In most eukaryotes, the meiotic chromosomal bouquet (comprising clustered chromosome ends) provides an ordered chromosome arrangement that facilitates pairing and recombination between homologous chromosomes. In the protist Tetrahymena thermophila, the meiotic prophase nucleus stretches enormously, and chromosomes assume a bouquet-like arrangement in which telomeres and centromeres are attached to opposite poles of the nucleus. We have identified and characterized three meiosis-specific genes [meiotic nuclear elongation 1-3 (MELG1-3)] that control nuclear elongation, and centromere and telomere clustering. The Melg proteins interact with cytoskeletal and telomere-associated proteins, and probably repurpose them for reorganizing the meiotic prophase nucleus. A lack of sequence similarity between the Tetrahymena proteins responsible for telomere clustering and bouquet proteins of other organisms suggests that the Tetrahymena bouquet is analogous, rather than homologous, to the conserved eukaryotic bouquet. We also report that centromere clustering is more important than telomere clustering for homologous pairing. Therefore, we speculate that centromere clustering may have been the primordial mechanism for chromosome pairing in early eukaryotes.

在大多数真核生物中，减数分裂染色体束（包括簇状染色体末端）提供有序的染色体排列，促进同源染色体之间的配对和重组。在原生生物嗜热四膜虫中，减数分裂前期核极大地伸展，染色体呈花束状排列，其中端粒和着丝粒附着在核的相对两极。我们已经鉴定并表征了三个控制核伸长以及着丝粒和端粒聚类的减数分裂特异性基因 [减数分裂核伸长 1-3 ( MELG1-3 )]。Melg 蛋白与细胞骨架和端粒相关蛋白相互作用，并可能重新调整它们的用途以重组减数分裂前期核。负责端粒聚类的四膜虫蛋白和其他生物体的花束蛋白之间缺乏序列相似性，这表明四膜虫花束与保守的真核生物花束是类似的，而不是同源的。我们还报告说，对于同源配对来说，着丝粒聚类比端粒聚类更重要。因此，我们推测着丝粒聚类可能是早期真核生物染色体配对的原始机制。