Study On The Function Of Cnb1 In Cytoplasmic Division

CN is a Ca2+/calmodulin dependent threonine/serine-specific phosphotase. CN can activate the transcription of a number of genes. The products of these genes can facilitate cell proliferation, help cell deal with environmental stress, and maintain calcium homeostasis. Schizosaccharomyces pombe CN is composed of regulatory subunit Cnbl and catalytic subunit Ppbl. Cnb1 plays important role in CN enzyme activity, because Ppbl can not display entire enzyme activity without Cnbl presented. Furthermore, present studies are focus on the function of catalytic subunit Ppbl. The study on regulatory subunit Cnbl is neglected. Our previous study of "genomewide screening of DNA damage response in Schizosaccharomyces pombe" got 19 genes related to cell cycle, and Cnbl is listed. This study aims at studing the biological function of CN regulatory subunit Cnbl, especially at its function in cytokinesis.cnb1+ gene is necessary in cell growth. Δcnbl strain shows a slower growth rate than wild type strain, and the septa is multipled, and cytokinesis is delayed. Cnbl and Ppbl can form CN enzyme complex, and colocalize with contractile ring at division site. Furthermore, Cnbl does not affect the assembly of contractile ring. Tubulin in Acnbl strain can across the septum, which suggests that the septum is not fully matured. Thus, Cnbl may function with contractile ring in the regulation of septum maturation. Further study shows that over 80% cells lack Spn2 and Spn3 localization in Acnbl strain, but Mid2, a kind of protein stabilizes septin ring, can localize to septin ring normally. This suggests that Cnbl is involved in the maintenance of septin ring stability after its assembly. Western Blot shows the protein expression level does not decline in Acnbl strain. Thus, Cnbl maintain the septin ring stability in a transcription-independent manner.In conclusion, our study suggests that Cnbl can regulate cytokinesis in two aspects. One is regulating the septum maturation process with contractile ring. Another is maintain the septin ring stability.