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Chromosome structure and meiotic recombination A “magic” interplay between structure and enzymology governs the function of chromosomes.
Franz Klein team
Lingzhi Huang Kuldeep Nangalia Feng Peng Silvia Prieler Viktoria Prast Martin Xaver Susanne Zich
During generation of gametes for sexual reproduction (meiosis), maternal and paternal chromosomes exchange fragments by recombination following the repair of meiotic DNAbreaks (DSBs), ensuring that each gamete receives a unique mix of parental properties. Chromosomes are made of DNA and dynamically attached proteins and are organized in distinct domains. This organization requires structural differentiation into axis (or cohesin) sites, telomeres, kinetochores etc. Meiotic recombination is embedded in this chromosomal landscape, as only loop sequences receive DSBs and recombine, while axis-sequences don’t. We have recently published a breakthrough in correlating structure and function for the meiotic chromosome: 1) The machinery Recombination-Initiation is based on the chromosome axis. Because initiation of meiotic recombination occurs at special sites in DNA loop regions, it was not understood why chromosome axis components play an important role for it. Using highresolution microarray technology, we were able to map components of the DSB machinery to axis associated DNA and to show the dependence of this localization on axis components. This finding has many significant implications. 2) Sumoylation of the yeast SUMO E2 converts it into a functional E3 and is essential for chromosome synapsis. Synapsis is the alignment of chromosome axes during meiotic prophase at 100nm distance, which affects the fate of meiotic breaks and The machine for DSB formation, (three colored balls symbolize three located components) was localized to the base of DNA loops (Panizza et al., Cell, 2011). In contrast, DSBs are made on chromosome loops (Blatt et al., Cell, 2002).
Glimpse into the nano-world – section of a chromosome with “DNA-break machines“. Loops of sister chromatids (blue and turquoise) are linked and held in shape by ring-molecules. The machines are anchored between the DNA-loops at the axis of the chromosome. The model is illustrative, but postulates unknown details, such as the way the ring-molecules hold DNA-loops.
prevents chromosome entangling. Our collaborator Andrea Pichler (MPI, Freiburg) found that upon Sumoylation of its K153K157, Ubc9*SUMO acquires E3 competence and stimulates SUMO-chain by Ubc9 formation in vitro. We discovered that the defect of unsumoylatable Ubc9-KR mutants is the lack of synapsis in meiosis. This result strongly points to a role of SUMO chains in the genesis of synapsis and to Ubc9 as its key regulator. 3) A key role for the Smc5/6 complex in meiotic recombination. Like the other structural maintenance of chromosomes (Smc) complexes, cohesin and condensin, the Smc5/6 complex is essential, but its role, particularly in meiosis, remains largely unknown. We have shown that this complex prevents the accumulation of Spo11 dependent recombination intermediates, called doubleHolliday Junctions (DHJ). The Smc5/6 associated SUMO ligase activity Mms21 is defective in preventing aberrant intermediates, which require Mus81/Mms4 for resolution. In the complete absence of Smc6, DHJs arise which can’t be resolved before anaphase, leading to catastrophic meiosis.
selected Publications Panizza S, Mendoza MA, Berlinger M, Huang L, Nicolas A, Shirahige K, Klein F. Spo11-accessory proteins link doublestrand break sites to the chromosome axis in early meiotic recombination. Cell. 2011 Aug 5;146(3):372-83. n Uanschou C, Siwiec T, Pedrosa-Harand A, Kerzendorfer C, Sanchez-Moran E, Novatchkova M, Akimcheva S, Woglar A, Klein F, Schlögelhofer P. A novel plant gene essential for meiosis is related to the human CtIP and the yeast COM1/SAE2 gene. EMBO J. 2007 Dec 12;26(24):5061-70. n Penkner AM, Prinz S, Ferscha S, Klein F. Mnd2, an essential antagonist of the anaphase-promoting complex during meiotic prophase. Cell. 2005 Mar 25;120(6):789-801. 30