Antifreeze Glycoproteins in Northern Cods: Gene Family Sizes, Sequences, Structures, Organizations, and Evolution
Yang, Chun
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https://hdl.handle.net/2142/87225
Description
Title
Antifreeze Glycoproteins in Northern Cods: Gene Family Sizes, Sequences, Structures, Organizations, and Evolution
Author(s)
Yang, Chun
Issue Date
2002
Doctoral Committee Chair(s)
Arthur DeVries
Chris Cheng-Devries
Department of Study
Molecular and Integrative Physiology
Discipline
Molecular and Integrative Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Fisheries and Aquaculture
Language
eng
Abstract
AFGPs have evolved convergently in unrelated fishes from both Antarctic and Arctic seas to prevent freezing in these cold ice-laden environments. Previous studies have shown that AFGPs of Antarctic notothenioids are encoded by a family of polyprotein genes, with each gene encoding a large precursor containing multiple AFGP molecules linked in tandem by cleavable small spacers (Chen et al., 1997a). High concentrations of AFGPs circulate in the serum of several northern cods either through the whole year or during winter. The size and compositional heterogeneity has been reported for several species of northern cods, but only three AFGP genes from a partial genomic library of polar cod have been characterized. Four more polar cod B. saida AFGP gene sequences, their structures, and organization in the genome are reported here. Genomic Southern analysis indicates that a large AFGP gene family exists in its genome. A high percentage of the AFGP member genes appear to be arranged in tandem and clustered within a short genomic distance, and the sequence alignment of these four genes strongly argues that they have evolved through the process of the whole AFGP gene duplication. Detailed sequence analyses of the four additional polar cod AFGP genes show a similar polyprotein structure to the previously characterized polar cod AFGP genes. Each AFGP polyprotein gene coding region contains multiple copies of AFGP molecules (7-15), linked in tandem by conserved putative spacers Arg or ArgAlaAlaArg. The AFGP polyprotein gene structure and multiple AFGP genes in the genome greatly expand the AFGP coding capacity, most likely a result of the selection pressure from the freezing environment B. saida inhabits. Three AFGP genes isolated separately from three other gadids, G. morhua, G. ogac, A. glacialis, are completely sequenced. The gene sequences and structures show conserved polyprotein AFGP gene structure, except for different ThrAlaAla codon bias and putative spacers. Also, the number and size of encoded AFGP molecules are variable from gene to gene.
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