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Argueso JL, Wanat J, Gemici Z, Alani E. Competing crossover pathways act during meiosis in Saccharomyces cerevisiae. Genetics 2005; 168:1805-16. [PMID: 15611158 PMCID: PMC1448724 DOI: 10.1534/genetics.104.032912] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In Saccharomyces cerevisiae the MSH4-MSH5, MLH1-MLH3, and MUS81-MMS4 complexes act to promote crossing over during meiosis. MSH4-MSH5, but not MUS81-MMS4, promotes crossovers that display interference. A role for MLH1-MLH3 in crossover control is less clear partly because mlh1Delta mutants retain crossover interference yet display a decrease in crossing over that is only slightly less severe than that seen in msh4Delta and msh5Delta mutants. We analyzed the effects of msh5Delta, mlh1Delta, and mms4Delta single, double, and triple mutants on meiotic crossing over at four consecutive genetic intervals on chromosome XV using newly developed computer software. mlh1Delta mms4Delta double mutants displayed the largest decrease in crossing over (13- to 15-fold) of all mutant combinations, yet these strains displayed relatively high spore viability (42%). In contrast, msh5Delta mms4Delta and msh5Delta mms4Delta mlh1Delta mutants displayed smaller decreases in crossing over (4- to 6-fold); however, spore viability (18-19%) was lower in these strains than in mlh1Delta mms4Delta strains. These data suggest that meiotic crossing over can occur in yeast through three distinct crossover pathways. In one pathway, MUS81-MMS4 promotes interference-independent crossing over; in a second pathway, both MSH4-MSH5 and MLH1-MLH3 promote interference-dependent crossovers. A third pathway, which appears to be repressed by MSH4-MSH5, yields deleterious crossovers.
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Affiliation(s)
- Juan Lucas Argueso
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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52
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Abstract
Most organisms use crossovers (chiasmata) to maintain physical connections between homologous chromosomes that ensure their proper segregation at the first meiotic division. The fission yeast Schizosaccharomyces pombe has a residual ability to segregate homologous chromosomes in the absence of meiotic recombination (achiasmate segregation). Using cytologically tagged chromosomes, we established a role for the microtubule motor dynein in meiotic chromosome segregation. Dhc1, the motor subunit of dynein, is required for chromosome segregation in both the presence and the absence of recombination. Dlc1, a member of the Tctex-1 dynein light-chain family, preferentially affects the segregation of achiasmate chromosomes. Dlc1 is the first identified protein, outside of Drosophila, that preferentially affects achiasmate chromosome segregation. We discuss possible roles of the dynein motor in this process.
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Affiliation(s)
- Luther Davis
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA
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53
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Anuradha S, Muniyappa K. Molecular aspects of meiotic chromosome synapsis and recombination. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2005; 79:49-132. [PMID: 16096027 DOI: 10.1016/s0079-6603(04)79002-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- S Anuradha
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
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54
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Abstract
As recently as 20 years ago, there was relatively little information about the number and distribution of recombinational events in human meiosis, and we knew virtually nothing about factors affecting patterns of recombination. However, the generation of a variety of linkage-based genetic mapping tools and, more recently, cytological approaches that enable us to directly visualize the recombinational process in meiocytes, have led to an increased understanding of human meiosis. In this review, we discuss the different approaches used to study meiotic recombination in humans, our understanding of factors that affect the number and location of recombinational events, and clinical consequences of variation in the recombinational process.
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Affiliation(s)
- Audrey Lynn
- Department of Genetics and Center for Human Genetics, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106, USA.
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55
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Murthy M, Schwarz TL. The exocyst component Sec5 is required for membrane traffic and polarity in the Drosophila ovary. Development 2003; 131:377-88. [PMID: 14681190 DOI: 10.1242/dev.00931] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The directed traffic of membrane proteins to the cell surface is crucial for many developmental events. We describe the role of Sec5, a member of the exocyst complex, in directed membrane traffic in the Drosophila oocyte. During oogenesis, we find that Sec5 localization undergoes dynamic changes, correlating with the sites at which it is required for the traffic of membrane proteins. Germline clones of sec5 possess defects in membrane addition and the posterior positioning of the oocyte. Additionally, the impaired membrane trafficking of Gurken, the secreted ligand for the EGF receptor, and Yolkless, the vitellogenin receptor, results in defects in dorsal patterning and egg size. However, we find the cytoskeleton to be correctly oriented. We conclude that Sec5 is required for directed membrane traffic, and consequently for the establishment of polarity within the developing oocyte.
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Affiliation(s)
- Mala Murthy
- Division of Neuroscience, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
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56
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Harris D, Orme C, Kramer J, Namba L, Champion M, Palladino MJ, Natzle J, Hawley RS. A Deficiency Screen of the Major Autosomes Identifies a Gene (matrimony) That Is Haplo-insufficient for Achiasmate Segregation in Drosophila Oocytes. Genetics 2003; 165:637-52. [PMID: 14573476 PMCID: PMC1462769 DOI: 10.1093/genetics/165.2.637] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
In Drosophila oocytes, euchromatic homolog-homolog associations are released at the end of pachytene, while heterochromatic pairings persist until metaphase I. A screen of 123 autosomal deficiencies for dominant effects on achiasmate chromosome segregation has identified a single gene that is haploinsufficient for homologous achiasmate segregation and whose product may be required for the maintenance of such heterochromatic pairings. Of the deficiencies tested, only one exhibited a strong dominant effect on achiasmate segregation, inducing both X and fourth chromosome nondisjunction in FM7/X females. Five overlapping deficiencies showed a similar dominant effect on achiasmate chromosome disjunction and mapped the haplo-insufficient meiotic gene to a small interval within 66C7-12. A P-element insertion mutation in this interval exhibits a similar dominant effect on achiasmate segregation, inducing both high levels of X and fourth chromosome nondisjunction in FM7/X females and high levels of fourth chromosome nondisjunction in X/X females. The insertion site for this P element lies immediately up-stream of CG18543, and germline expression of a UAS-CG18543 cDNA construct driven by nanos-GAL4 fully rescues the dominant meiotic defect. We conclude that CG18543 is the haplo-insufficient gene and have renamed this gene matrimony (mtrm). Cytological studies of prometaphase and metaphase I in mtrm hemizygotes demonstrate that achiasmate chromosomes are not properly positioned with respect to their homolog on the meiotic spindle. One possible, albeit speculative, interpretation of these data is that the presence of only a single copy of mtrm disrupts the function of whatever “glue” holds heterochromatically paired homologs together from the end of pachytene until metaphase I.
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Affiliation(s)
- David Harris
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
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57
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Abstract
In this review, we describe the pathway for generating meiotic crossovers in Drosophila melanogaster females and how these events ensure the segregation of homologous chromosomes. As appears to be common to meiosis in most organisms, recombination is initiated with a double-strand break (DSB). The interesting differences between organisms appear to be associated with what chromosomal events are required for DSBs to form. In Drosophila females, the synaptonemal complex is required for most DSB formation. The repair of these breaks requires several DSB repair genes, some of which are meiosis-specific, and defects at this stage can have effects downstream on oocyte development. This has been suggested to result from a checkpoint-like signaling between the oocyte nucleus and gene products regulating oogenesis. Crossovers result from genetically controlled modifications to the DSB repair pathway. Finally, segregation of chromosomes joined by a chiasma requires a bipolar spindle. At least two kinesin motor proteins are required for the assembly of this bipolar spindle, and while the meiotic spindle lacks traditional centrosomes, some centrosome components are found at the spindle poles.
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Affiliation(s)
- Kim S McKim
- Waksman Institute and Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854-8020, USA.
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58
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Maxfield Boumil R, Kemp B, Angelichio M, Nilsson-Tillgren T, Dawson DS. Meiotic segregation of a homeologous chromosome pair. Mol Genet Genomics 2003; 268:750-60. [PMID: 12655401 DOI: 10.1007/s00438-002-0796-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2002] [Accepted: 12/05/2002] [Indexed: 10/25/2022]
Abstract
During meiosis, the alignment of homologous chromosomes facilitates their subsequent migration away from one another to opposite spindle poles at anaphase I. Recombination is part of the mechanism by which chromosomes identify their homologous partners, and serves to link the homologs in a way that, in some organisms, has been shown to promote proper attachment to the meiotic spindle. We have built a diploid strain that contains a pair of homeologous chromosomes V': one is derived from Saccharomyces cerevisiae and one originates from S. carlsbergensis. Sequence analysis reveals that these chromosomes share 71% sequence identity. The homeologs experience high levels of meiotic double-stranded breaks. Despite their relatedness and their competence to initiate recombination, the meiotic segregation behavior of the homeologous chromosomes suggests that, in most meioses, they are partitioned by a meiotic segregation system that has been shown previously to partition non-exchange chromosomes and pairs with no homology. Though the homeologous chromosomes show a degree of meiotic segregation fidelity similar to that of other non-exchange pairs, our data provide evidence that their limited sequence homology may provide some bias in meiotic partner choice.
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Affiliation(s)
- R Maxfield Boumil
- Department of Molecular Biology and Microbiology, Tufts University, 136 Harrison Avenue, Boston, MA 02111, USA
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59
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Davis L, Smith GR. Nonrandom homolog segregation at meiosis I in Schizosaccharomyces pombe mutants lacking recombination. Genetics 2003; 163:857-74. [PMID: 12663528 PMCID: PMC1462471 DOI: 10.1093/genetics/163.3.857] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Physical connection between homologous chromosomes is normally required for their proper segregation to opposite poles at the first meiotic division (MI). This connection is generally provided by the combination of reciprocal recombination and sister-chromatid cohesion. In the absence of meiotic recombination, homologs are predicted to segregate randomly at MI. Here we demonstrate that in rec12 mutants of the fission yeast Schizosaccharomyces pombe, which are devoid of meiosis-induced recombination, homologs segregate to opposite poles at MI 63% of the time. Residual, Rec12-independent recombination appears insufficient to account for the observed nonrandom homolog segregation. Dyad asci are frequently produced by rec12 mutants. More than half of these dyad asci contain two viable homozygous-diploid spores, the products of a single reductional division. This set of phenotypes is shared by other S. pombe mutants that lack meiotic recombination, suggesting that nonrandom MI segregation and dyad formation are a general feature of meiosis in the absence of recombination and are not peculiar to rec12 mutants. Rec8, a meiosis-specific sister-chromatid cohesin, is required for the segregation phenotypes displayed by rec12 mutants. We propose that S. pombe possesses a system independent of recombination that promotes homolog segregation and discuss possible mechanisms.
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Affiliation(s)
- Luther Davis
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA
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60
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Kramer J, Hawley RS. The spindle-associated transmembrane protein Axs identifies a membranous structure ensheathing the meiotic spindle. Nat Cell Biol 2003; 5:261-3. [PMID: 12646877 DOI: 10.1038/ncb944] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2002] [Revised: 10/30/2002] [Accepted: 01/14/2003] [Indexed: 01/04/2023]
Abstract
Mutations in the aberrant X segragation (Axs) gene disrupt the segregation of achiasmate chromosomes during female meiosis in Drosophila melanogaster. We show that Axs encodes the founding member of an eukaryotic family of transmembrane proteins. Axs protein colocalizes with components of the endoplasmic reticulum and is present within a structure ensheathing the meiotic spindle. In both meiotic and mitotic cells, Axs is recruited to the microtubules of assembling spindles. We propose that Axs and the sheath represent novel mediators of meiotic spindle assembly and chromosome segregation.
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Affiliation(s)
- Joseph Kramer
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
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61
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Meneely PM, Farago AF, Kauffman TM. Crossover distribution and high interference for both the X chromosome and an autosome during oogenesis and spermatogenesis in Caenorhabditis elegans. Genetics 2002; 162:1169-77. [PMID: 12454064 PMCID: PMC1462340 DOI: 10.1093/genetics/162.3.1169] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Regulation of both the number and the location of crossovers during meiosis is important for normal chromosome segregation. We used sequence-tagged site polymorphisms to examine the distribution of all crossovers on the X chromosome during oogenesis and on one autosome during both oogenesis and spermatogenesis in Caenorhabditis elegans. The X chromosome has essentially one crossover during oogenesis, with only three possible double crossover exceptions among 220 recombinant X chromosomes. All three had one of the two crossovers in the same chromosomal interval, suggesting that crossovers in that interval do not cause interference. No other interval was associated with double crossovers. Very high interference was also found on an autosome during oogenesis, implying that each chromosome has only one crossover during oogenesis. During spermatogenesis, recombination on this autosome was reduced by approximately 30% compared to oogenesis, but the relative distribution of the residual crossovers was only slightly different. In contrast to previous results with other autosomes, no double crossover chromosomes were observed. Despite an increased frequency of nonrecombinant chromosomes, segregation of a nonrecombinant autosome during spermatogenesis appears to occur normally. This indicates that an achiasmate segregation system helps to ensure faithful disjunction of autosomes during spermatogenesis.
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Affiliation(s)
- Philip M Meneely
- Department of Biology, Haverford College, Pennsylvania 19041, USA.
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62
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63
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Lynn A, Koehler KE, Judis L, Chan ER, Cherry JP, Schwartz S, Seftel A, Hunt PA, Hassold TJ. Covariation of synaptonemal complex length and mammalian meiotic exchange rates. Science 2002; 296:2222-5. [PMID: 12052900 DOI: 10.1126/science.1071220] [Citation(s) in RCA: 222] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Analysis of recombination between loci (linkage analysis) has been a cornerstone of human genetic research, enabling investigators to localize and, ultimately, identify genetic loci. However, despite these efforts little is known about patterns of meiotic exchange in human germ cells or the mechanisms that control these patterns. Using recently developed immunofluorescence methodology to examine exchanges in human spermatocytes, we have identified remarkable variation in the rate of recombination within and among individuals. Subsequent analyses indicate that, in humans and mice, this variation is linked to differences in the length of the synaptonemal complex. Thus, at least in mammals, a physical structure, the synaptonemal complex, reflects genetic rather than physical distance.
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Affiliation(s)
- Audrey Lynn
- Department of Genetics, Case Western Reserve University, Cleveland, OH, USA
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64
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Abstract
Sexual reproduction and recombination are ubiquitous. However, a large body of theoretical work has shown that these processes should only evolve under a restricted set of conditions. New studies indicate that this discrepancy might result from the fact that previous models have ignored important complexities that face natural populations, such as genetic drift and the spatial structure of populations.
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Affiliation(s)
- Sarah P Otto
- Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada.
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65
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Giunta KL, Jang JK, Manheim EA, Subramanian G, McKim KS. subito encodes a kinesin-like protein required for meiotic spindle pole formation in Drosophila melanogaster. Genetics 2002; 160:1489-501. [PMID: 11973304 PMCID: PMC1462067 DOI: 10.1093/genetics/160.4.1489] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The female meiotic spindle lacks a centrosome or microtubule-organizing center in many organisms. During cell division, these spindles are organized by the chromosomes and microtubule-associated proteins. Previous studies in Drosophila melanogaster implicated at least one kinesin motor protein, NCD, in tapering the microtubules into a bipolar spindle. We have identified a second Drosophila kinesin-like protein, SUB, that is required for meiotic spindle function. At meiosis I in males and females, sub mutations affect only the segregation of homologous chromosomes. In female meiosis, sub mutations have a similar phenotype to ncd; even though chromosomes are joined by chiasmata they fail to segregate at meiosis I. Cytological analyses have revealed that sub is required for bipolar spindle formation. In sub mutations, we observed spindles that were unipolar, multipolar, or frayed with no defined poles. On the basis of these phenotypes and the observation that sub mutations genetically interact with ncd, we propose that SUB is one member of a group of microtubule-associated proteins required for bipolar spindle assembly in the absence of the centrosomes. sub is also required for the early embryonic divisions but is otherwise dispensable for most mitotic divisions.
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Affiliation(s)
- Kelly L Giunta
- Waksman Institute and Department of Genetics, Rutgers University, Piscataway, New Jersey 08854, USA
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66
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Abstract
When meiotic cells complete S phase, homologous chromosomes pair, synapse and undergo recombination. A checkpoint protein is somehow required for meiotic chromosome pairing in C. elegans, thus providing a direct link between S phase and the rest of the meiotic program.
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Affiliation(s)
- B Meier
- Department of Genetics, Coker Hall, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.
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67
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Davis L, Smith GR. Meiotic recombination and chromosome segregation in Schizosaccharomyces pombe. Proc Natl Acad Sci U S A 2001; 98:8395-402. [PMID: 11459981 PMCID: PMC37449 DOI: 10.1073/pnas.121005598] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In most organisms homologous recombination is vital for the proper segregation of chromosomes during meiosis, the formation of haploid sex cells from diploid precursors. This review compares meiotic recombination and chromosome segregation in the fission yeast Schizosaccharomyces pombe and the distantly related budding yeast Saccharomyces cerevisiae, two especially tractable microorganisms. Certain features, such as the occurrence of DNA breaks associated with recombination, appear similar, suggesting that these features may be common in eukaryotes. Other features, such as the role of these breaks and the ability of chromosomes to segregate faithfully in the absence of recombination, appear different, suggesting multiple solutions to the problems faced in meiosis.
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Affiliation(s)
- L Davis
- Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, A1-162, Seattle, WA 98109-1024, USA
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68
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Dobie KW, Kennedy CD, Velasco VM, McGrath TL, Weko J, Patterson RW, Karpen GH. Identification of chromosome inheritance modifiers in Drosophila melanogaster. Genetics 2001; 157:1623-37. [PMID: 11290718 PMCID: PMC1461595 DOI: 10.1093/genetics/157.4.1623] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Faithful chromosome inheritance is a fundamental biological activity and errors contribute to birth defects and cancer progression. We have performed a P-element screen in Drosophila melanogaster with the aim of identifying novel candidate genes involved in inheritance. We used a "sensitized" minichromosome substrate (J21A) to screen approximately 3,000 new P-element lines for dominant effects on chromosome inheritance and recovered 78 Sensitized chromosome inheritance modifiers (Scim). Of these, 69 decreased minichromosome inheritance while 9 increased minichromosome inheritance. Fourteen mutations are lethal or semilethal when homozygous and all exhibit dramatic mitotic defects. Inverse PCR combined with genomic analyses identified P insertions within or close to genes with previously described inheritance functions, including wings apart-like (wapl), centrosomin (cnn), and pavarotti (pav). Further, lethal insertions in replication factor complex 4 (rfc4) and GTPase-activating protein 1 (Gap1) exhibit specific mitotic chromosome defects, discovering previously unknown roles for these proteins in chromosome inheritance. The majority of the lines represent mutations in previously uncharacterized loci, many of which have human homologs, and we anticipate that this collection will provide a rich source of mutations in new genes required for chromosome inheritance in metazoans.
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Affiliation(s)
- K W Dobie
- Molecular Biology and Virology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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69
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Molnar M, Parisi S, Kakihara Y, Nojima H, Yamamoto A, Hiraoka Y, Bozsik A, Sipiczki M, Kohli J. Characterization of rec7, an early meiotic recombination gene in Schizosaccharomyces pombe. Genetics 2001; 157:519-32. [PMID: 11156975 PMCID: PMC1461520 DOI: 10.1093/genetics/157.2.519] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
rec7 is involved in intra- and intergenic meiotic recombination in all tested regions of the genome of the fission yeast Schizosaccharomyces pombe. Segregational analysis in a rec7 gene disruption mutant revealed frequent occurrence of two-spored asci. Spores giving rise to diploid colonies were shown to derive from skipping of the second meiotic division. Nondisjunction of homologous chromosomes at the first meiotic division was also frequent. The cytological structures and processes, such as formation of linear elements, pairing of homologous chromosomes, and clustering of telomeres and centromeres, are regular in the mutant. Northern blot experiments revealed meiosis-specific expression of rec7. Screening of a meiotic cDNA library also identified transcripts from the opposite strand in the rec7 region. A Rec7-GFP fusion protein was localized in the nucleus of whole cells before karyogamy, during prophase, and after meiosis I. On spreads of prophase nuclei approximately 50 foci of Rec7-GFP were counted. Some of the observed phenotypes of the disruption mutant and the N-terminal sequence homology suggest that Rec7p is a functional homolog of Rec114p of Saccharomyces cerevisiae. The observed phenotypes of the disruption and the appearance of Rec7-GFP in mating haploid cells and after meiosis I are consistent with Rec7p functions before, during, and after meiotic prophase.
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Affiliation(s)
- M Molnar
- Institute of Cell Biology, University of Bern, Baltzer-Str.4, CH-3012 Bern, Switzerland
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70
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Page SL, McKim KS, Deneen B, Van Hook TL, Hawley RS. Genetic studies of mei-P26 reveal a link between the processes that control germ cell proliferation in both sexes and those that control meiotic exchange in Drosophila. Genetics 2000; 155:1757-72. [PMID: 10924472 PMCID: PMC1461182 DOI: 10.1093/genetics/155.4.1757] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We present the cloning and characterization of mei-P26, a novel P-element-induced exchange-defective female meiotic mutant in Drosophila melanogaster. Meiotic exchange in females homozygous for mei-P26(1) is reduced in a polar fashion, such that distal chromosomal regions are the most severely affected. Additional alleles generated by duplication of the P element reveal that mei-P26 is also necessary for germline differentiation in both females and males. To further assess the role of mei-P26 in germline differentiation, we tested double mutant combinations of mei-P26 and bag-of-marbles (bam), a gene necessary for the control of germline differentiation and proliferation in both sexes. A null mutation at the bam locus was found to act as a dominant enhancer of mei-P26 in both males and females. Interestingly, meiotic exchange in mei-P26(1); bam(Delta)(86)/+ females is also severely decreased in comparison to mei-P26(1) homozygotes, indicating that bam affects the meiotic phenotype as well. These data suggest that the pathways controlling germline differentiation and meiotic exchange are related and that factors involved in the mitotic divisions of the germline may regulate meiotic recombination.
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Affiliation(s)
- S L Page
- Department of Genetics, Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA
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71
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Vernì F, Gandhi R, Goldberg ML, Gatti M. Genetic and molecular analysis of wings apart-like (wapl), a gene controlling heterochromatin organization in Drosophila melanogaster. Genetics 2000; 154:1693-710. [PMID: 10747063 PMCID: PMC1461031 DOI: 10.1093/genetics/154.4.1693] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mutations in the X-linked gene wings apart-like (wapl) result in late larval lethality associated with an unusual chromosome morphology. In brain cell metaphases of wapl mutants, sister chromatids of all chromosomes are aligned parallel to each other instead of assuming the typical morphology observed in wild type. This effect is due to a loosening of the adhesion between sister chromatids in the heterochromatic regions of the chromosomes. Despite this aberrant chromosome morphology, mutant brains exhibit normal mitotic parameters, suggesting that heterochromatin cohesion is not essential for proper centromere function. On the basis of these observations, we examined the role of wapl in meiotic chromosome segregation in females. wapl exhibits a clear dominant effect on achiasmate segregation, giving further support to the hypothesis that proximal heterochromatin is involved in chromosome pairing during female meiosis. We also examined whether wapl modulates position-effect variegation (PEV). Our analyses showed that wapl is a dominant suppressor of both white and Stubble variegation, while it is a weak enhancer of brown variegation. wapl maps to region 2D of the X chromosome between Pgd and pn. We identified the wapl gene within a previously conducted chromosomal walk in this region. The wapl transcriptional unit gives rise to two alternatively spliced transcripts 6.5- and 5-kb long. The protein encoded by the larger of these transcripts appears to be conserved among higher eukaryotes and contains a tract of acidic amino acids reminiscent of many chromatin-associated proteins, including two [HP1 and SU(VAR)3-7] encoded by other genes that act as suppressors of PEV.
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Affiliation(s)
- F Vernì
- Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Genetica e Biologia Molecolare, Universitá di Roma La Sapienza, 00185 Rome, Italy
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72
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Gallegos A, Jacobson DJ, Raju NB, Skupski MP, Natvig DO. Suppressed recombination and a pairing anomaly on the mating-type chromosome of Neurospora tetrasperma. Genetics 2000; 154:623-33. [PMID: 10655216 PMCID: PMC1460935 DOI: 10.1093/genetics/154.2.623] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Neurospora crassa and related heterothallic ascomycetes produce eight homokaryotic self-sterile ascospores per ascus. In contrast, asci of N. tetrasperma contain four self-fertile ascospores each with nuclei of both mating types (matA and mata). The self-fertile ascospores of N. tetrasperma result from first-division segregation of mating type and nuclear spindle overlap at the second meiotic division and at a subsequent mitotic division. Recently, Merino et al. presented population-genetic evidence that crossing over is suppressed on the mating-type chromosome of N. tetrasperma, thereby preventing second-division segregation of mating type and the formation of self-sterile ascospores. The present study experimentally confirmed suppressed crossing over for a large segment of the mating-type chromosome by examining segregation of markers in crosses of wild strains. Surprisingly, our study also revealed a region on the far left arm where recombination is obligatory. In cytological studies, we demonstrated that suppressed recombination correlates with an extensive unpaired region at pachytene. Taken together, these results suggest an unpaired region adjacent to one or more paired regions, analogous to the nonpairing and pseudoautosomal regions of animal sex chromosomes. The observed pairing and obligate crossover likely reflect mechanisms to ensure chromosome disjunction.
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Affiliation(s)
- A Gallegos
- Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA
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73
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Matthies HJ, Messina LG, Namba R, Greer KJ, Walker M, Hawley RS. Mutations in the alpha-tubulin 67C gene specifically impair achiasmate segregation in Drosophila melanogaster. J Cell Biol 1999; 147:1137-44. [PMID: 10601329 PMCID: PMC2168102 DOI: 10.1083/jcb.147.6.1137] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Drosophila melanogaster oocytes heterozygous for mutations in the alpha-tubulin 67C gene (alphatub67C) display defects in centromere positioning during prometaphase of meiosis I. The centromeres do not migrate to the poleward edges of the chromatin mass, and the chromatin fails to stretch during spindle lengthening. These results suggest that the poleward forces acting at the kinetochore are compromised in the alphatub67C mutants. Genetic studies demonstrate that these mutations also strongly and specifically decrease the fidelity of achiasmate chromosome segregation. Proper centromere orientation, chromatin elongation, and faithful segregation can all be restored by a decrease in the amount of the Nod chromokinesin. These results suggest that the accurate segregation of achiasmate chromosomes requires the proper balancing of forces acting on the chromosomes during prometaphase.
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Affiliation(s)
- Heinrich J.G. Matthies
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
| | - Lisa G. Messina
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
| | - Ruria Namba
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
| | - Kimberly J. Greer
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
| | - M.Y. Walker
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
| | - R. Scott Hawley
- Department of Genetics, Section of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616
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74
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Zwick ME, Cutler DJ, Langley CH. Classic Weinstein: tetrad analysis, genetic variation and achiasmate segregation in Drosophila and humans. Genetics 1999; 152:1615-29. [PMID: 10430587 PMCID: PMC1460678 DOI: 10.1093/genetics/152.4.1615] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
A maximum-likelihood method for the estimation of tetrad frequencies from single-spore data is presented. The multilocus exchange with interference and viability (MEIV) model incorporates a clearly defined model of exchange, interference, and viability whose parameters define a multinomial distribution for single-spore data. Maximum-likelihood analysis of the MEIV model (MEIVLA) allows point estimation of tetrad frequencies and determination of confidence intervals. We employ MEIVLA to determine tetrad frequencies among 15 X chromosomes sampled at random from Drosophila melanogaster natural populations in Africa and North America. Significant variation in the frequency of nonexchange, or E(0) tetrads, is observed within both natural populations. Because most nondisjunction arises from E(0) tetrads, this observation is quite unexpected given both the prevalence and the deleterious consequences of nondisjunction in D. melanogaster. Use of MEIVLA is also demonstrated by reanalyzing a recently published human chromosome 21 dataset. Analysis of simulated datasets demonstrates that MEIVLA is superior to previous methods of tetrad frequency estimation and is particularly well suited to analyze samples where the E(0) tetrad frequency is low and sample sizes are small, conditions likely to be met in most samples from human populations. We discuss the implications of our analysis for determining whether an achiasmate system exists in humans to ensure the proper segregation of E(0) tetrads.
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Affiliation(s)
- M E Zwick
- Center for Population Biology, University of California, Davis, California 95616, USA.
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75
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Sekelsky JJ, McKim KS, Messina L, French RL, Hurley WD, Arbel T, Chin GM, Deneen B, Force SJ, Hari KL, Jang JK, Laurençon AC, Madden LD, Matthies HJ, Milliken DB, Page SL, Ring AD, Wayson SM, Zimmerman CC, Hawley RS. Identification of novel Drosophila meiotic genes recovered in a P-element screen. Genetics 1999; 152:529-42. [PMID: 10353897 PMCID: PMC1460643 DOI: 10.1093/genetics/152.2.529] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The segregation of homologous chromosomes from one another is the essence of meiosis. In many organisms, accurate segregation is ensured by the formation of chiasmata resulting from crossing over. Drosophila melanogaster females use this type of recombination-based system, but they also have mechanisms for segregating achiasmate chromosomes with high fidelity. We describe a P-element mutagenesis and screen in a sensitized genetic background to detect mutations that impair meiotic chromosome pairing, recombination, or segregation. Our screen identified two new recombination-deficient mutations: mei-P22, which fully eliminates meiotic recombination, and mei-P26, which decreases meiotic exchange by 70% in a polar fashion. We also recovered an unusual allele of the ncd gene, whose wild-type product is required for proper structure and function of the meiotic spindle. However, the screen yielded primarily mutants specifically defective in the segregation of achiasmate chromosomes. Although most of these are alleles of previously undescribed genes, five were in the known genes alphaTubulin67C, CycE, push, and Trl. The five mutations in known genes produce novel phenotypes for those genes.
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Affiliation(s)
- J J Sekelsky
- Department of Genetics, Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA
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76
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Abstract
OBJECTIVES Correlations between parental age, aneuploidy in germ cells and recent findings on aetiological factors in mammalian trisomy formation are reviewed. METHODS Data from observations in human oocytes, molecular studies on the origin of extra chromosomes in trisomies, experiments in a mouse model system, and transgenic approaches are shown. RESULTS Errors in chromosome segregation are most frequent in meiosis I of oogenesis in mammals and predominantly predispose specific chromosomes and susceptible chiasmate configurations to maternal age-related nondisjunction. Studies on spindle structure, cell cycle and chromosome behaviour in oocytes of the CBA/Ca mouse used as a model for the maternal age-effect suggest that hormonal homeostasis and size of the follicle pool influence the quality, maturation competence and spindle size of the mammalian oocyte. Predisposition to errors in chromosome segregation are critically dependent on altered cell cycles. Compromised protein synthesis and mitochondrial function affect maturation kinetics and spindle formation, and cause untimely segregation of chromosomes (predivision), mimicking an aged phenotype. CONCLUSIONS Altered cell cycles and untimely resolution of chiasmata but also nondisjunction of late segregating homologues caused by asynchrony in cytoplasmic and nuclear maturation appear to be causal to errors in chromosome segregation with advanced maternal age. Oocytes appear to lack checkpoints guarding against untimely chromosome segregation. Genes and exposures affecting pool size, hormonal homeostasis and interactions between oocytes and their somatic compartment and thus quality of follicles and oocytes have the potential to critically influence chromosome distribution in female meiosis and affect fertility in humans and other mammals.
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77
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Coelho PA, Queiroz-Machado J, Hartl D, Sunkel CE. Pattern of chromosomal localization of the Hoppel transposable element family in the Drosophila melanogaster subgroup. Chromosome Res 1998; 6:385-95. [PMID: 9872668 DOI: 10.1023/a:1009277322626] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have isolated a Hoppel-like transposon from heterochromatin of the second chromosome of Drosophila melanogaster and used a conserved DNA sequence between the different elements of this family to determine their distribution in both mitotic and polytene chromosomes. The hybridization pattern of polytene chromosomes extends throughout the entire chromocentre, as well as a substantial portion of the fourth chromosome. Analysis of different wild-type strains of D. melanogaster shows variation in euchromatic insertion sites, although most insertions are found near the chromocentre. The positions and the number of heterochromatic clusters of Hoppel on mitotic chromosomes are conserved among the several strains analysed. Accurate mapping of this element was achieved by in situ hybridization on D. melanogaster mitotic chromosomes that had previously been banded with Hoechst 33258. To evaluate the evolutionary stability of this pattern, different species were analysed by in situ hybridization and Southern blotting. We conclude that Hoppel has a conserved distribution in mitotic heterochromatin within the D. melanogaster subgroup, established around 5 million years ago. The overall conservation of heterochormatic organization supports the notion that heterochormatin does perform important structural and functional roles.
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Affiliation(s)
- P A Coelho
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal
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78
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Bascom-Slack CA, Ross LO, Dawson DS. Chiasmata, crossovers, and meiotic chromosome segregation. ADVANCES IN GENETICS 1997; 35:253-84. [PMID: 9348650 DOI: 10.1016/s0065-2660(08)60452-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Meiotic recombination events are probably critical for the completion of several meiotic processes. In addition, recombination is likely to be involved in the events that lead up to synapsis of homologues in meiotic prophase. Recombination events that ultimately become resolved as exchanges are needed for the formation of chiasmata. Chiasmata maintain the association of paired homologues following loss of the synaptonemal complex and participate in the mechanism that signals that the bivalent has attached to the spindle in a bipolar orientation that will result in meiosis I disjunction.
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Affiliation(s)
- C A Bascom-Slack
- Department of Microbiology and Molecular Biology, Tufts University, Boston, Massachusetts 02111, USA
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79
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Affiliation(s)
- G S Roeder
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103 USA.
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80
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Chua PR, Roeder GS. Tam1, a telomere-associated meiotic protein, functions in chromosome synapsis and crossover interference. Genes Dev 1997; 11:1786-800. [PMID: 9242487 DOI: 10.1101/gad.11.14.1786] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The TAM1 gene of Saccharomyces cerevisiae is expressed specifically during meiosis and encodes a protein that localizes to the ends of meiotic chromosomes. In a tam1 null mutant, there is an increase in the frequency of chromosomes that fail to recombine and an associated increase in homolog nondisjunction at meiosis I. The tam1 mutant also displays an increased frequency of precocious separation of sister chromatids and a reduced efficiency of distributive disjunction. The defect in distributive disjunction may be attributable to overloading of the distributive system by the increased number of nonrecombinant chromosomes. Recombination is not impaired in the tam1 mutant, but crossover interference is reduced substantially. In addition, chromosome synapsis is delayed in tam1 strains. The combination of a defect in synapsis and a reduction in interference is consistent with previous studies suggesting a role for the synaptonemal complex in regulating crossover distribution. tam1 is the only known yeast mutant in which the control of crossover distribution is impaired, but the frequency of crossing over is unaffected. We discuss here possibilities for how a telomere-associated protein might function in chromosome synapsis and crossover interference.
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Affiliation(s)
- P R Chua
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA
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81
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Abstract
During meiosis, the pairing of chromosomes is crucial for a successful partitioning of the genetic material and its transmission into the developing gamete. The classical view of meiotic pairing involves recombination between homologues as an integral part of the pairing mechanism. But, in cases where no recombination occurs, how do chromosome partners find one another? And how do they pair up and then segregate appropriately? Recently, a combination of molecular genetics and fluorescence in situ hybridization appears to have provided an answer to these questions by demonstrating a crucial role for heterochromatin in chromosome pairing.
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82
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Koehler KE, Boulton CL, Collins HE, French RL, Herman KC, Lacefield SM, Madden LD, Schuetz CD, Hawley RS. Spontaneous X chromosome MI and MII nondisjunction events in Drosophila melanogaster oocytes have different recombinational histories. Nat Genet 1996; 14:406-14. [PMID: 8944020 DOI: 10.1038/ng1296-406] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Recent studies of human oocytes have demonstrated an enrichment for distal exchanges among meiosis I (MI) nondisjunction events and for proximal exchanges among meiosis II (MII) events. Our characterization of 103 cases of spontaneous X chromosome nondisjunction in Drosophila oocytes strongly parallels these observations. The recombinational histories of MI (97/103) and MII (6/103) nondisjunctional ova were strikingly different. MI nondisjunction occurred primarily in oocytes with non-exchange X chromosomes; of the new nondisjoining exchange bivalents, most carried distal crossovers. Thus, spontaneous MI nondisjunction reflects the failure of the achiasmate segregation systems. MII nondisjunction occurred only in oocytes with proximal exchanges. We propose several models to explain how very proximal exchanges might impair proper segregation.
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Affiliation(s)
- K E Koehler
- Department of Genetics, University of California at Davis 95616, USA
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83
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Dernburg AF, Sedat JW, Hawley RS. Direct evidence of a role for heterochromatin in meiotic chromosome segregation. Cell 1996; 86:135-46. [PMID: 8689681 DOI: 10.1016/s0092-8674(00)80084-7] [Citation(s) in RCA: 294] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We have investigated the mechanism that enables achiasmate chromosomes to segregate from each other at meiosis I in D. melanogaster oocytes. Using novel cytological methods, we asked whether nonexchange chromosomes are paired prior to disjunction. Our results show that the heterochromatin of homologous chromosomes remains associated throughout prophase until metaphase I regardless of whether they undergo exchange, suggesting that homologous recognition can lead to segregation even in the absence of chiasmata. However, partner chromosomes lacking homology do not pair prior to disjunction. Furthermore, euchromatic synapsis is not maintained throughout prophase. These observations provide a physical demonstration that homologous and heterologous achiasmate segregations occur by different mechanisms and establish a role for heterochromatin in maintaining the alignment of chromosomes during meiosis.
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Affiliation(s)
- A F Dernburg
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0554, USA
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84
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Abruzzo MA, Griffin DK, Millie EA, Sheean LA, Hassold TJ. The effect of Y-chromosome alpha-satellite array length on the rate of sex chromosome disomy in human sperm. Hum Genet 1996; 97:819-23. [PMID: 8641703 DOI: 10.1007/bf02346196] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Trisomy is the leading known cause of mental retardation and pregnancy loss in humans, yet virtually nothing is known of the underlying nondisjunctional mechanisms. Since studies of other organisms suggest an association between centromere size or sequence and meiotic nondisjunction, we recently initiated studies to examine the effect of centromere size variation on human nondisjunction. In the present report, we summarize studies correlating variation in the size of the Y-chromosome centromere with sex chromosome nondisjunction. In one set of studies, we used pulsed-field gel electrophoresis to estimate Y-chromosome alpha-satellite array lengths in normal males, and correlated these values with Y-chromosome sperm disomy levels as determined by fluorescence in situ hybridization. In a second set of studies, we determined the Y-chromosome alpha-satellite array length of 47,XYY males, since the karyotypes of these individuals are a consequence of Y chromosome nondisjunction. Neither set of studies provided evidence for an effect of Y-chromosome alpha-satellite array length on Y-chromosome nondisjunction. Thus, if there is an association between Y-chromosome centromere size and nondisjunction, the effect is subtle and below the detection levels of the present study or involves extreme size variants that were not represented in the present study population.
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Affiliation(s)
- M A Abruzzo
- Department of Genetics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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85
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Ross LO, Maxfield R, Dawson D. Exchanges are not equally able to enhance meiotic chromosome segregation in yeast. Proc Natl Acad Sci U S A 1996; 93:4979-83. [PMID: 8643515 PMCID: PMC39391 DOI: 10.1073/pnas.93.10.4979] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Homologous chromosomes pair, and then migrate to opposite poles of the spindle at meiosis I. In most eukaryotic organisms, reciprocal recombinations (crossovers) between the homologs are critical to the success of this process. Individuals with defects in meiotic recombination typically produce high levels of aneuploid gametes and exhibit low fertility or are sterile. The experiments described here were designed to test whether different crossovers are equally able to contribute to the fidelity of meiotic chromosome segregation in yeast. These experiments were performed with model chromosomes with which it was possible to control and measure the distributions of meiotic crossovers in wild-type cells. Physical and genetic approaches were used to map crossover positions on model chromosomes and to correlate crossover position with meiotic segregation behavior. The results show that crossovers at different chromosomal positions have different abilities to enhance the fidelity of meiotic segregation.
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Affiliation(s)
- L O Ross
- Department of Molecular Biology and Microbiology, Tufts University, Boston, MA 02111, USA
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86
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Choi T, Rulong S, Resau J, Fukasawa K, Matten W, Kuriyama R, Mansour S, Ahn N, Vande Woude GF. Mos/mitogen-activated protein kinase can induce early meiotic phenotypes in the absence of maturation-promoting factor: a novel system for analyzing spindle formation during meiosis I. Proc Natl Acad Sci U S A 1996; 93:4730-5. [PMID: 8643471 PMCID: PMC39347 DOI: 10.1073/pnas.93.10.4730] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Mitogen-activated protein kinase (MAPK) is selectively activated by injecting either mos or MAPK kinase (mek) RNA into immature mouse oocytes maintained in the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). IBMX arrests oocyte maturation, but Mos (or MEK) overexpression overrides this block. Under these conditions, meiosis I is significantly prolonged, and MAPK becomes fully activated in the absence of p34cdc2 kinase or maturation-promoting factor. In these oocytes, large openings form in the germinal vesicle adjacent to condensing chromatin, and microtubule arrays, which stain for both MAPK and centrosomal proteins, nucleate from these regions. Maturation-promoting factor activation occurs later, concomitant with germinal vesicle breakdown, the contraction of the microtubule arrays into a precursor of the spindle, and the redistribution of the centrosomal proteins into the newly forming spindle poles. These studies define important new functions for the Mos/MAPK cascade in mouse oocyte maturation and, under these conditions, reveal novel detail of the early stages of oocyte meiosis I.
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Affiliation(s)
- T Choi
- ABL-Basic Research Program, National Institute-Frederick Cancer Research & Development Center, MD 21702, USA
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87
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Abstract
Aneuploidy, the presence of an extra or missing chromosome, is the most frequent cause of mental retardation and pregnancy loss in our species. Studies can be divided into those of incidence, origin, and etiology. Trisomy 21 is the most common aneuploidy among liveborns whereas monosomy X and trisomy 16 are the most frequent causes of pregnancy loss. Aneuploidy primarily arises by the process of nondisjunction in the first meiotic division of maternal meiosis; however, this varies among chromosomes in that some show a significant proportion of paternal and/or meiosis II errors. The most common etiological factor associated with aneuploidy is advancing maternal age and it is generally agreed that this is a result of the increasing likelihood of nondisjunction in the aging ovary. There has been intense debate as to the existence of of a paternal age effect and recent studies on human sperm suggest that there may be a small effect for the sex chromosomes. Furthermore, recent molecular studies on trisomic conceptuses have revealed a second etiological factor associated with nondisjunction, namely, reduced genetic recombination.
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Affiliation(s)
- D K Griffin
- Department of Genetics, Case Western Reserve University, Cleveland, Ohio 44106, USA
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88
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López-León MD, Cabrero J, Camacho JP. Achiasmate segregation of X and B univalents in males of the grasshopper Eyprepocnemis plorans is independent of previous association. Chromosome Res 1996; 4:43-8. [PMID: 8653268 DOI: 10.1007/bf02254944] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
B chromosomes proved to be more frequent in males than females of the grasshopper Eyprepocnemis plorans collected from the population in Jete (Granada, Spain) in 1992. The meiotic behaviour of the X and B univalents was analysed in a high number of 1B males collected from this population in 1991 and 1992, and in males from another population (Salobreña, Granada, Spain) for comparison. These two chromosomes showed a significant tendency to migrate to opposite poles in the Jete population, during the 2 years analysed, but separated randomly in the Salobreña population. Thus, sex differences in the B frequency in Jete seemed to be due to the non-random X-B segregation during male meiosis. The analysis of association patterns between the two univalents over several stages of the first meiotic division indicated a heterochromatic affinity rather than association by chiasmata because most X-B associations had resolved by metaphase I. The X and B chromosomes share two different DNA sequences, so that some associations during prophase I undoubtedly involve homologous DNA sequences. The frequency with which X and B migrated to opposite poles at anaphase I in Jete, however, did not show any significant dependence on previous association at zygotene, diplotene or metaphase I.
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89
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Abstract
Recently many exciting advances have been achieved in our understanding of Drosophila meiosis due to combined cytological and genetic approaches. New techniques have permitted the characterization of chromosome position and spindle formation in female meiosis I. The proteins encoded by the nod and ncd genes, two genes known to be needed for the proper partitioning of chromosomes lacking exchange events, have been identified and found to be kinesin-like motors. The effects of mutations in these genes on the spindle and chromosomes, together with the localization of the proteins, have yielded a model for the mechanism of female meiosis I. In male meiosis I, the chromosomal regions responsible for homolog pairing have been resolved to the level of specific DNA sequences. This provides a foundation for elucidating the molecular basis of meiotic pairing. The cytological techniques available in Drosophila also have permitted inroads into the regulation of sister-chromatid segregation. The products of two genes (mei-S332 and ord) essential for sister-chromatid cohesion have been identified recently. Additional advances in understanding Drosophila meiosis are the delineation of a functional centromere by using minichromosome derivatives and the identification of several regulatory genes for the meiotic cell cycle.
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Affiliation(s)
- T L Orr-Weaver
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge 02142, USA
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90
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Afshar K, Scholey J, Hawley RS. Identification of the chromosome localization domain of the Drosophila nod kinesin-like protein. J Biophys Biochem Cytol 1995; 131:833-43. [PMID: 7490288 PMCID: PMC2200005 DOI: 10.1083/jcb.131.4.833] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The nod kinesin-like protein is localized along the arms of meiotic chromosomes and is required to maintain the position of achiasmate chromosomes on the developing meiotic spindle. Here we show that the localization of ectopically expressed nod protein on mitotic chromosomes precisely parallels that observed for wild-type nod protein on meiotic chromosomes. Moreover, the carboxyl-terminal half of the nod protein also binds to chromosomes when overexpressed in mitotic cells, whereas the overexpressed amino-terminal motor domain binds only to microtubules. Chromosome localization of the carboxyl-terminal domain of nod depends upon an 82-amino acid region comprised of three copies of a sequence homologous to the DNA-binding domain of HMG 14/17 proteins. These data map the two primary functional domains of the nod protein in vivo and provide a molecular explanation for the directing of the nod protein to a specific subcellular component, the chromosome.
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Affiliation(s)
- K Afshar
- Section of Molecular and Cellular Biology, University of California at Davis 95616, USA
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91
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Afshar K, Barton NR, Hawley RS, Goldstein LS. DNA binding and meiotic chromosomal localization of the Drosophila nod kinesin-like protein. Cell 1995; 81:129-38. [PMID: 7720068 DOI: 10.1016/0092-8674(95)90377-1] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The Drosophila no distributive disjunction (nod) gene encodes a kinesin-like protein that has been proposed to push chromosomes toward the metaphase plate during female meiosis. We report that the nonmotor domain of the nod protein can mediate direct binding to DNA. Using an antiserum prepared against bacterially expressed nod protein, we show that during prometaphase nod protein is localized on oocyte chromosomes and is not restricted to either specific chromosomal regions or to the kinetochore. Thus, motor-based chromosome-microtubule interactions are not limited to the centromere, but extend along the chromosome arms, providing a molecular explanation for the polar ejection force.
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Affiliation(s)
- K Afshar
- Department of Genetics, University of California, Davis 95616, USA
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92
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Charlesworth B, Sniegowski P, Stephan W. The evolutionary dynamics of repetitive DNA in eukaryotes. Nature 1994; 371:215-20. [PMID: 8078581 DOI: 10.1038/371215a0] [Citation(s) in RCA: 998] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Repetitive DNA sequences form a large portion of the genomes of eukaryotes. The 'selfish DNA' hypothesis proposes that they are maintained by their ability to replicate within the genome. The behaviour of repetitive sequences can result in mutations that cause genetic diseases, and confer significant fitness losses on the organism. Features of the organization of repetitive sequences in eukaryotic genomes, and their distribution in natural populations, reflect the evolutionary forces acting on selfish DNA.
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Affiliation(s)
- B Charlesworth
- Department of Ecology and Evolution, University of Chicago, Illinois 60637
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93
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Abstract
The demonstration by Zhang and Spradling (1) of efficient P element transposition into heterochromatic regions will aid ongoing studies of heterochromatin structure and function. P element insertions will provide entry points for further molecular analysis of heterochromatin and will allow the isolation of small and large heterochromatic deficiencies. The generation of heterochromatic P insertions also will aid the study of heterochromatic genes. Of the heterochromatic insertions isolated by Zhang and Spradling, five were homozygous lethal, and one of these defined a lethal locus not previously uncovered by heterochromatic deficiencies. P elements have previously been used to mutagenize and clone specific heterochromatic genes (14, 19, 26). New methods, like those described here (1, 32), should allow the efficient identification and molecular isolation of other single-copy heterochromatic genes. Furthermore, since position-effect suppression allowed the recovery of heterochromatic P insertions, it may also allow the recovery of insertions in euchromatic regions previously refractory to P mutagenesis. Studies of position-effect variegation show that genes normally found in heterochromatin require a heterochromatic context for normal expression and that heterochromatin is inhibitory to euchromatic gene expression (16). The physical basis of these related phenomena--chromatin assembly, nuclear positioning, and/or heterochromatin elimination--can be resolved only with a more thorough understanding of heterochromatin structure and functions. Analyzing heterochromatin also will help define the chromosomal components responsible for inheritance processes such as chromosome pairing, sister chromatid adhesion, and centromere function. These efforts will be facilitated by the effective use of P elements combined with other current molecular-genetic approaches.
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Affiliation(s)
- K R Cook
- Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037
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