Evolution of the myoglobin gene in Antarctic Icefishes (Channichthyidae)

Antarctic icefishes (Family: Channichthyidae) are the only adult vertebrate animals that do not express the circulatory oxygen-binding protein, hemoglobin. Six species of icefishes, including Dacodraco hunteri, also do not express myoglobin (Mb), an oxygen-binding protein found in ventricular tissue of Antarctic notothenioids. Sequence of the Mb gene from D. hunteri contains a duplicated TATA box in the promoter region of the Mb gene that is absent in Chionodraco rastrospinosus, an icefish species known to express Mb. The 15-base pair insertion in D. hunteri is identical to the duplicated TATA box that is thought to be directly responsible for preventing transcription of the Mb gene in C. aceratus, another icefish species that lacks Mb expression. Sequencing of the Mb promoter from the remaining channichthyid species revealed the duplicated TATA box in 14 of 16 icefish species, including 8 species known to express Mb. Based on the presence of the duplicated TATA box in promoters of both Mb-expressing and Mb-lacking species, loss of Mb expression in D. hunteri and C. aceratus is either independent of the duplicated TATA box, or the duplicated TATA box requires presence or absence of a distant regulatory element to prevent transcription.