In early C. elegans embryos the timing of cell division is both invariant and developmentally regulated, yet how the cell cycle is controlled in the embryo and how cell cycle timing impacts early development remain important, unanswered questions. Here, I focus on the cyclin B3 ortholog CYB-3, and show that this cyclin has the unusual property of controlling both the timely progression through S-phase and mitotic entry, suggesting that CYB-3 is both an S-phase-promoting and mitosis-promoting factor. Furthermore, I find that CYB-3 is asymmetrically distributed in the two-cell embryo, such that the somatic precursor AB cell contains ∼2.5-fold more CYB-3 than its sister cell, the germline progenitor P1. CYB-3 is not only physically limited in P1 but also functionally limited, and this asymmetry is controlled by the par polarity network. These findings highlight the importance of the CYB-3 B3-type cyclin in cell cycle regulation in the early embryo and suggest that CYB-3 asymmetry helps establish the well-documented cell cycle asynchrony that occurs during cell division within the P-lineage.
The author declares no competing or financial interests.
W.M.M. performed all experiments and wrote the manuscript.
This work was funded by the National Institute of General Medical Sciences, which is part of the National Institutes of Health [R01GM099825 to W.M.M.]. Deposited in PMC for release after 12 months.
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.141226.supplemental
- Received June 16, 2016.
- Accepted July 21, 2016.