Chromosome organization and function in time and space: meiosis, mitosis and E. coli

Harvard University, Cambridge MA

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Abstract

Enter the text here that is the new abstract information for your application. ABSTRACT We consider chromosomes to be "living, breathing objects" whose fluctuations in time and space underlie their basic functions. We compare meiotic and mitotic chromosomes and E. coli nucleoids to identify commonalities. Meiosis underlies sexual reproduction. Unique hallmarks are (i) pairing and (ii) recombination between maternal and paternal chromosomes, including "crossover interference" in which crossover sites are evenly spaced along chromosomes. Both processes depend critically on association of recombination complexes with chromosome axial structures. Pairing. Using our 4D low SNR tracking of locus-specific "spots" in budding yeast, we have provided a new understanding of recombination-mediated pairing. Key features will now be explored. We also analyze global pairing topology by tracking chromosome paths, recombination complex status and chromatin status in Sordaria macrospora in living cells and by Expansion Microscopy. Patterning. Yeast crossover interference, including our recent discovery that crossovers occur in short "runs", will be dissected using new assays provided by pairing studies. We have proposed that crossover patterning is mediated by mechanical forces along chromosome axes. In support, we find that Sordaria meiotic chromosomes exhibit axis deformations ("perversions"), diagnostic of mechanical axis stress, with periodicities related to those of recombination complexes. We will ask whether perversions are altered in mutants with altered interference. In C. elegans, we are analyzing a early chromosome axis "notch" that reflects patterning. We find that yeast crossoverinterference requires phosphatase PP2A, whose HEAT repeat we showed to sense/transduce mechanical stress. We will ask whether interference is affected by PP2A mutations predicted to alter stress transduction. Our mitotic chromosome studies have recently defined a new morphogenetic pathway involving stress-diagnostic axis perversions (presaging meiotic findings). We are developing nanoscale tools for fluorescence sensing of stress patterns in vivo. These will first be applied to mitotic chromosomes, with concomitant investigation of whether chromatin status influences perversion morphology (as expected). We are alsoinvesting in a unique live mouse ex vivo oocyte system, thus enabling eventual application of stress sensors to meiotic chromosomes, but with immediate applicability to analysis of prophase chromosome dynamics. In E. coli, we analyze nucleoid dynamics by 4D imaging of walled cells and membrane-enclosed L- forms. We will validate our recent discovery that sister chromosome segregation is rate-limiting for cell division and investigate our new hypothesis that tension at the nucleoid/membrane interface coordinates chromosome and cell division cycles as driven by our discovered periodic nucleoid length/width fluctuations.