Distribution of haploid chromosomes into separate nuclei in two pathogenic fungi

The presence of nuclei defines eukaryotes, enabling compartmentalization of macromolecules and cellular regulation. Inside the nucleus, chromosome numbers vary greatly across organisms, both in terms of ploidy status and haploid chromosome number. For cells harboring multiple nuclei as in many fungal mycelia and animal muscle cells, each healthy nucleus is traditionally believed to carry at least one haploid set of chromosomes. Abnormal chromosome numbers in nuclei are often associated with aging, diseases such as cancer, developmental disorders or lethality. Here we report a surprising discovery that chromosomes in haploid cells of the fungal species Sclerotinia sclerotiorum and Botrytis cinerea are segregated into separate nuclei, with each nucleus containing only a fraction of the chromosomes. This is the first report of eukaryotic cells that partition chromosome subsets into distinct nuclei, bringing new questions and opening fresh avenues for chromosome biology.