During mitosis, chromatin is condensed into mitotic chromosomes and transcription is inhibited, processes that might be opposed by the chromatin remodeling activity of the SWI/SNF complexes. Brg1 and hBrm, which are components of human SWI/SNF (hSWI/SNF) complexes, were recently shown to be phosphorylated during mitosis. This suggested that phosphorylation might be used as a switch to modulate SWI/SNF activity. Using an epitope-tag strategy, we have purified hSWI/SNF complexes at different stages of the cell cycle, and found that hSWI/SNF was inactive in cells blocked in G 2 -M. Mitotic hSWI/SNF contained Brg1 but not hBrm, and was phosphorylated on at least two subunits, hSWI3 and Brg1. In vitro, active hSWI/SNF from asynchronous cells can be phosphorylated and inactivated by ERK1, and reactivated by dephosphorylation. hSWI/SNF isolated as cells traversed mitosis regained activity when its subunits were dephosphorylated either in vitro or in vivo. We propose that this transitional inactivation and reactivation of hSWI/SNF is required for formation of a repressed chromatin structure during mitosis and reformation of an active chromatin structure as cells leave mitosis.

The uniformity of cell size in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether growth rates of individual cells 6Monitoring nuclear growth in live cells confirmed that these decreases in variance reflect a process that selectively inhibits the growth of large cells while accelerating growth of small cells. 8We also detected cell-size-dependent adjustments of G1 length, which further reduce variability.Combining our assays with chemical and genetic perturbations confirmed that cells employ two 10 strategies, adjusting both cell cycle length and growth rate, to maintain the appropriate size.Introduction:

We present an unprecedentedly comprehensive characterization of protein dynamics across early development in Xenopus laevis, available immediately via a convenient Web portal. This resource allows interrogation of the protein expression data in conjunction with other data modalities such as genome wide mRNA expression. This study provides detailed data for absolute levels of ~14K unique Xenopus proteins representing homologues of ~9K unique human genes --a rich resource for developmental biologists. The purpose of this manuscript is limited to presenting and releasing the data browser. Highlights:• Relative protein expression from stage IV oocyte, blastula, gastrula, neurula, and early organogenesis• Biological triplicates with confidence intervals on protein expression reflect certainty in dynamic patterns• Convenient time-series Web-browser integrated with the multi-media Xenbase portal • Gene-symbol search and multi-gene protein/mRNA juxtaposition capabilities Protein: agr2Save to SVG Save to SVG