Akirin Is Required for Muscle Function and Acts Through the TGF-β Sma/Mab Signaling Pathway in Caenorhabditis elegans Development

A critical role for the nuclear protein Akirin in larval development in Henosepilachna vigintioctopunctata

Akirin is a nuclear protein that controls development in vertebrates and invertebrates. The function of Akirin has not been assessed in any Coleopteran insects. We found that high levels of akirin transcripts in Henosepilachna vigintioctopunctata, a serious Coleopteran potato defoliator (hereafter Hvakirin), were present at prepupal, pupal and adult stages, especially in larval foregut and fat body. RNA interference (RNAi) targeting Hvakirin impaired larval development. The Hvakirin RNAi larvae arrested development at the final larval instar stage. They remained as stunted larvae, gradually blackened and finally died. Moreover, the remodelling of gut and fat body was inhibited in the Hvakirin depleted larvae. Two layers of cuticles, old and newly formed, were noted in the dsegfp-injected animals. In contrast, only a layer of cuticle was found in the dsakirin-injected beetles, indicating the arrest of larval development. Furthermore, the expression of three transforming growth factor-β cascade genes (Hvsmox, Hvmyo and Hvbabo), a 20-hydroxyecdysone (20E) receptor gene (HvEcR) and six 20E response genes (HvHR3, HvHR4, HvE75, HvBrC, HvE93 and Hvftz-f1) was significantly repressed, consistent with decreased 20E signalling. Conversely, the transcription of a juvenile hormone (JH) biosynthesis gene (Hvjhamt), a JH receptor gene (HvMet) and two JH response genes (HvKr-h1 and HvHairy) was greatly enhanced. Our findings suggest a critical role of Akirin in larval development in H. vigintioctopunctata.

Role of nuclear protein Akirin in the modulation of female reproduction in Nilaparvata lugens (Hemiptera: Delphacidae)

Introduction: Akirin as a highly conserved transcription factor, exerts a profound influence on the growth, development, immune response, and reproductive processes in animals. The brown planthopper (BPH), Nilaparvata lugens, a major pest in rice production in Asia, possesses high reproductive capacity, a critical factor contributing to reduced rice yields. The aims of this study were to demonstrate the regulatory role of Akirin in the reproduction of BPH. Methods: In this study, quantitative PCR (qPCR) was used to detect the mRNA expression of genes. RNA interference (RNAi) was used to downregulate the expression of Akirin gene, and RNA sequencing (RNA-seq) was used to screen for differentially expressed genes caused by Akirin downregulation. Hormone contents were measured with the enzyme linked immunosorbent assay (ELISA), and protein content was evaluated with the bicinchoninic acid (BCA) method. Results: Using BPH genome data, we screened for an Akirin gene (NlAkirin). An analysis of tissue-specific expressions showed that NlAkirin was expressed in all tissues tested in female BPH, but its expression level was highest in the ovary. After inhibiting the mRNA expression of NlAkirin in BPH females, the number of eggs laid, hatching rate, and number of ovarioles decreased. Transcriptome sequencing was performed, following a NlAkirin double-stranded RNA treatment. Compared with the genes of the control, which was injected with GFP double-stranded RNA, there were 438 upregulated genes and 1012 downregulated genes; the expression of vitellogenin (Vg) and vitellogenin receptor (VgR) genes as well as the mRNA expression of genes related to the target of rapamycin (TOR), juvenile hormone (JH), and insulin pathways involved in Vg synthesis was significantly downregulated. As a result of NlAkirin knockdown, the titers of JH III and Ecdysone (Ecd) were downregulated in unmated females but returned to normal levels in mated females. The ovarian protein contents in both unmated and mated females were downregulated. Discussion and conclusion: Our results suggest that NlAkirin affects female BPH reproduction by regulating the mRNA expression of genes related to the Vg, VgR, TOR, JH, and insulin signaling pathways, in addition to the titers of JH III and Ecd. The findings of this research provide novel insights into the regulatory role of Akirin in insect reproductive capacity.

AKIR-1 regulates proteasome subcellular function in Caenorhabditis elegans

Polyubiquitinated proteins are primarily degraded by the ubiquitin-proteasome system (UPS). Proteasomes are present both in the cytoplasm and nucleus. Here, we investigated mechanisms coordinating proteasome subcellular localization and activity in a multicellular organism. We identified the nuclear protein-encoding gene akir-1 as a proteasome regulator in a genome-wide Caenorhabditis elegans RNAi screen. We demonstrate that depletion of akir-1 causes nuclear accumulation of endogenous polyubiquitinated proteins in intestinal cells, concomitant with slower in vivo proteasomal degradation in this subcellular compartment. Remarkably, akir-1 is essential for nuclear localization of proteasomes both in oocytes and intestinal cells but affects differentially the subcellular distribution of polyubiquitinated proteins. We further reveal that importin ima-3 genetically interacts with akir-1 and influences nuclear localization of a polyubiquitin-binding reporter. Our study shows that the conserved AKIR-1 is an important regulator of the subcellular function of proteasomes in a multicellular organism, suggesting a role for AKIR-1 in proteostasis maintenance.

p53-mediated neurodegeneration in the absence of the nuclear protein Akirin2

Proper gene regulation is critical for both neuronal development and maintenance as the brain matures. We previously demonstrated that Akirin2, an essential nuclear protein that interacts with transcription factors and chromatin remodeling complexes, is required for the embryonic formation of the cerebral cortex. Here we show that Akirin2 plays a mechanistically distinct role in maintaining healthy neurons during cortical maturation. Restricting Akirin2 loss to excitatory cortical neurons resulted in progressive neurodegeneration via necroptosis and severe cortical atrophy with age. Comparing transcriptomes from Akirin2-null postnatal neurons and cortical progenitors revealed that targets of the tumor suppressor p53, a regulator of both proliferation and cell death encoded by Trp53, were consistently upregulated. Reduction of Trp53 rescued neurodegeneration in Akirin2-null neurons. These data: (1) implicate Akirin2 as a critical neuronal maintenance protein, (2) identify p53 pathways as mediators of Akirin2 functions, and (3) suggest Akirin2 dysfunction may be relevant to neurodegenerative diseases.

Akirin proteins in development and disease: critical roles and mechanisms of action

The Akirin genes, which encode small, nuclear proteins, were first characterized in 2008 in Drosophila and rodents. Early studies demonstrated important roles in immune responses and tumorigenesis, which subsequent work found to be highly conserved. More recently, a multiplicity of Akirin functions, and the associated molecular mechanisms involved, have been uncovered. Here, we comprehensively review what is known about invertebrate Akirin and its two vertebrate homologues Akirin1 and Akirin2, highlighting their role in regulating gene expression changes across a number of biological systems. We detail essential roles for Akirin family proteins in the development of the brain, limb, and muscle, in meiosis, and in tumorigenesis, emphasizing associated signaling pathways. We describe data supporting the hypothesis that Akirins act as a "bridge" between a variety of transcription factors and major chromatin remodeling complexes, and discuss several important questions remaining to be addressed. In little more than a decade, Akirin proteins have gone from being completely unknown to being increasingly recognized as evolutionarily conserved mediators of gene expression programs essential for the formation and function of animals.