[Cnb1 involved in cytokinesis in Schizosaccharomyces pombe]

Serine/Threonine-specific calcineurin (CN) is highly conserved in eukaryotes, which plays an important role in transcriptional regulation. In Schizosaccharomyces pombe, CN exists as a heterodimer composed by catalytic subunit Ppb1 and regulatory subunit Cnb1. Deletion of cnb1+ reduced the growth rate of cells, and caused a chained phenotype, and had delay in cytokinesis. In cytokinesis, Cnb1 could form CN complex with Ppb1 and could colocalize and constrict with the contractile ring at division plane. Tubulin could cross the septum in cnb1Δ strain, suggesting that the septum is not fully matured. These results suggest Cnb1 might be involved in maturation of septum. The signals of septins in cnb1Δ strain were also analyzed. Septins include Spn1, Spn2, Spn3, and Spn4. Septins help to guide hydrolytic enzymes for septum degrada-tion. Eighty percent of cnb1Δ cells lacked the signals of Spn2 or Spn3 at septum, and twenty percent of cnb1Δ cells lacked the signals of Spn1 or Spn4 at septum. The reduction of the septin signals was not due to impaired transcription of septins, since the protein levels of septins in the cnb1Δ cells were not decreased. These results imply that Cnb1 might regulate the stability of septin ring in a transcription-independent manner. In general, our study showed that Cnb1 contributes to the maturation of septum and the stability of septin ring and is important in the cytokinesis.