Biology subjects

Izumikawa, K.

Publications and source records attributed to Izumikawa, K..

3 recordsLinked to original sources

bioRxiv2025

Molecular basis of the autoregulatory mechanism of motor neuron-related splicing factor 30

Motor neuron-related splicing factor 30 (SPF30, also known as SMNDC1) is a paralog of the survival motor neuron protein that regulates the expression of various genes by affecting mRNA splicing. SPF30 has an autoregulatory mechanism that controls its expression. However, the detailed molecular mechanisms determining cellular levels of SPF30 remain unclear. Here, we demonstrated that SPF30 expression was controlled via the negative autoregulatory feedback, whereby increased SPF30 expression caused the inclusion of cassette exon within intron 2 and/or the generation of a newly spliced variant with exon 4a (produced by splicing 17 bp upstream of the canonical intron 3 and exon 4 junctions). Altered transcripts with cassette exon or exon 4a were subjected to nonsense-mediated mRNA decay, leading to reduced SPF30 mRNA levels. Conversely, the loss of SPF30 protein resulted in a drastic reduction in exon 4a inclusion compared to cassette exon inclusion, suggesting that exon 4a inclusion contributes more to adjusting SPF30 expression levels. An in vivo splicing assay designed to reflect exon 4a inclusion levels demonstrated that a short stretch of sequence within exon 4 of SPF30 mRNA was required for exon 4a inclusion. Additionally, the C-terminal region of SPF30 was crucial for the autoregulatory mechanism. Specifically, the C-terminal region of SPF30, including the latter part of -helix and a kink-like structure, was required for binding to RNA containing exon 4a. Collectively, these results reveal the molecular basis of the autoregulatory mechanism underlying SPF30 gene expression.

molecular biology↗

bioRxiv2023

Analysis of chronic host-aspergilloma interactions using a novel mouse model

An aspergilloma is a fungus ball caused by chronic infection of Aspergillus species in a pre- existing cavity, such as a destroyed lung or the sinuses. Patients with pulmonary aspergilloma are at risk of sudden life-threatening hemoptysis. Antifungal therapy is administered to aspergilloma patients who are ineligible for surgery, but its efficacy is limited. Understanding the pathophysiology of aspergilloma is crucial for developing further treatment strategies. The mechanism behind the long-term host response to aspergilloma is poorly understood. We created a novel mouse model to analyze the host response to aspergilloma by implanting a fungus ball of Aspergillus fumigatus into an air-filled subcutaneous cavity. Our findings indicate that a live fungus ball led to tissue invasion, even in immunized mice. When a fungus ball consisting of dead hyphae was implanted, it persisted for over three months and induced pathological findings simulating human aspergilloma, including an inflammatory cell infiltration into the fungus ball and angiogenesis in the cavity wall. Dead fungus ball induced Th1 and Th17 inflammatory cytokines and vascular endothelial growth factor. Neutrophils infiltrated the inside of the fungus ball immediately after implantation, and macrophages surrounded it after a one-week delay. The macrophages around the fungus ball were swollen with phagocytosed fragments of dead hyphae and transformed into foam cells containing fat droplets. We also confirmed in vitro that macrophages were damaged and transformed into foam cells by direct contact with dead hyphae. This model holds promise to provide new insights into the fungal-host interaction during aspergillomas. NOTATION OF PRIOR ABSTRACT PUBLICATION/PRESENTATIONNone IMPORTANCEChronic aspergillosis, which affects over 3 million people worldwide with a 5-year survival rate of 50%, is understudied compared to other forms. Our study focuses on aspergilloma, a key aspect of chronic aspergillosis, using a groundbreaking mouse model that mirrors clinical features over three months. By studying host-fungal interactions within aspergillomas, we discovered Th1 and Th17 inflammatory responses to dead fungal hyphae. Initially, neutrophils dominate, later giving way to macrophages with a lipid-accumulating foamy phenotype. This transition may impede aspergilloma clearance. In addition, even dead hyphae induce vascular endothelial growth factor and promote angiogenesis. Our findings, which are critical for the prevention of fatal hemoptysis, highlight the need for innovative treatments that target fungal clearance and challenge the limited efficacy of antifungal agents against dead fungal bodies. This research represents a significant step forward in the understanding of chronic aspergillosis.

microbiology↗

bioRxiv2023

Structure of mitoribosome reveals mechanism of mRNA binding, tRNA interactions with L1 stalk, roles of cofactors and rRNA modifications

The mitoribosome translates mitochondrial mRNAs and regulates energy conversion that is a signature of aerobic life forms. We present a 2.2 [A] resolution structure of human mitoribosome together with validated mitoribosomal RNA (rRNA) modifications, including aminoacylated CP-tRNAVal. The structure shows how mitoribosomal proteins stabilise binding of mRNA and tRNA helping to align it in the decoding center, whereas the GDP-bound mS29 stabilizes intersubunit communication. Comparison between different states, with respect to tRNA position, allowed to characterize a non-canonical L1 stalk, and molecular dynamics simulations revealed how it facilitates tRNA transition in a way that does not require interactions with rRNA. We also report functionally important polyamines that are depleted when cells are subjected to an antibiotic treatment. The structural, biochemical, and computational data illuminate the principal functional components of the translation mechanism in mitochondria and provide the most complete description so far of the structure and function of the human mitoribosome.

biochemistry↗