Abstract
The mechanism by which homologous chromosomes pair during meiosis, as a prelude to recombination, has long been mysterious. At meiosis, the telomeres in many organisms attach to the nuclear envelope and move together to form the telomere bouquet, perhaps to facilitate the homologous search. It is believed that diffusion alone is not sufficient to account for the formation of the bouquet, and that some directed movement is also required. Here we consider the formation of the telomere bouquet in a wheat-rye hybrid both experimentally and using mathematical modelling. The large size of the wheat nucleus and wheat's commercial importance make chromosomal pairing in wheat a particularly interesting and important process, which may well shed light on pairing in other organisms. We show that, prior to bouquet formation, sister chromatid telomeres are always attached to a hemisphere of the nuclear membrane and tend to associate in pairs. We study a mutant lacking the Ph1 locus, a locus ensuring correct homologous chromosome pairing, and discover that bouquet formation is delayed in the wild type compared to the mutant. Further, we develop a mathematical model of bouquet formation involving diffusion and directed movement, where we show that directed movement alone is sufficient to explain bouquet formation dynamics.
Highlights
Meiosis, an integral component of the mechanism of sexual reproduction, is a crucial process in eukaryotes, resulting in a halving of the number of chromosomes
After EdU treatment for 4 hr, anthers of wheat-rye hybrids, both with and without the Ph1 locus in the wheat genome, were labelled with a telomere probe by fluorescence in situ hybridization (FISH) and chromosomes were counterstained with 49,6-diamidino-2-phenylindole (DAPI), as described in detail in Materials and Methods
The arrangement of chromosomes within the nucleus is far from random, with radically different arrangements required during interphase, mitosis and meiosis
Summary
An integral component of the mechanism of sexual reproduction, is a crucial process in eukaryotes, resulting in a halving of the number of chromosomes. Such a process allows genetic material to be shared during fertilisation, whilst maintaining the same amount of DNA per cell. Many organisms attach telomeres to the nuclear membrane before pairing, how this is achieved is largely mysterious Many of these organisms move the telomeres together, until they form one cluster on the membrane producing the telomere bouquet [3,4,5,6,7,8]. It is known that numerous organisms contain pairs of SUN-KASH proteins, which link chromosomes to cytoskeletal motors, and potentially these motors could pull the telomeres around the nuclear membrane [10]
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