Two kinds of "recombination nodules" in Neurospora crassa

Genome ◽  
1989 ◽  
Vol 32 (2) ◽  
pp. 309-317 ◽  
Author(s):  
Maja Bojko
Keyword(s):  
Neurospora Crassa ◽  
Synaptonemal Complex ◽  
Nucleolus Organizer ◽  
Crossing Over ◽  
Dramatic Reduction ◽  
Recombination Nodules ◽  
Exchange Event ◽  
The Mean ◽  
Different Origin ◽  
Positive Interference

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene – pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene – pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.Key words: recombination nodules, Neurospora crassa, synaptonemal complex.

Recombination nodule mapping and chiasma distribution in spermatocytes of the pigeon, Columba livia

Genome ◽  
1999 ◽  
Vol 42 (2) ◽  
pp. 308-314 ◽  
Author(s):  
M I Pigozzi ◽  
A J Solari
Keyword(s):  
Synaptonemal Complex ◽  
Random Distribution ◽  
Phosphotungstic Acid ◽  
Columba Livia ◽  
Complex Karyotype ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Chiasma Distribution ◽  
The Mean ◽  
Good Agreement

Pigeon spermatocytes were processed with a drying-down technique and their synaptonemal complex (SC) complements were analyzed by electron microscopy. The synaptonemal complex karyotype of the macrobivalents shows an excellent correspondence with the mitotic karyotype. The number and distribution of recombination nodules (RNs) were scored in complete nuclei stained with phosphotungstic acid. The average number of RNs per nucleus is 64.7. The number of nodules per bivalent shows a clear linear relationship with SC length in the 10 longest synaptonemal complexes, while the microbivalents usually bear a single RN. The location of RNs has a non-random distribution along the largest synaptonemal complexes, with lower frequencies near kinetochores and higher frequencies toward the telomeres. The ZZ bivalent is the fourth in size and shows free recombination, having on average 3.8 RNs. The mean number of nodules per cell and the mean number of nodules in the largest bivalents show very good agreement with the corresponding number of chiasmata scored in metaphase-I spermatocytes. It is concluded that the recombination nodules provide a good check for reciprocal exchanges in this and other species of birds. Additionally, a new morphology for the recombination nodules is presented, consisting of groups of electron-dense particles measuring 43 nm in diameter.Key words: meiosis, chiasmata, recombination nodules, pigeon spermatogenesis.

scholarly journals Correlation between pairing initiation sites, recombination nodules and meiotic recombination in Sordaria macrospora.

Genetics ◽  
1992 ◽  
Vol 132 (1) ◽  
pp. 135-148 ◽  
Author(s):  
D Zickler ◽  
P J Moreau ◽  
A D Huynh ◽  
A M Slezec
Keyword(s):  
Synaptonemal Complex ◽  
Crossing Over ◽  
Chromosome 2 ◽  
Wild Type ◽  
Sordaria Macrospora ◽  
Recombination Nodules ◽  
Chromosome Arm ◽  
Serial Section Reconstruction ◽  
Pairing Initiation ◽  
Effective Pairing

Abstract The decrease of meiotic exchanges (crossing over and conversion) in two mutants of Sordaria macrospora correlated strongly with a reduction of chiasmata and of both types of "recombination nodules." Serial section reconstruction electron microscopy was used to compare the synapsis pattern of meiotic prophase I in wild type and mutants. First, synapsis occurred but the number of synaptonemal complex initiation sites was reduced in both mutants. Second, this reduction was accompanied by, or resulted in, modifications of the pattern of synapsis. Genetic and synaptonemal complex maps were compared in three regions along one chromosome arm divided into well marked intervals. Reciprocal exchange frequencies and number of recombination nodules correlated in wild type in the three analyzed intervals, but disparity was found between the location of recombination nodules and exchanges in the mutants. Despite the twofold exchange decrease, sections of the genome such as the short arm of chromosome 2 and telomere regions were sheltered from nodule decrease and from pairing modifications. This indicated a certain amount of diversity in the control of these features and suggested that exchange frequency was dependent not only on the amount of effective pairing but also on the localization of the pairing sites, as revealed by the synaptonemal complex progression in the mutants.

scholarly journals Premeiotic change of nucleolus organizer size in Neurospora.

Genetics ◽  
1989 ◽  
Vol 122 (4) ◽  
pp. 783-791 ◽  
Author(s):  
D K Butler ◽  
R L Metzenberg
Keyword(s):  
Neurospora Crassa ◽  
Gel Electrophoresis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Pulsed Field Gel Electrophoresis ◽  
Crossing Over ◽  
Tetrad Analysis ◽  
Homologous Chromosomes ◽  
Unequal Crossing Over

Abstract We have investigated the heritability of nucleolus organizer region (NOR) size in Neurospora crassa. By pulsed-field gel electrophoresis, we followed in genetic crosses the size of the normal or "terminal" NORs and the size of a small interstitial NOR. Tetrad analysis revealed that changes in NOR size occur frequently in the sexual phase. Moreover, most size changes occurred in the period between fertilization and meiosis, although some changes occurred during and after meiosis. Unexpectedly, increases and decreases in NOR size were not equally frequent: decreases were more common. The NOR size changes generated during meiosis were not the result of unequal crossing over between NORs on homologous chromosomes.

Localized chiasmata and meiotic nodules in the tetraploid onion Allium porrum

Genome ◽  
1996 ◽  
Vol 39 (4) ◽  
pp. 770-783 ◽  
Author(s):  
Stephen M. Stack ◽  
Dick Roelofs
Keyword(s):  
Key Words ◽  
Synaptonemal Complex ◽  
Allium Porrum ◽  
Crossing Over ◽  
High Fertility ◽  
Unusual Behavior ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Metaphase I

Allium porrum L. (cultivated leek) (2n = 4x = 32) is a fertile tetraploid that forms bivalents with pericentric chiasmata at metaphase I. To investigate the basis of this unusual behavior for a tetraploid, we describe the karyotype, axial cores, synaptonemal complexes (SCs), and meiotic nodules of A. porrum. The karyotype appears to be autotetraploid. This conclusion is also supported by presynaptic alignment of axial cores in groups of four and partner trades between pairs of SCs. Numerous early nodules are distributed all along axial cores and SCs during zygonema, but they are lost by late zygonema – early pachynema. Late (recombination) nodules (RNs) are present on SCs near kinetochores throughout the remainder of pachynema. This pattern of RNs corresponds to the pattern of pericentric chiasmata. Pachytene quadrivalents usually are resolved into bivalents because partner trades between SC lateral elements rarely occur between RNs on the same segment of SC. Thus, the patterns of crossing-over and partner trades promote balanced disjunction and high fertility in autotetraploid A. porrum. Rare quadrivalents observed at metaphase I must be due to infrequent partner trades between RNs. Polycomplexes, unusual in their number and size, were observed during zygonema. Key words : synaptonemal complex, recombination nodules, localized chiasmata, polycomplex, Allium porrum.

scholarly journals THE RELATIONSHIP BETWEEN SYNAPTINEMAL COMPLEXES, RECOMBINATION NODULES AND CROSSING OVER IN NEUROSPORA CRASSA BIVALENTS AND TRANSLOCATION QUADRIVALENTS

Genetics ◽  
1979 ◽  
Vol 91 (1) ◽  
pp. 1-17
Author(s):  
C B Gillies
Keyword(s):  
Neurospora Crassa ◽  
Linkage Map ◽  
Central Component ◽  
Crossing Over ◽  
Late Pachytene ◽  
Recombination Nodules ◽  
Crossover Event ◽  
Different Strains ◽  
The Relationship ◽  
Multiple Nodules

ABSTRACT Reconstruction of serially sectioned zygotene and pachytene nuclei has allowed the estimation of both the number and position of central component recombination nodules in the synaptinemal complexes of two chromosomally different strains of Neurospora crussa. In both strains the number of nodules is that expected if each nodule represents one crossover event (50 map units). The distribution of nodules within the arms of bivalents shows evidence of centromeric repulsion and telomeric localizatioa. Nodules appear quite early in the zygotene before pairing of chromosomes is complete. Evidence was found of size differences in nodules, and multiple nodules were occasionally seen. Chromosome lengths and nuclear sizes increased from early zygotene to late pachytene. The three quadrivalents present in the alcoy translocation heterozygotes were readily distinguishable in reconstructions, and their cytological dimensions were in agreement with predictions from linkage map distances.

Evidence from a maize desynaptic mutant points to a probable role of synaptonemal complex central region components in provision for subsequent chiasma maintenance

Genome ◽  
1993 ◽  
Vol 36 (5) ◽  
pp. 797-807 ◽  
Author(s):  
M. P. Maguire ◽  
R. W. Riess ◽  
A. M. Paredes
Keyword(s):  
Synaptonemal Complex ◽  
Central Region ◽  
Crossing Over ◽  
Recombination Nodules ◽  
Genetic Lesion ◽  
Molecular Studies ◽  
Synaptic Failure ◽  
Probable Role

Homozygotes for the dsy1 desynaptic mutant of maize show massive failure of chiasma maintenance during diplotene and diakinesis. Although some chiasmata persist until anaphase I in most microsporocytes expressing this mutant, homozygotes are completely or nearly completely sterile, owing apparently to disjunctive irregularities. Pachytene synaptic errors and some synaptic failure also are found, but recombination nodules are common in homologously synapsed regions, and equational separation of a heterozygous knob into univalents or open arms at diakinesis clearly demonstrates that chiasma failure occurs following crossing-over. A wider than normal synaptonemal complex central region and uniform apparent weakness of central region cross connections to spreading procedures strongly suggest the presence of a genetic lesion in a synaptonemal complex central region component. The dsy1 mutant may provide an especially important source of material for molecular studies on the nature of chiasma maintenance mechanism.Key words: chiasma maintenance, synaptonemal complex, meiotic mutant.

scholarly journals Genetic Control of Mammalian Meiotic Recombination. I. Variation in Exchange Frequencies Among Males From Inbred Mouse Strains

Genetics ◽  
2002 ◽  
Vol 162 (1) ◽  
pp. 297-306 ◽  
Author(s):  
Kara E Koehler ◽  
Jonathan P Cherry ◽  
Audrey Lynn ◽  
Patricia A Hunt ◽  
Terry J Hassold
Keyword(s):  
Meiotic Recombination ◽  
Inbred Mouse ◽  
Inbred Strains ◽  
Male Meiosis ◽  
Mouse Strains ◽  
Recombination Rates ◽  
The Mean ◽  
Genetic Background Effects ◽  
Exchange Patterns ◽  
Positive Interference

AbstractGenetic background effects on the frequency of meiotic recombination have long been suspected in mice but never demonstrated in a systematic manner, especially in inbred strains. We used a recently described immunostaining technique to assess meiotic exchange patterns in male mice. We found that among four different inbred strains—CAST/Ei, A/J, C57BL/6, and SPRET/Ei—the mean number of meiotic exchanges per cell and, thus, the recombination rates in these genetic backgrounds were significantly different. These frequencies ranged from a low of 21.5 exchanges in CAST/Ei to a high of 24.9 in SPRET/Ei. We also found that, as expected, these crossover events were nonrandomly distributed and displayed positive interference. However, we found no evidence for significant differences in the patterns of crossover positioning between strains with different exchange frequencies. From our observations of >10,000 autosomal synaptonemal complexes, we conclude that achiasmate bivalents arise in the male mouse at a frequency of 0.1%. Thus, special mechanisms that segregate achiasmate chromosomes are unlikely to be an important component of mammalian male meiosis.

Normal Synaptonemal Complex and Abnormal Recombination Nodules in Two Alleles of the Drosophila Meiotic Mutant mei-W68

Genetics ◽  
2003 ◽  
Vol 163 (4) ◽  
pp. 1337-1356 ◽  
Author(s):  
Adelaide T C Carpenter
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
High Frequency ◽  
Serial Section ◽  
The Other ◽  
Wild Type ◽  
Recombination Nodules ◽  
Section Electron ◽  
Serial Section Electron Microscopy ◽  
Section Electron Microscopy

Abstract The meiotic phenotypes of two mutant alleles of the mei-W68 gene, 1 and L1, were studied by genetics and by serial-section electron microscopy. Despite no or reduced exchange, both mutant alleles have normal synaptonemal complex. However, neither has any early recombination nodules; instead, both exhibit high numbers of very long (up to 2 μm) structures here named “noodles.” These are hypothesized to be formed by the unchecked extension of identical but much shorter structures ephemerally seen in wild type, which may be precursors of early recombination nodules. Although the mei-W68L1 allele is identical to the mei-W681 allele in both the absence of early recombination nodules and a high frequency of noodles (i.e., it is amorphic for the noodle phene), it is hypomorphic in its effects on exchange and late recombination nodules. The differential effects of this allele on early and late recombination nodules are consistent with the hypothesis that Drosophila females have two separate recombination pathways—one for simple gene conversion, the other for exchange.

scholarly journals Gene Conversion Alone Accounts for More Than 90% of Recombination Events at the am Locus of Neurospora crassa

Genetics ◽  
1996 ◽  
Vol 143 (1) ◽  
pp. 129-136 ◽  
Author(s):  
Frederick J Bowring ◽  
David E A Catcheside
Keyword(s):  
Molecular Markers ◽  
Neurospora Crassa ◽  
Gene Conversion ◽  
Holliday Junctions ◽  
Crossing Over ◽  
Gene Markers ◽  
General Significance ◽  
Flanking Sequences ◽  
Simple Conversion

Abstract We have used closely flanking molecular markers located ~4 kb distal and 6 kb proximal of the am locus to investigate the incidence of crossover events associated with the generation of prototrophic recombinants in a cross heteroallelic am1 am6. Ninety-three percent of prototrophs were generated by events that did not recombine the molecular markers, indicating that simple conversion accounts for the formation of most prototrophs and that associated crossovers are much less frequent (~0.07) than estimated previously using more distant flanking markers. This suggests that conversion and crossing over during meiosis may arise from distinct mechanisms or that if, as is widely supposed, conversion and crossing over result from alternate modes of resolution of Holliday junctions then, at least for the am locus of Neurospora, the mode of resolution is strongly biased in favor of retaining the parental association of flanking sequences. Because estimates of the association of conversion and crossing over based on more distant gene markers are similar for yeast and Neurospora (~0.35), our observation may have general significance.

scholarly journals Evidence for Negative Interference: Clustering of Crossovers Close to the am Locus in Neurospora crassa Among am Recombinants

Genetics ◽  
1999 ◽  
Vol 152 (3) ◽  
pp. 965-969
Author(s):  
Frederick J Bowring ◽  
David E A Catcheside
Keyword(s):  
Neurospora Crassa ◽  
Molecular Evidence ◽  
Crossing Over ◽  
Negative Interference

Abstract In response to a conflict between two mapping studies in the predicted orientation of the allele map with respect to the centromere, Fincham proposed that recombination events at the Neurospora am locus rarely have an associated crossover. Fincham considered that the elevated levels of crossing over between flanking markers in am recombinants resulted from negative interference, an increased probability of a nearby second event, and on this basis predicted a clustering of crossing over near am in these recombinants. In this article we reevaluate the data from three mapping studies of the am locus and report molecular evidence that shows crossovers to be clustered immediately proximal to am in am recombinants.

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