Fluorescence in situ hybridization in combination with synaptonemal complex and spindle pole body immunostaining to both spread and structurally preserved nuclei from time course experiments disclosed prominent telomere clustering during meiotic prophase of the yeast

Meiosis is the mechanism by which sexually reproducing organisms efficiently halve their diploid DNA content and thereby compensate for genome doubling at fertilization. As a prerequisite to this process homologues must recognize, align, pair and recombine during a lengthy first meiotic prophase (von Wettstein et al., 1984; John, 1990; Loidl, 1990; Roeder, 1997). A universal feature of first meiotic prophase in multicellular eukaryotes is the congregation of telomeres in the vicinity of the centrosome or spindle pole body (SPB), during the leptotene/zygotene transition (bouquet formation; for review see Bélar, 1928; Dernburg et al., 1995; Scherthan, 1997). Despite the considerable advances in understanding molecular and cytogenetic events during meiosis of Saccharomyces cerevisiae (for review see Roeder, 1995, 1997; Kleckner, 1996), cytological evidence for the formation of a chromosomal bouquet and its relation to homologous recombination has remained rudimentary (Dresser and Giroux, 1988; Klein et al., 1992; Weiner and Kleckner, 1994; Chua and Roeder, 1997; Conrad et al., 1997; Rockmill and Roeder, 1998). Furthermore, analysis of meiotic prophase cells by Rap1 immunostaining failed to detect telomere clustering during yeast prophase (Hayashi et al., 1998). Genetic and cytological analysis of Schizosaccharomyces pombe meiosis (Chikashige et al., 1997; Cooper et al., 1998; Nimmo et al., 1998) have fortified the view that meiotic telomere clustering may play a major role in aligning homologues during first meiotic prophase (Chikashige et al., 1997; Scherthan et al., 1994, 1996), at least in an asynaptic organism. Recent genetic analysis in budding yeast has indicated that telomere clustering may play an important role for homologue search and presynaptic alignment (Rockmill and Roeder, 1998). In the present study we have set out to determine the mode and dynamics of bouquet formation and its relation to recombination and synaptonemal complex (SC) formation after induction of synchronous meiosis in the S. cerevisiae SK1 strain.