The ASCB 2014 meeting is winding down here in Philadelphia, but yesterday I attended the minisymposium on “Cell Cycle Signaling and Regulation”.
The session covered an interesting mix of different cell cycle-regulated processes. Lars Jansen (Gulbenkian Institute, Oieras, Portugal), for example, explained why the specialized histone protein CENP-A – an epigenetic marker of centromeres – is only assembled onto centromeric chromatin during G1 in mammalian cells, and Alexandre Orthwein (from Daniel Durocher’s lab in the Lunenfeld-Tanenbaum Research Institute in Toronto) discussed how and why mitotic cells avoid repairing DNA double strand breaks.
In other talks, Chris Campbell (from Arshad Desai’s group at the Ludwig Institute for Cancer Research in La Jolla) challenged the existing model of how the mitotic kinase Aurora B promotes chromosomes’ biorientation on the mitotic spindle, and Jason Stumpff (University of Vermont) revealed the surprising finding that chromosomes don’t have to align in the center of the spindle in order to segregate accurately into daughter cells. Jake Herman (from Jennifer DeLuca’s lab at Colorado State University, Fort Collins) described how oncogenic Ras signaling weakens kinetochore-microtubule attachments in cancer cells (an observation that could have exciting therapeutic potential). And Keisuke Ishihara (from Tim Mitchison’s group at Harvard Medical School) discussed how non-centrosomal nucleation allows microtubule asters to expand throughout the cytosol of large Xenopus egg cells.
Three other talks highlighted some more unusual models for studying the cell cycle. Don Fox (Duke University) studies the unusual cell cycle behavior of Drosophila rectal papilla cells. During development, these cells initially become polyploidy by undergoing cycles of endoreplication – duplicating their DNA without passing through mitosis. Later in development, the papillar cells begin dividing mitotically, although these divisions are somewhat error prone. Interestingly, Fox showed that this odd pattern of cell cycle behavior is essential for both the form and function of the Drosophila rectum.
Huaiying Zhang (from session co-chair Amy Gladfelter’s lab at Dartmouth University) described the behavior of an RNA-binding protein called Whi3, which allows the multiple nuclei of the fungus Ashbya gossypii to go through the cell cycle independently, even though they share a common cytoplasm. And the other session co-chair, Frederick Cross (The Rockefeller University, New York) described a screen for genes controlling the cell cycle of the green alga Chlamydomonas reinhardtii. Cross based his approach on the original cell cycle genetic screens conducted on yeast cells in the 1970s. Yeast are sometimes described as a model for the “universal cell.” But Cross points out that fungi and animals (collectively known as opisthokonts) diverged from plants long ago, and that it is unclear whether the plant cell cycle is regulated identically. His screen represents the first step towards addressing that question.