Sako, Keisuke

写真a

Affiliation

School of Medicine, Department of Anatomy ( Shinanomachi )

Position

Senior Assistant Professor (Non-tenured)/Assistant Professor (Non-tenured)
 

Papers 【 Display / hide 】

  • Cells adapt to extracellular acidic pH through TM9SF3-mediated PI(4,5)P2 flop

    Sako K., Morimoto Y.V., Morioka S., Hasegawa J., Nakajima H., Fukumoto M., Nishida Y., Shintani Y., Sasaki J., Sasaki T., Kikuchi K., Mochizuki N.

    Nature Communications 16 ( 1 )  2025.12

    　View Summary

    The plasma membrane (PM), a physical barrier separating cells from their environment, responds to fluctuating extracellular environment through receptor-mediated signaling. While these pathways have been extensively studied, the role of PM lipids remains poorly understood. Here, we show that phosphatidylinositol 4,5-bisphosphate (PIP<inf>2</inf>), a multifunctional phospholipid, translocates from the inner to the outer leaflet of the PM in response to extracellular acidification. A genome-wide screening identifies Transmembrane 9 superfamily 3 (TM9SF3) as a critical regulator for PIP<inf>2</inf> translocation. During zebrafish gastrulation, when intracellular pH increases and extracellular interstitial fluid pH decreases, mutant anterior axial mesoderm lacking Tm9sf3 exhibits disorganized collective cell migration due to impaired PIP<inf>2</inf>-dependent cytoskeletal organization. Our results demonstrate that TM9SF3 mediates the PIP<inf>2</inf> translocation when cells encounter a low pH for adapting the cells to their environment. Given that “pH-dependent PIP<inf>2</inf> translocation” is evolutionarily conserved, cells may broadly employ lipid topology as a strategy to respond to extracellular stimuli.

  • Chemokine induces phase transition from non-directional to directional migration during angiogenesis

    Gui N., Sako K., Fukumoto M., Mochizuki N., Nakajima H.

    Cell Structure and Function 50 ( 1 ) 91 - 101 2025

    ISSN  03867196

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    During angiogenesis, sprouting endothelial cells (ECs) migrate and eventually connect to target vessels to form new vessel branches. However, it remains unclear how these sprouting vessels migrate toward the target vessels in three-dimensional space. We performed in vivo imaging of the cerebral capillary network formation in zebrafish to investigate how sprouting tip cells migrate toward their targets. Of note, we found that tip cells reach the target vessels through two phases: a non-directional phase and a directional phase. In the non-directional phase, sprouting tip cells dynamically extend and retract their protrusions at the leading front and have less directionality in their movement. In contrast, once tip cells enter the directional phase, they migrate directly toward the anastomotic targets. Chemokine receptor Cxcr4a and its ligand Cxcl12b are important for the phase transition to the directional phase. In cxcr4a mutants, sprouting tip cells lose their directionality and tend to connect to nearby sprouting ECs, resulting in altered capillary network patterning. Furthermore, in wild-type (WT) larvae, local Ca<sup>2+</sup> oscillations were detected in protrusions of tip cells, specifically in the non-directional phase, but almost disappeared in the directional phase as a result of the Cxcr4-dependent phase transition. Thus, this study provides evidence of a chemokine-induced phase transition in migrating tip cells, which is important for proper vascular network formation in the zebrafish brain.

  • Angpt1 binding to Tie1 regulates the signaling required for lymphatic vessel development in zebrafish

    Morooka N., Gui N., Ando K., Sako K., Fukumoto M., Hasegawa U., Hußmann M., Schulte-Merker S., Mochizuki N., Nakajima H.

    Development Cambridge 151 ( 10 )  2024.05

    ISSN  09501991

    　View Summary

    Development of the vascular system is regulated by multiple signaling pathways mediated by receptor tyrosine kinases. Among them, angiopoietin (Ang)/Tie signaling regulates lymphatic and blood vessel development in mammals. Of the two Tie receptors, Tie2 is well known as a key mediator of Ang/Tie signaling, but, unexpectedly, recent studies have revealed that the Tie2 locus has been lost in many vertebrate species, whereas the Tie1 gene is more commonly present. However, Tie1-driven signaling pathways, including ligands and cellular functions, are not well understood. Here, we performed comprehensive mutant analyses of angiopoietins and Tie receptors in zebrafish and found that only angpt1 and tie1 mutants show defects in trunk lymphatic vessel development. Among zebrafish angiopoietins, only Angpt1 binds to Tie1 as a ligand. We indirectly monitored Ang1/ Tie1 signaling and detected Tie1 activation in sprouting endothelial cells, where Tie1 inhibits nuclear import of EGFP-Foxo1a. Angpt1/ Tie1 signaling functions in endothelial cell migration and proliferation, and in lymphatic specification during early lymphangiogenesis, at least in part by modulating Vegfc/Vegfr3 signaling. Thus, we show that Angpt1/Tie1 signaling constitutes an essential signaling pathway for lymphatic development in zebrafish.

  • Endoderm-derived islet1-expressing cells differentiate into endothelial cells to function as the vascular HSPC niche in zebrafish

    Nakajima H., Ishikawa H., Yamamoto T., Chiba A., Fukui H., Sako K., Fukumoto M., Mattonet K., Kwon H.B., Hui S.P., Dobreva G.D., Kikuchi K., Helker C.S.M., Stainier D.Y.R., Mochizuki N.

    Developmental Cell 58 ( 3 ) 224 - 238.e7 2023.02

    ISSN  15345807

    　View Summary

    Endothelial cells (ECs) line blood vessels and serve as a niche for hematopoietic stem and progenitor cells (HSPCs). Recent data point to tissue-specific EC specialization as well as heterogeneity; however, it remains unclear how ECs acquire these properties. Here, by combining live-imaging-based lineage-tracing and single-cell transcriptomics in zebrafish embryos, we identify an unexpected origin for part of the vascular HSPC niche. We find that islet1 (isl1)-expressing cells are the progenitors of the venous ECs that constitute the majority of the HSPC niche. These isl1-expressing cells surprisingly originate from the endoderm and differentiate into ECs in a process dependent on Bmp-Smad signaling and subsequently requiring npas4l (cloche) function. Single-cell RNA sequencing analyses show that isl1-derived ECs express a set of genes that reflect their distinct origin. This study demonstrates that endothelial specialization in the HSPC niche is determined at least in part by the origin of the ECs.

  • Satb2 acts as a gatekeeper for major developmental transitions during early vertebrate embryogenesis

    Pradhan S.J., Reddy P.C., Smutny M., Sharma A., Sako K., Oak M.S., Shah R., Pal M., Deshpande O., Dsilva G., Tang Y., Mishra R., Deshpande G., Giraldez A.J., Sonawane M., Heisenberg C.P., Galande S.

    Nature Communications 12 ( 1 )  2021.12

    　View Summary

    Zygotic genome activation (ZGA) initiates regionalized transcription underlying distinct cellular identities. ZGA is dependent upon dynamic chromatin architecture sculpted by conserved DNA-binding proteins. However, the direct mechanistic link between the onset of ZGA and the tissue-specific transcription remains unclear. Here, we have addressed the involvement of chromatin organizer Satb2 in orchestrating both processes during zebrafish embryogenesis. Integrative analysis of transcriptome, genome-wide occupancy and chromatin accessibility reveals contrasting molecular activities of maternally deposited and zygotically synthesized Satb2. Maternal Satb2 prevents premature transcription of zygotic genes by influencing the interplay between the pluripotency factors. By contrast, zygotic Satb2 activates transcription of the same group of genes during neural crest development and organogenesis. Thus, our comparative analysis of maternal versus zygotic function of Satb2 underscores how these antithetical activities are temporally coordinated and functionally implemented highlighting the evolutionary implications of the biphasic and bimodal regulation of landmark developmental transitions by a single determinant.

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