ISSN:0192-253X    

DOI:10.1002/dvg.1020130602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTheREC104gene was initially defined by mutations that rescued the inviability of arad52 spo13haploid strain in meiosis. We have observed thatrec104mutant strains undergo essentially no induction of meiotic gene conversion, and we have not been able to detect any meiotic crossing over in such strains. TheREC104gene has no apparent role in mitosis, since mutations have no observable effect on growth, mitotic recombination, or DNA repair. The DNA sequence ofREC104reveals that it is a previously unknown gene with a coding region of 549‐bp, and genetic mapping has localized the gene to chromosome VIll nearFUR1.Expression of theREC104gene is induced in meiosis, and it appears that the gene is not transcribed in mitotic cells. Possible roles for theREC104gene product in meiosis are discussed. © 1993 Wiley‐Liss,

ISSN:0192-253X    

DOI:10.1002/dvg.1020130603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have utilized spreading methods as well as serial sectioning three‐dimensional reconstruction to examine meiotic chromosome behavior in cells homozygous for therad3‐1mutation inCoprinus cinereus.Comparison of 42 wild‐type nuclei that had been spread, stained with silver, and viewed by electron microscopy with 30 mutant nuclei treated in the same manner revealed several defects in the mutant. Axial core formation was defective in the mutant, although limited side‐by‐side association of axial cores was observed. To detect any differences in three‐dimensional architecture between the wild‐type and mutant nuclei, we reconstructed three of the former and six of the latter after serial sectioning. It was not possible to trace the expected number of axial cores from section to section in the mutant, although some tripartite synaptonemal complex was observed. Many axial core ends failed to terminate in the nuclear envelope in the mutant. This spectrum of defects (incomplete axial core assembly with some tripartite synaptonemal complex formation) had not been observed previously in eitherC. cinereusor other systems. We conclude that this combination of spreading and sectioning methods is very useful for analysis of meiotic mutants. © 1993 W

ISSN:0192-253X    

DOI:10.1002/dvg.1020130604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA modified enzyme digestion technique of ovary isolation followed by staining and squash preparation has allowed us to observe female meiosis in normal maize meiotically dividing megaspore mother cells (MMCs). The first meiotic division in megasporogenesis of maize is not distinguishable from that in mi‐crosporogenesis. The second female meiotic division is characterized as follows: (1) the two products of the first meiotic division do not simultaneously enter into the second meiotic division; as a rule, the chalazal‐most cell enters division earlier than the micropylar one, (2) often the second of the two products does not proceed with meiosis, but degenerates, and (3) only a single haploid meiotic product of the tetrad remains alive, and this cell proceeds with three rounds of mitoses without any intervening cell wall formation to produce the eight‐nucleate embryo sac. This technique has allowed us to study the effects of five meiotic mutations (aml, aml‐pral, afdl, dsy *‐9101, anddvl) on female meiosis in maize. The effects of the two alleles of theamlgene(amlandaml‐pral)and of theafdlanddsy *‐9101mutations are the same in both male and female meiosis. Theamlallele prevents the entrance of MMCs into meiosis and meiosis is replaced by mitosis; theaml‐pralpermits MMCs to enter into meiosis, but their progress is stopped at early prophase I stages. Theafdlgene is responsible for substitution of the first meiotic (reductional) division by an equational division including the segregation of sister chromatid centromeres at anaphase I. Thedsy * ‐9101gene exhibits abnormal chromosome pairing; paired homologous chromosomes are visible at pachytene, but only univalents are observed at diakinesis and metaphase I stages. These mutation specific patterns of abnormal meiosis are responsible for the bisexual sterility of these meiotic mutants.The abnormal divergent shape of the spindle apparatus and the resulting abnormal segregation of homologous chromosomes observed in micro‐sporogenesis in plants homozygous for thedv1mutation have not been found in meiosis of megasporogenesis. Only male sterility is induced by thedv1gene in the homozygous condition. ©

ISSN:0192-253X    

DOI:10.1002/dvg.1020130605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMeiotin‐1 is a chromatin associated, conserved protein found in meiocytes immediately preceding and during meiosis and is thought to have a role in determining the higher order structure of meiotic chromosomes [Riggs and Hasenkampf: Chromosoma 101:92–98, 1991]. In the studies reported here we utilized immunoblotting and immunocytochemical techniques to examine the temporal and spatial distribution of meiotin‐1 in the anthers ofLilium longiflorum.The results with the anti‐meiotin‐1 immune serum were compared with those obtained using an anti‐his‐tone Hl immune serum. The anti‐histone Hl immune serum gave constant immunostaining in all cell types of the anther at all of the stages tested. In contrast, the anti‐meiotin‐1 immune serum only gave immunostaining with the microsporocytes and to a lesser extent with the nutritive layer, the tapetum. It did not react with the cells of the anther wall. Meiotin‐1 immunostaining was first present in significant quantities in the microsporocytes as they accumulated in the G1 phase before the onset of premeiotic S phase and reached peak levels in the time interval between leptotene and pachytene—the same interval when chromosome synapsis occurs and when reciprocal genetic exchange is thought to occur. Immunostaining for both meiotin‐1 and histone H1 uniformly decorates the longitudinal axes of the chromosomes. Our data are consistent with the idea that the role of meiotin‐1 may be to tag certain sequences or to limit the degree of chromosome condensation that occurs during meiotic proph

ISSN:0192-253X    

DOI:10.1002/dvg.1020130606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAs an alternative to the production and use of monoclonal antisynaptonemal complex (SC) antibodies to isolate SC genes, we have explored the use of polyclonal anti‐SC antibodies to identify SC genes from a cDNA expression library. The method proved relatively simple, reliable, and fast and has yielded two SC genes. A homologue of one of these genes from a different species has previously been isolated in another laboratory. © 1993 Wiley‐Liss,

ISSN:0192-253X    

DOI:10.1002/dvg.1020130607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThere are numerous examples of the regular segregation of achiasmate chromosomes at meiosis I inDrosophila melanogasterfemales. Classically, the choice of achiasmate segregational partners has been thought to be independent of homology, but rather made on the basis of availability or similarities in size and shape. To the contrary, we show here that heterochromatic homology plays a primary role in ensuring the proper segregation of achiasmate homologs. We observe that the heterochromatin of chromosome4functions as, or contains, a meiotic pairing site. We show that free duplications carrying the4thchromosome pericentric heterochromatin induce high frequencies of4thchromosome nondisjunction regardless of their size. Moreover, a duplication from which some of the4thchromosome heterochromatin has been removed is unable to induce4thchromosome nondisjunction. Similarly, in the absence of either euchromatic homology or a size similarity, duplications bearing the X chromosome heterochromatin also disrupt the segregation of two achiasmate X chromosome centromeres. Although heterochromatic regions are sufficient to conjoin nonexchange homologues, we confirm that the segregation of heterologous chromosomes is determined by size, shape, and availability. The meiotic mutationAxsdifferentiates between these two processes of achiasmate centromere coorientation by disrupting only the homology‐dependent mechanism. Thus there are two different mechanisms by which achiasmate segregational partners are chosen. We propose that the absence of diplotene‐diakinesis during female meiosis allows heterochromatic pairings to persist until prometaphase and thus to co‐orient homologous centromeres. We also propose that heterologous disjunctions result from a separate and homology‐independent process that likely occurs during prometaphase. The latter process, which may not require the physical association of segregational partners, is similar to those observed in many insects, inSaccharomyces cerevisiaeand inC. elegansmales. We also suggest that the physical basis of this process may reflect known properties of theDrosophilameiotic spindle. © 1993 Wiley

ISSN:0192-253X    

DOI:10.1002/dvg.1020130608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTheDrosophila melanogasterribosomal DNA (rDNA) functions as an X‐Y meiotic pairing site. Deletions encompassing the X chromosomal rDNA block (located in the heterochromatin) disrupt X‐Y pairing and disjunction. Insertions of single, complete rRNA genes at ectopic locations on the heterochromatically deficient X partially restore X‐Y pairing capacity. This study was undertaken to test fragments of an rDNA repeat for the ability to stimulate X‐Y pairing and disjunction and to test for relationships between pairing capacity and two other phenotypes associated with rDNA insertions: transcription and the ability to organize a nucleolus. Insertions of three different fragments, all of which retained the rDNA promoter and upstream spacer sequences and which differed among each other in the length of downstream sequences, were obtained by P‐element mediated transformation. One of the fragments is truncated only 140bp downstream from the promoter. Insertions of all three fragments proved capable of stimulating X‐Y disjunction. Double insertions were substantially more effective than single insertions. RNA/PCR analysis was used to show that transcripts initiated at the inserted rDNA promoters are present in testis RNA from all insertions. Treatment with an antinucleolar antibody revealed that none of the insertions was associated with a mininucleolus. Thus promoter‐containing rDNA fragments are autonomously capable of being transcribed and of functioning as X‐Y pairing sites, but not of forming a mini‐nucleolus. © 19

ISSN:0192-253X    

DOI:10.1002/dvg.1020130609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractPulsed‐field gel electrophoresis (PFGE) has been used to study the timing, frequency, and distribution of double‐strand breaks (DSBs) in chromosomal‐sized DNA during meiosis in yeast. It has previously been shown that DSBs are associated with some genetic hotspots during recombination, and it is important to know whether meiotic recombination events routinely initiate via DSBs. Two strains have been studied here—a highsporulating homothallic wild type and a congenic mutant strain carrying arad50Smutation. This mutant has previously been reported to accumulate broken molecules in meiosis to much higher frequencies than wild type and to abolish the characteristic wild‐type processing of DNA that has been observed at the break sites. When whole chromosomes are resolved by PFGE, both strains show some broken molecules starting at the time that cells commit to genetic recombination. Breakage has been assessed primarily on ChromosomeIIIand Chr.XV, using Southern hybridization to identify these chromosomes and their fragments. At any one time, break frequency in wild type is much lower than the cumulative frequency of recombination events that occur during meiosis. However, there is suggestive evidence that each break is short‐lived, and it is therefore difficult to estimate the total number of breaks that may occur. Inrad50S, chromosome breaks accumulate to much higher levels, which are probably broadly consistent with the estimated number of recombination events in wild type. However, sincerad50Sis substantially defective in completing recombination, it is not known for certain if it initiates events at wild‐type frequencies.A surprising feature of the data is that a strong banding pattern is observed in the fragment distribution from broken chromosomes in both strains, implying that at least much of the breakage occurs at specific sites or within short regions. However, with the exception of the rDNA region on Chr.XII, assessment of the genetic map indicates that recombination can occur almost anywhere in the genome, although some regions are much hotter than others. Possible reasons for this apparent paradox are discussed. It may in part result from breakage levels too low for adequate detection in cold regions but may also imply that recombination events are localized more than previously realized. Alternatively, there may be a more indirect relationship between break sites and the associated recombination events. © 1993 W

ISSN:0192-253X    

DOI:10.1002/dvg.1020130610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe minimal length of contiguous homology required for successful completion of meiotic recombination was investigated by using heterologous insertions to delimit homologous segments of chromosome III in the yeastSaccharomyces cerevisiae.Constructs created in vitro by insertion of selectable markers into theLEU2locus were transplaced into haploid strains, which were then mated to create diploids containing pairs of insertion heterologies at various distances. Analysis of the meiotic products from these diploids revealed a gradient in the frequency of both reciprocal and nonreciprocal recombination declining monotonically from the 5′ end ofLEU2.Both types of event were found to be restricted by the presence of the insertion heterologies. Thespo 13single division meiosis was exploited to develop a plating assay in whichLEU2diploid spores containing reciprocally recombinant strands derived from events occurring completely within the interval flanked by the insertion heterologies were selected by random spore methods. Reciprocal recombination frequencies measured with this assay decreased linearly with extent, extrapolating to a minimal homology requirement of 150–250 nucleotides. When homology was most severely restricted, unexpected flanking marker configurations among reciprocal recombinants withinLEU2demonstrated the occurrence of complex recombination events. In addition to detecting reciprocal recombinants, the system is capable of measuring the probability that a non‐reciprocal recombination event will have one endpoint between the heterologous inserts and the other lying outside the interval. The minimal length of homology required for this aspect of recombination was found to be 25–60 nucleotides. © 1993 Wiley

ISSN:0192-253X    

DOI:10.1002/dvg.1020130611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY