GROVE, T.J.; HENDRICKSON, J.W.*; SIDELL, B.D.; Univ. of Maine, Orono; Univ. of Maine, Orono; Univ. of Maine, Orono: Pattern of cardiac myoglobin expression among all known species of Antarctic icefishes

Fishes of the Suborder Notothenioidei dominate ichthyofauna of coastal Antarctic waters. Species of the notothenioid family, Channichthyidae (Antarctic icefishes), among all vertebrates, uniquely lack the circulating oxygen-binding protein, hemoglobin. Icefish species also do not uniformly express the intracellular oxygen-binding protein, myoglobin (Mb), in oxidative tissues. Our laboratory previously characterized the pattern of Mb expression in 13 of the 16 known icefish species. This report completes the survey of cardiac Mb expression among all 16 known species of icefish. Using PAGE and immunoblot analyses, we demonstrate that both Channichthys rhinoceratus and Cryodraco atkinsoni express Mb in heart ventricle, while Champsocephalus esox does not express the protein. We determined and analyzed Mb gene sequences from C. rhinoceratus and C. esox genomic DNA. The Mb gene of C. esox contains the identical 5-base-pair duplication/insertion to that in the gene sequence from congeneric Champsocephalus gunnari, a species that also does not produce the protein. This duplication in exon 2 of the Champsocephalus spp. gene causes a shift in reading frame at a position normally encoding amino acid 91 and also results in a premature stop codon, thus disrupting translation of a normal protein. Six of 16 icefish species, thus, do not express cardiac Mb. These results confirm earlier conclusions that losses of Mb expression have occurred via at least four independent evolutionary events during evolution of Channichthyid icefishes. Extreme similarity of Mb genes in Champsocephalus congeners further suggests recent speciation despite very early divergence of this group from the lineage that led to more derived icefishes. Supported by NSF grants OPP 99-09055 and 01-25890 to B.D.S.