Dynamic Mosaicism Research Articles

Динамический тканеспецифичный мозаицизм кольцевой хромосомы 13

Кольцевая хромосома 13 является редкой структурной хромосомной аномалией. Изменение структуры хромосомы из линейной в кольцевую вызывает ее митотическую нестабильность, приводящую к соматическому динамическому мозаицизму вследствие которого формируются клоны клеток с различным вторичными числовыми и структурными хромосомными перестройками. Цитогеномный анализ культивированных лимфоцитов и фибробластов кожи в представленном случае кольцевой хромосомы 13 в кариотипе пациента с задержкой физического развития, микроцефалией и аномалиями развития выявил различную структуру вторичного геномного дисбаланса, вариабельный уровень динамического мозаицизма и избирательную эволюцию кариотипа. Ring chromosome 13 is a rare type of chromosome structural abnormalities. A change in the linear structure of the chromosome into a circular one causes its mitotic instability, leading to somatic dynamic mosaicism, which results in the formation of cell clones with various secondary numerical and structural chromosomal rearrangements. We report here a study on ring chromosome 13 instability in lymphocyte and fibroblast cultures established from a child with developmental delay, microcephaly and congenital abnormalities. The cytogenomic analysis revealed a different structure of secondary genomic imbalance, variable levels of dynamic mosaicism and selective karyotype evolution.

The past, present, and future for constitutional ring chromosomes: A report of the international consortium for human ring chromosomes.

SummaryHuman ring chromosomes (RCs) are rare diseases with an estimated newborn incidence of 1/50,000 and an annual occurrence of 2,800 patients globally. Over the past 60 years, banding cytogenetics, fluorescence in situ hybridization (FISH), chromosome microarray analysis (CMA), and whole-genome sequencing (WGS) has been used to detect an RC and further characterize its genomic alterations. Ring syndrome featuring sever growth retardation and variable intellectual disability has been considered as general clinical presentations for all RCs due to the cellular losses from the dynamic mosaicism of RC instability through mitosis. Cytogenomic heterogeneity ranging from simple complete RCs to complex rearranged RCs and variable RC intolerance with different relative frequencies have been observed. Clinical heterogeneity, including chromosome-specific deletion and duplication syndromes, gene-related organ and tissue defects, cancer predisposition to different types of tumors, and reproductive failure, has been reported in the literature. However, the patients with RCs reported in the literature accounted for less than 1% of its occurrence. Current diagnostic practice lacks laboratory standards for analyzing cellular behavior and genomic imbalances of RCs to evaluate the compound effects on patients. Under-representation of clinical cases and lack of comprehensive diagnostic analysis make it a challenge for evidence-based interpretation of clinico-cytogenomic correlations and recommendation of follow-up clinical management. Given recent advancements in genomic technologies and organized efforts by international collaborations and patient advocacy organizations, the prospective of standardized cytogenomic diagnosis and evidence-based clinical management for all patients with RCs could be achieved at an unprecedented global scale.

Dynamic epigenetic age mosaicism in the human atherosclerotic artery.

Accelerated epigenetic ageing, a promising marker of disease risk, has been detected in peripheral blood cells of atherosclerotic patients, but evidence in the vascular wall is lacking. Understanding the trends of epigenetic ageing in the atheroma may provide insights into mechanisms of atherogenesis or identify targets for molecular therapy. We surveyed DNA methylation age in two human artery samples: a set of donor-matched, paired atherosclerotic and healthy aortic portions, and a set of carotid artery atheromas. The well-characterized pan-tissue Horvath epigenetic clock was used, together with the Weidner whole-blood-specific clock as validation. For the first time, we document dynamic DNA methylation age mosaicism of the vascular wall that is atherosclerosis-related, switches from acceleration to deceleration with chronological ageing, and is consistent in human aorta and carotid atheroma. At CpG level, the Horvath epigenetic clock showed modest differential methylation between atherosclerotic and healthy aortic portions, weak association with atheroma histological grade and no clear evidence for participation in atherosclerosis-related cellular pathways. Our data suggest caution when assigning a unidirectional DNA methylation age change to the atherosclerotic arterial wall. Also, the results support previous conclusions that epigenetic ageing reflects non-disease-specific cellular alterations.

Митотическая нестабильность кольцевой хромосомы 3

Актуальность. Кольцевая хромосома 3 - редкая хромосомная аномалия, характеризующаяся выраженной вариабельностью фенотипических отклонений. Наиболее характерными проявлениями присутствия в кариотипе кольцевой хромосомы 3 являются пре- и постнатальная задержка роста, задержка психомоторного развития, микроцефалия и другие аномалии развития. Кольцевая структура может приводить к нарушению нормального расхождения хромосом при клеточном делении и вызывает митотическую нестабильность, приводящую к динамическому мозаицизму. В данном сообщении представлен случай митотической нестабильности кольцевой хромосомы 3 у ребенка с множественными пороками и аномалиями развития, демонстрирующий влияние вторичного хромосомного дисбаланса на степень выраженности фенотипических аномалий. Цель: исследование митотической нестабильности кольцевой хромосомы 3. Методы: FISH с ДНК-зондами на хромосому 3. Результаты. При стандартном цитогенетическом исследовании определен кариотип 46,XX,r(3)(p26q29). При FISH-анализе обнаружено наличие нескольких клонов клеток, содержащих различные варианты аномальных по структуре производных кольцевой хромосомы 3. Выводы. Присутствие кольцевых хромосом в геноме является причиной митотической нестабильности, что приводит к формированию соматического динамического мозаицизма. Соматический динамический мозаицизм, вследствие которого образуются клоны клеток с различным хромосомным дисбалансом, вносит существенный вклад в формирование аномального фенотипа. Ring chromosome 3 is a rare chromosomal abnormality with a highly variable phenotype principally characterized by pre- and postnatal growth retardation, developmental delay, mild to severe intellectual disability, microcephaly and mild dysmorphic features. The presence of a ring chromosome causes mitotic instability and often results in dynamic mosaicism with cells showing chromosomal or segmental aneuploidies and leading to various phenotypic consequences. We present a case of mitotic instability of ring chromosome 3 in a child with multiple malformations and developmental abnormalities. Aim: The investigation of ring chromosome 3 instability at mitosis. Methods: FISH with DNA probe on chromosome 3. Results: The karyotype of a child - 46,XX,r(3)(p26q29). FISH analysis revealed a mosaic clones derived from ring chromosome 3. Conclusions: The ring chromosomes are unstable at mitosis and lead to the formation of somatic dynamic mosaicism. Mitotic instability of ring chromosome 3 demonstrates the influence of secondary genetic imbalance on severity of symptoms in our patient.

Four-dimensional, dynamic mosaicism is a hallmark of normal human skin that permits mapping of the organization and patterning of human epidermis during terminal differentiation

Recent findings of mosaicism (DNA sequence variation) challenge the dogma that each person has a stable genetic constitution. Copy number variations, point mutations and chromosome abnormalities in normal or diseased tissues have been described. We studied normal skin mosaicism of a single nucleotide polymorphism (SNP) [rs1426654, p.Thr111Ala] in SLC24A5, an ion transporter gene. This SNP is unusual in that more than 90% of people of European descent have homozygous germline A/A alleles, while more than 90% of East Asians and Blacks have homozygous germline G/G alleles. We found mosaicism in neonatal foreskins as well as in 69% of nearly 600 skin surface scraping samples from 114 donors of different ages. Strikingly, donors with germline (buccal or blood) A/A, A/G or G/G genotypes had all three sequences (A/A, A/G or G/G) in the skin surface scrapings. SNP sequence differences extended within the epidermis in the vertical dimension from basal cell layer to the stratum corneum at the surface, as well as across the two-dimensions of the skin surface. Furthermore, repeated scrapings in the same location revealed variation in the sequences in the same individuals over time, adding a fourth dimension to this variation. We then used this mosaicism to track the movement of epidermal cells during normal differentiation and characterize the patterning of epidermal cells during terminal differentiation. In this coordinated proliferation model of epidermal differentiation, the skin surface is alternatively populated by synchronous, cycling of waves of cells, with each group having a different DNA sequence. These groups of cells abruptly flatten into large sheets at the surface providing patches of uniform SNP sequence. This four-dimensional mosaicism is a normal, previously unrecognized form of dynamic mosaicism in human skin.

30. Dynamic mosaicism of ring chromosomes as characterized by multiple cytogenetic methods: a ring 13 and ring 21 with discordant results between microarray, karyotype, and FISH

Ring chromosomes exhibit complex mitotic behavior with “dynamic mosaicism” resulting in complex and even discordant findings when studied by different methods. Here we present two cases of ring chromosomes identified in liveborn infants, one ring chromosome 13 [r(13)] and one ring chromosome 21 [r(21)]. In both cases, chromosomal microarray analysis identified terminal deletions, consistent with unbalanced rings, as well as mosaic gain across the remainder of the chromosome, suggestive of a sub-population having multiple copies or a double ring. The r(21) array showed an 8.1 Mb terminal deletion encompassing 21q22.2q22.3, and low-level mosaic gain of the remainder of the chromosome estimated at 12%. The r(13) case showed more complex array findings with multiple rearrangements at the breakpoint junctions, including an 11.6 Mb terminal loss of 13q33.1q34 and interstitial gains spanning 5.4 Mb of 13q32.1q33.1, and mosaic gain of the remainder of the chromosome estimated at 20%. In both cases, chromosome analyses confirmed the presence of a ring chromosome; however, clones with double rings or multiple copies of the ring were not found. Instead, monosomic cell populations were present, consistent with loss of the ring. Further characterization of the r(13) by interphase FISH on a direct (uncultured) specimen detected the monosomy 13 clone consistent with karyotype studies but no evidence of gain of 13. Interestingly, CMA performed prenatally showed results consistent with the presence of ring 13 and mosaic monosomy 13, rather than the gain of 13 observed postnatally. These findings demonstrate not only that the characterization of ring chromosomes can lead to different results when examined by different methods, but also when sampling different tissues. Complex array findings suggestive of ring chromosomes warrant additional follow-up to visualize the abnormalities and identify subpopulations masked by dynamic mosaicism that may have implications for prognosis and counseling.

The Laws of the Ring: Governing Mechanisms, Diagnostic Standards, and Therapeutic Potentials for Human Constitutional Ring Chromosomes

Human constitutional ring chromosomes are a rare type of chromosome structural abnormalities. The cytogenomic analysis of ring chromosome cases revealed different genomic imbalances and ring structures, variable levels of dynamic mosaicism, and selective karyotype evolution in different tissues. This cytogenomic heterogeneity is likely correlated with variable clinical manifestations of generalized features of ‘ring chromosome syndrome’, chromosome-specific and segmental aneuploidy related phenotypes, and risks of infertility and various types of cancers. Better understanding of the ‘biologic law’ governing ring chromosome formation and its mitotic segregation can contribute to the ‘diagnostic law’ guiding toward best practice in genetic analyses and the ‘therapeutic law’ for evidence-based treatment and management of ring chromosome disorders. Collaborative efforts are needed to study the biological processes involving ring chromosome formation, mitotic segregation and cell-autonomous correction, to develop cytogenomic diagnostic standards, and to generate registry of ring chromosome cases with defined genomic structures and dynamic mosaicism and detailed clinical manifestations. These efforts could provide more reliable karyotype-phenotype correlations for developing chromosome-specific guidelines and recommendations for genetic counseling and clinical treatment.

A role of stochastic phenotype switching in generating mosaic endothelial cell heterogeneity.

Previous studies have shown that biological noise may drive dynamic phenotypic mosaicism in isogenic unicellular organisms. However, there is no evidence for a similar mechanism operating in metazoans. Here we show that the endothelial-restricted gene, von Willebrand factor (VWF), is expressed in a mosaic pattern in the capillaries of many vascular beds and in the aorta. In capillaries, the mosaicism is dynamically regulated, with VWF switching between ON and OFF states during the lifetime of the animal. Clonal analysis of cultured endothelial cells reveals that dynamic mosaic heterogeneity is controlled by a low-barrier, noise-sensitive bistable switch that involves random transitions in the DNA methylation status of the VWF promoter. Finally, the hearts of VWF-null mice demonstrate an abnormal endothelial phenotype as well as cardiac dysfunction. Together, these findings suggest a novel stochastic phenotype switching strategy for adaptive homoeostasis in the adult vasculature.

Seasonal dynamics of feeding and food relationships of juveniles of Salmonidae in the basin of the Kol River (western Kamchatka)

Feeding of differentage juveniles of Salmonidae with a long freshwater period of life (coho salmon Oncorhynchus kisutsch, cherry salmon O. masou, king salmon O. tschawytscha, Dolly Varden char Salvelinus malma, East Siberian char S. leucomaenis, and Kamchatka steelhead Parasalmo mykiss) in the basin of the Kol River (western Kamchatka) in the summer-autumn period was studied. Comparative anal� ysis of their foraging in tributaries of different types, offchannel habitats, and the mainstem of the river in the period of July to September is provided. Spectra of consumed foods, indices of stomach fullness, and degree of food similarity between juveniles of different species and age classes at different sites of the river system were estimated. At each concrete river site and in each concrete period of time, juveniles of the studied species exhibit low selectivity and feed on highest mass and easily accessible groups of food objects. Biotopical deter� mination of feeding is typical of juveniles of all species. In the course of the vegetation period in juveniles of Salmonidae in the basin of the Kol River, frequent change of the consumed food and increase in indices of stomach fullness occur. The results obtained indicate dynamic mosaicism of trophic relations of juveniles of salmonids that formed in the ecosystem of the Kol River. DOI: 10.1134/S0032945215020125

Abstract 44: Organ-specific Stochastic Phenotype Switching is Required for Endothelial Health

Among unicellular organisms, stochastic phenotype switching is a documented strategy for survival. These populations "hedge their bets": while the majority of their cells are adapted to their present environment, a minority remains poised to thrive under drastically different conditions. Bet hedging has also been described in metazoan cells, primarily in vitro. However, its role in tissue homeostasis has yet to be established. Here, we show that von Willebrand factor (vWF) is expressed in a spatially heterogeneous manner in a small fraction of capillary endothelial cells in the heart, skeletal muscle, lung and brain. Moreover, these mosaic patterns are dynamic, in that vWF expression stochastically toggles ON/OFF over time. By contrast, expression of vWF in the aorta and liver is static in time. In cultured primary endothelial cells, biological noise resulted in mosaic vWF heterogeneity through a promoter-level DNA methylation switch. Finally, vWF-/- mice demonstrated extensive endothelial cell damage in capillaries of the heart and impaired cardiac function, but not kidney or aorta. Taken together, these findings suggest that dynamic mosaicism of vWF expression is functionally relevant and that bet hedging represents a previously unrecognized strategy for adaptive, organ-specific homeostasis.

The changing landscape of chromosome markers

The phenomenon of multiple supernumerary marker chromosomes (SMCs) is a rare event ( http://ssmc-tl.com/sSMC.html ). It is typically accompanied by somatic mosaic variation in the number of intracellular marker chromosomes and their morphology. This dynamic variation is associated with mitosis and complicates diagnosis, as well as predictions of the clinical severity. Until now, the mechanism of SMC formation remains poorly understood, with associated uncertainties about the familial recurrence risk. We describe a paediatric patient with multiple congenital abnormalities and developmental delay associated with dynamic mosaicism for up to three SMCs. Using a combination of conventional and molecular cytogenetic techniques, we clarified the origins of SMCs from five different genomic locations (1q21.1q21.3, 1q21.3q22, 8q11.1q11.23, 9p13.1p12 and 14q11.2). SNP microarray data and family-trio analysis excluded the possibility of secondary uniparental disomy, which may sometimes occur as a result of an accompanying chromosomal rescue event. It also demonstrated that the markers were of maternal origin and consistent with a meiosis II error. Our observations, in concert with published findings from in vitro fertilisation experiments, allow us to propose a novel mechanism to explain the origin of multiple SMCs.

Ring 18 molecular assessment and clinical consequences

Ring chromosome 18 is a rare condition which has predominantly been described by case reports and small case series. We assessed a cohort of 30 individuals with ring 18 using both microarray comparative genomic hybridization (aCGH) and fluorescence in situ hybridization (FISH). We determined that each participant had a unique combination of hemizygosity for the p and q arms. Four ring chromosomes had no detectable deletion of one of the chromosome arms using aCGH. However, two of these ring chromosomes had telomeric sequences detected using FISH. These data confirm the importance of molecular and cytogenetic analysis to determine both chromosome content and morphology. We failed to find dramatic changes in mosaicism percentage between cytogenetic measurements made at the time of diagnosis and those made years later at the time of this study, demonstrating that dynamic ring mosaicism is unlikely to be a major cause of phenotypic variability in the ring 18 population. Lastly, we present data on the clinical features present in our cohort, though the extreme genotypic variability makes it impossible to draw direct genotype-phenotype correlations. Future work will focus on determining the role of specific hemizygous genes in order to create individualized projections of the effect of each person's specific ring 18 compliment.

Ring autosomes: some unexpected findings.

Ring chromosomes are rare entities, usually associated with phenotypic abnormalities in correlation with the loss of genetic material. There are various breakpoints and sometimes there is a dynamic mosaicism that is reflected in clinical features. Most of the ring chromosomes are de novo occurrences. Our study reflects the experience of three Romanian cytogenetic laboratories in the field of ring chromosomes. We present six cases with ring chromosomes involving chromosomes 5, 13, 18, and 21. All ring chromosomes were identified after birth in children with plurimalformative syndromes. The ring chromosome was present in mosaic form in three cases, and this feature reflects the ring’s instability. In case of ring chromosome 5, we report a possible association with oculo-auriculo-vertebral spectrum.

Three Unusual but Cytogenetically Similar Cases With up to Five Different Cell Lines Involving Structural and Numerical Abnormalities of Chromosome 18

We report two prenatal and two postnatal diagnosed cases (the latter monozygotic twins) with ring chromosomes after GTG banding. All four, de novo r(18), cases turned out to be more complex after application of high-resolution molecular cytogenetics techniques such as use of fluorescence in situ hybridization, centromeric probes, multicolor banding, and locus-specific probes for chromosome 18. All four cases are mosaics involving chromosome 18 in up to five different cell lines, including 46,r(18); 46,dr(18); 47,r(18)x2; 46,mar(18); and 45,-18. Mosaicism sharing both numerical and structural anomalies is rare, but rings often appear as mosaics due to their mitotic instability. Overall, patients with ring chromosome 18 usually share clinical features of 18q- syndrome and, less frequently, those of 18p- syndrome. High-resolution molecular cytogenetics techniques were useful in the characterization of cases with dynamic mosaicism and in establishing the relationship between loss or gain of chromosomal material and the phenotype.

Del(X)(p22.1)/r(X)(p22.1q28) dynamic mosaicism in a Turner syndrome patient

We report on a 16-year-old patient with Turner syndrome who presented a mos 46,X,del(X)(p22.1)〚35〛/45,X〚19〛/46,X,r(X)(p22.1q28) 〚6〛 GTG-band karyotype. The R-banding showed that the abnormal X-chromosome was inactive in all 61 cells analyzed. Fluorescence in situ hybridization with a Xp/Yp subtelomeric probe revealed that both abnormal chromosomes lacked the complementary sequences, a fact consistent with a terminal deletion. Besides, the molecular analysis of the human androgen receptor gene showed that the rearranged chromosome was paternal in origin. Since the deleted and the ring chromosomes had the same size and banding pattern, and because the former was the predominant cell line, it was inferred that the Xp– formed a ring in some cells apparently without further loss of genetic material. However, the reverse sequence and even a simultaneous origin due to a complex intrachromosomal exchange are also conceivable. The mild Turner syndrome phenotype is explained by the mosaicism and by the size of the deleted segment.

FISH characterisation of dynamic mosaicism involving an inv dup(15) in a patient with mental retardation

FISH characterisation of dynamic mosaicism involving an inv dup(15) in a patient with mental retardation

FISH characterisation of dynamic mosaicism involving an inv dup(15) in a patient with mental retardation

We report on a man with mental retardation and a complex karyotype with cells containing up to three morphologically distinct supernumerary marker chromosomes (SMCs) in most metaphases. Fluorescence in situ hybridisation studies using chromosome 15-specific probes characterised the presence of seven SMCs all derived from chromosome 15. The results suggest that the patient originally had a large inv dup(15) containing two copies of the Prader-Willi/Angelman critical region which became mitotically unstable, and by a process of dynamic mosaicism various morphologically distinct SMCs arose.

A newborn with ring chromosome 10, aganglionic megacolon, and renal hypoplasia.

A newborn infant is reported who had aganglionic megacolon, renal hypoplasia, severe growth retardation, generalised hypotonia, and various dysmorphic features. Chromosome analysis of lymphocytes and fibroblasts showed a ring chromosome 10 with breakpoints at p13-15 and q26. AluI digestion showed that the ring chromosome was monocentric. FISH with an alpha satellite probe specific for chromosome 10 showed one signal only in about 20% of interphase nuclei. It is suggested that aganglionic megacolon could result from dynamic somatic mosaicism owing to loss of the ring chromosome.

Oriented pattern of membrane-associated vesicles in fibroblasts

The topography of membrane-associated (“pinocytic” or “surface”) vesicles was investigated with freeze-fracturing of cultured human (MRC-5) fibroblasts. The vesicles were found to have a tendency to form longitudinal rows in the direction of the long axis of the cell or its main cytoplasmic processes. Parallel rows often formed irregular areas leaving smooth membrane surfaces between them. Cells in both confluent and nonconfluent cultures showed a similar tendency of the vesicles to be arranged in longitudinal rows. This arrangement was partially disturbed by 10−5 and 10−6 M colchicine and was completely abolished by Cytochalasin B in concentrations of 5, 8, and 10 μg/ml. The linear orientation of the vesicles is thought to be induced by close association of oriented microfilament bundles with the plasma membrane. The patchy distribution of the vesicles on the membrane indicates that the membrane is heterogeneous in structure (dynamic mosaicism of the membrane).