Analysis Of Human Chromosomes Research Articles

Mapping Retrotransposon LINE-1 Sequences into Two Cebidae Species and Homo sapiens Genomes and a Short Review on Primates.

This work focuses on the distribution of LINE-1 (a Long Interspersed Nuclear Element) in primates and its role during evolution and as a constituent of the architecture of primate genomes. To pinpoint the LINE-1 repeat distribution and its role among primates, LINE-1 probes were mapped onto chromosomes of Homo sapiens (Hominidae, Catarrhini), Sapajus apella, and Cebus capucinus (Cebidae, Platyrrhini) using fluorescence in situ hybridisation (FISH). The choice of platyrrhine species are due to the fact they are taxa characterised by a high level of rearrangements; for this reason, they could be a useful model for the study of LINE-1 and chromosome evolution. LINE-1 accumulation was found in the two Cebidae at the centromere of almost all acrocentric chromosomes 16–22 and on some bi-armed chromosomes. LINE-1 pattern was similar in the two species but only for chromosomes 6, 8, 10, and 18, due to intrachromosomal rearrangements in agreement with what was previously hypothesised as through g banding. LINE-1 interstitial accumulation was found in humans on the 1, 8, 9, 13–15, and X chromosomes; on chromosomes 8, 9, and 13–15, the signal was also at the centromeric position. This is in agreement with recent and complete molecular sequence analysis of human chromosomes 8 and some acrocentric ones. Thus, the hypothesis regarding a link between LINE-1 and centromeres as well as a link with rearrangements are discussed. Indeed, data analysis leads us to support a link between LINE-1 and inter- and intrachromosomal rearrangements, as well as a link between LINE-1 and structural functions at centromeres in primates.

Analysis of human chromosomes by imaging flow cytometry.

Chromosomal analysis is traditionally performed by karyotyping on metaphase spreads, or by fluorescent in situ hybridization (FISH) on interphase cells or metaphase spreads. Flow cytometry was introduced as a new method to analyze chromosomes number (ploidy) and structure (telomere length) in the 1970s with data interpretation largely based on fluorescence intensity. This technology has had little uptake for human cytogenetic applications primarily due to analytical challenges. The introduction of imaging flow cytometry, with the addition of digital images to standard multi-parametric flow cytometry quantitative tools, has added a new dimension. The ability to visualize the chromosomes and FISH signals overcomes the inherent difficulties when the data is restricted to fluorescence intensity. This field is now moving forward with methods being developed to assess chromosome number and structure in whole cells (normal and malignant) in suspension. A recent advance has been the inclusion of immunophenotyping such that antigen expression can be used to identify specific cells of interest for specific chromosomes and their abnormalities. This capability has been illustrated in blood cancers, such as chronic lymphocytic leukemia and plasma cell myeloma. The high sensitivity and specificity achievable highlights the potential imaging flow cytometry has for cytogenomic applications (i.e., diagnosis and disease monitoring). This review introduces and describes the development, current status, and applications of imaging flow cytometry for chromosomal analysis of human chromosomes.

Involving FCGR images in studying fractality and multifractality in human chromosome 22 and bacteria complete genome

The frequency chaos game representation (FCGR) is a simple yet powerful visualization method of DNA sequences. It provides the possibility of representing genomes by images, revealing in such a way different fractal structures. In this paper, we perform a fractal and multifractal analysis of Human chromosome 22 and some complete genomes based on the FGCR image. We used the fractal dimension (FD) and the multifractality degree (ΔDq) to characterize and distinguish genomes. First, we construct the FCGR image with different orders of human chromosome 22. Next, we calculate the fractal dimension, the general dimension spectrum and the multifractal spectrum of each FCGR image using the box-counting method. Then, we examine the FCGR image fractal and multifractal characteristics impact on highlighting the existence of repetitive DNA sequences in human chromosome 22. We also observe the relationship between fractality and multifractality. After that, we apply this study to bacteria completes genomes and C.elegans chromosome I. The obtained results show that the multifractal spectra of all organisms studied are multifractal-like and chromosome 22 strong multifractality proves its richness of repetitive sequences. Also, we observed that with the increasing the FCGR order value, the multifractality grows and the fractal dimension lessens. Finally, by assigning to each sequence a point in two-dimensional space (FD, ΔDq), we obtained three classes of genomes. We can easily distinguish the human chromosome 22 from other genomes and Bacteria are almost close in the spaces (FD, ΔDq).

Role of mosaic aneuploidy in the development and progression of Huntington's disease

AbstractBackgroundHuntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion mutation in the huntingtin (HTT) gene. HTT encodes the huntingtin protein, which has been shown to localize to spindle poles and is required for proper mitotic spindle orientation, chromosome segregation, and cell cycle regulation. Mutations in HTT lead to the production of a mature huntingtin protein with an expanded polyglutamine region (>35 repeats) at its N terminus. Previous studies have shown that mouse models of HD exhibit defects in microtubule function and in cell cycle regulation. HD is a progressive condition characterized by decline in cognitive and executive functions. Over the years, studies from our laboratory and others have shown elevated levels of aneuploidy in many neurodegenerative disorders that are characterized by cognitive deficits, including Alzheimer’s disease (AD) and frontotemporal lobar degeneration (FTLD). Here, we investigated whether chromosome segregation defects that lead to mosaic aneuploidy and consequent apoptosis may also contribute to neuronal loss in HD.MethodSingle cell suspensions were prepared from human brain samples (cortex and cerebellum) and fibroblast cell lines from HD donors and age‐matched controls and were processed for FISH analysis of human chromosome 21, NeuN immunostaining, and/or TUNEL staining. Single cell suspensions from cerebellum were prepared from mouse models of HD and age‐matched controls for FISH analysis of mouse chromosome 5 or 16, which is syntenic to human chromosome 21.ResultWe observed increased levels of mosaic aneuploidy and associated apoptosis in brain tissues and in cultured fibroblasts from HD donors compared to age‐matched controls. We also observed increased levels of mosaic aneuploidy in brain tissue from HD mice compared to age‐matched controls.ConclusionTogether with our previous studies of AD and FTLD, these data provide evidence that chromosome segregation defects that lead to genomic instability may serve as a shared mechanism underlying many neurodegenerative disorders. Our findings highlight the need to further investigate the biological mechanism(s) underlying HD pathology and set the stage for novel therapeutic approaches to HD that may also be applied to other neurodegenerative disorders.

Segmentation of overlapping chromosome images using U-Net with improved dilated convolutions

Chromosome visualization has been used in human chromosome analysis and is a crucial step in clinical diagnosis and drug development. An important step in chromosome visualization is the extraction of chromosomes from chromosome images obtained by light microscopy. Chromosomes often overlap in a complex and variable manner, resulting in significant challenges in chromosome segmentation. The process of chromosome visualization requires manual intervention and is tedious. A method based on a neural network is proposed for the automatic segmentation of overlapping chromosome images to speed up the workflow of visualizing chromosomes. Three improved dilated convolutions are used in the chromosome image segmentation models based on U-Net. The proposed models successfully segment overlapping chromosomes in two publicly available overlapping chromosome data sets. Our models have better performance than existing overlapping chromosome segmentation methods based on U-Net. In summary, it is demonstrated that the improved dilated convolutions can be used for the automatic segmentation of overlapping chromosome images. The proposed improved dilated convolutions have a stable performance improvement, can be easily extended to the segmentation of multiple overlapping chromosomes, and are suitable as general neural network operations to replace standard convolutions in any network.

Overlapping Chromosome Segmentation using U-Net: Convolutional Networks with Test Time Augmentation

An effective human metaphase chromosome analysis system can be used by doctors as a second opinion during diagnosis. Segmentation is necessary in developing this system to identify and distinguish between individual chromosomes. The main challenge in chromosome segmentation is the separation of overlapping chromosomes. Deep convolutional neural networks have been widely used for medical segmentation, especially with U-Net. This study investigated how Test time augmentation with a suitable number of U-Net layers can improve the design for this semantic segmentation problem. The proposed architecture was trained, validated and tested with 13,434 greyscale images with 88 × 88 pixels of overlapping chromosome pairs. With the implementation of the proposed method, the training result became more accurate without any mislabelling and additional pre-processing became unnecessary. An improved segmentation accuracy of 99.68% was obtained, which was higher than the 99.22% obtained using the method of Hu et al.

The short-sequence design of DNA and its involvement in the 3-D structure of the genome

Recent investigations have shown that isochores are characterized by a 3-D structure which is primarily responsible for the topology of chromatin domains. More precisely, an analysis of human chromosome 21 demonstrated that low-heterogeneity, GC-poor isochores are characterized by the presence of oligo-Adenines that are intrinsically stiff, curved and unfavorable for nucleosome binding. This leads to a structure of the corresponding chromatin domains, the Lamina Associated Domains, or LADs, which is well suited for interaction with the lamina. In contrast, the high-heterogeneity GC-rich isochores are in the form of compositional peaks and valleys characterized by increasing gradients of oligo-Guanines in the peaks and oligo-Adenines in the valleys that lead to increasing nucleosome depletions in the corresponding chromatin domains, the Topological Associating Domains, or TADs. These results encouraged us to investigate in detail the di- and tri-nucleotide profiles of 100 Kb segments of chromosome 21, as well as those of the di- to octa-Adenines and di- to octa-Guanines in some representative regions of the chromosome. The results obtained show that the 3-D structures of isochores and chromatin domains depend not only upon oligo-Adenines and oligo-Guanines but also, to a lower but definite extent, upon the majority of di- and tri-nucleotides. This conclusion has strong implications for the biological role of non-coding sequences.

Machine learning approach for homolog chromosome classification

AbstractAutomated analysis of human chromosomes is a necessary procedure to attain karyotyping and it is highly effective in cytology analysis to detect birth defects in metaspread chromosomes. In this, chromosomes are partitioned into “abnormal” and “normal” categories. However, the success of most traditional classification methods relies on the presence of accurate chromosome segmentation. Despite many years of research in this field, accurate segmentation and classification remains a challenge in the presence of cell clusters and pathologies. Many classification methods focused on hand crafted features, such as length, centromere positions. In this manuscript, proposed method focused on chromosome classification based on deep features using convolutional neural network. It is subsequently trained on various chromosome datasets consisting of adaptively resampled image patches. In the testing phase, average the prediction scores of a similar set of image patches is performed. The proposed method is evaluated on different overlapped, nonoverlapped chromosomes and normal, abnormal datasets. Proposed method better performs than previous algorithms in classification accuracy with 98.7%, area under the curve AUC is 0.97 values, and abnormality detection accuracy is 98.4%.

Structural analysis of human chromosome by FIB/SEM

Structural analysis of human chromosome by FIB/SEM

Relevance of Human Chromosome Analysis Activities against Mutation Concept in Genetics Course

This study describes the relevance of human chromosome analysis activities against genes and cromosomes mutation in genetics course. This activities is to analyze the images of photomicrograph chromosomes of various cases and disorders caused by irregularities of human chromosome number or structure in the form of a karyotype. The purpose of this analysis is to gain relevance practicum against the theory course. Object of this research is the lab activities of analysis human chromosomes. Source of data derived from syllabus documentation, SAP, genetics lecture, lab instructions, journals genetics, and 40 respondents taken by purposive sampling. The results showed analysis of human chromosomes activities can only preach of chromosome mutation concept only. The use of inquiry-based lab project can be to preach more concept of gene mutations with more knowledge coverage, the allocation of more time, greater cost, fewer students so that it matches given to undergraduate student biology deepen molecular genetics. Conclusion of this studies, analysis of human chromosomes activities is relevant to preach human chromosome mutation concept but can not be used to preach concept of gene mutations

Phosphoproteomic analysis of human mitotic chromosomes identified a chromokinesin KIF4A.

Protein phosphorylation is the prime post-translational modification to drive cell division. Identification of phosphorylated proteins and their related kinases has uncovered molecular networks underlying mitotic processes, including chromosome assembly. Here we aimed to identify phosphoproteins from a mitotic chromosome-enriched lysate biochemically using mass spectrometry. We employed the Polo-box domain (PBD) of Polo-like kinase to tether phosphorylated proteins in the lysate. Resulting candidates included a number of chromosomal proteins that would not be identified unless using chromosome-enriched fractions. Among them, we focused to a chromokinesin KIF4A which becomes concentrated along the longitudinal axis of mitotic condensed chromatids. We found that KIF4A is phosphorylated specifically during mitosis, depending on the activity of Cdk1 and Aurora B, which turned out to be required for KIF4A to interact with condensin I. The molecular link between KIF4A and condensin raises an interesting possibility that the interaction of two distantly related ATPases is triggered by mitotic phosphorylation.

Abstract PR02: Aneuploidy as a driver of liver cancer

Abstract Aneuploidy has long been associated with cancer but whether it is a cause or consequence of oncogenesis remains unknown. Hepatocellular Carcinomas have frequent aberrations in chromosomes 1 and 8, and oncogene addiction has yet to be clearly demonstrated in this tumor type. Therefore, we developed a mouse model to test the hypothesis that chromosome instability was a driver of liver cancer. To induce chromosomal instability in mouse hepatocytes, we generated a floxed allele of the spindle accessory checkpoint protein Mad2 and induced Cre-mediated deletion in hepatocytes by intercrossing with an Albumin-Cre transgenic. Loss of Mad2 in hepatocytes resulted in the development of both benign Hepatocellular Adenomas (HCA) and malignant Hepatocellular Carcinomas (HCC) by 12 mo. Backcrossing onto a p53-deficient background increased the penetrance and speed of disease with nearly all double deficient mice having HCC by 4 mo. Analysis of the tumor genome by array CGH showed recurrent gain and loss of whole chromosomes with a lack of small focal alterations. We showed whole chromosomes were under selective pressure by comparing HCCs with HCAs as well as T cell lymphomas that arose in the Mad2 floxed line crossed to an Lck-Cre transgenic. Comparing HCCs to HCAs showed that the magnitude but not the pattern of chromosomal aberrations is what distinguishes these tumor types. Further genetic analysis of HCCs and HCAs from the same mouse showed half of the tumor pairs shared a common ancestor, suggesting that in this model HCAs can progress to HCCs through continuing chromosomal instability. Comparing the genomes of HCCs and T cell lymphomas that resulted from Mad2-deficiency in these different tissues showed tissue-specific gain and loss patterns. Chromosomes 4 and 12 were specifically lost in HCCs but gained in lymphomas while chromosome 18 was gained in HCCs but lost in lymphomas. In addition, chromosome 15 was frequently gained in both tumors. Combined these findings show that gain and loss of whole chromosomes can be evolutionarily selected, resulting in tumorigenesis. Next, we tested how aneuploidy alters cell phenotype to induce cancer by performing matched array CGH and gene expression arrays on 29 HCCs. Gene dosage significantly altered expression since chromosome ploidy was significantly correlated with mRNA expression from that chromosome. We also identified a set of twelve genes that was recurrently over-expressed in over 80% of HCCs; most of this set was also over-expressed in human HCCs. Notably Igf2 in murine HCC was over-expressed by 50 fold. IGF2 over-expression in human HCCs has been linked to aneuploidy through loss of loss of Chr8p which causes global demethylation and loss of imprinting at the IGF2 locus. Thus, aneuploidy events are also able to affect the expression of specific genes. Since aneuploidy is frequently observed in human HCC, we performed a synteny analysis of human and mouse chromosomes to find regions that are gained or lost in both species. Five regions were found to be significantly gained by aneuploidy in both species. These regions were located on human chromosomes 1q and 8q, and mouse chromosomes 1 and 15, with the most frequently amplified region containing MYC (hChr8q/mChr15). In total, we show that chromosomal instability is sufficient to drive liver cancer through evolutionary selection acting on whole chromosomes, that aneuploidy alters cell phenotype through gene dosage and other mechanisms, and that the genetic and phenotypic similarities between this mouse model and human liver cancer suggest that aneuploidy is also a driver of human cancer. Citation Format: Lee A. Albacker, Floris Foijer, Ying Yue, Darin Takemoto, Stehpanie Davis, Rodney T. Bronson, Peter K. Sorger. Aneuploidy as a driver of liver cancer. [abstract]. In: Proceedings of the AACR Special Conference on Translation of the Cancer Genome; Feb 7-9, 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 1):Abstract nr PR02.

Disease specific characteristics of fetal epigenetic markers for non-invasive prenatal testing of trisomy 21

BackgroundNon-invasive prenatal testing of trisomy 21 (T21) is being actively investigated using fetal-specific epigenetic markers (EPs) that are present in maternal plasma. Recently, 12 EPs on chromosome 21 were identified based on tissue-specific epigenetic characteristics between placenta and blood, and demonstrated excellent clinical performance in the non-invasive detection of fetal T21. However, the disease-specific epigenetic characteristics of the EPs have not been established. Therefore, we validated the disease-specific epigenetic characteristics of these EPs for use in non-invasive detection of fetal T21.MethodsWe performed a high-resolution tiling array analysis of human chromosome 21 using a methyl-CpG binding domain-based protein (MBD) method with whole blood samples from non-pregnant normal women, whole blood samples from pregnant normal women, placenta samples of normal fetuses, and placenta samples of T21 fetuses. Tiling array results were validated by bisulfite direct sequencing and qPCR.ResultsAmong 12 EPs, only four EPs were confirmed to be hypermethylated in normal placenta and hypomethylated in blood. One of these four showed a severe discrepancy in the methylation patterns of T21 placenta samples, and another was located within a region of copy number variations. Thus, two EPs were confirmed to be potential fetal-specific markers based on their disease-specific epigenetic characteristics. The array results of these EPs were consisted with the results obtained by bisulfite direct sequencing and qPCR. Moreover, the two EPs were detected in maternal plasma.ConclusionsWe validated that two EPs have the potential to be fetal-specific EPs which is consistent with their disease-specific epigenetic characteristics. The findings of this study suggest that disease-specific epigenetic characteristics should be considered in the development of fetal-specific EPs for non-invasive prenatal testing of T21.

Large scale chromosomal mapping of human microRNA structural clusters

MicroRNAs (miRNAs) can group together along the human genome to form stable secondary structures made of several hairpins hosting miRNAs in their stems. The few known examples of such structures are all involved in cancer development. A large scale computational analysis of human chromosomes crossing sequence analysis and deep sequencing data revealed the presence of >400 structural clusters of miRNAs in the human genome. An a posteriori analysis validates predictions as bona fide miRNAs. A functional analysis of structural clusters position along the chromosomes co-localizes them with genes involved in several key cellular processes like immune systems, sensory systems, signal transduction and development. Immune systems diseases, infectious diseases and neurodegenerative diseases are characterized by genes that are especially well organized around structural clusters of miRNAs. Target genes functional analysis strongly supports a regulatory role of most predicted miRNAs and, notably, a strong involvement of predicted miRNAs in the regulation of cancer pathways. This analysis provides new fundamental insights on the genomic organization of miRNAs in human chromosomes.

AIM1 and LINE-1 Epigenetic Aberrations in Tumor and Serum Relate to Melanoma Progression and Disease Outcome

Aberrations in the methylation status of non-coding genomic repeat DNA sequences and specific gene promoter region are important epigenetic events in melanoma progression. Promoter methylation status in LINE-1 and Absent in melanoma-1(AIM1;6q21) associated with melanoma progression and disease outcome was assessed. LINE-1 and AIM1 methylation status was assessed in paraffin-embedded archival tissues(PEAT)(n=133) and melanoma patients’ serum(n=56). LINE-1 U-Index(hypomethylation) and AIM1 were analyzed in microdissected melanoma PEAT sections. The LINE-1 U-Index of melanoma(n=100) was significantly higher than that of normal skin(n=14) and nevi(n=12)(P=0.0004). LINE-1 U-Index level was elevated with increasing AJCC stage(P<0.0001). AIM1 promoter hypermethylation was found in higher frequency(P=0.005) in metastatic melanoma(65%) than in primary melanomas(38%). When analyzed, high LINE-1 U-Index and/or AIM1 methylation in melanomas were associated with disease-free survival(DFS) and overall survival(OS) in Stage I/II patients (P=0.017, 0.027; respectively). In multivariate analysis, melanoma AIM1 methylation status was a significant prognostic factor of OS(P=0.032). Furthermore, serum unmethylated LINE-1 was at higher levels in both stage III(n=20) and stage IV(n=36) patients compared to healthy donors(n=14)(P=0.022). Circulating methylated AIM1 was detected in patients’ serum and was predictive of OS in Stage IV patients (P=0.009). LINE-1 hypomethylation and AIM1 hypermethylation have prognostic utility in both melanoma patients’ tumors and serum.

Human mitotic chromosome structure: what happened to the 30-nm fibre?

EMBO J 31 7, 1644–1653 February172012 The long-standing view of chromosome packaging is that 10-nm beads-on-a string chromatin fibres fold into higher-order 30-nm fibres, which further twist and coil to form highly condensed chromosomes. After four decades of intense pursuit of the structure and properties of 30-nm chromatin fibres, work of Nishino et al (2012) in this issue of The EMBO Journal demonstrates that regular 30-nm fibres are absent from human mitotic chromosomes. The emerging view is that chromosome-level condensation can be achieved through packaging of 10-nm fibres in a fractal manner.

High Sensitivity TSS Prediction: Estimates of Locations Where TSS Cannot Occur

BackgroundAlthough transcription in mammalian genomes can initiate from various genomic positions (e.g., 3′UTR, coding exons, etc.), most locations on genomes are not prone to transcription initiation. It is of practical and theoretical interest to be able to estimate such collections of non-TSS locations (NTLs). The identification of large portions of NTLs can contribute to better focusing the search for TSS locations and thus contribute to promoter and gene finding. It can help in the assessment of 5′ completeness of expressed sequences, contribute to more successful experimental designs, as well as more accurate gene annotation.MethodologyUsing comprehensive collections of Cap Analysis of Gene Expression (CAGE) and other transcript data from mouse and human genomes, we developed a methodology that allows us, by performing computational TSS prediction with very high sensitivity, to annotate, with a high accuracy in a strand specific manner, locations of mammalian genomes that are highly unlikely to harbor transcription start sites (TSSs). The properties of the immediate genomic neighborhood of 98,682 accurately determined mouse and 113,814 human TSSs are used to determine features that distinguish genomic transcription initiation locations from those that are not likely to initiate transcription. In our algorithm we utilize various constraining properties of features identified in the upstream and downstream regions around TSSs, as well as statistical analyses of these surrounding regions.ConclusionsOur analysis of human chromosomes 4, 21 and 22 estimates ∼46%, ∼41% and ∼27% of these chromosomes, respectively, as being NTLs. This suggests that on average more than 40% of the human genome can be expected to be highly unlikely to initiate transcription. Our method represents the first one that utilizes high-sensitivity TSS prediction to identify, with high accuracy, large portions of mammalian genomes as NTLs. The server with our algorithm implemented is available at http://cbrc.kaust.edu.sa/ddm/.

Structural Analyses of Chromosomes and Their Constituent Proteins

The importance of chromosome structural study is first described. Then an overview of historical imaging methods that enable us to quantitatively understand chromosome images and structure is given with special reference to the identification of small plant chromosomes and development of their quantitative chromosome maps. A three-dimensional understanding of chromosome distribution within a nucleus answers why the gene-rich regions localize at both ends of chromosomes, especially in the case of species with Rabl orientation. Not only imaging methods but also proteomic approaches are effective in understanding chromosome structure. Over 200 proteins have been identified by proteome analysis of human metaphase chromosomes, and are categorized into four distinct groups according to their nature and localization on chromosomes. These are chromosome coating proteins (CCPs), chromosome peripheral proteins (CPPs), chromosome structural proteins (CSPs), and chromosome fibrous proteins (CFPs). A chromosome four layer model has been developed accordingly. Case studies on individual identified proteins are further described, and the functional similarities of CPPs are exemplified. In addition the controversial roles of CSPs (topoisomerase and condensin), especially for development of higher-order chromosome structure, are discussed. Finally, it is concluded that further advances in chromosome research are necessary to solve an enigma lasting nearly two centuries, that is, why chromosomes retain the same shape in plants and animals.

Structural analysis of human chromosomes by atomic force and light microscopy in relation to the distribution of topoisomerase II.ALPHA.

The relationship between the higher-order structure of human metaphase chromosomes and the distribution of topoisomerase IIα was analyzed by a comparison of atomic force microscope (AFM) and fluorescence microscope images of the same chromosome. AFM imaging of chromosomes in liquid revealed the presence of alternating ridges and grooves on the surfaces of the sister chromatids. In contrast, the fluorescence image of the chromosomes stained with the anti-topoisomerase IIα antibody showed that the fluorescence intensity of topoisomerase IIα was not uniform and that there were alternating strong and weak spots along the chromosome axes. A comparison of the AFM image with a fluorescence microscope image of the same chromosome further demonstrated that ridges and grooves corresponded to strong and weak fluorescence intensities of topoisomerase IIα, respectively. These findings suggest that the distribution of topoisomerase IIα has a close connection with the higher-order structure of human metaphase chromosomes.

Chromosome Aberrations in Peripheral Blood Lymphocytes of Croatian Hospital Staff Occupationally Exposed to Low Levels of Ionising Radiation

Medical staff is an occupational group exposed to different agents suspected to induce genetic damage. Among them ionising radiation is the most studied. Cytogenetic analysis of human chromosomes in peripheral lymphocytes allows direct detection of mutation in somatic cells. This study investigated the cytogenetic effects of low-level ionising x-radiation in 48-hour peripheral blood lymphocyte cultures sampled from 765 hospital staff occupationally exposed to several agents known or suspected to induce chromosome damage and compared them with 200 control subjects. The exposed subjects were divided in eight (8) groups according to their specialties and job titles. The exposed groups manifested an increase in all types of chromosome aberrations. Acentric fragments were the most frequent chromosome-type aberration. Dicentric chromosomes were statistically significant only in urologists/gynaecologists. Age and smoking significantly influenced the incidence of dicentrics in the exposed groups. The frequency of ring chromosomes was low in all exposed groups (range: 0-2), and none were found in the control group. These findings indicate the importance of periodic medical checkups of hospital staff occupationally exposed to low doses of ionising radiation. The purpose is to create an individual cytogenetic register, where changes could evidence individual risks.