Fast chromosomal evolution and karyotype instability: recurrent chromosomal rearrangements in the peach potato aphid Myzus persicae (Hemiptera: Aphididae)

The occurrence of karyotype variations with respect to both chromosome number and structure has been frequently reported in aphids. Here, we review recent data attesting to the presence of recurrent chromosomal changes in the karyotype of the peach potato aphid Myzus persicae, where clones presenting metaphases with different chromosome number (from 12 to 17) have been observed, also comparing plates obtained within the same embryo. According to the available data, M. persicae autosomes 3 and 1 are the chromosomes mostly involved in changes compared to other autosomes, suggesting that they could have sites more susceptible to fragmentation. Chromosomal fissions involving the X chromosomes have also been observed, suggesting that they may have fragile sites located at the termini opposite to the nucleolar organizer regions‐bearing telomere. The presence of holocentric chromosomes and reproduction by apomictic parthenogenesis, together with a constitutive expression of telomerase, could explain the inheritance of the observed chromosomal instability in aphids. Considering that chromosomal changes may affect the host choice and could also favour speciation, it would be intriguing to confirm whether the observed karyotype variants have effects over short temporal and spatial scales.     

A high degree of macronuclear chromosome polymorphism is generated by variable DNA rearrangements in Paramecium primaurelia during macronuclear differentiation.

DNA rearrangements in Paramecium lead to the formation of macronuclear chromosomes, the sizes of which range from 50 and 800 kb (1 kb is 10(3) base-pairs). This process does not appear to be a simple size reduction of the micronuclear chromosomes by specific and reproducible DNA sequence elimination and chromosomal breakage followed by chromosomal amplification. On the contrary, this process generates a variety of different, but sequence-related, macronuclear chromosomes from a unique set of micronuclear chromosomes. This paper describes an attempt to understand the nature of the diversity of the macronuclear chromosomes and the mechanisms of their production. The structure of three macronuclear chromosomes, 480, 250 and 230 kb in size, have been determined utilizing chromosome-jumping and YAC-cloning techniques. The two smallest chromosomes correspond roughly to the two halves of the longest chromosome. The main contribution to the diversity arises from the chromosomal ends and is due to variable positions of the telomere addition sites and/or to variable rearrangements of DNA sequences. The 480 kb chromosome contains a region of variable length, which is likely to be due to a variable deletion, located at the position of telomerization seen in the two small chromosomes. A model of chromosomal breakage is proposed to rationalize this result where micronuclear DNA is first amplified, broken and degraded to various extent from the newly formed ends, which subsequently are either telomerized or religated. Potential implications of these processes for gene expression is discussed. Known phenotypes that have a macronuclear determinism could be explained by this type of process.     

Structural chromosomal abnormalities in patients with mental retardation and/or multiple congenital anomalies: a new series of 24 patients

Chromosomal abnormalities are a major cause of mental retardation and/or multiple congenital anomalies (MCA/MR). Screening for these chromosomal imbalances has mainly been done by standard karyotyping. The objective of this study was to report standard chromosome analysis and FISH screening of a series of 24 patients with MCA/MR. Structural chromosomal abnormalities were detected in 24 alterations and included 5 deletions, 2 duplications, 6 unbalanced translocations, 3 inversions, 2 insertions, 3 derivative chromosomes, 2 marker chromosomes and 1 isochromosome. We confirm that a high percentage of MCA/MR cases hitherto considered idiopathic is caused by chromosomal imbalances. We conclude that patients with MCA/MR should be routinely karyotyped.     

De novo complex chromosomal rearrangement of 46, XY,t (3; 16; 8) (p26; q13; q21.2) in a non-obstructive azoospermic male

Complex Chromosomal Rearrangements (CCRs) are rare structural abnormalities that are usually associated with infertility or subfertility in male carriers. We described clinical and chromosomal features of a non-obstructive azoospermic male that has been referred for infertility. Cytogenetic analysis showed three chromosomes, i.e. 3, 8 and 16, which have been involved and caused spermatogenesis failure.     

Comparative insect karyology: Current state and applications

The current state of the comparative insect karyology and the main applications of chromosomal analysis of insects are reviewed. The most important characteristics of insect karyotypes in mitosis and meiosis are considered. Karyological studies provide important information on the genetic structure, life cycles and ecological characteristics, evolution, taxonomy, and phylogeny of insects. Insects have two principal mechanisms of sex determination: more common mechanism is based on the presence of sex chromosomes, and another, on haplodiploidy. Karyotypic analysis allows a number of linkage groups as well as the primary sex ratio to be determined. Chromosomal rearrangement can be used for the ecological monitoring of various insect populations and for pest control. Although a full-scale use of karyotypic details for constructing phylogenies of large insect taxa (except for Diptera which have polygene chromosomes) is possible only in combination with other features, chromosomal characters are still very important for phylogenetic purposes because their evolution is more or less independent of the environment. Chromosomal analysis can be used to reveal and identify sibling species, as well as to identify immature phases of insects. Studies of insect chromosomes may reveal cases of hybridization between forms with different karyotypes. At present, squashed and air-dried preparations are used for studying insect chromosomes. Together with morphometric analysis, differential chromosome staining methods, such as C-and AgNOR-banding, fluorochrome staining, in situ hybridization (including chromosome painting), restriction banding, etc. are being used to detect and document karyotypic differences. An outline of trends and prospects of the comparative insect karyology is given.     

Multiple sequence versions of the Oxytricha fallax 81-MAC alternate processing family

The 81-MAC family consists of three sizes of macronuclear chromosomes in Oxytricha fallax. Clones of these and of micronuclear homologs have been classified according to DNA sequence into three highly homologous (95.9-97.9%), but distinct versions. Version A is represented by a micronuclear clone and by clones of two different-sized macronuclear chromosomes, showing that alternate processing of micronuclear DNA is responsible for the variety of sizes of macronuclear chromosomes. Three Internal Eliminated Sequences (IES's) are demonstrated in Version A micronuclear DNA. Two have been sequenced and show short, flanking direct repeats but no inverted terminal repeats. Version C micronuclear DNA has interruptions in the macronuclear homology which correspond closely to the Version A IES's. Whether they are true IES's is unknown because no Version C macronuclear DNA has been demonstrated. Version C micronuclear DNA may be "macronuclear-homologous" but "micronucleus-limited" and not "macronucleus-destined." Version B is represented by macronuclear DNA clones, but no micronuclear clones. Vegetative micronuclear aneuploidy is suggested. The possible role of micronuclear defects in somatic karyonidal senescence is discussed in light of the precise macronuclear chromosome copy controls demonstrated within the 81-MAC family. These controls apparently operate throughout karyonidal life to maintain 1) a constant absolute amount of 81-MAC sequences in the macronucleus and 2) a constant stoichiometry within the family, both according to version and chromosome size.     

DNAse I digestion of fixed chromosomes specifically reveals NORs in man

Chromosomal preparations were digested with different concentrations of DNAse I for various periods of time and then stained with Giemsa. It was found that this endonuclease rapidly modifies the structure of the chromosomes which then lose most of their stainability. However, small chromosomal segments corresponding to the nucleolar organizers (NORs) in man have been consistently observed. Although DNAse I treatment has permitted us to observe that some NORs are stained less intensely than others, comparisons with silver nitrate-stained NORs have shown a strict correspondence, in metaphase as well as in interphase. Chromosomal proteins seem responsible for this staining.     

The structure of higher eukaryotic chromosomes

Chromosomal structure has been analyzed from the standpoint of core structure and the relationship between interphase and metaphase chromosomal forms. A possible relationship between prokaryotic and eukaryotic chromosomes has also been proposed. The general structural plan offered is a series of DNA-histone loops extending laterally from a core held together by disulfide bond linkages. The models proposed have been derived from a loop model with core very recently proposed by H. Sobell. A short experimental section of this paper demonstrates that S-S cleaving agents as well as trypsin cause easily observable effects on human metaphase chromosomes.     

Analysis of the number of normochromic erythrocytes with micronuclei in the peripheral blood of mice as a method of detecting mutagens

Cytogenic damages both in the bone marrow (5.5-fold increase in the number of cells with chromosomal aberrations) and in the peripheral blood of mice (4.5-fold increase in the frequency of micronuclear polychromatic erythrocytes and 3-fold rise in the number of micronuclear normochromic erythrocytes, as compared to the control) have been observed after a two-week administration of 0.01% cyclophosphamide with drinking water. The micronuclear test on mature erythrocytes from peripheral blood of mice can be an effective method for the identification of mutagenic properties of the factor under study during its long-term action.     

Multiple Sequence Versions of the Oxytricha fallax 81-MAC Alternate Processing Family1

The 81-MAC family consists of three sizes of macronuclear chromosomes in Oxytricha fallax. Clones of these and of micronuclcar homologs have been classified according to DNA sequence into three highly homologous (95.9–97.9%), but distinct versions. Version A is represented by a micronuclear clone and by clones of two different-sized macronuclear chromosomes, showing that alternate processing of micronuclear DNA is responsible for the variety of sizes of macronuclcar chromosomes. Three Internal Eliminated Sequences (IES's) are demonstrated in Version A micronuclcar DNA. Two have been sequenced and show short, flanking direct repeats but no inverted terminal repeats. Version C micronuclear DNA has interruptions in the macronuclear homology which correspond closely to the Version A IES's. Whether they are true IES's is unknown because no Version C macronuclear DNA has been demonstrated. Version C micronuclear DNA may be “macronuclear-homologous” but “micronucleus-limited” and not “macronucleusdestined.” Version B is represented by macronuclear DNA clones, but no micronuclear clones. Vegetative micronuclear aneuploidy is suggested. The possible role of micronuclear defects in somatic karyonidai senescence is discussed in light of the precise macronuclear chromosome copy controls demonstrated within the 81-MAC family. These controls apparently operate throughout karyonidai life to mairitain 1) a constant absolute amount of 81-MAC sequences in the macronuclcus and 2) a constant sioichiometry within the family, both according to version and chromosome size.     

Génotoxicité des chimiothérapies et radiothérapies: Quelles sont les conséquences pour le spermatozoïde humain?

The prognosis of cancer in young men of childbearing potential has been considerably improved over recent decades as a result of therapeutic progress. Chemotherapy and radiotherapy have well known effects on spermatogenesis. Apart from quantitative and qualitative impairment of spermatogenesis, animal studies have also demonstrated nuclear lesions (aneuploidy, presence of adducts, DNA fragmentation, etc.) and sometimes lesions affecting the F1 and F2 generations. Chromosomal studies of human spermatozoa after radiotherapy have demonstrated an increased frequency of chromosomal anomalies. The first studies concerning the effects of chemotherapy used the heterospecific fertilization technique to demonstrate spermatozoal chromosomal anomalies. More recently, thefluorescence in situ hybridization (FISH) technique has been used to study several chromosomes on a large number of spermatozoa. The results of various studies based on small sample sizes vary as a function of the therapeutic protocol administered and the time of sperm collection in relation to the end of treatment. We studied 5 patients who provided a semen sample 6 to 17 months after completing the BOE chemotherapy protocol (Bleomycin, Etoposide, Cisplatin). We demonstrated an increased rate of aneuploid and diploid spermatozoa. The results of our study and those reported by R. Martin et al. [45, 47] suggest the possibility of a transient effect of chemotherapy on gamete chromosomes. Other studies, conducted in the context of Hodgkin’s disease, have demonstrated the transient nature of the aneuploidy effect. Apart from the harmful action on chromosomes, treatments could also damage spermatozoal DNA. Studies conducted on larger sample sizes and using other methods of analysis therefore appear to be essential. In the meantime, it appears preferable to systematically propose semen cryopreservation before treatment and to provide very cautious advice to patients desiring a pregnancy soon after completion of treatment.     

Gene-sized macronuclear DNA molecules are clustered in micronuclear chromosomes of the ciliate Oxytricha nova.

Following the sexual phase of its life cycle, the hypotrichous ciliate Oxytricha nova transforms a copy of its chromosomal micronucleus into a macronucleus containing short, linear DNA molecules with an average size of 2.2 kilobase pairs. In addition, more than 90% of the DNA sequences in the micronuclear genome are eliminated during this process. We have examined the organization of macronuclear DNA molecules in the micronuclear chromosomes. Macronuclear DNA molecules were found to be clustered and separated by less than 550 base pairs in two cloned segments of micronuclear DNA. Recombinant clones of two macronuclear DNA molecules that are adjacent in the micronucleus were also isolated and examined by DNA sequencing. The two macronuclear DNA molecules were found to be separated by only 90 base pairs in the micronuclear genome.     

Chromosomal abnormalities and the morphology of mouse sperm heads.

In the mouse, numerous mutagens, teratogens and carcinogens have been shown to induce marked elevations in the fraction of sperm with head shape abnormalities. Since carcinogens and teratogens may act by causing genetic damage, a likely explanation of these results is that the sperm abnormalities are also caused by genetic damage. There are two more or less distinct classes of genetic damage, chromosomal aberrations and point mutations. In this paper, we provide evidence, that in general, chromosomal aberrations are not responsible for causing abnormally shaped sperm. Chromosomal aberrations could have caused abnormal sperm morphology in a number of ways. One possibility was that the mere presence of a translocated chromosome within the germ cell led to the malformation of the sperm head. A second possibility was that chromosomal imbalance, i.e., aneuploidy, duplications or deficiencies, within the spermatid or haploid cells caused abnormalities in shape. We tested these hypotheses by measuring the level of abnormally shaped sperm in mice homozygous and heterozygous for 24 various reciprocal and Robertsonian translocations. The diploid cells of these mice are known to be chromosomally balanced, containing translocated chromosomes. A predictable proportion of their gametes are, however, chromosomally unbalanced and carry translocated chromosomes. It was found that the levels of sperm abnormalities in these mice were convincingly unrelated to the levels predicted by any of the above hypotheses. Based on these results it seems that sperm abnormalities in mice are not due to the mere presence of translocated chromosomes in germ cells and also not due to chromosomal aneuploidy or duplication-deficiencies of chromosomal segments in the spermatid during development of the sperm.     

A Method for Mapping Germ Line Sequences in Tetrahymena Thermophila Using the Polymerase Chain Reaction

A method for mapping DNA sequences to specific germinal chromosomes in the ciliated protozoan Tetrahymena thermophila has been developed. This mapping technique (PCR mapping) utilizes the polymerase chain reaction and template DNA derived from nullisomic strains to directly assign micronuclear DNA sequences to specific micronuclear chromosomes. Using this technique, a number of unique sequences and short repetitive sequences flanked by unique sequences have been mapped to four of the five germinal chromosomes.     

Fluorescent in situ identification of human marker chromosomes using flow sorting and Alu element-mediated PCR.

A novel approach to the identification of human chromosomes has been developed. Chromosomal in situ hybridization (or "chromosome painting") has been performed using Alu element-mediated PCR products from small quantities (250-500) of flow-sorted normal and abnormal chromosomes. Chromosome paints for various normal chromosomes, including 5, 6, 7, 14, 18, 19, 21, and 22, were generated and shown to be effective in the identification of the appropriate chromosomes. In addition, certain abnormal chromosomes, including a mental retardation-associated deletion chromosome 11 (q22-q23), the products of the constitutional translocation t(11;22), and the CML-associated t(9;22), were used to generate region-specific paints. In each case, the appropriate regions of the chromosomes were highlighted and this strategy is, therefore, well suited to the identification of previously unidentified marker chromosomes. A further direct consequence of this work is that chromosome paints specific for the common aberrant chromosomes, such as the Philadelphia chromosome, can be generated and made widely available. These may find particular use in the analysis of complex or masked chromosomal translocations.     

Studies on the Mitotic Prophase Chromosomal Fibers in Vicia faba

The observations have been made on the structures of mitotic prophase nuclei and chromosomes in Vicia faba root meristematic cells. Two methods, i.e., the cell squashing and the nucleus isolation methods, were applied in present study to prepare the specimen of chromosomes and nuclei. Chromosomal fibers 0.3—0.5 μm in diameter were observed in the squashed preparations stained with Giemsa, and in the isolated nucleus preparations treated with 0.05% EDTA followed by Giemsa staining. Using Feulgen reaction, it has been demonstrated that these fibers are nuclear origin containing DNA. The results suggest that this order of chromosomal fiber may be one structural level in the chromosomes in Vicia faba. This conclusion is in support of the view which holds that there exists an intermediate level of structure between the 250–300Å chromatin fiber and the chromosome.     

Cytogenetic effects of methyl isocyanate exposure in Bhopal

Summary Among human survivors following the methyl isocyanate (MIC) gas tragedy the major complaints have been related to deep-seated suffocation, terrible pain in breathing, and severe ocular irritations. In order to assess the possible genetic effects we have used lymphocyte cultures and screened chromosomes by two techniques; one by looking for chromosomal aberrations and the other by estimating sister-chromatid exchange (SCE) frequencies. Both these paramaters are good indicators of genetic damage in chromosomal DNA. SCE frequencies in lymphocytes have been increased more than three times in MIC-exposed persons. The results were compared to two groups of controls (one group comprising persons present in the same house; the second group of persons were chosen from distant places, 20–50 km away from the incident). Chromosomal breaks have been observed in 10 out of 14 MIC-affected people (71.4%) studied while only 6 out of 28 (21.4%) controls had chromosomal breaks. Some MIC-exposed persons had chromatin bodies in addition to the normal 46 chromosomes. These observations suggest that chromosomal DNA has been damaged.     

The foldback-like transposon Galileo is involved in the generation of two different natural chromosomal inversions of Drosophila buzzatii

Chromosomal inversions are the most common type of genome rearrangement in the genus Drosophila. Although the potential of transposable elements (TEs) for generating inversions has been repeatedly demonstrated in the laboratory, little is known on their role in the generation of natural inversions, which are those effectively contributing to the adaptation and/or evolution of species. We have cloned and sequenced the two breakpoints of the polymorphic inversion 2q7 of D. buzzatii. The sequence analysis of the breakpoint regions revealed the presence in the inverted chromosomes of large insertions, formed by complex assemblies of transposons, that are absent from the chromosomes without the inversion. Among the transposons inserted, the Foldback-like element Galileo, that was previously found responsible of the generation of the widespread inversion 2j of D. buzzatii, is present at both 2q7 breakpoints and is the most likely inducer of the inversion. A detailed study of the nucleotide and structural variation in the breakpoint regions of six chromosomal lines with the 2q7 inversion detected no nucleotide differences between them, which suggests a monophyletic and recent origin. In contrast, a remarkable degree of structural variation was observed in the same six chromosomal lines. It thus appears that the two breakpoints of the inverted chromosomes have become genetically unstable hotspots, as was previously found for the 2j inversion breakpoints. The possibility that this instability is caused by structural properties of Foldback elements is discussed.