Our fish results support this hypothesis and revealed that homolog pairing can be lost during synapsis, resulting in seemingly normal sc between heterologous sequences. Meiosis is the specialized cell division program that accomplishes separation of. Meiotic prophase i is a complex process involving homologous chromosome homolog pairing, synapsis, and recombination. Synaptonemal complex extension from clustered telomeres. Recombination, pairing, and synapsis of homologs during meiosis.
A defective meiotic outcome of a failure in homologous pairing. Centromeric smc1 promotes centromere clustering and. These interactions include homolog pairing, chromosome synapsis i. Pairing centers recruit a pololike kinase to orchestrate. Together, these data indicate that spo11 is required for the initiation andor stabilization of synapsis and homolog juxtaposition in males and females. In this study we validate a nearly centuryold model for chromosome pairing in flatworms and provide a molecular description of meiotic prophase in flatworms. For the x chromosomes, pc pairing is contemporaneous with autosomal pairing, but autosomes complete synapsis earlier on average than x chromosomes, implying that x chromosomes have a delay in onset andor a slower rate of sc assembly. Chromosomal events and meiotic recombination are coordinated to ensure various processes of homolog pairing, synapsis, dsb repair. This search drives the homolog pairing and alignment, ultimately leading to the lengthwise pairing and synapsis the stabilization of homolog interactions by the polymerization of a proteinacious structure called the synaptonemal complex of all homologs achieved by pachytene. In this study, we determined that osdmc1a and osdmc1b are functionally redundant during meiosis.
Moreover, the failure to complete pairingsynapsis and recombination suggest that bouquet formation is required for efficient homology searching and homologous recombination. The rad51dmc1 foci gradually disappear throughout prophase i until dsb repair is complete in midpachynema, at which point autosomes are essentially devoid of foci moens et al. Htp1dependent constraints coordinate homolog pairing and. Specifically, we validate jozsef geleis proposal that chromosome pairing in flatworms results from the formation of a telomere bouquet followed by the extension of synapsis from the base of the bouquet, thus facilitating homolog. Although pairing and synapsis refer to similar and interrelated processes, important distinctions must be made when referring to analysis of meiotic chromosome behavior. Synapsisdependent and independent mechanisms stabilize homolog pairing during meiotic prophase in c. Hence, it was possible that in the absence of homolog pairing and pc znfs, synapsis initiation would fail and chromosomes would remain unsynapsed throughout meiotic progressionon the other hand, homolog pairing and synapsis in c. Here, we find that the meiotic axis component htp3 links dsb formation with homolog pairing and synapsis. Dec 03, 20 although an essential role for centromere clustering has not been demonstrated, it may facilitate homolog pairing, synapsis, or accurate segregation, particularly given that the homologous telomeres do not pair into a bouquet formation in drosophila meiosis 15, 16. The interaction between oshop2 and a transverse filament protein of sc zep1 indicates that oshop2 plays a key role in promoting the full.
A genomewide screen identifies genes that affect somatic. This search drives the homolog pairing and alignment, ultimately leading to the lengthwise pairing and synapsis the stabilization of homolog interactions by the polymerization of a proteinacious structure called the synaptonemal complex of. Aug 28, 2018 image stacks were reconstructed by the nikon nis software. Pairing centers mediate meiotic chromosome dynamics in c. The g1 phase also called the first gap phase initiates this stage and is focused on cell growth. The atrad51c gene is required for normal meiotic chromosome. Recombination, pairing, and synapsis of homologs during. Osdmc1 is not required for homologous pairing in rice meiosis. Pdf the telomere bouquet is a hub where meiotic double. Homolog pairing, synapsis, meiosis, recombination, nuclear. Hamamatsu controlled through cellsens dimension software. Maize meiotic mutants with improper or nonhomologous. These findings reveal the regulatory role for a novel fbox protein in early meiotic events. Surprisingly, the analysis of meiotic pairing and synapsis for three laco.
The histone marker, h1t, allows for differentiation of pachytene cells into early and late, since h1t only associates with the latter population wiltshire et al. By analyzing multiple features of the meiotic program at time points. Chromosome pairing and synapsis proceed independently of recombination in worms and flies, suggesting a paradoxical lack of coregulation. Aug 03, 2016 meiosis is preceded by an interphase consisting of three stages. Meiosisspecific cohesin mediates homolog recognition in.
This search drives the homolog pairing and alignment, ultimately leading to the lengthwise pairing and synapsis the stabilization of homolog interactions by the polymerization of a proteinacious structure called the synaptonemal complex of all homologs achieved by pachytene neale and keeney, 2006. Rather, homologous pairing and synapsis defects are limited to nonpc parts of the chromosomes in this mutant. The fbox protein zygo1 mediates bouquet formation to. Interplay between synaptonemal complex, homologous. However, defects in homologous chromosome pairing and synapsis during the. Homolog pairing is highly structured, encompassing tightly and loosely paired regions. Homologous pairing preceding spo11mediated doublestrand. Although homolog pairing, synapsis and co recombination during meiosis. Successful pairing and synapsis give rise to chromosome bivalents that can be observed by conventional microscopy during middle and late meiotic prophase. The telomere bouquet is a hub where meiotic doublestrand breaks, synapsis, and stable homolog juxtaposition are coordinated in the zebrafish, danio rerio. Synapsisdependent and independent mechanisms stabilize. Pair2 is essential for homologous chromosome synapsis in rice. Meiosis is preceded by an interphase consisting of three stages. Sc assembly on autosomes begins immediately after pc pairing is detected and is completed within.
The majority of mutants in this collection fail to form or maintain bivalents, usually due to defects in homologous pairing, synapsis or recombination. Image stacks were reconstructed by the nikon nis software. Mixing and matching chromosomes during female meiosis mdpi. Moreover, the failure to complete pairing synapsis and recombination suggest that bouquet formation is required for efficient homology searching and homologous recombination. Mutation of the atpase domain of muts homolog5 msh5. At the beginning of this study, we hypothesized that the crossover defect in mcm5 a7 mutants was due to a homolog pairing deficiency.
Structured illumination microscopy imaging reveals. Our fish results support this hypothesis fig 1 and revealed that homolog pairing can be lost during synapsis, resulting in seemingly normal sc between heterologous sequences fig 2. A family of zinc finger proteins is required forchromosome. Dec 02, 2014 in this study we validate a nearly centuryold model for chromosome pairing in flatworms and provide a molecular description of meiotic prophase in flatworms. Franklin ae, golubovskaya i, bass hw, and cande wz. Osdmc1 is not required for homologous pairing, but it functions in sc assembly. Synapsis also called syndesis is the pairing of two homologous chromosomes that occurs during meiosis. Thus, homolog pairing andor synapsis initiationprogression does not rely on a fully functional muts. Highly structured homolog pairing reflects functional. Herewe show that loss of him8function causes profound xchromosomespecific defects in homolog pairingand synapsis. Somatic pairing of homologous chromosomes is similar to pre and early meiotic pairing see article. Although homolog pairing has been recognized for over a century, relatively little is known about its regulation. Although an essential role for centromere clustering has not been demonstrated, it may facilitate homolog pairing, synapsis, or accurate segregation, particularly given that the homologous telomeres do not pair into a bouquet formation in drosophila meiosis 15, 16. The discovery that pairing center regions of chromosomes can promote local, scindependent pairing stabilization raises the possibility that homotypic interactions between pairing centers might serve to coordinate initial homolog pairing with synapsis progression.
Evidence for the coincident initiation of homolog pairing and. Jul 01, 2012 although homolog pairing has been recognized for over a century, relatively little is known about its regulation. The telomere bouquet is a hub where meiotic doublestrand. The result of the synapsis process is a bivalent homologous pair or a tetrad. Sep 15, 2002 synapsisdependent and independent mechanisms stabilize homolog pairing during meiotic prophase in c.
Immunocytological and electron microscopic analyses indicate that pair2 proteins associate with axial elements aes at leptotene and zygotene, and is removed from the aes of arm. A mutation in the highly conserved sun domain of sun1. Table 1 lists 15 mutants in our collection with abnormal synapsis. Our point probe fish assays indicate that the timing of homolog pairingsynapsis is similar between the arm and subtelomeric regions in wildtype and spo11 knockout spermatocytes figs. Chromosomal events and meiotic recombination are coordinated to ensure various. To characterize synapsis in these mutants further, the maize zyp1 gene was cloned and a zyp1 antibody was generated. Repair of meiotic dna breaks and homolog pairing in mouse. The pair2 gene is required for homologous chromosome synapsis at meiosis i in rice oryza sativa l. We performed a genomewide rnaibased screen that monitored the xspecific localization of the malespecific lethal msl complex, and we identified 59 candidate genes whose knockdown via rnai causes a change in the pattern of msl.
In addition to hr, homologous pairing and synapsis also play critical. Events informs mechanisms of homolog pairing and synapsis in. Spatiotemporal asymmetry of the meiotic program underlies. Timecourse analysis of early meiotic prophase events informs. In mutant females, synapsis and pairing were also disrupted as was seen in males fig 9, s3 fig.
Sep 01, 2017 sc assembly on autosomes begins immediately after pc pairing is detected and is completed within. Meiosis is key to sexual reproduction and genetic diversity. Bass laboratory research, department of biological sciences. Interhomolog crossingover and synapsis in arabidopsismeiosis are dependent on the chromosome axis protein atasy3 maheen ferdous1. It is generally believed that bouquet formation is necessary for homologous pairing scherthan, 2001. The fbox protein zygo1 mediates bouquet formation to promote. In addition, rad51 is required for meiosis and its arabidopsis arabidopsis thaliana ortholog is important for normal meiotic. The multiply inverted x chromosome balancer fm7 strongly suppresses, or eliminates, the occurrence of crossing over when heterozygous with a normal sequence homolog. In the absence of oshop2, homologous pairing and synapsis are disturbed and the hei10 bright foci only localize on the synapsed region fig. Centromeric smc1 promotes centromer clustering and stabilizes. A spontaneous mutation in mutlhomolog 3 hvmlh3 affects.
Recombinationmediated processes occur in physical and functional linkage with meiotic axial chromosome structure, with interplay in both directions, before, during, and after formation and dissolution of the synaptonemal complex sc, a highly conserved meiosisspecific structure that links homolog axes along their lengths. Surprisingly, the analysis of meiotic pairing and synapsis for three. Evidence for the coincident initiation of homolog pairing and synapsis during the telomereclustering bouquet stage of meiotic prophase. Htp3 links dsb formation with homolog pairing and crossing. We have demonstrated roles for telomeres and for centromeres in the pairing of homologous chromosomes. The complex juxtaposition of homologs that would be required to fully pair both x. The pairing profiles exhibited by syp1 mutants indicate that meiotic chromosome pairing in c. The budding yeast saccharomyces cerevisiae rad51 gene is known to be important for recombination and dna repair in the mitotic cell cycle. When homologous chromosomes synapse, their ends are first attached to. It allows matchingup of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Thus, activation of the synapsis checkpoint is not expected. Dernburg begins with an overview of meiosis, the process of cell division that gives rise to germ cells such as eggs, sperm, pollen and spores, and how it differs from mitosis. The him8 gene is essential for proper meiotic segregationof the x chromosomes in c. Analysis of meiosis in pristionchus pacificus reveals plasticity in.
Moreover, conversely, in the canonical program, recombinationindependent homologous interactions likely make a. Although the mrg1 mutant exhibits a synapsis defect, it undergoes successful homologous pairing and synapsis at the pcs. Centromere proteins cenpc and cal1 functionally interact in. Full paper a spontaneous mutation in mutlhomolog 3 hvmlh3 affects synapsis and crossover resolution in the barley desynaptic mutant des10. Synapsis dependent and independent mechanisms stabilize homolog pairing during meiotic prophase in c. Synapsis does not initiate at centromeres in the absence of recombination.
1414 1048 1 850 627 1160 1183 1242 1139 774 1465 94 1091 846 814 755 515 556 1338 573 290 343 294 1479 1282 824 1462 460 623 49 545 984 731 509 135 229 267 401 817 364 673 503 151 699 1387 730