocean (family Channichthyidae, suborder Notothenioidei) are unique among vertebrates in their inability to synthesize hemoglobin. We have shown previously (Cocca, E., Ratnayake-Lecamwasam, M., Parker, S. K., Camardella, L., Ciaramella, M., di Prisco, G., and Detrich, H. W., III (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 1817-1821) that icefishes retain inactive genomic remnants of adult notothenioid alpha-globin genes but have lost the gene that encodes adult beta-globin. Here we demonstrate that loss of expression of the major adult alpha-globin, alpha1, in two species of icefish (Chaenocephalus aceratus and Chionodraco rastrospinosus) results from truncation of the 5' end of the notothenioid alpha1-globin gene. The wild-type, functional alpha1-globin gene of the Antarctic yellowbelly rockcod, Notothenia coriiceps, contains three exons and two A + T-rich introns, and its expression may be controlled by two or three distinct promoters. Retained in both icefish genomes are a portion of intron 2, exon 3, and the 3'-untranslated region of the notothenioid alpha1-globin gene. The residual, nonfunctional alpha-globin gene, no longer under positive selection pressure for expression, has apparently undergone random mutational drift at an estimated rate of 0.12-0.33%/million years. We propose that abrogation of hemoglobin synthesis in icefishes most likely resulted from a single mutational event in the ancestral channichthyid that deleted the entire beta-globin gene and the 5' end of the linked alpha1-globin gene.
authors.affiliation: Department of Biology, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: M
authors.initials: M
authors.lastname: Ratnayake-Lecamwasam
authors.forename: S K
authors.initials: SK
authors.lastname: Parker
authors.forename: E
authors.initials: E
authors.lastname: Cocca
authors.forename: L
authors.initials: L
authors.lastname: Camardella
authors.forename: G
authors.initials: G
authors.lastname: di Prisco
authors.forename: H W
authors.initials: HW
authors.lastname: Detrich
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000864:Antarctic Regions; D001483:Base Sequence; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D005399:Fishes; D017353:Gene Deletion; D005914:Globins / Q000737:chemistry* / Q000235:genetics; D006454:Hemoglobins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion / Q000235:genetics; D013696:Temperature
chemical_list: D006454:Hemoglobins; D005914:Globins