Improved compression properties of polypropylene extrusion foams by supramolecular additives

Owing to the high lightweight design potential polymer foams become increasingly important. For rigid polymer foams, requiring high dimensional stability under load, a high compression modulus is a key feature. Here, we demonstrate how supramolecular additives can be utilized to control the foam morphology and to significantly improve the compression behavior of extruded foams made of linear isotactic polypropylene. Three different 1,3,5-benzenetrisamides were selected as supramolecular additives. These additives are soluble in the polymer melt and form a supramolecular nanofiber network upon cooling, acting as nucleating sites for both, foam cells and polymer crystals. It is shown that the in situ formed nanofiber network is very effective in reducing the cell size of extruded foams. Depending on the molecular structure and the concentration of the supramolecular additives, the compression modulus of polypropylene-polymer foams can be significantly increased compared to a reference foam with talc. Unexpectedly, an improvement of 100% with a concentration of only 0.02 wt% of a supramolecular additive compared to the neat polypropylene foam featuring similar densities is achieved. This improvement cannot be correlated with the foam morphology and is most likely attributed to the presence of the supramolecular nanofiber network.

Distribution of (TTAGGG)n telomeric sequences in karyotypes of the Xenopus species complex

The chromosomal distribution of the conserved vertebrate telomeric (TTAGGG)(n) sequence was studied by fluorescence in situ hybridization (FISH) in four Xenopus species and the triploid Silurana tropicalis. As expected, hybridization signals were observed at the distal ends of every chromosome in all species. In addition, the hybridization pattern demonstrates varied organization of (TTAGGG)(n) sequences in the different karyotypes. In X. borealis and X. muelleri hybridization signals intensely labeled one end of a homologous chromosome pair that coincides with the sites containing ribosomal RNA gene clusters. The karyotype of X. clivii remarkably differs from other Xenopus karyotypes in displaying numerous interstitial telomeric sites (ITS). C-banding analysis shows that the non-telomeric sites appear to correspond to the interstitially located constitutive heterochromatin. This suggests that interstitial telomeric sites in X. clivii do not necessarily represent the relic of ancestral telomeres resulting from the fusion of chromosomes, but their occurrence is due to the fact that (TTAGGG)(n) repeat arrays may be a constituent of highly repetitive DNA.

An intriguing Y chromosome in Heteromys anomalus (Rodentia, Heteromyidae)

The mitotic chromosomes of the pocket mouse Heteromys anomalus (Rodentia, Heteromyidae) from Venezuela were analyzed by means of conventional staining and various banding techniques. The karyotype of this species is distinguished by a Y chromosome with exceptional banding properties. The very large heterochromatic Y long arm shows a remarkable bright quinacrine fluorescence, but only moderate or dull fluorescence when labeled with other AT base pair-specific fluorochromes. The implications of these findings are discussed.

Disruption of the FA/BRCA pathway in bladder cancer

Bladder carcinomas frequently show extensive deletions of chromosomes 9p and/or 9q, potentially including the loci of the Fanconi anemia (FA) genes FANCC and FANCG. FA is a rare recessive disease due to defects in anyone of 13 FANC genes manifesting with genetic instability and increased risk of neoplasia. FA cells are hypersensitive towards DNA crosslinking agents such as mitomycin C and cisplatin that are commonly employed in the chemotherapy of bladder cancers. These observations suggest the possibility of disruption of the FA/BRCA DNA repair pathway in bladder tumors. However, mutations in FANCC or FANCG could not be detected in any of 23 bladder carcinoma cell lines and ten surgical tumor specimens by LOH analysis or by FANCD2 immunoblotting assessing proficiency of the pathway. Only a single cell line, BFTC909, proved defective for FANCD2 monoubiquitination and was highly sensitive towards mitomycin C. This increased sensitivity was restored specifically by transfer of the FANCF gene. Sequencing of FANCF in BFTC909 failed to identify mutations, but methylation of cytosine residues in the FANCF promoter region was demonstrated by methylation-specific PCR, HpaII restriction and bisulfite DNA sequencing. Methylation-specific PCR uncovered only a single instance of FANCF promoter hypermethylation in surgical specimens of further 41 bladder carcinomas. These low proportions suggest that in contrast to other types of tumors silencing of FANCF is a rare event in bladder cancer and that an intact FA/BRCA pathway might be advantageous for tumor progression.

SNP-Array genotyping and spectral karyotyping reveal uniparental disomy as early mutational event in MSS- and MSI-colorectal cancer cell lines

In this study nine colorectal cancer cell lines were analysed by 10K SNP-arrays and spectral karyotyping (SKY). Complex chromosomal alterations and breakpoints of deleted or translocated fragments found by SKY could further be characterized by SNP-array analysis. Interestingly many monoallelic regions identified by SNP-array analysis display no copy number alterations, representing uniparental disomy (UPD). It was demonstrated that UPD seems to be involved in activation of early-acting tumor suppressor genes in MSS- (APC, CDKN2A) and MSI- (MLH1, MSH2, APC, CDKN2A) colorectal cancer cell lines. Genes involved later on in the adenoma-carcinoma sequence (i.e. TP53/SMAD4) were not found to be inactivated by UPD. Furthermore, identified amplified monoallelic regions may include oncogenes activated by allele-specific-amplification (i.e. Cyclin D1). However, at present, the majority of the monoallelic regions located in the present study have not yet been associated with known tumor suppressor genes and oncogenes. Further studies are warranted to identify relevant genes in the respective regions and to further verify the results presented here.

Characterization of chromosomal aberrations in diffuse large B-cell lymphoma (DLBL) by G-banding and spectral karyotyping (SKY)

Cytogenetic chromosome analysis by classical G-banding was supplemented by spectral karyotyping (SKY) in 12 cases of diffuse large B-cell lymphoma (DLBL). SKY is a fluorescence in-situ-based, genome-wide screening technique allowing identification of genetic material even in highly condensed metaphase chromosomes of poor morphology. By simultaneous hybridization of whole chromosome painting probes onto tumor chromosome spreads genetic rearrangements are visualized permitting the clarification of even complex karyotype alterations and the identification of genetic material of previously unknown origin, so-called marker chromosomes. Taking the SKY results into account, we reevaluated the G-banding karyotypes initially carried out, thus generating a more precise karyotype in ten of twelve (83%) cases investigated. In particular, thirteen chromosomal rearrangements not correctly recognized by classical cytogenetics were identified, the genetic origin of seven marker chromosomes was elucidated and three structural genetic rearrangements were redefined. We found SKY to be a valuable technique to establish a definite karyotype in addition to classical cytogenetics.

Cytogenetics of the bleak (Alburnus alburnus), with special emphasis on the B chromosomes

Some of the largest B chromosomes so far discovered in vertebrates are present in the cyprinid fish Alburnus alburnus. Previous cytogenetic analyses revealed a diploid chromosome number of 2n = 50. In addition, in some individuals one or two unusually large B chromosomes are present. Two morphologically different types of B chromosomes were observed. The frequency of animals bearing a supernumerary chromosome was found to vary considerably between different populations. A more detailed analysis of the A and B chromosomes of A. alburnus by conventional banding techniques, as well as fluorescence in-situ hybridization (FISH) with the telomeric DNA repeats (GGGTTA)7/(TAACCC)7, 18S + 28S rDNA and 5S rDNA were performed in the present study. Furthermore, a B chromosome-specific DNA probe obtained by amplified length polymorphism (AFLP) was hybridized on metaphases of A. alburnus carrying supernumerary B chromosomes. The banding analyses showed that the B chromosomes are completely heterochromatic, consist of GC-rich DNA sequences, replicate their DNA in the very late S-phase of the cell cycle and are composed mainly of a specific retrotransposable DNA element. Finally, blood probes from A. alburnus were collected for DNA-flow cytometric measurements. It could be shown that the huge supernumerary chromosomes represent nearly 10% of the total genome size of A. alburnus.

Mosaicism for an ectopic NOR at 8pter and a complex rearrangement of chromosome 8 in a patient with severe psychomotor retardation

We describe a 3-year-old girl with severe delays in mental and motor skills, a history of generalized seizures, and subtle dysmorphic features. Conventional cytogenetics revealed a mosaic karyotype. A de novo ectopic NOR at the telomeric region of the short arm of one chromosome 8 (8ps) was found in 90% of lymphocyte and in 98% of fibroblast metaphases. A small NOR-bearing marker chromosome and a large derivative chromosome 8 without short arm satellites (der(8)) were present in the remaining cells. FISH with a probe specific for centromeres 14 and 22 labeled both the telomeric region of 8ps and the small marker centromere. Der(8) included an inverted duplication of 8p and a rearranged duplication of 8q but lacked a second centromere. A subtelomeric probe for 8p revealed a cryptic deletion in 8ps and der(8). Thus, the karyotype represents a combination of submicroscopic partial monosomy 8pter and mosaic trisomy 8.

Chromosome banding in Amphibia

The present study reports for the first time on the numerical and structural chromosome anomalies that spontaneously arise in aging cultured fibroblast cells of Amphibia. The analyses were conducted on kidney fibroblasts of three anuran species with extremely divergent genome sizes (Bufo rubropunctatus, Scaphiopus holbrooki, Gastrotheca riobambae), in the sixth up to the 14th culture passage. The chromosomal rearrangements were identified by means of the 5-bromodeoxyuridine/deoxythymidine (BrdU/dT) replication banding technique. The aberrations can be either confined to a single chromosome, or else involve all chromosomes of the karyotype. The most frequent structural aberrations in the cell cultures of S. holbrooki and G. riobambae are tandem fusions between two or more chromosomes. These tandem fusions originating in vitro in long-termed cell cultures reflect the chromosome mutations which also took place during amphibian phylogenesis.

Multicolor spectral karyotyping of rat chromosomes

Rat and mouse have become important animal models to study various human diseases such as cancer. Cytogenetic analysis of the respective karyotypes is frequently required to investigate the causative genetic defects and especially neoplastic cells often show complex chromosome aberrations and many different marker chromosomes. However, structural homogeneity of the chromosomes in these species as well as less pronounced differences in banding patterns make it difficult to assign genetic abnormalities to certain chromosomes by conventional banding techniques. Here we report for the first time the successful application of multicolor spectral karyotyping (SKY) to rat chromosomes, which allows unequivocal identification of all rat chromosomes with the exception of chromosomes 13 and 14 in different colors, thus enabling the elucidation of even complex rearrangements in the rat karyotype. Flow-sorted chromosome specific painting probes for all 22 rat chromosomes (20 autosomes, X, and Y) were combinatorially labeled by a set of five different fluorochromes and hybridized in situ to metaphase spreads of a healthy rat, to diakineses from testicular material, and to cells from a rat FAO hepatoma cell line. Measuring the complete spectrum at each image point by using the SpectraCube((R)) spectral imaging system and respective computer software allowed identification of the individual rat chromosomes by their specific emission spectra. Classification algorithms in the analysis software can then display the rat chromosomes in specific pseudo-colors and automatically order them in a karyotype table. After its successful application to human and mouse chromosomes, spectral karyotyping of rat chromosomes now also allows cytogenetic screening of the complete rat genome by a single hybridization.

Chromosome banding in Amphibia. XXIX. The primitive XY/XX sex chromosomes of Hyla femoralis (Anura, Hylidae)

The karyotype of the pine woods treefrog, Hyla femoralis, is characterized by primitive XY female/XX male sex chromosomes. The sole difference between the X and the Y is the presence of a nucleolus organizer region (NOR) in the X. Due to a deletion of the NOR in the Y, this chromosome is distinctly smaller than the X. Since no autosomal NORs exist in the karyotype of this species, the NOR deletion in the Y results in a sex-specific difference in the number of ribosomal RNA genes, with a female:male ratio of about 2:1. Interphase nuclei of male animals contain always one silver-stained nucleolus, whereas most nuclei of female specimens exhibit two nucleoli. This is in agreement with the absence of dosage compensation for sex-linked genes in amphibian cells. The consequences of the loss of about 50% of ribosomal RNA genes for the viability of male individuals and spermatogenesis are discussed.

Chromosome banding in Amphibia. XXVIII. Homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus riveroi (Anura, Leptodactylidae)

Extensive cytogenetic analyses on a population of the leptodactylid frog Eleutherodactylus riveroi in northern Venezuela revealed the existence of multiple XXAA male/XYAA female/XAA(Y) female sex chromosomes. The XAA(Y) karyotype originated by a centric (Robertsonian) fusion between the original, free Y chromosome and an autosome. 46.2% of the male individuals in this population are carriers of this Y-autosome fusion. In male meiosis the XAA(Y) sex chromosomes pair in the expected trivalent configuration. In the same population 53.8% of the male animals still possess the original, free XY sex chromosomes. E. riveroi is only the second vertebrate species discovered in which a derived Y-autosome fusion coexists with the ancestral free XY sex chromosomes. The free XY sex chromosomes, as well as the multiple XA(Y) sex chromosomes are still in a very primitive (homomorphic) stage of differentiation. With no banding technique applied it is possible to distinguish the Y from the X. Various banding techniques and in situ hybridizations have been carried out to characterize the karyotypes. DNA flow cytometric measurements show that the genome size of E. riveroi resembles that of other Eleutherodactylus species. The cytogenetic data obtained in E. riveroi are compared with those of the sole other vertebrate known to possess the extremely rare, multiple XXAA male/XYAA female/XAA(Y) female sex chromosomes. Surprisingly enough, this vertebrate again is a frog belonging to the genus Eleutherodactylus [E. ((maussi) biporcatus] which lives exactly in the same habitat in northern Venezuela as does E. riveroi.

X chromosomes of American marsupials contain minimal amounts of euchromatin

The karyotypes of four South American didelphid marsupials, representing diploid numbers of 2n = 14 and 18, have been analyzed by a variety of banding techniques. The 2n = 14 karyotypes display a high degree of homoeology, but there also exist distinct similarities between the 2n = 14 and 2n = 18 karyotypes. The interspecific differences found are due to centric fissions, pericentric inversions, and variations in the amount and composition of the constitutive heterochromatin. Contrary to the evolutionary conservation of the banding patterns in all autosomal arms, there are multiple differences in the number and chromosomal location of the nucleolus organizer regions. In species with X-linked nucleolus organizers, the 18S + 28S ribosomal RNA genes escape inactivation in female cells. Measurements on the X chromosomes of Marmosa fuscata and Micoureus demerarae unexpectedly reveal the lowest quantities of euchromatin so far determined in the X chromosomes of mammals: 1.5% and 1.8%, respectively, of their haploid female genomes. This is significantly less than the amount of euchromatin in the basic X chromosomes of other marsupials (3%) or eutherians (5%).

Chromosome banding in Amphibia. XXVI. Coexistence of homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus maussi (Anura, Leptodactylidae)

A 15-year cytogenetic survey on one population of the leaf litter frog Eleutherodactylus maussi in northern Venezuela confirmed the existence of multiple XXAA male symbol /XAA(Y) female symbol sex chromosomes which originated by a centric (Robertsonian) fusion between the original Y chromosome and an autosome. 95% of the male individuals in this population are carriers of this Y-autosome fusion. In male meiosis the XAA(Y) sex chromosomes pair in the expected trivalent configuration. In the same population, 5% of the male animals still possess the original, free XY sex chromosomes. In a second population of E. maussi analyzed, all male specimens are characterized by these ancestral XY chromosomes which form normal bivalents in meiosis. E. maussi apparently represents the first vertebrate species discovered in which a derived Y-autosome fusion still coexists with the ancestral free XY sex chromosomes. The free XY sex chromosomes, as well as the multiple XA(Y) sex chromosomes are still in a very primitive (homomorphic) stage of differentiation. With no banding technique applied it is possible to distinguish the Y from the X. DNA flow cytometric measurements show that the genome of E. maussi is among the largest in the anuran family Leptodactylidae. The present study also supplies further data on differential chromosome banding and fluorescence in situ hybridization experiments in this amphibian species.

The giant B chromosome of the cyprinid fish Alburnus alburnus harbours a retrotransposon-derived repetitive DNA sequence

The cyprinid fish Alburnus alburnus possesses one of the largest supernumerary chromosomes in all vertebrates. In the present study, amplified fragment length polymorphism analyses (AFLP) and fluorescence in-situ hybridization (FISH) were performed in order to characterize these extraordinary chromosomes in detail. Sequence analysis of the B chromosome-specific DNA revealed a strong homology to a Drosophila Gypsy/Ty3 retrotransposon and also to a medaka (Oryzias latipes) one. The sequence is highly abundant on the B chromosome but undetectable in the normal A chromosome complement. It is also absent from the B chromosome of the closely related species, Rutilus rutilus, suggesting a specific spreading of the mobile element during evolution of the giant supernumerary chromosome within A. alburnus. Meitotic chromosomes were in-situ hybridized with the B chromosome-specific probe, documenting that the additional chromosome behaves as an autopaired ring chromosome in diakineses. Our results suggest that the supernumerary chromosome of A. alburnus is not derived from the normal chromosome complement but has evolved independently.

Chromosome banding in Amphibia. XXVII. DNA replication banding patterns in three anuran species with greatly differing genome sizes

The mitotic chromosomes of three anuran species, Scaphiopus holbrooki, Litoria infrafrenata and Odontophrynus americanus, were analyzed by means of the 5-bromodeoxyuridine/deoxythymidine (BrdU/dT) replication banding technique. These species exhibit large differences in their genome sizes: S. holbrooki possesses one of the smallest genomes among vertebrates, L. infrafrenata has a genome size near the modal DNA value of most Amphibia, whereas O. americanus is a tetraploid species. BrdU/dT labeling induces reproducible and reliable R- and G-replication bands along the metaphase chromosomes of all three species. Irrespective of the genome size of the species considered, the number of early (R-) and late (G-) replicating bands per haploid karyotype is nearly the same. The chromosomes of the autotetraploid O. americanus can be arranged into sets of four homologous chromosomes (quartets). C-bands and BrdU/dT replication bands reveal heterogeneity within the quartets 1, 3 and 4 that are interpreted as the initiation of a diploidization process.

Spectral karyotype analysis of colon cancer cell lines of the tumor suppressor and mutator pathway

BACKGROUND AND AIMS

Microsatellite instability (MSI) is characterized by the size variation of microsatellites in tumor DNA as compared to matching normal DNA due to defects in the mismatch repair system. To examine the chromosomal differences in microsatellite-stable (MSS) and -unstable (MSI) tumors in detail, we analyzed MSS (Caco-2, Colo-205, SW948) and MSI (HCT-15, HCT-116, LoVo) cell lines by spectral karyotyping (SKY).

METHODS

SKY is a sensitive method to detect chromosome aberrations by visualizing each chromosome in a different color. Metaphases were hybridized with a SKY probe mixture. Images were visualized with the SpectraCube system and analyzed with the SKYview imaging software.

RESULTS

The average number of chromosomes was 49 in LoVo, 45 in HCT-116, 46 in HCT-15, 71 in Colo-205, 89 in Caco-2 and 66 in SW-948. Three aberrant chromosomes were detected in LoVo, three in HCT-116, two in HCT-15, seventeen in Colo-205, fourteen in Caco-2 and nine in SW948.

CONCLUSION

The karyotypes of MSS colon cancer cells displayed complex numerical and structural aberrations. In contrast the chromosomes of MSI colon cancer cells were mostly unaltered but displayed a few isolated numerical and structural aberrations. We speculate that these isolated aberrations may be specifically involved in the pathogenesis of MSI tumors.

Chromosome banding in Amphibia. XXII. Atypical y chromosomes in Gastrotheca walkeri and Gastrotheca ovifera (Anura, Hylidae)

The chromosomes of the rare South American marsupial frogs Gastrotheca walkeri and G. ovifera were extensively reexamined with various banding techniques. The karyotypes of both species are distinguished by a new category of XY female symbol /XX male symbol female sex chromosomes. The unusual Y chromosomes are characterized by containing the least amount of constitutive heterochromatin in the karyotypes. This is in contrast to all previously known amphibian Y chromosomes and does not fit the evolutionary model of early XY differentiation in vertebrates. In male meiosis, the heteromorphic XY chromosomes of both species still exhibit the same pairing configurations as the autosomes. DNA flow cytometric measurements show the nuclear DNA amount of G. walkeri to be 10.90 pg. The significance of the XY/XX sex chromosomes of these marsupial frogs, the various classes of constitutive heterochromatin detected, and the data obtained from meiotic analyses are discussed in detail.

Chromosome banding in amphibia. XXIII. Giant W sex chromosomes and extremely small genomes in Eleutherodactylus euphronides and Eleutherodactylus shrevei (Anura, Leptodactylidae)

Highly differentiated, heteromorphic ZZ female symbol /ZW male symbol sex chromosomes were found in the karyotypes of the neotropical leptodactylid frogs Eleutherodactylus euphronides and E. shrevei. The W chromosomes are the largest heterochromatic, female-specific chromosomes so far discovered in the class Amphibia. The analyses of the banding patterns with AT- and GC base-pair specific fluorochromes show that the constitutive heterochromatin in the giant W chromosomes consists of various categories of repetitive DNA sequences. The W chromosomes of both species are similar in size, morphology and banding patterns, whereas their Z chromosomes exhibit conspicuous differences. In the cell nuclei of female animals, the W chromosomes form very prominent chromatin bodies (W chromatin). DNA flow cytometric measurements demonstrate clear differences in the DNA content of male and female erythrocytes caused by the giant W chromosome, and also shows that these Eleutherodactylus genomes are among the smallest of all amphibian genomes. The importance of the heteromorphic ZW sex chromosomes for the study of Z-linked genes, the similarities and differences of the two karyotypes, and the significance of the exceptionally small genomes are discussed.

Chromosome banding in Amphibia. XXIV. The B chromosomes of Gastrotheca espeletia (Anura, Hylidae)

The mitotic chromosomes of an Ecuadorian population of the marsupial frog Gastrotheca espeletia were analyzed by means of banding techniques and fluorescence in situ hybridization. This species is characterized by unusual supernumerary (B) chromosomes. The maximum number of B chromosomes is 9 and they occur in three different morphological types. Banding analyses show that the B chromosomes are completely heterochromatic, consist of AT base pair-rich repeated DNA sequences, replicate their DNA in very late S-phase of the cell cycle, and are probably derived from a centromeric or paracentromeric region of a standard (A) chromosome. Exceptionally, the B chromosomes carry 18S + 28S ribosomal RNA genes and the conserved vertebrate telomeric DNA sequence appears to be underrepresented. Flow cytometric measurements of the nuclear DNA content differentiate between individuals with different numbers of B chromosomes. Significantly more B chromosomes are present in female than in male animals.

Chromosome banding in Amphibia. XXV. Karyotype evolution and heterochromatin characterization in Australian Mixophyes (Anura, Myobatrachidae)

The mitotic chromosomes of the Australian ground frogs Mixophyes fasciolatus and M. schevilli were analyzed by means of banding techniques and restriction endonuclease digestions. Chromosomal differentiation in these two species occurred exclusively by considerable changes in the amount of telomeric and centromeric heterochromatin, whereas the sizes and locations of interstitial heterochromatic regions, the sizes of all euchromatic segments as well as the positions of centromeres remained nearly identical during karyotype evolution. The major heterochromatic regions in the karyotypes of M. fasciolatus and M. schevilli amount to 30.2% and 20.7%, respectively. They consist of AT base pair-rich repetitive DNA sequences that are brightly labeled by AT-specific fluorochromes and display quenched fluorescence after staining with GC-specific fluorochromes. The heterochromatic regions can be differentiated by treatment of metaphase chromosomes and interphase cell nuclei with various restriction enzymes which either disclose the complete set of C-band patterns in the karyotypes of both species, or else reveal several subsets of these C-bands.

Cytogenetic characterization of the TM4 mouse Sertoli cell line. I. Conventional banding techniques, FISH and SKY

Permanent Sertoli cell lines provide an ideal system for the in vitro analysis of function and responsiveness to biochemical/hormonal factors of this particular cell type. In general, cytogenetic analyses of cell lines often reveal remarkable chromosomal changes that may be associated with functional characteristics. In the present study we investigated the mouse Sertoli cell line TM4 by C-banding, silver staining, FISH and spectral karyotyping (SKY). A highly increased chromosome number (average 85-95) as well as five stable marker chromosomes were detected by the conventional staining techniques. SKY identified the markers as a translocation chromosome T(1;3), isochromosomes 11 and 18 and two different-sized microchromosomes. The results show the usefulness of combining SKY and conventional banding methods for the evaluation of chromosome alterations in widely used cell lines.

Two supernumerary marker chromosomes, originating from chromosomes 6 and 11, in a child with developmental delay and craniofacial dysmorphism

The interpretation of the significance of marker chromosomes, which can be encountered at prenatal diagnosis, is extremely problematic. Various factors contribute to the difficulty of clarifying the phenotypic risks of supernumerary marker chromosomes, including differences in the size, structure, and origin of marker chromosomes, as well as the occurrence of multiple marker chromosomes of different origin in the same proband. Research on marker chromosomes is currently in a data-accumulation phase. We report the presence of two marker chromosomes, originating from chromosomes 6 and 11, in a child with developmental delay and craniofacial dysmorphism and discuss the related literature.

Sex chromosomes, sex-linked genes, and sex determination in the vertebrate class amphibia

In this chapter the different categories of homomorphic and heteromorphic sex chromosomes, types of sex-determining mechanisms, known sex-linked genes, and data about sex-determining genes in the Amphibia have been compiled. Thorough cytogenetic analyses have shown that both XY/XX and ZW/ZZ sex chromosomes exist in the order Anura and Urodela. In some species quite unusual systems of sex determination have evolved (e.g. 0W-females/00-males or the co-existence of XY/XX and ZW/ZZ sex chromosomes within the same species). In the third order of the Amphibia, the Gymnophiona (or Apoda) there is still no information regarding any aspect of sex determination. Whereas most species of Anura and Urodela present undifferentiated, homomorphic sex chromosomes, there is also a considerable number of species in which an increasing structural complexity of the Y and W chromosomes exists. In various cases, the morphological differentiation of the sex chromosomes occurred as a result of quantitative and/or qualitative changes to the repetitive DNA sequences in the constitutive heterochromatin of the Y and W chromosomes. The greater the structural differences between the sex chromosomes, the lesser the extent of pairing in meiosis. No dosage compensation of the sex-linked genes in the somatic cells of the homogametic (XX or ZZ) individuals have been detected. The genes located to date on the amphibian sex chromosomes lead to the conclusion that there is no common ancestral or conserved sex-linkage group. In all amphibians, genetic sex determination (GSD) seems to operate, although environmental factors may influence sex determination and differentiation. Despite the accumulated evidence that GSD is operating in Anura and Urodela, there is little substantial information about how it functions. Although several DNA sequences homologous to the mammalian ZFY, SRY and SOX genes have been detected in the Anura or Urodela, none of these genes is an appropriate candidate to explain sex determination in these vertebrates.

Spectral karyotyping of Werner syndrome fibroblast cultures

Fibroblast cultures from two Werner syndrome patients were analyzed by spectral karyotyping. There were multiple, pseudodiploid clones in both cultures, mostly marked by random balanced reciprocal translocations. One of the cultures contained a clone with three-way exchanges involving chromosomes 2, 3, and 16. Duplication-deficiencies were exceptional, as were completely normal metaphases. The most frequent breakpoint occurred at 16q22 which corresponds to FRA16B, possibly reflecting difficulties of WS cells in replicating AT-rich repetitive DNA structures. Both cultures ceased proliferation after eight in vitro passages, but a single clone with exceptional growth potential emerged in one of the senescing cultures. Due to its identical translocations, the derivation of this near tetraploid clone (with tetrasomy for all autosomes except chromosomes 4 and 6) could be traced to the most prevalent pseudodiploid clone of the parental mass culture. Our study confirms the existence of variegated translocation mosaicism as the cytogenetic hallmark of WS fibroblast cultures and suggests that tetraploidization in combination with certain chromosome rearrangements and selective chromosome dosage may overcome the severely limited in vitro lifespan of WS fibroblasts.

An interstitial nucleolus organizer region in the long arm of human chromosome 7: cytogenetic characterization and familial segregation

An unusual NOR-bearing chromosome 7 was detected in a phenotypically normal, healthy 29-year-old male proband. Differential banding techniques as well as in situ hybridization employing various DNA-probes were performed in order to characterize the chromosome in detail. The nucleolus organizer region was found to be located between bands 7q21.3 and 7q22.1. No further rearrangements were detected in this chromosome. Analysis of spontaneously occurring micronuclei revealed 9% of them to contain a 7q fragment distal to (or including) the inserted NOR, suggesting that the inserted secondary constriction represents a potential hot spot for chromosomal breakage and rearrangement. Segregation analysis of the variant chromosome 7 in 51 members of the probands' family showed transmission in a Mendelian fashion. 27 individuals were found to be heterozygous for the inserted chromosome. A three-year-old child in the consanguineous marriage of two heterozygous carriers exhibited the NOR-insertion in both of his chromosome 7 homologues. To our knowledge, this is the first report on a homozygous carrier of a non-acrocentric NOR-bearing chromosome.

Spectral karyotyping of the human colon cancer cell lines SW480 and SW620

The cell lines SW480 and SW620, derived from different stages of colon carcinoma in the same patient, have been used for a number of biochemical, immunological, and genetic studies on colon cancer. A comparative analysis of their karyotypes may identify chromosomal aberrations that might represent markers for metastatic spread. In the present study spectral karyotyping (SKY) was applied to these two colon cancer cell lines. Compared to previously reported G-banded karyotypes, 9 (SW480) and 7 (SW620) markers were identical, 3 (SW480) and 3 (SW620) markers could be redefined, 5 (SW480) and 8 (SW620) markers were newly identified, and 4 (SW480) and 5 (SW620) of the previous described markers could not be confirmed. The redefined aberrations include very complex rearrangements, such as a der(16) t(3;16;1;16;8;16; 1;16;10) and a der(18)t(18;15;17)(q12; p11p13;??) in SW620 and a der(19)t(19;8;19;5) in SW480, that have not been identified by conventional banding techniques. The resulting chromosome gains (5q11-->5q15, 7pter-->q22, 11, 13q14-->qter, 20pter-->p12, X) and losses (8pter-->p2, 18q12-->qter, Y) found in both SW480 and SW620 were in good agreement with those frequently described in colorectal tumors as primary changes in the stem cell. Abnormalities found exclusively in SW620 cells only (gains of 5pter-->5q11, 12q12-->q23, 15p13-->p11, and 16q21-->q24 and losses of 2pter-->2p24, 4q28-->qter, and 6q25-->qter) can be viewed as changes that occurred in a putative metastatic founder cell.

Gross chromosomal rearrangements and genetic exchange between nonhomologous chromosomes following BRCA2 inactivation

Cancer-causing mutations often arise from gross chromosomal rearrangements (GCRs) such as translocations, which involve genetic exchange between nonhomologous chromosomes. Here we show that murine Brca2 has an essential function in suppressing GCR formation after chromosome breakage. Cells that harbor truncated Brca2 spontaneously incur GCRs and genomic DNA breaks during division. They exhibit hypersensitivity to DNA damage by interstrand cross-linkers, which even at low doses trigger aberrant genetic exchange between nonhomologous chromosomes. Therefore, genetic instability in Brca2-deficient cells results from the mutagenic processing of spontaneous or induced DNA damage into gross chromosomal rearrangements, providing a mechanistic basis for cancer predisposition.

Noninvasive determination of genome size and ploidy level in fishes by flow cytometry: detection of triploid Poecilia formosa

BACKGROUND

In order to understand the evolutionary significance of single triploids among the mostly diploid Poecilia formosa we have developed a simple, noninvasive technique for DNA content and ploidy determination.

METHODS

From dorsal fin clips of 14 different fish species single cell suspensions were obtained by chopping the material in 2.1% citric acid/0.5% Tween20, passing it through a 0. 6-gauge needle and incubating it for 20 min at room temperature (RT) with gentle agitation. After overnight fixation in 70% ethanol, the cells were treated with 1ml 0.5% pepsin/0.1 M HCl for 15 min at RT before adding DAPI to a final volume of 2 ml. The cells were stained for 1-3 h and then analyzed by flow cytometry.

RESULTS

We obtained good measurements with CVs ranging from 1.23% to 3.36%. The poeciliid species measured contain from 1.6 to 2.0 pg/nucleus, Oryzias latipes (Medaka) exhibits a nuclear DNA content of 2.2 pg, Danio rerio (zebrafish) 4.6 pg, Tetraodon fluviatilis (freshwater fugu) 0.70 pg. All values except zebrafish are in good agreement with the literature.

CONCLUSIONS

The identification of living specimens of different ploidy for breeding experiments, behavioral studies and tissue transplantations is now made possible. With slight modifications the method can be extended to a field technique, providing therefore a useful tool for a variety of researchers.

Noninvasive determination of genome size and ploidy level in fishes by flow cytometry: detection of triploid Poecilia formosa

BACKGROUND

In order to understand the evolutionary significance of single triploids among the mostly diploid Poecilia formosa we have developed a simple, noninvasive technique for DNA content and ploidy determination.

METHODS

From dorsal fin clips of 14 different fish species single cell suspensions were obtained by chopping the material in 2.1% citric acid/0.5% Tween20, passing it through a 0. 6-gauge needle and incubating it for 20 min at room temperature (RT) with gentle agitation. After overnight fixation in 70% ethanol, the cells were treated with 1ml 0.5% pepsin/0.1 M HCl for 15 min at RT before adding DAPI to a final volume of 2 ml. The cells were stained for 1-3 h and then analyzed by flow cytometry.

RESULTS

We obtained good measurements with CVs ranging from 1.23% to 3.36%. The poeciliid species measured contain from 1.6 to 2.0 pg/nucleus, Oryzias latipes (Medaka) exhibits a nuclear DNA content of 2.2 pg, Danio rerio (zebrafish) 4.6 pg, Tetraodon fluviatilis (freshwater fugu) 0.70 pg. All values except zebrafish are in good agreement with the literature.

CONCLUSIONS

The identification of living specimens of different ploidy for breeding experiments, behavioral studies and tissue transplantations is now made possible. With slight modifications the method can be extended to a field technique, providing therefore a useful tool for a variety of researchers.

Ectopic NORs on human chromosomes 4qter and 8q11: rare chromosomal variants detected in two families

Two different NOR bearing non-acrocentric chromosomes were detected during prenatal diagnosis performed on two probands because of advanced maternal age. In the first case, a chromosome 4 carried a NOR in the telomeric region of the long arm (4qs), while in the second case a NOR was inserted into chromosome 8q11. Family analysis showed the variant chromosomes to be transmitted through at least three generations in each family. There were no reports of reproductive problems or phenotypic effects in the carriers of these chromosomes, indicating the benign character of the aberrant chromosomes. In order to characterise the chromosomal variants more precisely, various differential banding techniques were applied.

Localization of the human membrane-type 2 matrix metalloproteinase gene (MMP15) to 16q12.1 near DNA elements that are part of centromeric and non-centromeric heterochromatin of 11 human chromosomes

We have localized a second gene for membrane-type matrix metalloproteinases, MT2-MMP, to chromosome 16q12 by in situ hybridization. FISH experiments using a genomic PAC clone containing the MT2-MMP gene resulted in an unusual hybridization pattern detecting centromeric and non-centromeric heterochromatin regions or its flanking sequences in 11 human chromosomes in addition to the MT2-MMP locus on chromosome 16q12. The detailed analysis of this hybridization pattern using molecular cytogenetic methods together with the specific hybridization of the MT2-MMP cDNA allowed a refined mapping of the gene to 16q12.1, directly adjacent to the 16q heterochromatin. Our findings may give some insights into the evolution of the MMP gene family.

Identification of dynein heavy chain genes expressed in human and mouse testis: chromosomal localization of an axonemal dynein gene

Dynein heavy chains are involved in microtubule-dependent transport processes. While cytoplasmic dyneins are involved in chromosome or vesicle movement, axonemal dyneins are essential for motility of cilia and flagella. Here we report the isolation of dynein heavy chain (DHC)-like sequences in man and mouse. Using polymerase chain reaction and reverse-transcribed human and mouse testis RNA cDNA fragments encoding the conserved ATP binding region of dynein heavy chains were amplified. We identified 11 different mouse and eight human dynein-like sequences in testis which show high similarity to known dyneins of different species such as rat, sea urchin or green algae. Sequence similarities suggest that two of the mouse clones and one human clone encode putative cytoplasmic dynein heavy chains, whereas the other sequences show higher similarity to axonemal dyneins. Two of nine axonemal dynein isoforms identified in the mouse testis are more closely related to known outer arm dyneins, while seven clones seem to belong to the inner arm dynein group. Of the isolated human isoforms three clones were classified as outer arm and four clones as inner arm dynein heavy chains. Each of the DHC cDNAs corresponds to an individual gene as determined by Southern blot experiments. The alignment of the deduced protein sequences between human (HDHC) and mouse (MDHC) dynein fragments reveals higher similarity between single human and mouse sequences than between two sequences of the same species. Human and mouse cDNA fragments were used to isolate genomic clones. Two of these clones, gHDHC7 and gMDHC7, are homologous genes encoding axonemal inner arm dyneins. While the human clone is assigned to 3p21, the mouse gene maps to chromosome 14.

Amplification of (GACA)n simple repeats in an exceptional 14p+ marker chromosome

An inherited 14p+ marker chromosome with an unusually large differentially staining region (DSR) on the short arm was examined with a number of banding techniques and by non-radioactive in situ hybridization using various repetitive DNA probes. The increase in the size of this variant chromosome was 40% that of a normal chromosome 14. The extra chromosomal material in the DSR consisted mainly of GC-rich constitutive heterochromatin within which two equally sized clusters of 18S + 28S ribosomal RNA genes were located. In situ hybridization demonstrated that the DNA in the DSR was highly enriched in simple tetrameric (GACA)n sequences, whereas the centromeric alphoid sequences and the (TTAGGG)n telomeric repeats were not amplified. Silver staining of the two nucleolus organizer regions (NORs) within the DSR showed that the telomerically located NOR was always more active than the paracentromerically located NOR. A comparison with other DSRs found in human acrocentric autosomes revealed a gradient of transcriptional activity of adjacent multiple NORs. This gradient decreased in the order of their telomeric-paracentromeric-interstitial position, regardless on which acrocentric chromosome the DSR was located.