Biology subjects

Izumi, N.

Publications and source records attributed to Izumi, N..

6 recordsLinked to original sources

bioRxiv2025

Perturbing postural stability during treadmill walking with dysfunctional electrical stimulation

Functional electrical stimulation is commonly used to enhance human movement through low-level electrical activation of muscles. More recently, dysfunctional electrical stimulation (DFES) has been proposed as a method to perturb gait by artificially inducing discomfort and mimicking inadequate muscle activity. Here we investigated strategies to induce internal perturbations during treadmill walking using DFES by systematically varying the timing and target muscle. Eleven healthy participants walked at three different speeds while DFES was applied to the tibialis anterior (TA), soleus (SOL), rectus femoris (RF), and biceps femoris (BF) muscles at 25%, 50%, 75%, and 100% of the gait cycle, each for a duration of 0.2 seconds. The gait cycle was time-locked to heel contact (0%). Results showed a significant reduction in the anterior-posterior margin of stability compared to baseline, particularly when DFES was applied to the SOL at 75%, the RF at 50%, and the BF at 75% of the gait cycle. Under these conditions, increased knee flexion and shorter stride intervals were observed relative to baseline. In conclusion, we identified effective DFES conditions to induce postural instability during walking. By mimicking inadequate muscle activity, DFES provides a promising method to study dynamic balance control and mechanisms underlying falls in neurological populations.

bioengineering↗

bioRxiv2025

Generation of iPSC-derived CD4+ Th1 cells enhancing chimeric antigen receptor-T cell cytotoxicity

CD4+ T cells are anticipated to enhance the overall immune response, including the anti-tumor activity of chimeric antigen receptor (CAR)-T cell therapy. In the past, we established a culture system to generate CD8+ T cells from iPS cells (iPSCs); however, it was challenging to generate CD4+ T cells. Drawing inspiration from the observation that adult T cell leukemia (ATL) cells are consistently CD4+ and possess Treg characteristics, we successfully generated CD4+ Treg cells by reprogramming ATL cells into iPSCs and then differentiating them into T cells. Gene expression analysis of this generation system suggested that RUNX3 serves as a key regulator in T cell differentiation within the ex vivo generation system. By knocking out RUNX3, we demonstrated the generation of antigen-specific CD4+ Th1 cells via the iPSC route, thereby enhancing the activity of CD8+ CAR-T cells against GD2-expressing lymphoma. These technologies hold significant promise for contributing to "off-the-shelf" immunotherapies against malignant tumors, including solid tumors.

immunology↗

bioRxiv2024

Autonomous Shaping of the piRNA Sequence Repertoire by Competition between Adjacent Ping-Pong Sites

PIWI-interacting RNAs (piRNAs) are crucial for silencing transposable elements (TEs). In many species, piRNAs are generated via a complex process known as the ping-pong pathway, which couples TE cleavage with new piRNA amplification. However, the biological significance of this complexity and its impact on the piRNA sequence repertoire remain unclear. Here, we systematically compared piRNA production patterns in two closely related silkworm cell lines and found significant changes in their piRNA sequence repertoire. Importantly, the changeability of this repertoire showed a strong negative correlation with the efficiency of piRNA biogenesis. This can be explained by competition between adjacent ping-pong sites, as supported by our mathematical modeling. Moreover, this competition can rationalize how piRNAs autonomously avoid deleterious mismatches to target TEs. These findings unveil the intrinsic plasticity and adaptability of the piRNA system to combat diverse TE sequences and highlight the universal power of competition and self-amplification to drive autonomous optimization.

molecular biology↗

bioRxiv2023

The dual role of Spn-E in supporting heterotypic ping-pong piRNA amplification in silkworms

The PIWI-interacting RNA (piRNA) pathway plays a crucial role in silencing transposons in the germline. piRNA-guided target cleavage by PIWI proteins triggers biogenesis of new piRNAs from the cleaved RNA fragments. This process, known as the ping-pong cycle, is mediated by the two PIWI proteins, Siwi and BmAgo3, in silkworms. However, the detailed molecular mechanism of the ping-pong cycle remains largely unclear. Here, we show that Spindle-E (Spn-E), a putative ATP-dependent RNA helicase, is essential for BmAgo3-dependent production of Siwi-bound piRNAs in the ping-pong cycle and that this function of Spn-E requires its ATPase activity. Moreover, Spn-E acts to suppress homotypic Siwi-Siwi ping-pong, but this function of Spn-E is independent of its ATPase activity. These results highlight the dual role of Spn-E in facilitating proper heterotypic ping-pong in silkworms.

molecular biology↗

bioRxiv2022

The two Gtsf paralogs in silkworms orthogonally activate their partner PIWI proteins for target cleavage

The PIWI-interacting RNA (piRNA) pathway is a protection mechanism against transposons in animal germ cells. Most PIWI proteins possess piRNA-guided endonuclease activity, which is critical for silencing transposons and producing new piRNAs. Gametocyte-specific factor 1 (Gtsf1), an evolutionarily conserved zinc finger protein, promotes catalysis by PIWI proteins. Many animals have multiple Gtsf1 paralogs; however, their respective roles in the piRNA pathway are not fully understood. Here, we dissected the roles of Gtsf1 and its paralog Gtsf1-like (Gtsf1L) in the silkworm piRNA pathway. We found that Gtsf1 and Gtsf1L preferentially bind the two silkworm PIWI paralogs, Siwi and BmAgo3, respectively, and facilitate the endonuclease activity of each PIWI protein. This orthogonal activation effect was further supported by specific reduction of BmAgo3-bound Masculinizer piRNA and Siwi-bound Feminizer piRNA, the unique piRNA pair required for silkworm feminization, upon depletion of Gtsf1 and Gtsf1L, respectively. Our results indicate that the two Gtsf paralogs in silkworms activate their respective PIWI partners, thereby facilitating the amplification of piRNAs.

biochemistry↗

bioRxiv2021

The tiny, conserved zinc-finger protein GTSF1helps PIWI proteins achieve their full catalytic potential

Argonaute proteins use nucleic acid guides to find and bind specific DNA or RNA target sequences. Argonaute proteins can be found in all kingdoms of life, and play diverse biological functions including genome defense, gene regulation, and chromosome partitioning. Many Argonautes retain their ancestral endoribonuclease activity, cleaving the phosphodiester bond between target nucleotides t10 and t11. In animals, a specialized class of Argonautes, the PIWI proteins, use 21-35 nt PIWI-interacting RNAs (piRNAs) to direct transposon silencing, protect the germline genome, and regulate gene expression during gametogenesis1. The piRNA pathway is required for fertility in one or both sexes of nearly all animals. Both piRNA production and function require RNA cleavage catalyzed by PIWI proteins. Spermatogenesis in mice and other placental mammals requires three distinct, developmentally regulated PIWI proteins: MIWI (PIWIL1), MILI (PIWIL2), and MIWI2 (PIWIL4)2-4. The piRNA-guided endoribonuclease activities of MIWI and MILI are essential to produce functional sperm5, 6. piRNA-directed silencing in mice and insects also requires Gametocyte-Specific Factor 1 (GTSF1), a PIWI-associated protein of unknown function7-12. Here, we report that GTSF1 potentiates the weak, intrinsic, piRNA-directed RNA cleavage activities of PIWI proteins, transforming them into efficient endoribonucleases. GTSF1 represents the first example of an auxiliary protein that potentiates the catalytic activity of an Argonaute protein.

biochemistry↗