9 Meiotic Telomeres

Abstract

The peculiar behavior of chromosomes and their ends during the prophase of the first meiotic division fascinated cytologists of the late 19th century, long before the capping function of telomeres was realized a half century later (for a historical overview, see Chapter 1). At that time, investigations centered around reproductive tissues, because a high rate of cell division and the condensation of meiotic chromosomes within the intact nuclear envelope (NE) facilitated chromosome analysis. Moreover, germ cells were a favorite subject of cytology in the search for a process that would compensate for the genome doubling that occurs at fertilization. The acidic heavy metal staining techniques of the early days (Flemming 1895) left somatic nuclei with a more-or-less reticulate staining, but revealed threadlike chromosomes that had their ends bundled together at a limited region of the nuclear periphery in differentiating germ cells (e.g., Platner 1885; Schreiner and Schreiner 1905; Gelei 1921; for an overview see Wilson 1925). This remarkable clustering of meiotic telomeres was baptized “chromosomal bouquet” because of its resemblance to bundled flower stems (Fig. 1A) (Eisen 1900). Telomere clustering occurs near the centrosome in species with a locally defined microtubule-organizing center (MTOC), as is the case in animals, algae, and fungi (Fig. 1A,B). It was soon reasoned that the polarization of meiotic chromosomes could represent a stage where homologous chromosomes undergo homology search (Boveri 1904), which ascribed a special role to meiotic telomeres. Despite more than a century of research, however, the mechanisms underlying meiotic telomere behavior remain largely...