cyb-1, a C. elegans B-type cyclin, maintains proper position and number of centrosomes during spermatogenesis

Abstract

Depletion of cyb-1, a major B-type cyclin expressed during C. elegans spermatogenesis, caused a meiotic division arrest in diakinesis-stage spermatocytes with multiple and mispositioned centrosomes. Association of SUN-1 and ZYG-12, two nuclear membrane proteins, is critical for centrosome–nuclear envelope attachment. We found that sun-1 depletion caused centrosome defects similar to those caused by cyb-1 depletion in diakinesis-stage spermatocytes. In addition, Ser8 and Ser43 residues in SUN-1 were dephosphorylated in cyb-1-depleted diakinesis-stage spermatocytes. Nevertheless, dephosphorylation of these residues was not sufficient to reproduce the cyb-1-related centrosome defects. We then found that the ZYG-12::GFP signal in the nuclear envelope was significantly reduced in the cyb-1-depleted diakinesis-stage spermatocytes. However, only mispositioned but not multiplied centrosomes were observed in zyg-12-mutant diakinesis-stage spermatocytes, suggesting that zyg-12 is not involved in the centrosome duplication at this stage. CYB-1 possibly serves a novel function to maintain proper positioning of centrosomes during the spermatogenesis by regulating phosphorylation of SUN-1, which is conceivably critical for the association between SUN-1 and ZYG-12. This phosphorylation of SUN-1 may be also critical to regulate centrosome duplication independent of ZYG-12.