DNA degradation during maturation of erythrocytes - molecular cytogenetic characterization of Howell-Jolly bodies

Intra-erythrocytic vacuoles in asplenic patients: elusive genesis and original clearance of unique organelles

The spleen plays a dual role of immune response and the filtration of red blood cells (RBC), the latter function being performed within the unique microcirculatory architecture of the red pulp. The red pulp filters and eliminates senescent and pathological RBC and can expell intra-erythrocytic rigid bodies through the so-called pitting mechanism. The loss of splenic function increases the risk of infections, thromboembolism, and hematological malignancies. However, current diagnostic tests such as quantification of Howell-Jolly Bodies and splenic scintigraphy lack sensitivity or are logistically demanding. Although not widely available in medical practice, the quantification of RBC containing vacuoles, i.e., pocked RBC, is a highly sensitive and specific marker for hyposplenism. The peripheral blood of hypo/asplenic individuals contains up to 80% RBC with vacuoles, whereas these pocked RBC account for less than 4% of RBC in healthy subjects. Despite their value as a spleen function test, intraerythrocytic vacuoles have received relatively limited attention so far, and little is known about their origin, content, and clearance. We provide an overview of the current knowledge regarding possible origins and mechanisms of elimination, as well as the potential function of these unique and original organelles observed in otherwise "empty" mature RBC. We highlight the need for further research on pocked RBC, particularly regarding their potential function and specific markers for easy counting and sorting, which are prerequisites for functional studies and wider application in medical practice.

Mature Red Blood Cells Contain Long DNA Fragments and Could Acquire DNA from Lung Cancer Tissue

Red blood cells (RBC) are commonly known as cells with no nucleus or mitochondria and are assumed to be a transportation vehicle. This study confirms that RBC contain long DNA fragments inside with stain by both microscope and flow cytometry, which covers most nuclear and mitochondrial genome regions by next-generation sequencing (NGS). Such characteristics demonstrate a significant difference compared with A549 cell line or paired peripheral blood mononuclear cell as nucleated cells. To further explore the characteristics of RNA DNA, DNA from 20 RBC samples is sequenced by NGS. Interestingly, several gaps and multiple regions with copy number variation are observed significantly different between different samples, which could be used to distinguish samples with different health status accurately. Using an in vitro co-culture system, it is shown that RBC could absorb DNA-bearing tumorigenic mutations from cancer cell lines but requires cell-to-cell contact. Finally, based on a small scale clinical trial, it is confirmed that common genetic mutations of cancer tissues could be detected in RBC from patients with early-stage non-small-cell lung cancer. This study highlights a new biological phenomenon involving RBC and its translational potential as a novel liquid biopsy technology platform for early cancer screening and diagnosis of malignancy.

Micronuclei as biomarkers of DNA damage, aneuploidy, inducers of chromosomal hypermutation and as sources of pro-inflammatory DNA in humans

Micronuclei (MNi) are among the most widely studied biomarkers of DNA damage and chromosomal instability in humans. They originate from chromosome fragments or intact chromosomes that are not included in daughter nuclei during mitosis. The main reasons for their formation are a lack of functional centromere in the chromosome fragments or whole chromosomes or defects in one or more of the proteins of the mitotic system that, consequently, fails to segregate chromosomes properly. Assays have been developed to measure MNi in peripheral blood lymphocytes, red blood cells as well as various types of epithelial cells such as buccal, nasal, urothelial and cervical cells. Some of the assays have been further developed into micronucleus (MN) cytome assays to include additional nuclear anomalies, cell death and nuclear division biomarkers. In addition, the use of molecular probes has been adopted widely for the purpose of understanding the mechanistic origin of MNi. MN assays in humans are used for the purpose of investigating the genotoxic effects of adverse environmental, life-style and occupational factors, genetic susceptibility to DNA damage, and for determining risk of accelerated aging and diseases affected by genomic instability such as developmental defects and cancer. The emerging new knowledge showing that chromosomes trapped in MNi can undergo a high rate of fragmentation and become massively re-arranged have highlighted the possibility that MN formation is not only a biomarker of induced DNA damage but also a mechanism that drives hypermutation. Furthermore, another line of recent research showed that DNA and chromatin leaking from disrupted MNi triggers the innate immune cGAS-STING mechanism that promotes inflammation which can cause a wide-range of age-related diseases if left unresolved. For these reasons, MN assays in humans have become an increasingly important biomarker of disease initiation and progression across all life-stages.

From Human Cytogenetics to Human Chromosomics

BACKGROUND

The concept of "chromosomics" was introduced by Prof. Uwe Claussen in 2005. Herein, the growing insights into human chromosome structure finally lead to a "chromosomic view" of the three-dimensional constitution and plasticity of genes in interphase nuclei are discussed. This review is dedicated to the memory of Prof. Uwe Claussen (30 April 1945⁻20 July 2008).

RECENT FINDINGS

Chromosomics is the study of chromosomes, their three-dimensional positioning in the interphase nucleus, the consequences from plasticity of chromosomal subregions and gene interactions, the influence of chromatin-modification-mediated events on cells, and even individuals, evolution, and disease. Progress achieved in recent years is summarized, including the detection of chromosome-chromosome-interactions which, if damaged, lead to malfunction and disease. However, chromosomics in the Human Genetics field is not progressing presently, as research interest has shifted from single cell to high throughput, genomic approaches.

CONCLUSION

Chromosomics and its impact were predicted correctly in 2005 by Prof. Claussen. Although some progress was achieved, present reconsiderations of the role of the chromosome and the single cell in Human Genetic research are urgently necessary.

Image-based modeling and scoring of Howell-Jolly Bodies in human erythrocytes

The spleen selectively removes cells with intracellular inclusions, for example, detached nuclear fragments in circulating erythrocytes, called Howell–Jolly Bodies (HJBs). With absent or deficient splenic function HJBs appear in the peripheral blood and can be used as a simple and non‐invasive risk‐indicator for fulminant potentially life‐threatening infection after spleenectomy. However, it is still under debate whether counting of the rare HJBs is a reliable measure of splenic function. Investigating HJBs in premature erythrocytes from patients during radioiodine therapy gives about 10 thousand times higher HJB counts than in blood smears. However, we show that there is still the risk of false‐positive results by unspecific nuclear remnants in the prepared samples that do not originate from HJBs, but from cell debris residing above or below the cell. Therefore, we present a method to improve accuracy of image‐based tests that can be performed even in non‐specialized medical institutions. We show how to selectively label HJB‐like clusters in human blood samples and how to only count those that are undoubtedly inside the cell. We found a “critical distance” d_crit referring to a relative HJB‐Cell distance that true HJBs do not exceed. To rule out false‐positive counts we present a simple inside‐outside‐rule based on d_crit—a robust threshold that can be easily assessed by combining conventional 2D imaging and straight‐forward image analysis. Besides data based on fluorescence imaging, simulations of randomly distributed HJB‐like objects on realistically modelled cell objects demonstrate the risk and impact of biased counting in conventional analysis. © 2017 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of ISAC.

H2AX deficiency is associated with erythroid dysplasia and compromised haematopoietic stem cell function

Myelodysplastic syndromes (MDS) are clonal disorders of haematopoiesis characterised by dysplastic changes of major myeloid cell lines. However, the mechanisms underlying these dysplastic changes are poorly understood. Here, we used a genetically modified mouse model and human patient data to examine the physiological roles of H2AX in haematopoiesis and how the loss of H2AX contributes to dyserythropoiesis in MDS. H2AX knockout mice showed cell-autonomous anaemia and erythroid dysplasia, mimicking dyserythropoiesis in MDS. Also, dyserythropoiesis was increased in MDS patients with the deletion of chromosome 11q23, where H2AX is located. Although loss of H2AX did not affect the early stage of terminal erythropoiesis, enucleation was decreased. H2AX deficiency also led to the loss of quiescence of hematopoietic stem and progenitor cells, which dramatically compromised their bone marrow engraftment. These results reveal important roles of H2AX in late-stage terminal erythropoiesis and hematopoietic stem cell function.

Entstehungsmechanismen von Zellmosaiken

Zellmosaike bilden sich im Zusammenhang mit „nondisjunction“, Translokationen (balanciert oder unbalanciert), nichthomologem „crossing over“ oder sonstigen chromosomalen oder subchromosomalen „rearrangements“ aus, aber auch durch kompletten oder gewebsspezifischen Chimärismus. Am bekanntesten und häufigsten nachgewiesen sind Zellmosaike, die auf Aneuploidien beruhen, während über die Häufigkeit von submikroskopischen, nur molekulargenetisch oder zytogenetisch nachweisbaren, aber niedriggradigen Zellmosaiken nur wenig bekannt ist. Als Grundlage für die Entstehung von Zellmosaiken gelten „Trisomic“- und/oder „Monosomic-rescue“-Vorgänge. Auch „replikative Fehler“ oder „Endoreduplikation“ einzelner oder mehrere Chromosomen, Isochromosomenbildung oder postzygotisches „non-homologous crossing-over“ werden als Entstehungsmechanismen von Zellmosaiken in der Literatur genannt. Insgesamt ist jedoch festzustellen, dass praktisch alle bekannten Modelle zur Mosaikentstehung bislang auf der deskriptiven Ebene verharren. Ein grundlegendes Verständnis über die tatsächlich z. B. beim Trisomic oder Monosomic rescue ablaufenden Vorgänge ist derzeit mangels Daten nicht vorhanden.

Marker chromosomes

Marker chromosomes are a morphologically heterogeneous group of structurally abnormal chromosomes that pose a significant challenge in prenatal diagnosis. Phenotypes associated with marker chromosomes are highly variable and range from normal to severely abnormal. Clinical outcomes are very difficult to predict when marker chromosomes are detected prenatally. In this review, we outline the classification, etiology, cytogenetic characterization, and clinical consequences of marker chromosomes, as well as practical approaches to prenatal diagnosis and genetic counseling.

Somatic mosaicism in cases with small supernumerary marker chromosomes

Somatic mosaicism is something that is observed in everyday lives of cytogeneticists. Chromosome instability is one of the leading causes of large-scale genome variation analyzable since the correct human chromosome number was established in 1956. Somatic mosaicism is also a well-known fact to be present in cases with small supernumerary marker chromosomes (sSMC), i.e. karyotypes of 47,+mar/46. In this study, the data available in the literature were collected concerning the frequency mosaicism in different subgroups of patients with sSMC. Of 3124 cases with sSMC 1626 (52%) present with somatic mosaicism. Some groups like patients with Emanuel-, cat-eye- or i(18p)- syndrome only tend rarely to develop mosaicism, while in Pallister-Killian syndrome every patient is mosaic. In general, acrocentric and non-acrocentric derived sSMCs are differently susceptible to mosaicism; non-acrocentric derived ones are hereby the less stable ones. Even though, in the overwhelming majority of the cases, somatic mosaicism does not have any detectable clinical effects, there are rare cases with altered clinical outcomes due to mosaicism. This is extremely important for prenatal genetic counseling. Overall, as mosaicism is something to be considered in at least every second sSMC case, array-CGH studies cannot be offered as a screening test to reliably detect this kind of chromosomal aberration, as low level mosaic cases and cryptic mosaics are missed by that.

Cytogenetic contribution to uniparental disomy (UPD)

Uniparental disomy (UPD) is often considered as an event to be characterized exclusively by molecular genetic or epigenetic approaches. This review shows that at least one third of UPD cases emerge in connection with or due to a chromosomal rearrangement. Thus, additional (molecular) cytogenetic characterization of UPD cases is essential. Up to now > 1,100 UPD cases detected in clinical, non-tumor cases are reported in the literature. Recently, these cases were summarized in a regularly updated, freely available online database http://www.med.uni-jena.de/fish/sSMC/00START-UPD.htm. Based of this, here the presently known imprinting syndromes, the chromosomal contribution to UPD phenomenon, and the cytogenetic subgroups of UPD, including cases with normal, abnormal balanced or unbalanced karyotype (like e.g. small supernumerary marker chromosomes and Robertsonian translocations) and segmental UPD are reviewed. Furthermore, chromosome fragmentation as a possible mechanism of trisomic rescue is discussed, which might help to explain the observed 1:9 rate of maternal versus paternal UPD present in cases with original trisomic karyotypes. Overall, as UPD is more but an interesting rarity, the genetic background of each "UPD-patient" needs to be characterized besides by molecular methods, also by molecular cytogenetics in detail.