The Anaphase Promoting Complex or cyclosome (APC/C) is a multi-subunit E3 Ubiquitin Ligase that targets proteins for 26S proteosome-dependent proteolytic degradation. APC/C dependent degradation of key regulatory proteins promotes important transitions in M-phase of the cell cycle. Destruction of Pds1/Securin promotes chromosome separation at anaphase by facilitating the release of metaphase chromosome cohesion. Destruction of cyclin B promotes M-phase exit by turning off cyclin dependent kinase 1 activity. An important regulatory subunit of the APC/C is CDC27. Studies of the C. elegans CDC27 ortholog (CeCDC27) indicate that CDC27 plays an essential role in promoting cell cycle progression during oocyte meiosis I. Like the majority of the other APC/C subunits, RNAi depletion of CeCDC27 in fertilized embryos prevents cell cycle progression past metaphase of meiosis I. These embryos arrest as meiotic one-cell embryos, and fail to complete zygotic development and initiate cleavage (Davis et al., 2002). We previously reported the isolation of several temperature sensitive mutations in the gene
mat-1 (Golden et al., 2001). Sequencing of CeCdc27 from the various alleles revealed that
mat-1 encodes the C. elegans CDC27 ortholog. Shifting
mat-1 L4 larvae or young adult hermaphrodites to restrictive temperatures causes them to produce clutches of one-cell arrested embryos. Like the CeCdc27 RNAi depleted embryos,
mat-1 mutant embryos contain oocyte chromosomes that congress onto a metaphase plate within a barrel-shaped metaphase spindle. However, the first meiotic division fails to occur, anaphase is never observed, and polar bodies are never extruded. In addition, M-phase exit does not occur; pronuclei never form, sperm chromosomes remain condensed and the sperm centrosome remains quiescent. Consequently, the metaphase I arrested one-cell embryos fail to exit the meiotic cell cycle and complete zygotic development. To broaden our understanding of APC/Cs role in the promotion of chromosome segregation and M-phase exit in C. elegans, we generated a temperature dependent allelic series for
mat-1. The analysis of the various hypomorphic phenotypes seen in
mat-1 mutants confirms that CeCDC27 is required for cell cycle progression in somatic, germline and embryonic tissues. These studies also provide the first evidence that the APC/C promotes normal progression through oocyte meiosis II. Our phenotypic studies of the various
mat-1 strains reared under hypomorphic temperature conditions provide additional evidence of an interdependence between proper cell cycle progression and normal development in C. elegans.