Characterization of meiosis-deficient mutants by electron microscopy and mapping of four essential genes in the fission yeast Schizosaccharomyces pombe

Abstract

Meiosis-deficient mutants of the fission yeast Schizosaccharomyces pombe carrying mei1, mei2, mei3, mei4 and mes1 mutant alleles were characterized by electron microscopy and staining of the nucleus with 4', 6-diamidino-2-phenylindole. Zygotes of either mei1, mei2 or mei3 mutants contained one round nucleus with a single spindle pole body (SPB). These mutants were arrested before premeiotic DNA synthesis. Zygotes of mei4 mutants had one elongated nucleus containing thick electron-dense filaments (linear elements). In the mes1 mutant, the first meiotic division was completed but the SBPs did not duplicate. Modification of the SPB (outer plaque formation) was also blocked and the forespore membrane was not assembled. By haploidization, random spore and tetrad analyses, four essential genes for meiosis (mei2, mei3, mei4 and mes1) were mapped. Gene mei2 was located on chromosome I 14.2 cM distant from ura2. Gene mei3 was linked to ade7 (45.4 cM) on chromosome II. Gene mei4 was linked to cdc2 (0.6 cM) on chromosome II. Gene mes1 was linked to ura3 (25.3 cM) on chromosome I.

Fission yeast Myo51 is a meiotic spindle pole body component with discrete roles during cell fusion and spore formation

“…Cells lacking Mes1 arrest at the end of meiosis I because of the premature degradation of the pool of cyclin B required for onset of meiosis II (Izawa et al, 2005;Shimoda et al, 1985). As predicted, mes1 + cells underwent normal meiotic SPB segregation, with the expected increase in Myo51 signal during meiosis II (Fig.…”

The Schizosaccharomyces pombe septation initiation network (SIN) is required for spore formation in meiosis

“…Spore formation is initiated during the second meiotic division, when the SPB undergoes a drastic modification to form a complex structure called the meiotic plaque, which is essential for spore formation but not for the second meiotic division (Hirata and Shimoda, 1992;Ikemoto et al, 2000). The meiotic plaque is a multilayered extension of the SPB and many SPB components become incorporated into this structure (Bahler et al, 1993;Hirata and Shimoda, 1994;Shimoda et al, 1985). The protein Spo15p (Ikemoto et al, 2000) is located on the meiotic plaque and is required for its formation.…”

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). …”