Studies on the mechanisms of ascidian fertilization

• Project/Area Number: 20K06621
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 44010:Cell biology-related
• Research Institution: Kinjo Gakuin University
• Principal Investigator: Sawada Hitoshi 金城学院大学, 生活環境学部, 教授 (60158946)
• Co-Investigator(Kenkyū-buntansha): 齋藤 貴子 静岡大学, 農学部, 助教 (10778038)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Project Status: Completed (Fiscal Year 2023)
• Budget Amount: ¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000); Fiscal Year 2022: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2021: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2020: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000)
• Keywords: 受精 / 自家不稔性 / 自家不和合性 / 精子 / ライシン / ホヤ / 自家不稔

Outline of Research at the Start

精子と卵の相互作用で開始される受精現象は、種認識や同種異個体細胞認識（雌雄同体生物の場合）など、様々なプロセスで巧妙に制御されることにより、単精受精を可能にしている。しかし、その受精の分子メカニズに関しては未だに不明な点が多い。本研究では、配偶子調製と受精実験の容易な海産無脊椎動物ホヤ（脊索動物）を用いて、受精機構の解明を目指す。特に、卵黄膜に精子通過孔を開ける卵黄膜ライシンに関する研究と、雌雄同体のホヤが自家受精を防ぐ自家不和合性機構の研究に焦点を絞る。この2点の研究を通して、ホヤの受精機構に関する理解を深め、哺乳類を含む新口動物全体における受精の共通原理の解明を目指す。

Outline of Final Research Achievements

Molecular mechanisms of sperm penetration through the vitelline coat (VC) and of self-sterility were investigated using hermaphroditic ascidians (Urochordate). We previously reported that sperm proteasome plays a key role in sperm penetration of the VC in ascidians, Halocynthia roretzi and Ciona intestinalis. In addition, we also showed that sperm astacin-like metalloproteases (tasts) play key roles in sperm penetration of the VC in C. intestinalis. Here, we showed that tasts also play key roles in fertilization of H. roretzi. On the other hand, we previously reported that three pairs of sperm s-Themis and VC v-Themis are responsible for self-sterility in C. intestinalis by genetic analysis. Here, we showed that s-Themis proteins are expressed in the sperm surface by biochemical analysis.

Academic Significance and Societal Importance of the Research Achievements

我が国では夫婦4.4組に１組が不妊症で、その約半数は男性側に原因があると言われている。男性不妊症への対応として、ICSI(卵細胞質内精子注入法)等の人工授精法がとられているが、受精の分子機構に関する研究は進んでいない。　私は受精実験の容易なホヤを用いて、精子プロテアソームが受精時にライシンとして機能することを初めて報告し、その後哺乳類でも同様であることが報告された。またホヤの自家不稔性に関わる精子タンパク質のホモログが哺乳類精子にも存在し、個体間多型があるという。これらの知見は、男性不妊症の一因がライシン系の異常や男女間の遺伝的近縁関係に関わる可能性を示唆しており、興味深い基礎研究といえる。

Research Products

• [Journal Article] Involvement in Fertilization and Expression of Gamete Ubiquitin-Activating Enzymes UBA1 and UBA6 in the Ascidian Halocynthia roretzi (2023)
  • Author(s): Sawada Hitoshi、Inoue Shukumi、Saito Takako、Otsuka Kei、Shirae-Kurabayashi Maki
  • Journal Title: International Journal of Molecular Sciences Volume: 24 Issue: 13 Pages: 10662-10662
  • DOI: 10.3390/ijms241310662
  • Peer Reviewed / Open Access
• [Journal Article] Mechanisms of sperm-egg interactions: What ascidian fertilization research has taught us. (2022)
  • Author(s): Hitoshi Sawada, Takako Saito
  • Journal Title: Cells Volume: 11 Issue: 13 Pages: 2096-2096
  • DOI: 10.3390/cells11132096
  • Peer Reviewed / Open Access
• [Journal Article] Fertilization of Ascidians: Gamete Interaction, Self/Nonself Recognition and Sperm Penetration of Egg Coat (2022)
  • Author(s): Saito Takako、Sawada Hitoshi
  • Journal Title: Frontiers in Cell and Developmental Biology Volume: 9 Pages: 827214-827214
  • DOI: 10.3389/fcell.2021.827214
  • Peer Reviewed / Open Access
• [Journal Article] Removal of the block to self-fertilization by low-calcium artificial seawater in the ascidian Ciona intestinalis. (2022)
  • Author(s): Hashimoto, S. Kinjo, K., Saito, T., and Sawada, H.
  • Journal Title: Zygote Volume: -
  • Peer Reviewed
• [Journal Article] A dynein-associated photoreceptor protein prevents ciliary acclimation to blue light (2021)
  • Author(s): Kutomi O, Yamamoto R, Hirose K, Mizuno K, Nakagiri Y, , , , , , , Shibata D, Shibata M, Shiba K, Kita M, Kigoshi H, Tanaka Y, Yamasaki Y, Asahina Y, Song C, Nomura M, Nomura M, Nakajima A, Nakachi M, Yamada L, Nakazawa S, Sawada H, Murata K, Mitsuoka K, Ishikawa T, Wakabayashi K, Kon T, Inaba K
  • Journal Title: Science Advances Volume: 7 Issue: 9
  • DOI: 10.1126/sciadv.abf3621
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Phylogenetic comparisons reveal mosaic histories of larval and adult shell matrix protein deployment in pteriomorph bivalves (2020)
  • Author(s): Ran Zhao, Takeshi Takeuchi, Ryo Koyanagi, Alejandro Villar-Briones, Lixy Yamada, Hitoshi Sawada, Akito Ishikawa, Shunsuke Iwanaga, Kiyohito Nagai, Yuqi Che, Noriyuki Satoh, Kazuyoshi Endo
  • Journal Title: Scientific Reports Volume: 10(1) Issue: 1 Pages: 22140-22140
  • DOI: 10.1038/s41598-020-79330-x
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] カタユウレイボヤ精子における自他認識分子s-Themis-A/Bの検出と相互作用分子の同定 (2023)
  • Author(s): 花﨑可奈、橋井則貴、金城敬太、澤田均、齋藤貴子
  • Organizer: 日本動物学会
• [Presentation] ホヤにおける卵膜ライシンに関する総括と新展開について (2023)
  • Author(s): 澤田均
  • Organizer: ホヤ研究会
• [Presentation] Sperm astacin-like metalloproteases are involved in sperm penetration through the vitelline coat during ascidian fertilization. (2022)
  • Author(s): Hitoshi Sawada
  • Organizer: 11th International Tunicate Meeting
  • Int'l Joint Research / Invited
• [Presentation] カタユウレイボヤの自家不和合性に及ぼす細胞外カルシウムイオン濃度と精子濃度の影響 (2022)
  • Author(s): 金城敬太、笹浪知宏、澤田 均、齋藤貴子
  • Organizer: 日本動物学会
• [Presentation] ホヤの受精における自己非自己細胞認識とライシン系について (2021)
  • Author(s): 澤田 均
  • Organizer: 日本動物学会 第39回ホヤの生物学談話会
  • Invited
• [Presentation] ホヤの自家不和合機構と精子プロテアーゼの役割 (2020)
  • Author(s): 澤田 均
  • Organizer: 第5回ホヤ研究会
• [Presentation] ホヤの受精研究から学んだこと (2020)
  • Author(s): 澤田 均
  • Organizer: 第7回生殖若手の会
  • Invited