第1470回生物科学セミナー
Mechanisms and origins of egg-sperm fusion in plants, protists, and mammals
Prof. Benjamin Podbilewicz（Department of Biology, Technion - Israel Institute of Technology）
2023年09月05日(火) 13:30-15:00 理学部2号館223号室及びZoom
Fusion between gametes is essential for sexual reproduction. It is widely accepted that sex is an ancient trait of eukaryotes and was probably present in their last common ancestor. Archaea (prokaryotes without nuclei) are the progenitors of the eukaryotic nucleocytoplasm and current evidence suggests that cell fusion probably originated in archaea. Indeed, sex-like exchange of genetic material via fusion is known to occur in archaea from the Dead and Mediterranean seas. These archaea can form cytoplasmic bridges visible by electron microscopy that then enable large-scale eukaryotic-like recombination. However, neither molecular nor cellular mechanisms of cell fusion have been described in archaea. A few types of protein machineries that are both necessary and sufficient to fuse eukaryotic cells (fusogens) have been identified and studied. Our lab discovered the first two, EFF-1 and AFF-1 from C. elegans, that are now known to be a member of a diverse protein family1,2. In eukaryotes, sexual reproduction depends on the GCS1(HAP2) plasma membrane protein that is necessary in plants and protists for gamete fusion3,4. GCS1 is related to class II viral glycoproteins (e.g. from Zika and Dengue viruses) and have structural and functional similarity to fusion proteins from animals (e.g. EFF-1 and AFF-1)5-8. We named this family of fusogens from gametes, enveloped viruses, and somatic cells Fusexins: fusion proteins essential for sexual reproduction and exoplasmic merger of plasma membranes6. More recently we found fusexins in archaea and determined the crystal structure of the prokaryotic Fsx19. Moreover, Fsx1 can fuse heterologous mammalian cells demonstrating that they are fusogens9. To understand the origin of eukaryotic sexual reproduction we study the functions and evolutionary history of Fsx1 and we also found that the mouse sperm adhesion protein IZUMO110 is also a fusogen that is unrelated to fusexins11. Thus, different families of fusogens can fuse gamete plasma membranes essential for sexual reproduction, using different mechanisms.
References:
1. Mohler et al (2002) Dev Cell 2(3):355–362; 2. Sapir et al (2007) Dev Cell 12(5):683–698; 3. Mori et al., (2006) Nat Cell Biol 8(1):64–71; 4. Johnson et al., (2004) Genetics 168(2):971–98; 5. Perez-Vargas et al., (2014) Cell 157, 407-419; 6. Valansi, Moi et al (2017) J Cell Biol 216(3):571–581; 7. Fedry et al (2017) Cell 168(5):904-915.e10; 8. Pinello et al (2017) Curr Biol 27(5):651–660; 9. Moi, Nishio. Li. et al. (2022) Nat Commun. 13: 3880; 10. Inoue et al., (2005) Nature 434: 234–238; 11. Brukman, Nakajima et al. (2023) J Cell Biol 222 (2): e202207147
Contact： Higashiyama Lab 生物科学専攻・東山研究室
