NICODEMUS, J*; SILIC, S; ZHU, T; GHILIOTTI, L; CHENG, C-H; Univ. of Illinois, U-C; Univ. of Illinois, U-C; Univ. of Illinois, U-C; Univ. of Genova; Italy; Univ. of Illinois, U-C: Evolutionary analyses of the antifreeze glycoprotein genomic locus in Antarctic Notothenioid fish

Notothenioid fishes comprise the predominant teleost suborder in the Antarctic Ocean. Their ability to survive in icy, freezing seawater relies on the novel blood-borne ice-binding antifreeze glycoproteins (AFGPs). AFGPs consist of tandem ThrAlaAla repeats, and their encoding gene originated from the expansion of a 9-nt ThrAlaAla coding element within an ancestral trypsinogen-like protease (TLP) gene. Current Antarctic notothenioid AFGP gene families are large, and member genes encode a large polyprotein precursor of multiple AFGP molecules linked by small cleavable spacers, indicating extensive intra- and whole gene duplications have occurred under strong freezing selection to provide an abundance of the survival protein. To fully characterize the AFGP gene family and its evolution, we are currently sequencing the AFGP gene locus of the giant Antarctic toothfish (nototheniid) Dissostichus mawsoni screened from a BAC library. FingerPrinting Contig analyses of AFGP/TLP-positive BAC clones and FISH of toothfish chromosomes show most AFGP/TLP genes localize to one genomic region of about 325kbp. High-throughput shotgun sequencing and sequence assembly thus far uncovered at least 8 AFGP polyprotein genes, 3 AFGP/TLP chimeric genes and 2 TLP genes, in close proximity to tandem trypsinogen genes, confirming the evolutionary linkage of AFGP to trypsinogen-type serine proteases. Complete sequencing of the AFGP gene locus will provide insight into the mechanism of evolution and expansion of this crucial gene family that conferred ecological success and dominance of the notothenioids in the freezing Antarctic seas.