Cloning and analysis of transcription of the mei2 gene responsible for initiation of meiosis in the fission yeast Schizosaccharomyces pombe

Abstract

We have isolated a hybrid plasmid, pDB(mei2)2, containing a 7.4-kilobases (kb) DNA fragment from a Schizosaccharomyces pombe genomic library which is able to complement the mei2 mutation of S. pombe. Integration of the cloned DNA sequence at the mei2 site on chromosome I demonstrated that it contained the mei2 gene. This gene was localized on a 4.7-kb HindIl-Pvull fragment in the subclone pFMV402. Transcriptional regulation was studied by Northern blot analysis in which polyadenylated RNA was prepared from a heterozygous (h+N/h-s) diploid strain cultured either in nitrogen-rich growth medium or in nitrogen-free sporulation medium. The size of the major mei2 mRNA, which always gave a broad band, was estimated to be 4.2 ± 0.2 kb, and a few minor bands (e.g., 3.2 and 1.8 kb) appeared as well. These transcripts appeared more abundantly in sporulating cells than in growing cells. Neither the mating type genes (mat) nor the mei3 gene was essential for transcription of the mei2 gene, since ample mei2 mRNA was detected in sporulation-deficient cells transferred to sporulation medium, such as h+N/h+N and h-s/h-s homozygotes, as well as meil and mei3 mutants.Nutritional starvation is one of the major signals for sexual reproduction in a wide range of organisms. In the fission yeast Schizosaccharomyces pombe, sexual processes (mating in haploids and meiosis in diploids) are induced by the depletion of a nitrogen source from the culture medium (8, 9).Heterozygosity at the mating type locus (mat) is another prerequisite for the initiation of meiosis, implying that both matl-P and matl-M products are required for this process (9). In addition to the mat genes, two additional genes, mei2 and mei3, are involved in the initial step of meiosis as positive regulators (5, 16).Recently, Iino and Yamamoto (11,12) and Nurse (15) have isolated a conditional mutant, pati or rani, which is able to undergo meiosis at the restrictive temperature even in the presence of a nitrogen source and from a haploid state. The meiotic defect caused by the mutations in mat and mei3 genes is bypassed by pat], whereas the mei2 mutation suppresses the pat] mutation. On the basis of these facts, Iino and Yamamoto (12) proposed a negative control mechanism for meiosis in the fission yeast. The model suggests that pat] products repress mei2 activity to block the initiation of meiosis under nitrogen-rich growth conditions. Thus, derepression of mei2 activity appears to be a key step for the induction of meiosis.To elucidate the regulatory network operating during the initiation of meiosis, we cloned the mei2 gene and studied its transcriptional regulation. MATERIALS AND METHODSStrains and culture conditions. The S. pombe and Escherichia coli strains used in the present study are listed in Table 1. E. coli cells were cultured in L broth at 37°C. When

The S. pombe SAGA complex controls the switch from proliferation to sexual differentiation through the opposing roles of its subunits Gcn5 and Spt8

“…lanes 2 and 8). Starvation-regulated expression of multiple mei2 + transcripts has been previously described (Shimoda et al 1987). Together, these results show that Gcn5, Ada2, and Ada3 act in a common pathway to specifically repress ste11 + and mei2 + expression, suggesting that the HAT module of the SAGA complex negatively regulates mating gene expression in nutrient-rich conditions.…”

Fission Yeast Ste9, a Homolog of Hct1/Cdh1 and Fizzy-related, Is a Novel Negative Regulator of Cell Cycle Progression during G1-Phase

“…Many fission yeast genes responsible for sexual development are transcriptionally induced in response to nitrogen starvation depending on the Ste11 transcription factor (Sugimoto et al, 1991). mei2 is one such gene, and its transcription occurs in a mating-type or pheromone signaling-independent manner (Shimoda et al, 1987). Northern analysis revealed that transcription of mei2 was strongly induced by nitrogen starvation in ste9 cells as well as in wildtype cells (our unpublished results).…”

A Brief History ofSchizosaccharomyces pombeResearch: A Perspective Over the Past 70 Years

“…Most of Egel's mutants were unable to complete meiosis and failed to produce spores. Egel sent the mutants to Shimoda, whose lab cloned several of the mei and related genes required for ascospore formation (Shimoda et al 1985(Shimoda et al , 1987). …”