Molecular cloning and functional characterization of the hypoxia-inducible factor-1α in bighead carp (Aristichthys nobilis).

HIF-l is the earliest documented and most widely studied hypoxia-inducible factor (HIF) and plays a key role in the cell hypoxia signal transduction pathway. Particularly, the HIF-1α protein is sensitive to oxygen and plays a critical role in hypoxia regulation. This study is the first to report on the molecular cloning and characterization of HIF-1α in bighead carp (Aristichthys nobilis; anHIF-1α). The full-length cDNA of anHIF-1α was 2361 bp, and encodes an estimated 674 amino acids with a predicted molecular mass of 76.10 kDa and a theoretical isoelectric point of 7.72. Moreover, the conserved basic Helix-Loop-Helix domain along with two Per-ARNT-Sim domains (A/B), and C-TAD were identified in this protein. Interestingly, the tertiary structure of the anHIF-1α protein was found to be extremely similar to that of mice. Multiple comparison and phylogenetic tree results demonstrated that anHIF-1α was highly conserved. Under normoxic conditions, anHIF-1α mRNA transcripts could be detected in all tissues examined with the highest expression level in the heart. With gradually decreasing oxygen concentrations, anHIF-1α mRNA level was upregulated significantly in the gill, liver, kidney, spleen, intestine, brain, and muscle tissues (P < 0.05). Similarly, anHIF-1α was expressed in all examined bighead carp tissues, and the results suggested that the upregulation of anHIF-1α at the transcriptional level may be an important stress response adaptation to hypoxia in bighead carp. Finally, based on the tertiary structure comparative analyses between anHIF-1α with mouse HIF-1α, we think the physiological function, and protein structure of HIF-1α could be compared between fish and mammal in the future.