Multicellularity in Volvox may have arisen from Rb's cell cycle tricks.

David Kirk

A newly discovered Rb protein in the unicellular green alga Chlamydomonas reinhardtii sets a size limit for cell division, and may help explain how multicellularity evolved in algae such as Volvox.

Growth and division are uncoupled in Chlamydomonas cell cycles. During the day, cells remain in G1 to concentrate on photosynthesis, often growing to many times their original size. At night, however, cells undergo multiple alternating rounds of S phase and mitosis to produce 2n daughter cells.

Jim Umen and Ursula Goodenough of Washington University (St. Louis, MO) found that cells with a deletion in the mat3 gene of Chlamydomonas are smaller because of two perturbations in this cell cycle regimen. Mutant cells committed to entering a cell division cycle at a smaller than normal size, and those cells then...

The Rockefeller University Press
2001
The Rockefeller University Press
2001
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