79 Mutants in which telomeres coalesce normally but that are incapable of spindle pole body–driven nuclear movements show more severely impaired meiotic recombination than mutants with impaired bouquet formation, indicating that the horsetail movements of the nucleus are more critical for recombination events in S. The spindle pole body then proceeds to drag the entire nucleus backward and forward, powered by a meiosis-specific dynein motor while meiotic recombination is taking place. During this so-called horsetail motion, 78 the telomeres gather in a tight bouquet adjacent to the spindle pole body (the microtubule organizing center that is itself outside the nuclear membrane on the cytoplasmic side) early in prophase I. pombe, are particularly noteworthy due to their long-lived activity and their dramatic motion through the nuclear space. The oscillatory rapid chromosome movements of the fission yeast, S. 73,74 However, the relative importance of rapid chromosome movements and bouquet formation appears to be species specific, since, for example, in Sordaria macrospora, the bouquet stage follows homolog pairing 75 and also follows early synapsis in female mice, 76 while in Saccharomyces cerevisiae, rapid chromosome movements appear to be more critical than bouquet formation for pairing. The bouquet describes the clustering of telomeres at one location across the nuclear envelope, and is noted in many meiotic species. 71,72 Driven by the Sad1p, UNC-84 (SUN)–Klarsicht, ANC1, syne homology (KASH) family of nuclear membrane–bound proteins, rapid chromosome movements are propagated by telomere connections to cytoplasmic motors that drive oscillatory movements.Īnother important feature of chromosome interactions during early prophase I is the “telomere bouquet”. 70 The congregation of pairing centers coincides with the generation of highly conserved rapid chromosome movements, which have been demonstrated for many species, including mammals and both budding and fission yeast. For example, in many organisms, while pairing may occur at numerous sites along chromosomes, there are often defined locations where initial pairing interactions take place. Almost certainly, numerous mechanisms exist to promote homolog recognition and pairing, and these may be utilized to differing degrees in different organisms. It is notable that although there exists a large body of data concerning the molecular events that occur following synapsis of chromosomes, far less is known about how homologs recognize and pair with one another. The reorganization of the nuclear contents, and their situation with respect to the nuclear envelope, are, quite understandably, critical to the success of homolog alignment and, as a consequence, are essential for prophase I progression. One of the fascinating aspects of meiotic prophase I is the delicate, yet dramatic, orchestrated “dance” that occurs between homologous chromosomes. Kim Holloway, in Knobil and Neill's Physiology of Reproduction (Fourth Edition), 2015 Chromosome Movements, Telomere Clustering, and Telomere Bouquet Formation Second, injection of recombinant MSP can restore meiotic maturation in females. Two lines of evidences suggest that MSP is indeed the sperm-derived factor that triggers oocyte maturation ( Miller et al., 2001): First, injection of anti-MSP antibody reduced ovulation rate in wild-type worms. They then fractionated sperm-conditioned medium by HPLC and analyzed a fraction that retained its activity by MALDI-TOF mass spectrometry, and identity of the active component was revealed as MSP. Prior incubation of the sperm-conditioned medium with protease abolished its ability to trigger meiotic maturation and gave them the clue that the active component is protein. The female worms supplemented with sperm-conditioned medium underwent normal meiotic maturation. let the isolated sperm stay in a buffer for few hours and injected the cell-free supernatant (sperm-conditioned medium) into the uterus of female worms. performed a series of experiments and found that MSP is the sperm-derived factor that triggers meiotic maturation in oocytes ( Miller et al., 2001). What component in the sperm triggers meiotic maturation in oocytes? Toward answering this question, Miller et al. When the sperm are supplied to these spermless worms through males, the oocytes resume meiosis and undergo normal meiotic maturation. In mutant worms that do not produce any sperm, the oocytes are arrested for prolonged period in meiotic prophase I. The resumption of meiosis depends on the cues from sperm. Oocytes are arrested in meiotic prophase I in many animals, including C. Gunasekaran Singaravelu, Andrew Singson, in International Review of Cell and Molecular Biology, 2011 5.1 MSP triggers oocyte maturation
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