Meeting Abstract
The long evolution of the Antarctic perciform suborder of Notothenioidei in the stable, cold, oxygen-rich waters of the Southern Ocean may have eliminated their capacity to respond to hypoxia, especially in Channichthyidae family (icefishes), which lack hemoglobin and are benthic, sedentary fishes with low activity levels. We hypothesized that icefishes may have lost the capacity to induce protective mechanisms against hypoxia, and specifically, that hypoxia-inducible factor-1α (HIF-1α) may be functional in red-blooded notothenioids but not in icefishes. HIF-1α cDNA was sequenced in heart ventricles of the red-blooded notothenioid Notothenia coriiceps and the icefish Chaenocephalus aceratus using 3′ and 5′ rapid amplification of cDNA ends (RACE). HIF-1α cDNA in N. coriiceps is 4500 base pairs (bp) long and encodes 755 amino acids (AA). In C. aceratus HIF-1α is 3576 bp long and encodes 779 AA. All functional domains of HIF-1α are conserved when compared to HIF-1α in other teleosts, but HIF-1α contains a polyglutamine/glutamic acid (polyQ/E) repeat 9 AA long in N. coriiceps and 34 AA long in C. aceratus. Sequencing of this region in 4 additional species of notothenioids revealed that the polyQ/E repeat varies in length based on phylogeny. Icefishes, the crown species of notothenioids, contain the longest repeats of 16-34 AA long, whereas the basal, cold-temperate notothenioid, Eleginops maclovinus, contains a repeat of 4 AA. PolyQ/E repeats could cause protein misfolding and/or altered mRNA structure, monopolizing RNA processing proteins, resulting in decreased protein production. Without functional HIF-1α, the hypoxia response may be blunted, potentially lowering thermotolerance in icefishes with longer HIF-1α polyQ/E repeats compared to red-blooded notothenioids.
