Alteration of nuclear distribution in B-mutant strains of Schizophyllum Commune

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Abstract
Sexual morphogenesis in Schizophyltum commune, a higher basidiomycete, is controlled by two incompatibility factors, A and B. A key event, the migration of nuclei from each mate throughout the mycelium of the other, is controlled by the B factor and occurs in A = B ‡ = matings. The distribution of nuclei in the resulting heterokaryon is irregular, and anucleate, uninucleate, binucleate and multinucleate cells are found. A similar distribution of nuclei is found in homokaryons carrying a mutation in the B factor. Because of their developmental history, strains that carry a mutated B factor offer a relatively simple system for the study of the events associated with nuclear migration. Growth of mutant-B germlings occurs in three stages: (I) most cells are binucleate; (II) most cells are uninucleate; (III) cells contain varied numbers of nuclei. The ratio of nuclei: cells remains constant during the transition from stage II to stage III. Changes in nuclear distribution result from movement of the nuclei from cell to cell, and the movement is associated with the disruption of the dolipore septum. The mutant-B system appears to offer an opportunity for the biochemical resolution of the events related to nuclear migration.