SPINDLES, SPINDLE PLAQUES, AND MEIOSIS IN THE YEAST SACCHAROMYCES CEREVISIAE (HANSEN)

Abstract

The intranuclear spindle of yeast has an electron-opaque body at each pole . These spindle plaques lie on the nuclear envelope . During mitosis the spindle elongates while the nuclear membranes remain intact. After equatorial constriction there are two daughted nuclei, each with one spindle plaque . The spindle plaque then duplicates so that two side-by-side plaques are produced . These move rapidly apart and rotate so that they bracket a stable 0 .8 µm spindle. Later, during mitosis, this spindle elongates, etc . Yeast cells placed on sporulation medium soon enter meiosis . After 4 hr the spindle plaques of the more mature cells duplicate, producing a stable side-by-side arrangement . Subsequently the plaques move apart to bracket a 0.8 µm spindle which immediately starts to elongate . When this meiosis I spindle reaches its maximum length of 3-5 µm, each of the plaques at the poles of the spindle duplicates and the resulting side-by-side plaques increase in size . The nucleus does not divide . The large side-by-side plaques separate and bracket a short spindle of about 1 µm which elongates gradually to 2 or 3 µm . Thus there are two spindles within one nucleus at meiosis II . To the side of each of the four plaques a bulge forms on the nucleus . The four bulges enlarge while the original nucleus shrinks . These four developing ascospore nuclei are partially surrounded by cytoplasm and by a prospore wall which originates from the cytoplasmic side of the spindle plaque . Eventually the spore nuclei pinch off and the spore wall closes . In some of the larger yeast cells this development is completed after 8 hr on sporulation medium.

Meiotic behaviours of chromosomes and microtubules in budding yeast: relocalization of centromeres and telomeres during meiotic prophase

“…As spindle microtubules disappeared after meiosis I, the divided masses of the chromosomes approached each other once again to form a single mass of chromosomes. The backlash motion probably reflects a unique feature of the nuclear membrane during meiosis in S. cerevisiae, in which two rounds of meiotic chromosome segregation take place without a separation of the nuclear membrane, as has been shown in electron microscopy (Moens & Rapport 1971). Such a backlash motion is not observed in S. pombe (Chikashige et al 1994), in which the nuclear membrane divides to form an individual nucleus for each set of the segregated chromosomes each time at meiosis I and II (Tanaka & Hirata 1982).…”

“…The arrangement of microtubules is summarized along with the temporal sequence of meiotic events. The behaviour of nuclear membrane is based on the previous report (Moens & Rapport 1971). measured in synchronous populations after induction of meiosis. Results indicate a clear tendency for the relocalization of centromeres during meiosis (Fig.…”

Nucleation of microtubules in vitro by isolated spindle pole bodies of the yeast Saccharomyces cerevisiae.

“…One way to circumvent this problem is to concentrate on so-called simpler systems, organisms in which the spindle is composed of relatively few microtubules and which are amenable to combined biochemical, ultrastructural, and genetic analysis. In the yeast, structures, designated spindle pole bodies (SPBs), embedded in the nuclear membrane, and a larger number of so-called discontinuous or chromosomal microtubules which extend between the SPBs and the replicating chromatin (4,5,15,16,18,21). The SPBs arise at the commencement of bud emergence by the duplication of the single pole body seen in the interphase nucleus (4,5,18).…”

The use of karyotyping in the systematics of yeasts

“…Analysis of synaptonemal complexes by serial sectioning (see Zickler et al 1984) has been applied to some yeasts (Moens & Rapport 1971;Zickler & Olsen 1975). However, these electron microscopic methods are very time consuming.…”