RETRACTED ARTICLE: Molecular Cloning, Sequence Characterization, and Tissue Expression Analysis of Hi-Line Brown Chicken Akirin2

Molecular characterization and functional analysis of Akirin from black tiger shrimp (Penaeus monodon)

Akirin, which are members of the NF-κB signaling pathway, play critical roles in regulating the expression of antimicrobial peptides. In the present study, the Akirin gene from Penaeus monodon was identified from a transcriptome database and designated as PmAkirin. The complete sequence of the PmAkirin cDNA was 1508 bp, encoding a protein of 213 amino acids, and it showed 99% amino acid identity to the Litopenaeus vannamei Akirin. Two predicted nuclear localization signals (NLSs) were found, and the amino acid sequence alignments showed that PmAkirin was highly conserved at the N-terminus and C-terminus. PmAkirin expression was found to be the highest in the hemolymph, followed by the heart, gill, stomach, hepatopancreas, intestine, and muscle. When challenged with Vibrio parahaemolyticus infection, the PmAkirin mRNA and three antimicrobial peptides (AMPs: PmALF2, PmALF3, and PmCrus4) were upregulated. However, another five AMPs (PmALF6, PmCrus1, PmPEN3a, PmPEN3b, and PmPEN5) were downregulated by V. parahaemolyticus infection. Silencing PmAkirin by dsRNA significantly decreased the expression of the eight AMPs, which lead to an increase in the blood concentration of V. parahaemolyticus and higher mortality in the shrimp. In contrast, the overexpression of PmAkirin significantly increased the expression of the eight AMPs, which led to a reduction in the blood concentration of V. parahaemolyticus and promoted the survival of the shrimp. Taken together, we concluded that PmAkirin plays an important role in regulating the expression of AMPs in black tiger shrimp to defend against V. parahaemolyticus infection.

Evolution of akirin family in gene and genome levels and coexpressed patterns among family members and rel gene in croaker

Akirins, which are highly conserved nuclear proteins, are present throughout the metazoan and regulate innate immunity, embryogenesis, myogenesis, and carcinogenesis. This study reports all akirin genes from miiuy croaker and analyzes comprehensively the akirin gene family combined with akirin genes from other species. A second nuclear localization signal (NLS) is observed in akirin2 homologues, which is not in akirin1 homologues in all teleosts and most other vertebrates. Thus, we deduced that the loss of second NLS in akirin1 homologues in teleosts likely occurred in an ancestor to all Osteichthyes after splitting with cartilaginous fish. Significantly, the akirin2(2) gene included six exons interrupted by five introns in the miiuy croaker, which may be caused by the intron insertion event as a novel evidence for the variation of akirin gene structure in some species. In addition, comparison of the genomic neighborhood genes of akirin1, akirin2(1), and akirin2(2) demonstrates a strong level of conserved synteny across the teleost classes, which further proved the deduction of Macqueen and Johnston 2009 that the produce of akirin paralogues can be attributed to whole-genome duplications and the loss of some akirin paralogues after genome duplications. Furthermore, akirin gene family members and relish gene are ubiquitously expressed across all tissues, and their expression levels are increased in three immune tissues after infection with Vibrio anguillarum. Combined with the expression patterns of LEAP-1 and LEAP-2 from miiuy croaker, an intricate network of co-regulation among family members is established. Thus, it is further proved that akirins acted in concert with the relish protein to induce the expression of a subset of downstream pathway elements in the NF-kB dependent signaling pathway.

The identification of the first molluscan Akirin2 with immune defense function in the Hong Kong oyster Crassostrea hongkongensis

The Akirin protein is a nuclear factor in the innate immune system that is highly conserved from insects to mammals and plays key roles in diverse biological processes, including immunity, myogenesis, development and the cellular stress response. However, the function of Akirins in mollusk, the second most diverse group of animals, is still poorly understood. In this study, we report the discovery of an Akirin2 gene homolog (ChAkirin2) and its biological functions in the Hong Kong oyster Crassostrea hongkongensis. ChAkirin2 is 189 amino acids in length and shares significant homology with invertebrate homologs. Phylogenetic analysis results revealed that ChAkirin2 is clustered with invertebrate Akirin2s. A sequence analysis of the 5' flanking regions of ChAkirin2 indicated that it harbors several potential PAMP-activated transcription factor binding sites (TFB), including sites for NF-κB, C/EBPα, AP-1, SRF, Oct-1 and GATA-1. An RT-PCR analysis showed that ChAkirin2 mRNA was ubiquitously expressed in various tissues and at different embryonic and larval stages. Additionally, upon infection by pathogens (Vibrio alginolyticus, Staphylococcus haemolyticus and Saccharomyces cerevisiae) and pathogen-associated molecular patterns (PAMPs: LPS, PGN and polyI:C), the expression of ChAkirin2 was significantly up-regulated. Moreover, fluorescence microscopy observations show that ChAkirin2 is located in the nuclei of HeLa cells, and the overexpression of ChAkirin2 activated the transcriptional activities of the NF-κB reporter gene in HEK293T cells. Altogether, this report provided the first experimental demonstration that mollusks possess a functional Akirin2 that is involved in the innate defense and embryogenesis processes of the oyster.

Identification and expression analysis of immune-related genes linked to Rel/NF-κB signaling pathway under stresses and bacterial challenge from the small abalone Haliotis diversicolor

Inhibitor of NF-κB (IκB), nuclear factor-κB (NF-κB), and Akirin2 are all important members of Rel/NF-κB signaling pathway, which plays a pivotal role in regulating the innate immune response of vertebrates and invertebrates. In this study, the IκB (SaIκB) and Akirin2 (SaAkirin2) cDNAs of small abalone Haliotis diversicolor were cloned and characterized. The full length cDNA of SaIκB and SaAkirin2 were 1748 bp and 1452 bp respectively, encoding a protein of 401 aa and 187 aa respectively. A conserved degradation motif (DS56GIYS60) and six ankyrin repeats were identified in the SaIκB by SMART analysis. Meanwhile, a typical nuclear localization signal (NLS) was found at the N-terminal region of the SaAkirin2 protein. Also, the mRNA expression level of SaIκB, SaAkirin2, and AbNF-κB were detected by quantitative real-time PCR. The results revealed that all these three genes were ubiquitously expressed in 7 selected tissues. The expression level of SaIκB in gills was higher than that in other tissues (P < 0.05) while the expression level of AbNF-κB was significantly higher in hepatopancreas and haemocytes. The highest expression level of SaAkirin2 was detected in hepatopancreas, followed by mantle. The mRNA expression levels in either gills or haemocytes of SaIκB, SaAkirin2, and AbNF-κB were significantly up-regulated (P < 0.05) post thermal stress, hypoxia exposure, thermal plus hypoxia stress and the injection of Vibrio parahaemolyticus. These results indicated that these three NF-κB signaling pathway-related genes are involved in response to bacterial infection and play essential roles in response to thermal and hypoxia stress.

Molecular cloning, sequence analysis and tissue-specific expression of Akirin2 gene in Tianfu goat

The Akirin2 gene is a nuclear factor and is considered as a potential functional candidate gene for meat quality. To better understand the structures and functions of Akirin2 gene, the cDNA of the Tianfu goat Akirin2 gene was cloned. Sequence analysis showed that the Tianfu goat Akirin2 cDNA full coding sequence (CDS) contains 579bp nucleotides that encode 192 amino acids. A phylogenic tree of the Akirin2 protein sequence from the Tianfu goat and other species revealed that the Tianfu goat Akirin2 was closely related with cattle and sheep Akirin2. RT-qPCR analysis showed that Akirin2 was expressed in the myocardium, liver, spleen, lung, kidney, leg muscle, abdominal muscle and the longissimus dorsi muscle. Especially, high expression levels of Akirin2 were detected in the spleen, lung, and kidney whereas lower expression levels were seen in the liver, myocardium, leg muscle, abdominal muscle and longissimus dorsi muscle. Temporal mRNA expression showed that Akirin2 expression levels in the longissimus dorsi muscle, first increased then decreased from day 1 to month 12. Western blotting results showed that the Akirin2 protein was only detected in the lung and three skeletal muscle tissues.

Role of akirin in skeletal myogenesis

Akirin is a recently discovered nuclear factor that plays an important role in innate immune responses. Beyond its role in innate immune responses, Akirin has recently been shown to play an important role in skeletal myogenesis. In this article, we will briefly review the structure and tissue distribution of Akirin and discuss recent advances in our understanding of its role and signal pathway in skeletal myogenesis.