Time to split A yeast cell can stand out from the crowd by hastening or delaying meiosis. A yeast master regulator protein helps cells determine when to enter meiosis, as Iftach Nachman, Aviv Regev, and Sharad Ramanathan (Harvard University, Cambridge, MA) report. Starvation spurs yeast to begin meiosis. But the process is complicated and irreversible, and cells that start too early or too late...

Our understanding of meiosis springs from two suggestions made by Weismann in 1887. One was that meiosis would be found to compensate for fertilization in the life cycles of both sexes and all organisms. The other was that the development of sexual reproduction in evolution depended on the value of meiosis in exposing the results of genetic recombination to natural selection. In confirming thes...

Initiation of meiosis in Saccharomyces cerevisiae is regulated by mating type and nutritional conditions that restrict meiosis to diploid cells grown under starvation conditions. Specifically, meiosis occurs in MATa/MATalpha cells shifted to nitrogen depletion media in the absence of glucose and the presence of a nonfermentable carbon source. These conditions lead to the expression and activati...

The requirement of the cdc2, cdc13 and cdc25 genes for meiosis in Schizosaccharomyces pombe was investigated using three different conditions to induce meiosis. These genes were known to be required for meiosis II. cdc13 and cdc25 are essential for meiosis I. The cdc2 gene, which is required for the initiation of both mitotic S-phase and M-phase, is essential for premeiotic DNA synthesis and me...

We have characterized a new gene, SWI1, involved in sister chromatid cohesion during both male and female meiosis in Arabidopsis thaliana. A first allele, swi1.1, was obtained as a T-DNA tagged mutant and was described previously as abnormal exclusively in female meiosis. We have isolated a new allele, swi1.2, which is defective for both male and female meiosis. In swi1.2 male meiosis, the clas...

Meiosis halves the chromosome number because its two divisions follow a single round of DNA replication. This process involves two cell transitions, the transition from prophase to the first meiotic division (meiosis I) and the unique meiosis I to meiosis II transition. We show here that the A-type cyclin CYCA1;2/TAM plays a major role in both transitions in Arabidopsis. A series of tam mutants...

The lethal and recombinational responses to ultraviolet light irradiation (UV) by excision-proficient (RAD+) and deficient strains (rad1) of Saccharomyces cerevisiae has been examined in cells undergoing meiosis. Cells that exhibit high levels of meiotic synchrony were irradiated either at the beginning or at various times during meiosis and allowed to proceed through meiosis. Based on survival...

Cohesins are important for chromosome structure and chromosome segregation during mitosis and meiosis. Cohesins are composed of two structural maintenance of chromosomes (SMC1-SMC3) proteins that form a V-shaped heterodimer structure, which is bridged by a α-kleisin protein and a stromal antigen (STAG) protein. Previous studies in mouse have shown that there is one SMC1 protein (SMC1β), two α-k...

Our understanding of meiosis springs from two suggestions made by Weismann in 1887. One was that meiosis would be found to compensate for fertilization in the life cycles of both sexes and all organisms. The other was that the development of sexual reproduction in evolution depended on the value of meiosis in exposing the results of genetic recombination to natural selection. In confirming thes...

The meiosis II spindle of Drosophila oocytes is distinctive in structure, consisting of two tandem spindles with anastral distal poles and an aster-associated spindle pole body between the central poles. Assembly of the anastral:astral meiosis II spindle occurs by reorganization of the meiosis I spindle, without breakdown of the meiosis I spindle. The unusual disk- or ring-shaped central spindl...