Study of human male meiosis II-Q-banding in pachytene bivalents

Summary In continuation of the research on male human meiosis within the study of pachytene bivalents, results from the analysis of 125 cells are presented. The aim of this work is to establish Q-banding patterns and make a detailed study of chromosomere counting and distribution. To obtain Q-bands Quinacrine and Pseudoisocyanine staining techniques have been used.     

Karyotype,heterochromatin content and meiotic features ofPoecilocera picta (Orthoptera,Acrididae)

Cytological study of three distinctly separated populations ofPoecilocera picta revealed a chromosome number of 2N = 18 + XO/ XX. Except for the hemizygosity of a procentric heterochromatic block in the M₆ pair of the Bangalore population, the basic karyotype of the three populations is markedly similar. The autosomal karyotype formula is 2Lt + 4Mt + 1 Mst + 2S st and the telocentric X chromosome is the longest of the complement. All bivalents at pachytene carried procentric heterochromatic blocks. The M₄ is the nucleolus organiser with the NOR region situated interstitially but proximal to the centromere. About 11 μm (4%) of the total (290 μm) autosomal pachytene complement is heterochromatic; a major portion of it is contributed by the S₉ pair which is mostly heterochromatic. Chiasmata are localized proximally and distally and in the S₉ pair their formation is confined to the short procentric euchromatic segment of the long arm. Female meiosis did not reveal any chromomere pattern at pachytene and, unlike in the male, the sex bivalent in the female is indistinguishable from the autosomal bivalents. G- and C-banding patterns in males showed procentric bands in all the chromosomes. In addition there are eight telomeric and two interstitial bands which are C negative. The S₉ pair showed only two bands. The G-banding pattern of the sex chromosome in meiosis showed only a centric band while the heterochromatic body of the facultatively heterochromatic X remained G negative.     

Synapsis in Robertsonian heterozygotes and homozygotes of Dichroplus pratensis (Melanoplinae, Acrididae) and its relationship with chiasma patterns

Dichroplus pratensis has a complex system of Robertsonian rearrangements with central-marginal distribution; marginal populations are standard telocentric. Standard bivalents show a proximal-distal chiasma pattern in both sexes. In Robertsonian individuals a redistribution of chiasmata occurs: proximal chiasmata are suppressed in fusion trivalents and bivalents which usually display a single distal chiasma per chromosome arm. In this paper we studied the synaptic patterns of homologous chromosomes at prophase I of different Robertsonian status in order to find a mechanistic explanation for the observed phenomenon of redistribution of chiasmata. Synaptonemal complexes of males with different karyotypes were analysed by transmission electron microscopy in surface-spread preparations. The study of zygotene and early pachytene nuclei revealed that in the former, pericentromeric regions are the last to synapse in Robertsonian trivalents and bivalents and normally remain asynaptic at pachytene in the case of trivalents, but complete pairing in bivalents. Telocentric (standard) bivalents usually show complete synapsis at pachytene, but different degrees of interstitial asynapsis during zygotene, suggesting that synapsis starts in opposite (centromeric and distal) ends. The sequential nature of synapsis in the three types of configuration is directly related to their patterns of chiasma localisation at diplotene-metaphase I, and strongly supports our previous idea that Rb fusions instantly produce a redistribution of chiasmata towards chromosome ends by reducing the early pairing regions (which pair first, remain paired longer and thus would have a higher probability of forming chiasmata) from four to two (independently of the heterozygous or homozygous status of the fusion). Pericentromeric regions would pair the last, thus chiasma formation is strongly reduced in these areas contrary to what occurs in telocentric bivalents.     

Electron microscopy of meiosis in Drosophila melanogaster females

Complete reconstruction of the synaptonemal complex in 12 pachytene (defined here as that stage in which the synaptonemal complex is continuous throughout the bivalents) nuclei from one wild-type germarium has permitted the following observations. 1) Drosophila melanogaster bivalents at pachytene exhibit a chromocentral arrangement; the pericentric heterochromatin of all bivalents lies in one region of the nucleus, the chromocenter. Telomeric ends do not appear to abutt the nuclear envelope. 2) Synaptonemal complex is present in the pericentric heterochromatin; however, it is morphologically distinct from that present in the euchromatic portion of the bivalents. 3) Length of the synaptonemal complex of the bivalent arms is greatest at early pachytene; the synaptonemal complex then becomes progressively shorter. Minimum length is approximately one-half of the maximum. 4) Decrease in length of synaptonemal complex is accompanied by an increase in thickness. Reconstruction of 20 pachytene nuclei from an additional 8 germaria suggests that these observations are typical. Correlations between these cytological observations and genetic observations (e.g., patterns of crossing-over) are discussed.     

Preparation and analysis of spermatocyte meiotic pachytene bivalents of pigs for gene mapping

Well-spread meiotic pachytene bivalents were obtained by using the prolonged hypotonic treatment combined with high chloroform Carnory's fixative solution from cells of the testes of domestic pigs. Comparison in the division index and length of pachytene bivalents with metaphase chromosomes showed that those of the former are 5 times higher and 3.42(1.87-5.98) times longer than those of the latter. Comparative studies on chromomere maps of bivalents and mitotic chromosomal G-bands were conducted by using the chromosome 12 as a example. Sex vesicle and various shapes of synaptic sex chromosomes have been observed. Two-color PRimed IN Situ (PRINS) labeling has been conducted successfully on pachytene bivalents of pigs.     

Preparation and analysis of spermatocyte meiotic pachytene bivalents of pigs for gene mapping

Well-spread meiotic pachytene bivalents were obtained by using the prolonged hypotonic treatment combined with high chloroform Carnory's fixative solution from cells of the testes of domestic pigs. Comparison in the division index and length of pachytene bivalents with metaphase chromosomes showed that those of the former are 5 times higher and 3.42(1.87-5.98) times longer than those of the latter. Comparative studies on chromomere maps of bivalents and mitotic chromosomal G-bands were conducted by using the chromosome 12 as a example. Sex vesicle and various shapes of synaptic sex chromosomes have been observed. Two-color PRimed IN Situ (PRINS) labeling has been conducted successfully on pachytene bivalents of pigs.     

Why plant chromosomes do not show G-bands

Summary Giemsa techniques have refused to reveal G-banding patterns in plant chromosomes. Whatever has been differentially stained so far in plant chromosomes by various techniques represents constitutive heterochromatin (redefined in this paper). Patterns of this type must not be confused with the G-banding patterns of higher vertebrates which reveal an additional chromosome segmentation beyond that due to constitutive heterochromatin. The absence of G-bands in plants is explained as follows: 1) Plant chromosomes in metaphase contain much more DNA than G-banding vertebrate chromosomes of comparable length. At such a high degree of contraction vertebrate chromosomes too would not show G-bands, simply for optical reasons. 2) The striking correspondence of pachytene chromomeres and mitotic G-bands in higher vertebrates suggests that pachytene chromomeres are G-band equivalents, and that this may also be the case in plants. G-banded vertebrate chromosomes are on the average only 2.3 times shorter in mitosis than in pachytene; the chromomeric pattern therefore still can be shown. In contrast, plant chromosomes are approximately 10 times shorter at mitotic metaphase; their pachytene-like arrangement of chromomeres is therefore no longer demonstrable.     

Location and variation of the constitutive heterochromatin in Petunia hybrida

The location of heterochromatin in the chromosomes of Petunia hybrida (2n=14) is presented. C-banded mitotic metaphase chromosomes and carmine-stained pachytene bivalents have been studied. It is shown that the heterochromatin is predominantly located near the centromeres and at the secondary constrictions of the satellite chromosomes. The distribution of chromomeres in pachytene bivalents also reveals that heterochromatin is not restricted to distinct blocks, as is the case in tomato, but occurs in smaller chromomeres which gradually decrease in size towards the ends. Conspicuous telomeres have not been observed. Both C-banding technique and pachytene analysis demonstrate large variation of heterochromatin between different lines of Petunia. The study of pachytene morphology has been hampered by a high degree of non-specific stickiness of the bivalents. Both techniques prove to be unsuitable tools for large-scale chromosome identification of Petunia lines.     

Mapping of pachytene bivalents of female codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae)

Spread pachytene nuclei of codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae) females of a Syrian strain (SY) were used to investigate chromomere patterns of chromosome bivalents and determine their length. The karyotype of female codling moths consists of 28 chromosome bivalents, of which seven are clearly distinguishable using chromosome length and the number and size of the chromomeres in the pachytene stage. One autosome bivalent has two nucleolar organizing regions (NORs) that are located at the opposite ends of the chromosome and appear as distinct structural landmarks. In female codling moths, the WZ sex chromosome bivalent was easily identified in pachytene oocytes according to the heterochromatic thread of the W chromosome. This study contributed to the knowledge and identification of pachytene chromosomes of female codling moths.     

Complete autosomal chromomere maps of human early and mid/late pachytene spermatocytes.

Specific identification of each bivalent of human spermatocytes at early and mid/late pachytene was obtained from chromomere maps developed by analyzing complete, well-spread cells from five subjects aged 31-49. The total number of chromomeres on the early autosomal bivalents was 499 and 386 at the mid/late stage. Regional analysis revealed more chromomeres at early pachytene than at mid/late, with 12 exceptions having equal numbers. Correspondence of chromomeres with mitotic prometaphase G-bands was found in all bivalents. Four chromomeres were found in region 1 of the 9q at early pachytene and two at mid/late. Differences between the map for chromosome no. 10 observed in this study and others were noted.     

Model of chromosome associations in Mus domesticus spermatocytes

Understanding the spatial organization of the chromosomes in meiotic nuclei is crucial to our knowledge of the genome's functional regulation, stability and evolution. This study examined the nuclear architecture of Mus domesticus 2n=40 pachytene spermatocytes, analyzing the associations among autosomal bivalents via their Centromere Telomere Complexes (CTC). The study developed a nuclear model in which each CTC was represented as a 3D computer object. The probability of a given combination of associations among CTC was estimated by simulating a random distribution of 19 indistinguishable CTC over n indistinguishable "cells" on the nuclear envelope. The estimated association frequencies resulting from this numerical approach were similar to those obtained by quantifying actual associations in pachytene spermatocyte spreads. The nuclear localization and associations of CTC through the meiotic prophase in well-preserved nuclei were also analyzed. We concluded that throughout the meiotic prophase: 1) the CTC of autosomal bivalents are not randomly distributed in the nuclear space; 2) the CTC associate amongst themselves, probably at random, over a small surface of the nuclear envelope, at the beginning of the meiotic prophase; 3) the initial aggregation of centromere regions occurring in lepto-zygotene likely resolves into several smaller aggregates according to patterns of preferential partitioning; 4) these smaller aggregates spread over the inner face of the nuclear envelope, remaining stable until advanced stages of the meiotic prophase or even until the first meiotic division.     

Pachytene mapping of the C 9 and acrocentric bivalents in the human oocyte

Summary Provisional maps are presented for all acrocentric bivalents and bivalent 9, according to their chromomere patterns at pachytene in the human oocyte. Each G band is subdivided into several sub-bands whose number varies according to the degree of chromosomal compacting. Chromomere number and sequence are in basic agreement with those observed in late prophase mitotic chromosomes. Thus, metaphase G bands of mitotic chromosomes result from progressive compressing together of smaller chromomeres whose individuality disappears as chromosomal condensation increases with progression of prophase.     

粳稻三体的染色体G—显带鉴定

采用有丝分裂染色体的G-显带技术,对供试的6个三体的额外染色体进行了鉴定。结果表明:A型、B型、C型、D型、E型和H型三体的额外染色体分别为K5、K6、K12、K7、K8和K10。用不同的分裂时期的细胞所鉴定出的结果完全一致。与过去所用的三体鉴定的方法相比较,利用G-显带技术鉴定三体的方法具有准确性高,稳定性和重复性好以及简便易行的优点。     

Damaging effect of antibiotics on the structure of synaptonemal complexes of meiotic chromosome of mice

The structure of synaptonemal complexes (SCs) of chromosomes of mouse primary spermatocytes were studied using electron microscopy on days 1, 10, and 36 after the completion of per os administration of drugs belonging to three groups of antibiotics: tetracyclins, macrolides, and fluoroquinolones. The antibiotics were administered to mice during ten days. At the substages of early and middle pachytene, heteromorphic SC bivalents and fragments of chromosome-core elements were detected in spermatocytes at all times studied after the administration of the antibiotics of three groups. As cells passed through the period from early to middle pachytene, the number of cells containing heteromorphic SC bivalents and the fragments of chromosome cores gradually decreased, which could be an indication of selection of cells with chromosomal aberrations. A high level of associations between the X chromosome and autosome bivalents (including heteromorphic ones) also favors this suggestion. A gradual decrease in the number of chromosomal aberrations was detected, as time elapsed from the completion of antibiotics administration. The study of sperm obtained from epididymises of males did not reveal significant differences in both morphology and motility of sperm between males of the control and experimental groups.     

家猪减数分裂粗线期二价体与有丝分裂中期染色体的比较研究

以性成熟公猪睾丸和外周血为材料,采用长低渗、高氯仿卡诺固定液固定和外周血细胞培养制备减数分裂粗线期二价体和有丝分裂中期染色体,通过对二价体和有丝分裂中期染色体分裂指数和长度的比较研究,发现二价体的分裂指数和长度分别是有丝分裂中期染色体的5倍和3．42倍（1．87～5．98）;同时以12号染色体为例,比较了二价体上的染色粒结构带与有丝分裂中期染色体G－带,表明染色粒结构带比中期染色体G－带纹丰富,而与早中期G－带带织吻合。     

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, ellipsoïdal 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.     

Differential elongation of autosomal pachytene bivalents related to their DNA content in human spermatocytes

The establishment of the complete karyotype of human pachytene spermatocytes reveals differences in stretching of chromosomes between meiosis and mitosis. Bivalents or specific regions of bivalents which exhibit many R-bands are particularly elongated. In mitotic chromosomes, the DNA contained in such bands is known to be early replicating. The study of variations in the total length and the centromeric index of bivalent 1 suggests that differential elongation of pachytene bivalents is a premeiotic event, taking place during the last DNA replication.     

Damaging Effect of Antibiotics on the Structure of Synaptonemal Complexes of Meiotic Mouse Chromosomes

The structure of synaptonemal complexes (SCs) of chromosomes of mouse primary spermatocytes were studied using electron microscopy on days 1, 10, and 36 after the completion of per os administration of drugs belonging to three groups of antibiotics: tetracyclins, macrolides, and fluoroquinolones. The antibiotics were administered to mice during ten days. At the substages of early and middle pachytene, heteromorphic SC bivalents and fragments of chromosome-core elements were detected in spermatocytes at all times studied after the administration of the antibiotics of three groups. As cells passed through the period from early to middle pachytene, the number of cells containing heteromorphic SC bivalents and the fragments of axial cores gradually decreased, which could be an indication of selection of cells with chromosomal aberrations. A high level of associations between the X chromosome and autosome bivalents (including heteromorphic ones) also favors this suggestion. A gradual decrease in the number of chromosomal aberrations was detected, as time elapsed from the completion of antibiotics administration. The study of sperm obtained from epididymises of males did not reveal significant differences in both morphology and motility of sperm between males of the control and experimental groups.     

Mechanisms of chromosome banding

The G-band patterns of mitotic metaphase chromosomes No. 1 and 2 of the Chinese hamster cells correlate closely to the chromomere patterns of the meiotic pachytene bivalents. This is interpreted to indicate that the regions of centromeric and intercalary heterochromatin, which are more tightly condensed or more tightly packaged during interphase, tend to remain so during meiosis and mitosis.     

A search for the synaptic adjustment phenomenon in maize

It has recently been suggested from several laboratories that complex synaptic configurations (required for homologous synapsis in the presence of heterozygosity for chromosome rearrangements, or resulting from multivalent formation in polyploids, or even resulting from interlocking of normal bivalents) may be formed initially, but are altered by dissolution of the central element of the synaptonemal complex followed by its reinstatement in such a way that only free bivalents, typical of normal sequence homozygotes in diploids, are usually found at late pachytene. It has been suggested that the synaptic adjustment inferred may be a process of widespread occurrence. Maize microsporocytes heterozygous for a paracentric inversion were studied at early and late pachytene and also at early diplotene. Clear remnants of loop configurations typical of homologous synapsis of the inverted region were found in a number of cells at early diplotene, and synaptic failure of the inverted region was common at both early and late pachytene. In maize microsporocytes a synaptic adjustment process comparable to that which has been reported in mammals seems to be absent.