The Chlamydomonas cell cycle

Abstract

SummaryThe position of Chlamydomonas within the eukaryotic phylogeny makes it a unique model in at least two important ways: as a representative of the critically important, early‐diverging lineage leading to plants; and as a microbe retaining important features of the last eukaryotic common ancestor (LECA) that has been lost in the highly studied yeast lineages. Its cell biology has been studied for many decades and it has well‐developed experimental genetic tools, both classical (Mendelian) and molecular. Unlike land plants, it is a haploid with very few gene duplicates, making it ideal for loss‐of‐function genetic studies. The Chlamydomonas cell cycle has a striking temporal and functional separation between cell growth and rapid cell division, probably connected to the interplay between diurnal cycles that drive photosynthetic cell growth and the cell division cycle; it also exhibits a highly choreographed interaction between the cell cycle and its centriole–basal body–flagellar cycle. Here, we review the current status of studies of the Chlamydomonas cell cycle. We begin with an overview of cell‐cycle control in the well‐studied yeast and animal systems, which has yielded a canonical, well‐supported model. We discuss briefly what is known about similarities and differences in plant cell‐cycle control, compared with this model. We next review the cytology and cell biology of the multiple‐fission cell cycle of Chlamydomonas. Lastly, we review recent genetic approaches and insights into Chlamydomonas cell‐cycle regulation that have been enabled by a new generation of genomics‐based tools.

Evidence That an Unconventional Actin Can Provide Essential F-Actin Function and That a Surveillance System Monitors F-Actin Integrity inChlamydomonas

“…nap1-2 cells plated on LatB early in the growth cycle (4 hr after refeeding, while cells were still small) showed little increase in cell size and no cell divisions over the succeeding 22 hr, whereas wildtype controls with or without LatB, or nap1-2 cells without LatB, all grew and carried out multiple division cycles in this time ( Figure 10A). This defect could be due to a direct requirement for IDA5 or NAP1 for division; alternatively, the cells could fail division as a secondary consequence of failing to reach a critical cell size (Cross and Umen 2015). To test this, we examined wild-type and nap1-2 cells plated on LatB 12 hr after refeeding, when they were large and would normally divide within a few hours.…”

“…The Chlamydomonas cell cycle is separated into a long growth phase, during which cells can increase in size by .10-fold, followed by a rapid series of cell divisions; entry into cell division, and the number of divisions carried out, is dependent on cell size (reviewed by Cross and Umen 2015). We obtained a partial synchronization of wild-type and nap1-2 cells by inoculation into low-nitrogen medium; upon depletion of the medium, such cultures consist mostly of small newborn cells.…”

High-Throughput Robotically Assisted Isolation of Temperature-sensitive Lethal Mutants in <em>Chlamydomonas reinhardtii</em>

“…Both from prior knowledge and from sequence analysis, we expect cell cycle genes in the Chlamydomonas to be around 500 genes 2 , although most, but probably not all, are essential. We will evaluate the necessity for additional mutagenesis rounds as more mutants are collected and the level of saturation rises.…”

“…The haploid unicellular green algae Chlamydomonas reinhardtii has a plant-like gene set, but it diverged from land plants before multiple genome duplications in the land plant lineage 2 . In principle, lack of gene duplication and a mainly haploid life cycle greatly facilitates loss-of-function genetic approaches.…”

The Aging‐related Approach to Detection of Mitotic Factor in Thoracic Duct Lymph of Rabbits

“…[5] Recently, it was pointed out that efficient approach to the clear understanding of mitosis mechanisms is still underway. [6,7] Regulating machine of mitoses is investigated in normal [8] and pathology, tumors. [9,10] At present mitosis has remained the most important prognostic factor.…”