Identification and characterization of a novel Foxo transcription factors in Apostichopus japonicus

• The first AjFoxo was identified from Apostichopus japonicus.
• AjFoxo mRNA transcripts were constitutively expressed in all examined tissues.
• AjFoxo displayed similar expression profiles to that of AjIκB towards Vibrio splendidus challenge.
• AjIκB was also significantly depressed in AjFoxo silenced coelomocytes.

The forkhead box O (Foxo) transcription factors are involved in multiple signaling pathways and play key roles in immunoregulation in vertebrates. In the present study, we firstly identified a novel Foxo gene in Apostichopus japonicus coelomocytes using transcriptome sequencing and RACE approaches (denoted as AjFoxo). The full-length cDNA of AjFoxo was of 2248 bp with a 5′ untranslated region (UTR) of 177 bp, a 3′ UTR of 367 bp and an ORF of 1704 bp encoding a polypeptide of 567 amino acid residues. The highly conserved forkhead domain was also identified in AjFoxo with remarkably higher degree of structural conservation. AjFoxo transcripts could be detected in all examined tissues with predominant expression in the coelomocytes and muscle, and slightly weak in the tissues of tentacle, intestine and respiratory trees. Concerning the time-course expression of AjFoxo in coelomocytes, the relative expression of AjFoxo was dramatically decreased to 0.44-fold at 48 h compared with that in the control group after Vibrio splendidus challenge, which was consistent with that of AjIκB. RNA interference of AjFoxo in primary coelomocytes also significantly depressed the relative expression of AjIκB with a 0.37-fold decrease compared with control group. Taken together, these results indicated that AjFoxo was a novel immune regulator and might be involved in the processes of anti-bacteria response in sea cucumber through activating the transcription of AjIκB.