Bouquet formation in budding yeast: initiation of recombination is not required for meiotic telomere clustering

Fluorescence in situ hybridization in combination with synaptonemal complex and spindle pole body immunostaining to both spread and structurally prese rved nuclei from time course experiments disclosed prominent telomere clust ering during meiotic prophase of the yeast Saccharomyces cel cerevisiae. It was found that centromere clustering, which dominates vegetative nuclear s tructure, is rapidly Lost after induction of meiosis, Telomeres tightly clu stered during leptotene/zygotene-equivalent stages in the vicinity of the s pindle pole body, giving rise to a classical chromosomal bouquet arrangemen t. This arrangement dissolved later during prophase. Painting of chromosome s XI revealed that initially compacted chromosome dterritories adopt an out stretched morphology in bouquet nuclei. This conformational state was assoc iated with alignment and pairing, Chromosome condensation during pachytene rendered condensed and compact bivalents, and dispersed telomeres. Both the spell and rad50S recombination mutants formed bouquets, demonstrating that bouquet formation is recombination and synapsis independent.