The C-group pachytene bivalent with a locus characteristic for parachromosomally situated particulate bodies (parameres): a provisional map in human males

Organization of repetitive DNA sequences at pachytene chromosomes of gilthead seabream Sparus aurata (Pisces, Perciformes)

A method of preparing two-dimensional surface spreads of fish synaptonemal complexes (SCs) associated with fluorescent in-situ hybridization is described. This technique permits a novel approach to the analysis of chromatin organization and the construction of physical maps at meiosis, since surface-spread pachytene chromosomes are several times the length of metaphase chromosomes and the decondensed chromatin loops are attached to the lateral elements of the SC. We have applied this technique to analyze the location and organization of three different repetitive DNA sequences, rDNA, an EcoRI satellite DNA of the Sparidae family and telomere DNA in the gilthead seabream Sparus aurata. Our observations indicate that, depending on the type of sequence, the chromatin has different properties with regard to anchorage to the SC.

Combined immunocytogenetic and molecular cytogenetic analysis of meiosis I human spermatocytes

We have used a combination of immunocytogenetic and molecular cytogenetic technology on human spermatocytes to investigate (1) meiosis I chromosome pairing, and (2) organization of synaptonemal complex (SC)-associated chromatin with respect to whole chromosome paints, unique DNA sequences and repetitive DNA of heterochromatic blocks, centromeres and telomeres. It is evident that synapsis normally starts at the termini of homologues. In general, synapsis proceeds synchronously from termini towards the centre of bivalents without any indication of interstitial initiation. Some aberrant meiosis I spermatocytes showed asynchronous pairing, demonstrating not only large differences in the degree of SC formation between bivalents, but also chromosome alignment without synapsis as well as clear interstitial synaptic initiation. It may be the case that alignment normally takes place along the entire length of homologues before synapsis occurs and that the potential for synaptic initiation exists along the length of chromosomes. Telomeric sequences were seen tightly associated with the SCs, as might be expected considering their kinetic properties in relation to the nuclear membrane. Other repetitive DNA, i.e. centromeric alpha-satellites and classical satellites of the heterochromatic blocks 1qh and 9qh, were all found to form loops that are associated with SCs only at their bases. A unique DNA cosmid probe (21q22.3) was found to produce a hybridization pattern consisting of spots located outside SC. The fluorescence in situ hybridization (FISH) signals of these spread DNA sequences have a granular appearance, probably reflecting the pattern of coiling and chromatin condensation of the target DNAs.

The volumes and morphology of human chromosomes in mitotic reconstructions

Ten unpretreated normal human male fibroblast cells in mitosis were completely reconstructed from micrographs of between 82 and 119 consecutive serial sections. All 46 chromosomes and their centromeres could be reconstructed in every cell. Measurements of chromosome volumes and centromere indices are presented. The data enabled allocation of all chromosomes to their groups (A to G), and chromosomes 1, 2, 3, 6, 9, 16, 17, 18 and Y were individually identified. Comparisons with published karyotypes showed that volume measurements correlated well with measurements of DNA content and chromosome length. Centromere indices also showed good correlation, but the acrocentric chromosomes were more unequally armed than found by length measurement. Secondary constrictions at the nucleolar organising region were visible on about a third of the acrocentric chromosomes. One chromosome of the C group, number 9, had a diffuse subcentromeric region (DSR) on the long arm, at the position of the constitutive heterochromatin and (in meiotic cells) the paramere.

Electron microscopy of the parameres formed by the centromeric heterochromatin of human chromosome 9 at pachytene

The structure and arrangement of the parameres, which are small bodies representing part of the heterochromatin of human chromosome 9 at pachytene, were studied using transmission and scanning electron microscopy. Parameres appear to be denser than other parts of the chromosomes but have a similar fibrous substructure. The most common arrangement is clusters on the axis of the bivalent, consisting of varying numbers of parameres of variable size. The parameres are joined to each other and to the rest of the chromosome by interconnecting fibres. No evidence was obtained for the organisation of parameres into paired lateral loops, as proposed by previous workers using light microscopy. The combination of osmium impregnation of pachytene chromosomes with a backscattered electron detector in the scanning electron microscope produced very clear images of the pattern of chromomeres. This procedure may prove valuable for pachytene mapping of chromosomes because of the greatly improved resolution compared with light microscopy.

Specific staining of 9h in human somatic interphase cells by D 287/170

Somatic interphase cells from males and females with normal karyotypes and with variants of the heterochromatic regions on chromosomes 9 and Y were stained with the fluorochrome D 287/170. The results showed that only 9h retained the ability to stain with D 287/170 in the interphase state, whereas 15ph and Yqh lost the specific staining pattern seen in metaphase. The number and size of the specific stained interphase bodies correlated with the ploidy of the cell population and the size of the 9h as seen in metaphase.

A simple reproducible method for prometaphase chromosome analysis

A method is described for the analysis of chromosomes in prophase and early metaphase. It involves culturing the lymphocytes in medium RPMI-1640, supplemented with 10% autologous plasma instead of fetal bovine serum. Living cells are treated with actinomycin D and colcemid for 1 h prior to harvest and harvested early at 65 h of incubation, using a hypotonic solution formulated by Ohnuki (1968). The method has been tested on several hundred clinical samples on a routine basis. On average, 30% of the dividing cells were in prometaphase.

Aspects of evaluation, significance, and evolution of human C-band heteromorphism

The C-band heteromorphism may be evaluated in different forms. The results obtained from classification are easily influenced by subjective factors, and the conclusions of such types of data are acceptable only if they are well matched with a control. The length measurement is simple to obtain, and a quantitative presentation of the data, with correction for the contraction stage of the chromosomes, is considered the most efficient method to evaluate the C-band size heteromorphism. Excluding the acrocentrics, whose short arms present a complex heteromorphism, and the chromosome Y, whose variable C band is terminal, all others present C-band location heteromorphism except pair 16. It is possible to multiply the detectable heteromorphisms in some bands by using diverse staining methods. The present state of knowledge about the role of heterochromatin in the cell is analyzed, as is the effect of C-band variability on the phenotype, the reproductive fitness, and the individual viability. Although a great amount of data is available, no result can be considered definitive as yet. Aspects in which the use of C-band heteromorphisms are profitable are considered.

Structural organization of the heterochromatic region of human chromosome 9

Giemsa-11, G-banding and Lateral Asymmetry staining techniques were used to define the substructure of the C-band heterochromatin of human chromosome 9, in a sample of 108 different chromosomes 9, from 54 individuals. In this sample, the juxtacentromeric portion of the C-band region stained positive by the G-banding technique while Giemsa-11 delineated a more distally located block. Examination of the pericentric inversions generally revealed that the entire C-band region is changed with the substructural organization left intact; i.e. the G-band is proximal, the G-11 distal to the centromere. The "partial pericentric inversions" were found to have larger than average amounts of G-band heterochromatin on the short arm. The G-11 staining was in its usual position on the long arm with none on the short arm. Such apparent inversions therefore may not represent true inversions. Long heterochromatic regions frequently had a segmented appearance when stained with G-11; there was a dark G-band within the pale heterochromatic region when stained with the G-banding technique which corresponded in location to the achromatic gap produced by G-11. This extra G-band may have been derived from the juxtacentromeric G-band by processes analogous to unequal crossing over. Simple lateral asymmetry was consistently present only in the G-band heterochromatin of those chromosomes 9 containing large blocks of G-band positive material. Examination of the portion of the C-band which would correspond to the G-11 positive material revealed no consistent patterns of asymmetry. Usually both strands were heavily stained and symmetrical but occasionally there were light areas present on one strand suggestive of compound lateral asymmetry.

Study of the human male meiosis. I. G-banding in pachytene bivalents

Results obtained from a meiotic study of 250 pachytene cells from four normal human males are presented. G-banding patterns for pachytene bivalents, obtained using trypsin treatment, are also presented; a comparative study between G-banding patterns of pachytene bivalents and G-banding patterns of mitotic chromosomes, and a study of chromomere counting and distribution, have also been made.

Pachytene mapping of the C9 and acrocentric bivalents in the human oocyte

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 numbers 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.

Identification of pachytene bivalents in human male meiosis using G-banding technique

G-banding of human pachytene bivalents is obtained using trypsin digestion. Each of the 22 autosomal bivalents is clearly identified. Such an identification leads to construction of the human pachytene map. Our results show the equivalence between the G-band patterns of mitotic chromosomes and meiotic bivalents. The G-band patterns of mitotic-meiotic chromosomes also correlate closely with the chromomere sequence of pachytene bivalents. Thus, study of chromomeres should constitute an excellent approach to comprehension of G-banding mechanism.