Cyclin B-cdk1 controls pronuclear union in interphase.
In sexual reproduction, the union of the male and female pronuclei occurs in fertilized eggs to mix genetic materials derived from both parents, thereby creating a new genome for the next generation [1-4]. The process leading to pronuclear union consists of pronuclear congression, which depends on astral microtubules derived from sperm centrosome [5-8], and the subsequent pronuclear fusion or karyogamy. The union process progresses in parallel with the first embryonic cell cycle, but the molecular mechanisms involved are poorly understood. Here, we devise a labeling method with Dendra2 to track both pronuclei individually in living starfish eggs. Although pronuclear union naturally proceeds while G1 arrest is released by fertilization and S phase progresses [9], we show that the cell-cycle resumption and progression are not prerequisites for pronuclear union. However, low levels of cyclin B- (but not cyclin A-) Cdk1 activity are detectable even in interphase, and are indispensable for pronuclear union, by contributing at least to pronuclear congression through formation of sperm aster. Pronuclear congression thus requires the activity of M-phase cell-cycle regulator in interphase, independently of the cell-cycle regulation. These findings not only provide a clue to the regulatory aspect of creation of new genome with fertilization, but also reveal a novel role for the M-phase Cdk1 during interphase.
Tachibana
Kazunori
K
Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan.
Hara
Masatoshi
M
Hattori
Yukako
Y
Kishimoto
Takeo
T
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000201:enzymology* / Q000648:ultrastructure; D019926:Cyclin B / Q000378:metabolism*; D005260:Female; D007399:Interphase / Q000502:physiology*; D008297:Male; D010063:Ovum / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D013094:Spermatozoa / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D013215:Starfish / Q000166:cytology* / Q000201:enzymology
D019926:Cyclin B; D016203:CDC2 Protein Kinase