NOR associations with heterochromatin

Associations between nucleolus organizer regions (NORs) and non-acrocentric chromosomes were scored in 2,800 metaphase spreads from PHA-stimulated lymphocyte cultures (48 h) from 14 individuals. The preparations were both silver stained and C-banded. In order to calculate the expected values for associations, the ratio of heterochromatin length to euchromatin length was established for each subject. Individual C-band lengths and centromeric lengths were also determined. When silver connective (SC) associations with heterochromatin were compared to SC associations with euchromatin, the number of associations with heterochromatin was significantly greater than expected (P less than 0.000001) for each subject. The SC associations were not distributed randomly over the heterochromatin of the non-acrocentrics. Chromosomes 1 and 2 had significantly more than expected. Chromosomes 17, 18, 19, 20, and the Y had fewer than expected. NOR associations with euchromatic segments also showed a nonrandom pattern of distribution.     

Evidence for a highly differentiated sex chromosome heteromorphism in the salamander Necturus maculosus (Rafinesque)

The mitotic chromosomes of the neotenic (sensu Gould, 1977, and Alberch et al., 1979) salamander Necturus maculosus (Rafinesque) have been examined using a C-band technique to demonstrate the distribution of heterochromatin. The C-banded mitotic chromosomes provide evidence of a highly differentiated XY male/XX female sex chromosome heteromorphism, in which the X and Y chromosomes differ greatly in size and morphology, and in the amount and distribution of C-band heterochromatin. The X chromosome represents one of the largest biarmed chromosomes in the karyotype and is indistinguishable from similar sized autosomes on the basis of C-band heterochromatin. The Y chromosome, on the other hand, is diminutive, morphologically distinct from all other chromosomes of the karyotype, and is composed almost entirely of C-band heterochromatin. The discovery of an X/Y chromosome heteromorphism in this species is consistent with the observation by King (1912) of a heteromorphic spermatogenic bivalent. Karyological and phylogenetic implications are discussed.     

中国两种波腿蝗（蝗总科：癞蝗科）染色体C带核型研究

报道中国两种波腿蝗的染色体C带核型,结果表明：红胫波腿蝗Asiotmethis zacharjini (Bei-Bienko, 1926) 2n ♂ =18, neo-X为亚中着丝粒染色体,其他均为近端着丝粒染色体,染色体除强染的着丝粒C带,S8染色体具强染端部C带带纹,neo-Y染色体还具有一条宽的弱染的近着丝粒端居间C带,性别决定机制是neo-XY ♂型,该种染色体组成和性别决定机制在我国癞蝗中为首次报道,蓝胫波腿蝗Asiotmethis jubatus (Uvarov, 1926) 2n＝19♂,均为近端着丝粒染色体,仅具有明显强染的着丝粒C带,性别决定机制是XO ♂型;两种波腿蝗的异染色质含量存在显著性差异（α=0.05）。     

C-band length variability and reproductive wastage

Summary The possible influence of total Y chromosome length and the C-band size variability of chromosomes 1, 9, 16, and Y, on reproductive wastage was investigated. One hundred couples with recurrent reproductive wastage and 106 control couples with at least two healthy children and no miscarriages were cytogenetically studied. Total Y chromosome length was evaluated as the Y/F index and the C-band size was analyzed quantitatively according to the linear measurement method of Baliek et al. (1977). The different degrees of mitotic contraction were corrected on the basis of the linear correlation found between heterochromatin and euchromatin length. Statistical comparison between results of Y chromosome from both samples demonstrated, in the test group, an increase in the mean value of the Y/F index, but the increase of Y C-band length did not reach significance. In addition mean values of C-band length on chromosomes 1, 9, and 16 in couples from the test group and especially those who had had two or more abortions, were lower than those in the controls. Among the latter the frequency of chromosomes included in the category of very large heterochromatin size is higher. However these length differences have been demonstrated only in specific subgroups, and in each one for a different chromosome. Our results indicated that Y chromosome length as well as C-band size variabilities are not directly related to reproductive wastage.     

Length of human C-bands in relation to the degree of chromosome condensation

Summary The C-band length of human chromosome 1 in prophase and prematurely condensed interphase chromosomes is relatively shorter than in metaphase chromosomes. However, even in chromosomes with the same degree of contraction the absolute length of the C-band varies considerably. This allocyclic behaviour of human constitutive heterochromatin has to be kept in mind if C-bands of different individuals are compared.Sponsored by the Deutsche Forschungsgemeinschaft (Sp 144)     

Unequal crossing over and heterochromatin exchange in the X-Y bivalents of the deer mouse,Peromyscus beatae

Differences in length of the heterochromatic short arms of the X and Y chromosomes in individuals ofPeromyscus beatae are hypothesized to result from unequal crossing over. To test this hypothesis, we examined patterns of synapsis, chiasma formation, and segregation for maleP. beatae which were either heterozygous or homozygous for the amount of short-arm sex heterochromatin. Synaptonemal complex analysis demonstrated that mitotic differences in heterochromatic shortarm lengths between the X and Y chromosomes were reflected in early pachynema as corresponding differences in axial element lengths within the pairing region of the sex bivalent. These length differences were subsequently eliminated by synaptic adjustment such that by late pachynema, the synaptonemal complex configurations of the XY bivalent of heterozygotes were not differentiable from those of homozygotes. Crossing over between the heterochromatic short arms of the XY bivalent was documented by the routine appearance of a single chiasma in this region during diakinesis/metaphase I. Sex heterochromatin heterozygotes were characterized by the presence of asymmetrical chiasma between the X and Y short arms at diakinesis/metaphase I and sex chromosomes with unequal chromatid lengths at metaphase II. These data corroborate our hypothesis on the role of unequal crossing over in the production and propagation of X and Y heterochromatin variation and suggest that, in some cases, crossing over can occur during the process of synaptic adjustment.     

Distribution of C-band heterochromatin in the ZW sex chromosomes of European and American eels (Anguillidae, Teleostomi)

The ZW sex chromosomes of the European eel, Anguilla anguilla, and the American eel, A. rostrata, were examined with C-band and fluorescent staining to demonstrate the C-band heterochromatin. The W as well as Z chromosomes in both species are C-band negative except for a small amount of C-band heterochromatin in the centromeric region, in contrast to the W or Y elements of most other vertebrates. No fluorescing W-associated body is evident either in interphase nuclei or in metaphase plates. The ZW chromosomes of the two species have substantially similar size, morphology, and patterns of C-band heterochromatin. Karyologic and evolutionary implications are discussed.     

Sister chromatid exchange points in the heterochromatin and euchromatin regions of Chinese hedgehog chromosomes

Summary The Chinese hedgehog has a diploid chromosome number of 48 in which there are eleven pairs of telo- or subtelocentric autosomes, twelve pairs of meta- or submetacentric autosomes, a metacentric X chromosome and a telocentric Y chromosome. The heterochromatin is almost completely distributed in five large distal segments of chromosomes nos. 9 to 12 and no. 18. There is no positive C-band in the centromeres of the chromosomes except for the X chromosome which has a small, weakly stained C-band in the centromere. In Chinese hedgehog cells 52.1% of SCEs are found at the junction between the euchromatin and the heterochromatin, 39.5% in the heterochromatin and 8.4% in the auchromatin. The SCE number per unit C-band is double the SCE number per unit euchromatin. The SCE rate in the heterochromatin or euchromatin regions is not proportional to their chromosome length and can be quite different between different pairs of the chromosomes. Our results indicate that there is a non-uniform distribution of the SCEs in the Chinese hedgehog cells.     

C-band polymorphisms in exotic inbred strains of mice: a method for mapping centromeric ends of chromosomes.

The major satellite DNA of Mus musculus appears as a pericentromeric heterochromatin block in all chromosomes but the Y. While C-banding readily reveals the presence of this heterochromatin block, there is considerable polymorphism in C-band size among the chromosomes and among different subspecies. We have studied the distribution of C-band size differences in the chromosomes of 15 exotic inbred laboratory strains and substrains derived from wild populations of different subspecies of M. musculus. The variation in C-band size among these inbred strains can serve as a useful codominant cytological marker for estimating recombinational distances between the centromere and proximal genes in linkage crosses.     

Quantitative analysis of C bands in chromosomes 1, 9, and 16 of Brazilian Indians and Caucasoids

Summary Densitometric C-band measurements in chromosomes 1, 9, and 16 of 394 Indians and 40 Caucasoids living in Brazil are reported. No significant intratribal variability in the average length of these regions was observed, and the intertribal variation showed no consistent patterns. But the Caucasoids always presented lower means. The relative C-band sizes of these three chromosomes, however, were very similar in Indians and Caucasoids. The indices of heteromorphism displayed analogous results; only in chromosome 16 are they dissimilar in these two ethnic groups. An unexpected sex difference was observed in the C-band sizes of this chromosome, females uniformly presenting higher averages than males. Centromeric heterochromatin appeared in 6% and 9% respectively of the short arms of chromosomes 1 and 9 among the Caucasoids, while among the Indians its prevalence was 2% in both chromosomes.     

Further evidence of intraspecific heterochromatin variants in Drosophila melanogaster

The analysis of inter-strain heterochromatin polymorphism in mitotic chromosomes of Drosophila melanogaster was extended to some stocks characterized by chromosomal mutations. In particular, the present investigation aims to compare, in the same cell, the quinacrine banding of two different Y chromosomes of male hybrids derived from crosses using special stocks. A direct comparison of homologous heteromorphic chromosomes in F₁ hybrids provided additional evidence of differences in the fluorescence pattern of the Y chromosome, as well as in the length of the heterochromatin segment of the X chromosome.     

Comparison of two measuring methods for the evaluation of C-heterochromatin in human chromosomes

Summary In this study two different methods for evaluating the size of the C heterochromatin blocks of human chromosomes 1, 9, 16, and Y were compared. The first method measured the lengths of both the euchromatin and the C heterochromatin parts of the p and q arms of chromosomes 1, 9, 16, and Y. The second method analyzed the same chromosome segments, but by measuring the areas.In the comparison, the relative C heterochromatin value (length or surface) of each chromosome, the mean for each individual, the standard deviation, and the coefficient of variation were taken into account. It is proposed that the best estimation for the size of a C heterochromatin segment is the ratio of its length to the total length of the chromosome; accurate estimation requires at least 20 metaphases.     

Regional differences in immunostainability of isolated metaphase chromosomes of Indian muntjac with anti-Z-DNA antibody

The distribution of Z-form DNA along the length of metaphase chromosomes of Indian muntjac was studied by indirect immunofluorescence procedures using an antibody specific to the Z-DNA conformation. Several fixation conditions were compared for reproducible detection of Z-DNA in isolated metaphase chromosomes. Fixation of chromosomes with 45% acetic acid alone gave reproducible reactivity with the antibody. When fixation was done either with Carnoy's solution (3:1 methanol:acetic acid) or with 75% alcohol alone, the antibody binding was at background level. Acetic acid-fixed chromosomes exhibited intense fluorescence both at C-band heterochromatin and at nucleolus organizer regions (NORs). The euchromatic regions had weakly, but clearly, stained bands, which were quite similar to the chromomycin A₃ R-bands. After treatment with topoisomerase I, the immunofluorescence at NORs and R-bands disappeared, but only a slight decrease in immunofluorescence intensity was observed at C-band regions. We suggest that this difference in the immunoreactivity of NORs and R-bands from C-bands reflects a difference in gene activity among these regions. Possible molecular mechanisms involved in Z-DNA immunoreactivity are discussed, based on SDS-polyacrylamide gel electrophoretic analysis of chromosomal proteins after extraction of metaphase chromosomes with different fixative solutions.Abbreviations PI propidium iodide - NOR(s) nucleolus organizer region(s) - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis Deceased, April 23, 1988     

The segregation of C-band polymorphisms on chromosomes 1, 9, and 16.

Eleven normal families with at least four children were studied cytogenetically using the C-band technique to identify polymorphisms in the constitutive heterochromatin of chromosomes 1, 9 and 16. Thirteen individuals showed one or more variants in such chromosomes. The analysis of the segregation ratios in the 35 offspring of these 13 individuals showed that these marker chromosomes generally segregated according to the expected 50:50. However, one of these variants, chromosome no. 9 with an increased heterochromatin block in the secondary constriction, has an apparently preferential segregation, when the findings from this study are combined with those of other authors.     

The chromosomes of two Drosophila races: D. nasuta nasuta and D. n. albomicana

Heterochromatin distribution and differentiation in metaphase chromosomes of two morphologically identical Drosophila races, D. nasuta nasuta and D. n. albomicana, have been studied by C- and N-banding methods. — The total heterochromatin values differ only slightly between these races. However, homologous chromosomes of the two Drosophila forms show striking differences in the size of heterochromatin regions and there is an alternating pattern in D. n. nasuta and D. n. albomicana of chromosomes which contain more, or respectively less heterochromatin than their counterparts in the other race. — Three different N-banding patterns could be obtained depending on the conditions of the method employed: One banding pattern occurs which corresponds to the C-banding pattern. Another pattern is the reverse of the C-band pattern; the euchromatic chromosome regions and the centromeres are stained whereas the pericentric heterochromatin regions remain unstained. In the Y chromosomes of both races and in chromosome 4 of D. n. albomicana, however, the heterochromatin is further differentiated. In the third N-banding pattern only the centromeres are deeply stained. Furthermore, between the races, subtle staining differences in the pericentric heterochromatin regions can be observed as verified in F₁ hybrids. On the basis of C- and N-banding results specific aspects of chromosomal differences between D. n. nasuta and D. n. albomicana are discussed.Dedicated to Prof. W. Beermann on the occasion of his 60th birthday     

Triploidy in Hochstetter's frog,Leiopelma hochstetteri,from New Zealand

Abstract

Autotriploidy is described in a female of the endemic New Zealand frog Leiopelma hochstetteri. This frog was found to have 3n=33 chromosomes plus 2 supernumerary chromosomes. All the chromosomes in the karyotype of this species contained C-band heterochromatin at the centromeres. A prominent C-band was found to be associated with a secondary constriction on chromosome no. 7. The supernumerary chromosomes in this species appear to be mitotically stable and contain C-band heterochromatin at the centromeres. From the limited data presently available, the triploid individual may have resulted from the fertilisation of a diploid egg produced when the second meiotic division had been suppressed.     

Complex sex chromosome system in Eigenmannia sp. (Pisces,Gymnotiformes)

Chromosomes of Eigenmannia sp. (7 males and 15 females) collected from the Tietê River in Botucatu (SP, Brazil) were examined from gill, kidney and testicular cells. The diploid chromosome number in males was 2n=31 and in females, 2n=32. In both sexes the number of chromosomal arms was 40. The difference in diploid number was due to the fusion of two acrocentrics. Mitotic and meiotic studies suggested that one of the fused acrocentrics was the Y chromosome. The sex-determining mechanism in Eigenmannia sp. could therefore be XX, AA in the female and X, \-YA A in the males. One of the males presented 2n=30 chromosomes due to the occurrence of another fusion of acrocentrics. C-banding analysis of the mitotic chromosomes revealed constitutive heterochromatin in the centromeric regions of all acrocentrics. However, small metacentrics were C-band negative. The YA chromosome is C-band negative except for a small amount of heterochromatin in the centromeric region. The nucleolar organizer region as identified by Ag-staining is present in the interstitial region of chromosome pair No. 10.     

Chromosome markers in Mus musculus: Differences in C-banding between the subspecies M. m. musculus and M. m. molossinus

Quinacrine (Q-band) and centromeric heterochromatin (C-band) patterns of metaphase chromosomes of two subspecies of Mus musculus were compared. M. m. musculus (the laboratory mouse) and M. m. molossinus (a subspecies from Southeast Asia) had similar Q-band patterns along the length of the chromosomes, but differences were observed in the centromeric region of some chromosomes. The two subspecies had very different distributions of C-band material. Antibodies to 5-methylcytosine were bound to regions of the chromosome corresponding to the C-bands in each animal. These findings support the idea that satellite DNA, which is concentrated in the C-band region, changes more quickly than bulk DNA. The interfertility of these two subspecies permits the development of a musculus strain carrying normal marker chromosomes for genetic studies.     

Pericentromeric location of the telomeric DNA sequences on the European grayling chromosomes

The chromosomal characteristics, locations and variations of the C-band positive heterochromatin and telomeric DNA sequences were studied in the European grayling karyotype (Thymallus thymallus, Salmonidae) using conventional C-banding, endonucleases digestion banding, silver nitrate (AgNO₃), chromomycin A₃ and 4′,6-diamidino-2-phenylindole staining techniques as well as fluorescence in situ hybridization (FISH) and primed in situ labelling. Original data on the chromosomal distribution of segments resistant to AluI restriction endonuclease and identification of the C-banded heterochromatin presented here have been used to characterize the grayling karyotype polymorphism. Structural and length polymorphism of the chromosome 21 showing a conspicuous heterochromatin block adjacent to the centromere seems to be the result of the deletion and inversion. Two pairs of nuclear organizer regions (NOR)-bearing chromosomes were found to be polymorphic in size and displaying several distinct forms. FISH with telomeric peptide nucleic acid probe enabled recognition of the conservative telomeric DNA sequences. The karyotype of the thymallid fish is thought to experienced numerous pericentric inversions and internal telomeric sites (ITSs) observed at the pericentromeric regions of the six European grayling metacentric chromosomes are likely relics of the these rearrangements. None of the ITS sites matched either chromosome 21 or NOR bearing chromosomes.     

DNA replication,3H-cRNA in situ hybridization and C-band patterns in the polycentric chromosomes ofLuzula purpurea Link

DNA late-replication,³H-cRNA in situ hybridization, and C-band distribution patterns were studied inLuzula purpurea Link chromosomes (2n=6). With each technique it was possible to identify homologous chromosomes. DNA late-replicating regions were present at the ends and in the middle of one chromosome pair (pair 1), on both ends of another chromosome pair with one end having more late-replicating regions than the other end (pair 2), and all along the length of the final pair (pair 3). The distribution of label following in situ hybridization of³H-cRNA complementary to Cot 1-reassociated DNA was similar to the DNA late-replication patterns. One chromosome pair had grains concentrated at the ends and in the middle of the chromosomes; another pair had grains at both ends with a greater grain concentration at one end; the final chromosome pair had grains distributed all along the length. C-band distribution patterns were also similar to the DNA late-replication and³H-cRNA in situ-hybridized ones. The results demonstrate that the constitutive heterochromatin ofL. purpurea polycentric chromosomes is similar to the constitutive heterochromatin of monocentric animal chromosomes in that it consists of highly repeated DNA sequences which are replicated late in the S stage of interphase.