cDNA Cloning and Characterization of Transcription Factor Activating Protein AP2α from Yellow Drum, Nibea albiflora

The transcription factor activating protein 2α (AP2α) is a nuclear transcription factor that specifically binds to DNA and is involved in the regulation of animal embryonic development, cell growth, apoptosis, tumorigenesis, immunity, and other biological processes. In our previous study, the transcription factor AP2α was discovered as a key disease-resistance candidate gene in the yellow drum, Nibea albiflora, in response to a Vibrio harveyi infection through genome-wide association analysis. In the present study, the AP2α gene, which encodes a protein of 424 amino acids, was cloned from a yellow drum. The N-terminal is a trans-activation domain rich in proline and glutamine (P/Q-rich domain), and the middle is a central basic structure (central basic region), which is a highly conserved helix-span-helix motif responsible for DNA binding and protein dimerization. Multiple alignments of amino acid sequences showed that AP2α was highly conserved, with a homology of more than 84.63% among the detected fish, amphibians, birds, and mammals. Quantitative RT-PCR demonstrated that AP2α was widely distributed in the nine tested tissues, with the highest expression in the blood. Moreover, its transcription was significantly activated in the liver, spleen, and head kidney by V. harveyi infection, especially in the liver wherein the transcript level of AP2α reached a peak at 24 h post infection. Subcellular localization by constructing the recombinant eukaryotic expression plasmid pGEFP-AP2α and transfection into HEK293T cells revealed that AP2α was localized in the nucleus. In addition, the soluble GST-AP2α fusion protein was expressed in Escherichia coli BL21. These results demonstrate that AP2α plays an important role in the immune response against V. harveyi in N. albiflora. We provide new insights into the role of AP2α in the innate immunity of teleost fishes and provide a basis for studies on immune mechanisms and disease-resistant breeding in N. albiflora and other marine fish.