Synaptonemal Complex Length Research Articles

Synaptic behaviour and recombination nodules in the human XY pair.

A sample of 90 XY pairs from men with normal karyotypes has been analyzed by measuring their morphological features in electron micrographs of microspread spermatocytes. The classification of human XY types (Solari, 1980) has been given stricter definitions. Stepwise splitting of the axes is seen in types 1 and 2. The development of axial branches and lengthening of the X axis is seen in type 3. In the two subtypes a and b of type 4 the net-like filamentous array grows in length to a maximum (average = 59.7 microns) in subtype b. The location of the putative Y kinetochore defines a short arm that measures 22.34% of Y axis length, and the kinetochore of the X axis defines a short arm of 38.15% of the axial length. The average number of excrescences in the X axis is 19.9 and in the Y is 4.3. The frequency of a non-homologous, distal end-joining grows steadily from type 0 to type 3. The average length of the synaptonemal complex (SC) in 51 XY pairs of types 1 and 2 is 1.33 microns (SD = 0.65) and it corresponds to 25.54% of the Y axis length. Thus, the average SC covers the short arm of the Y and the pericentromeric region. Maximum lengths of this SC may reach up to 81.8% of the Y axis. 30 recombination nodules (RNs) were located in 26 XY pairs, and 90% of the nodules are located in the distal half of the short arm of the Y axis. Thus, RNs are restricted to a segment much shorter than the length of the average SC. A gradient of decreasing probability of recombination may reach up to the centromeric region of the Y chromosome. Some possible consequences of these facts are discussed.

Chromosomal analysis of insecticide resistant and susceptible mosquitofish

The meiotic karyotypes of insecticide-resistant (R) and susceptible (S), and SR F1 mosquitofish were analyzed by preparing spread, silver-stained wholemounts of synaptonemal complexes (SC) from spermatocytes. The method reveals statistically significant differences in the relative length of certain SC's between susceptible and resistant individuals. However, careful study of SCs from SR F1 fish does not reveal detectable heterozygosity for chromosomal rearrangements. It is concluded that populations of SS and RR mosquitofish are geographically isolated and that minor karyotypIc differentiation has occurred. This differentiation may or may not be causally related to the acquisition of Insecticide resistance.

Recombination nodules in the oocytes of the chicken, Gallus domesticus.

Chicken oocytes at pachytene were processed with the microspreading technique (Moses, 1977), and their synaptonemal complex (SC) complements were analyzed by electron microscopy. Ellipsoidal nodules, 140 X 120 nm in diameter, were associated with the central space of synaptonemal complexes. The average number of nodules per pachytene oocyte was 57.5. The number of nodules per bivalent showed a clear linear relationship with SC length, except for the microchromosomes, which showed a single obligatory nodule. The distribution of nodules along the 10 longest SCs was nonrandom, with low frequencies in the vicinity of kinetochores and high frequencies near the telomeres. The microchromosomes showed a single nodule whose average location was 1.21 micron from the kinetochore. In the ZW pair there was a single nodule whose average location was 0.31 micron from the paired telomeres and not more than 0.65 micron from them. The total number of nodules per cell and the number of nodules in each of the five major bivalents showed good agreement with the total number of chiasmata and the number of chiasmata of the major bivalents of roosters. Thus, these nodules share the characteristics of recombination nodules described in other organisms. The single, obligatory, strictly localized recombination nodule found in the pairing end of the ZW pair strongly suggests that recombination between the Z and W chromosomes in the female chicken is a regular process that may be similar to the obligatory recombination between the pairing ends of the human X and Y chromosomes that was recently described in studies using DNA probes.

Karyotypic Analysis of Plasmodiophora Diplantherae

Synaptonemal complexes (SCs) in nuclei of transitional plasmodia of Plasmodiophora diplantherae were counted through serial section analysis. On this basis the haploid chro? mosome number was nine, the lowest haploid number known for Plasmodiophoromycetes. Total length (TL) of SCs per nucleus (approx. 39 /nm) was similar to that of P. brassicae (n = 20, TL = approx. 47 jim, vol. = approx. 15 ixm3), but nuclear volume (approx. 28 /um3) was similar to those of Polymyxa betae (n = 30, TL = approx. 73 /um, vol. = approx. 26 ^m3), P. graminis (n = 30, TL = approx. 70 jim, vol. = approx. 24 /um3), and Sorosphaera veronicae (n = 33, TL = approx. 76 /ttm, vol. = approx. 25 Mm3).

Karyotypic Analysis of Plasmodiophora diplantherae

Synaptonemal complexes (SCs) in nuclei of transitional Plasmodia of Plasmodiophora diplantherae were counted through serial section analysis. On this basis the haploid chromosome number was nine, the lowest haploid number known for Plasmodiophoromycetes. Total length (TL) of SCs per nucleus (approx. 39 μm) was similar to that of P. brassicae (n = 20, TL = approx. 47 μm, vol. = approx. 15 μm3), but nuclear volume (approx. 28 μm3) was similar to those of Polymyxa betae (n = 30, TL = approx. 73 μm, vol. = approx. 26 μm3), P. graminis (n = 30, TL = approx. 70 μm, vol. = approx. 24 μm3), and Sorosphaera veronicae (n = 33, TL = approx. 76 μm, vol. = approx. 25 μ3).

The relationship between genome size and synaptonemal complex length in higher plants

There appears to be only a weak correlation between genome size and the corresponding total length of a complete set of synaptonemal complexes (SCs) based on published evidence for several fungal, plant, and animal species. This result is unexpected, considering the strong positive correlations between genome size (DNA amount) and total chromosome length and volume and between relative lengths of chromosomes and SCs. Because the observed weak correlation was based on limited data, we systematically investigated the relationship between genome size and SC length, using ten higher plant species. Two-dimensional spreads of SCs from primary microsporocytes at pachytene were prepared using a hypotonic bursting technique. The SC spreads were examined either by light or electron microscopy, and the lengths of at least ten complete sets of SCs were measured for each of the ten species. Additionally, the genome size of each species was determined from pollen tetrad protoplasts using flow cytometry. A strong correlation ( r=0.97) between total SC length and genome size was observed for higher plants, indicating a constant amount of DNA is associated with a given length of SC, at least when averaged over the whole genome.

Synaptonemal complexes of normal and mutant yeast chromosomes (Saccharomyces cerevisiae)

Synaptonemal complex (SC) analysis of six laboratory yeast strains showed the SC karyotypes to be repeatable within strains. Chromosomal differences were found between strains. In five of the strains, two SCs insert into the nucleolus. This represents a single bivalent with a nucleolar organizer in a medial position as is suggested by genetic data or two bivalents each with a terminal nucleolar organizer. In the first interpretation, n = 16; in the second, n = 17. Strain Tris has a single nucleolar SC and n = 17. In strains DCx374, DCx416 and x8366a the genetically determined rearrangements of linkage group III could not be identified. Presumably the short SC (0.33 micron) associated with linkage group III cannot accommodate an inversion loop or a translocation configuration. The strains however were found to harbour a reciprocal translocation involving the nucleolar chromosome. Trisomy for one of the longer chromosomes was observed in Tris and spo10. It is concluded that rearrangements of the medium and long but not short yeast chromosomes can be detected cytologically. Measurements of nuclear volumes show SC length to vary with artifactually induced swelling of the nucleus. Linear regression of SC length over nuclear radius indicates that actual SC length is only about one-half the observed length. As a result the DNA packing per SC unit length is higher than previously estimated.

An electron microscopic study of synaptonemal complex formation at zygotene in rye

A spreading technique was used to allow ultrastructural analysis of seventeen zygotene nuclei of rye (Secale cereale). Twenty pachytene nuclei were also examined. Lateral element lengths of the haploid complements decreased from 742 μm at the beginning of zygotene to 451 μm at the end of zygotene. Variation in pachytene synaptonemal complex lengths was also noted. Zygotene synaptonemal complex formation in rye is characterised by: (1) existence of a bouquet, with telomeric pairing initiation earliest; (2) multiple sites of initiation in each bivalent (maximum of 76 synaptonemal complex segments seen in one nucleus); (3) the potential number of pairing initiation sites may be higher (the average spacing of 4.42 μm would allow approximately 160 sites per nucleus); (4) new pairing initiations occur almost until the end of zygotene; (5) initiation of new synaptonemal complexes and extension of existing synaptonemal complexes occur simultaneously. A simple zipping up of a few initiation sites is not the case in rye. Pairing in different bivalents of a nucleus is not completely synchronised, and the NOR in particular is often late to pair. Interlocking of lateral elements and synaptonemal complexes may lead to delayed completion of pairing in portions of bivalents, but interlocks are ultimately resolved. This resolution may involve breakage and rejoining of lateral elements.

Karyotypic analysis of Polymyxa graminis (Plasmodiophoromycetes) based on serial sections of synaptonemal complexes

Three pachytene nuclei of Polymyxa graminis Ledingham were reconstructed from serial thin sections. Thirty synaptonemal complexes (SCs) were counted, indicating the identical haploid number (30) that was reported for Polymyxa betae. SCs of P. graminis and P. betae were similar in structure, and nuclear volumes and total lengths of SCs per nucleus were not significantly different for the two species.

Heterochromatin, the synaptonemal complex and crossing over.

A combined light- and electron-microscopic examination of chromosomes from two angiospermous plants, Plantago ovata and Lycopersicon esculentum, and a mammal, Mus musculus, was performed. From this investigation three observations have been made that may be relevant to the observed lack of crossing over in heterochromatin. (1) Differential staining indicates that heterochromatin represents a smaller fraction of the length of pachytene chromosomes than it represents in the length of mitotic metaphase chromosomes. Since the synaptonemal complex (SC) runs throughout the length of these pachytene chromosomes, it is under-represented in heterochromatin. Considering the evidence for a rough correlation between the length of SC and the amount of crossing over, this could result in less crossing over in heterochromatin than expected on the basis of its length in mitotic metaphase chromosomes. (2) Electron microscopy indicates that, unlike the SC in euchromatin, the SC in heterochromatin is densely ensheathed in highly compact chromatin. If crossing over occurs in the SC or even in the surrounding chromatin, the compaction of the chromatin may prevent the penetration of enzymes needed in recombination. (3) Finally, a difference in the structure of SCs in euchromatin versus heterochromatin was observed that could be associated with the lack of crossing over in heterochromatin.

Linkage group-chromosome correlations in Sordaria macrospora: Chromosome identification by three dimensional reconstruction of their synaptonemal complex

Reconstruction of serially sectioned zygotene and pachytene nuclei has allowed, by measuring the lengths of synaptonemal complexes, an assignment of the 7 linkage (LG) groups to the 7 chromosomes in the fungus Sordaria macrospora. The 7 LG have been established using 19 mutants showing low second division segregation frequencies. Eight chromosomal rearrangements mapped on the 7 LG were used to identify the chromosomes involved. The following one to one assignment of the 7 LG to specific chromosomes was obtained: LG a: chromosome (chr) 1, LG b: chr5, LG c: chr6, LG d: chr7, LG e: chr4, LG f: chr3 and LG g: chr2 (the chromosome carrying the nucleolus organizer region).

Synaptonemal complex and recombination nodules in rye (Secale cereale)

Meiotic prophase in rye was investigated by serial-section reconstruction of pollen mother cell nuclei. In the mid-late zygotene nucleus, all lateral elements were continuous from telomere to telomere, and 9–20 pairing initiation sites per bivalent were observed. Chromosome and bivalent interlockings detected during zygotene were resolved at early pachytene when pairing was completed. In the three pachytene nuclei, the relative synaptonemal complex (SC) lengths and arm ratios were found to be in good correlation with light microscopic data of pachytene bivalents. Spatial tracing of the bivalents showed that they occupy separate areas in the nucleus. Three types of recombination nodules were observed: large, ellipsoidal and small nodules at early pachytene and irregularly shaped nodules mainly associated with chromatin at late pachytene. Their number and position along the bivalents correlated well with the number and distribution of chiasmata. The classification of the seven bivalents was based on arm ratio and heterochromatic knob distribution.

The synaptonemal complex karyotypes of palearctic hamsters, Phodopus roborovskii satunin and P. sungorus pallas

Synaptonemal complex (SC) karyotyping is used to analyse the relationship of two Palearctic hamsters. Male Phodopus sungorus have 13 SCs plus an X-Y pair while P. roborovskii has 16 SCs and an X-Y pair. P. sungorus has four nucleolar organizers as opposed to two in P. roborovskii. Centromeres of the X and Y are juxtaposed in the pairing region of the latter but not in the former. SC lengths and relative arm ratios are also discussed. Comparisons with karyotypes of other hamster genera indicate large intergeneric karyotypic differences and expectedly much smaller variation within each genus. Data on the two Phodopus species suggest that their presently accepted congeneric status warrants further examination.

KARYOTYPE, SYNAPTONEMAL COMPLEXES AND POSSIBLE RECOMBINATION NODULES OF THE OOMYCETE FUNGUSSAPROLEGNIA

Pachytene nuclei of the fungus Saprolegnia ferax (Gruith.) Thuret were analyzed by serial section electron microscopy. These nuclei contained 21 synaptonemal complexes, all of which terminated at both ends on the nuclear envelope. These complexes range from 1.6 μm to 5.5 μm in length and are composed of two rather diffuse lateral elements, lack a continuous central element and contain discontinuous central nodes. These nodes occur at about 1 per μm of synaptonemal complex length, have a diameter of approximately 50 nm, are predominantly short (<200 nm) and appear to occur as multiples of a basic 50 nm length. These nodes are in many respects similar to previously reported recombination nodules. The complexes were not seen to form a bouquet stage. Based on nuclear DNA content and synaptonemal complex length, the chromosomes are calculated to contain 2C values of between 5.2 and 17.3 fg of DNA, with a mean value of 9.3 fg. Thus it seems that Saprolegnia has large chromosomes relative to other fungi and a haploid complement of 21.

Two-Dimensional Spreads of Synaptonemal Complexes from Solanaceous Plants. I. The Technique

Using beta-glucuronidase the cell walls of tomato and potato primary microsporocytes can be digested. When the resulting protoplasts are exposed to distilled water, they burst, and complete sets of synaptonemal complexes are released to settle on plastic coated slides. After drying and formalin fixation, the synaptonemal complexes can be stained with silver or phosphotungstic acid and observed in the light and/or electron microscope. Silver staining gives better contrast for both light and electron microscopy but stains only lateral elements and kinetochores. Phosphotungstic acid staining gives little or no contrast for light microscopy, but stains both the lateral and central elements of the synaptonemal complex, kinetochores, and structures that are probably recombination nodules for electron microscopy. This technique offers a powerful tool for genome analysis by allowing (1) the determination of relative and absolute lengths of synaptonemal complexes and chromosome arm ratios at pachytene, (2) the analysis of complex patterns of synapsis, and (3) the location of what are probably recombination nodules along the length of synaptonemal complexes.

Pachytene karyotype analysis of tetraploid Meloidogyne hapla females by electron microscopy.

Pairing of homologous chromosomes results in the formation of 34 synaptonemal complexes (SC) at pachytene, corresponding to the 34 bivalents at metaphase I. No multivalent associations were observed and pairing occurs two-by-two. The modified SC, which lacks a central element, does not affect the pairing process. Only one end of the SC is attached to the nuclear envelope, although either end can attach. Total SC length and the number of recombination nodules in the tetraploid were about 1.5 times greater than in the diploid.

Synaptosomal complexes and associated structures in microspread human spermatocytes.

Human spermatocytes processed with a modified microspreading technique which involves the use of sodium dodecyl-sulphate (SDS) have been used to construct synaptonemal complex (SC) karyotypes. Twenty two pachytene spermatocytes were selected for length quantitation. The mean values of relative lengths and centromeric indexes of each SC agree closely with values obtained by three-dimensional reconstructions (Holm and Rasmussen, 1977), except for SCs #4--5, 6--7 and 19--20. Absolute lengths are consistently longer in spreads (10.7% longer than in sections, on average). The mean total length of the SC complement is 258.7 micrometer. Six morphological types of XY pairs have been described. On the basis of the relationships between the XY pair, nucleolar development and autosome behavior, these six XY types are assumed to develop in succession. Type O XY pairs occur during late zygotene, types I and II XY pairs occur during early to mid-pachytene, and types III, IV and V occur during later pachytene substages. Alignment of the X and Y axes is observed at late zygotene, and formation of the SC occurs in relation with type I XY pairs. Progressive desynapsis occurs in types II and III. Splitting and fusion of the X and Y axes attain a maximum in types IV and V. The breakdown of the dense bodies associated with the X and Y axes occurs during stage V. --Bar-like structures, having a mean length of 2,100 A are associated with SCs in all the pachytene substages defined by the XY types. The average number of bars per nucleus is 46.2 (SD = 8.4, N = 20), and the average SC length per bar is 5.57 micrometer. The distribution along the SCs of 923 bars shows that near-termini locations are preferred (SC length per bar, 2.98 micrometer) and centromere regions are avoided (SC length per bar, 16.9 micrometer). --On the basis of these data, bars are similar to recombination nodules described in other organisms. The availability of a standard SC karyotype for microspreads and a temporal sequence given by the XY pair provide a basis for rapid screening of chromosome aberrations in human testicular biopsies.

Time of recombination in the Drosophila melanogaster oocyte. II. Electron microscopic and genetic studies of a temperature-sensitive recombination mutant.

A test has been carried out to determine if the restrictive temperature (31 degrees) acts to reduce recombination in the temperature-sensitive recombination-deficient genotype rec-l26/rec-l16 by reducing or eliminating the synaptonemal complex. Measurements of the length of synaptonemal complexes in heat-treated and untreated stage 1 oocytes, following termination of the temperature-sensitive period, reveal less than a 5% difference, with the greater length present in the treated oocytes. Alterations are not observed in synaptonemal complex distribution within the nucleus or in its fine structure. Parallel genetic studies confirm earlier observations that the restrictive temperature, whose action is confined to a 36-h sensitive period virtually coextensive with premeiotic-S, drastically reduces recombination to approximately 10% of normal. The results are most simply interpreted to mean that the restrictive temperatures acts directly on the recombination process.

The pachytene karyotype of Schizophyllum commune analyzed by three dimensional reconstruction of synaptonemal complexes

Three dimensional reconstructions of 15 pachytene nuclei of Schizophyllum commune have revealed in each nucleus 11 distinct synaptonemal complexes, demonstrating a haploid chromosome number of 11. Each bivalent contained one short region of condensed chromatin marking the position of the centromere. The synaptonemal complex of, each bivalent contained from 0 to six recombination nodules. A high correlation was found between the total length of the synaptonemal complexes in a nucleus and the number of recombination nodules. Total synaptonemal complex length correlated only weakly with the nuclear volume.

Ultrastructural analysis of female pachynema and the relationship between synaptonemal complex length and crossing-over in zea mays

The synaptonemal complexes at pachynema of megasporocytes and microsporocytes in a single genotype of maize were reconstructed from electron micrographs of serial sections. The structure of the synaptonemal complexes, the structure of centromeres and knobs, the continuity of the synaptonemal complex through centromeres and interstitial knobs, centromere fusion, knob fusion and the mode and amount of telomere attachment to the nuclear envelope are consistent features of female and male meiocytes. The absence of large vacuoles within the nucleoli of megasporocytes is the most conspicuous difference between the two types of meiocytes. The mean total synaptonemal complex length of three female nuclei was 413 μm and not significantly different from total bivalent length in reconstructed male nuclei. The size of female and male pachytene nuclei was likewise similar. The plant studied carried a large terminal knob on the short arm of bivalent 9. According to RHOADES (42), the presence of this knob causes a sex difference in crossing-over in the short arm of bivalent 9, reducing the female crossing-over value between the genes C and Wx. The female synaptonemal complex length of the short arm of chromosome 9 was found to be 66% of that of the male. No significant sex difference in synaptonemal complex length was detectable for the long arm of chromosome 9 or for chromosome 6. It is proposed that the sex difference in crossing-over frequency is causally related to the difference in synaptonemal complex length.