The basidiomycete Coprinus cinereus has many advantages as a model organism for studying sexual development and meiosis, but it has been difficult to investigate using reverse-genetics methods, such as gene disruption by homologous recombination. Here, gene repression by dsRNA-mediated gene silencing was tried as an alternative method for reverse-genetics studies. It was shown that transformation of the LIM15/DMC1 dsRNA expression construct (LIM15dsRNA) resulted in genomic insertion of LIM15dsRNA and paucity of the LIM15/DMC1 transcript. First, LIM15dsRNA was transformed into the homothallic strain AmutBmut to generate a homozygote in which both nuclei had a copy of LIM15dsRNA. The LIM15/DMC1-repressed strain showed abnormal homologous chromosome synapsis during meiosis. Basidiospore production was reduced to 16 % by the induction of dsRNA. However, approximately 60 % of basidiospores were viable. Next, a heterozygote was generated in which one nucleus had a copy of LIM15dsRNA. The phenotype was similar to that of the homozygote. These results are not only the first demonstration of dsRNA-mediated gene silencing in a member of the homobasidiomycete fungi, to which 90 % of mushroom species belong, but also the first successful use of a reverse-genetics approach in C. cinereus research.

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Lim15/Dmc1 is a meiosis specific RecA-like protein. Here we propose its participation in meiotic chromosome pairing-related events along with DNA topoisomerase II. Analysis of protein–protein interactions using in vitro binding assays provided evidence that Coprinus cinereus DNA topoisomerase II (CcTopII) specifically interacts with C.cinereus Lim15/Dmc1 (CcLim15). Co-immunoprecipitation experiments also indicated that the CcLim15 protein interacts with CcTopII in vivo. Furthermore, a significant proportion of CcLim15 and CcTopII could be shown to co-localize on chromosomes from the leptotene to the zygotene stage. Interestingly, CcLim15 can potently activate the relaxation/catenation activity of CcTopII in vitro, and CcTopII suppresses CcLim15-dependent strand transfer activity. On the other hand, while enhancement of CcLim15's DNA-dependent ATPase activity by CcTopII was found in vitro, the same enzyme activity of CcTopII was inhibited by adding CcLim15. The interaction of CcLim15 and CcTopII may facilitate pairing of homologous chromosomes.

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Hollow spherical particles with protein-silica hybrid shell structures have been synthesized through a combination of the catalytic activity of the protein and sonochemical treatment; the morphologies of the particles were controlled by varying the protein concentration.