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PubMed1981

Pure and mosaic clones--a reflection of differences in mechanisms of mutagenesis by different agents in Saccharomyces cerevisiae.

The induction of pure and mosaic clones has been studied in haploid G1 cells of Saccharomyces cerevisiae. Following treatments with ultraviolet light, methyl methanesulfonate, ethyl methanesulfonate, nitrous acid, and N-methyl-N'-nitro-N-nitrosoguanidine, the relative proportions of pure mutant clones varied from 25 to 100% at comparable survival levels. Ultraviolet light and methyl methanesulfonate produced mainly pure mutant clones, whereas ethyl methanesulfonate and nitrous acid produced mainly mosaics at 59 to 100% survival levels. The ratio of pure to mosaic clones induced by nitrosoguanidine fell between these two classes. These results are consistent with a classification of mutagens on the basis of repair and replication-dependent mechanisms of mutagenesis in other organisms. Agents having actions similar to ultraviolet light may produce mainly pure clones through a pre-replicative process involving an error-prone DNA repair process. Others may produce mainly mosaic mutants due to the different nature of DNA lesions which may require a replication-dependent process for fixation of mutations. Preliminary data from combined treatments of mutagens belonging to two different classes (i.e. ultraviolet light and nitrous acid) suggest the possibility of an interaction between these agents, resulting in a higher proportion of pure clones, possibly due to an inducible process. Studies of induced frequencies of pure and mosaic clones may be useful in the characterization of mutagens with functional differences.

DNA Repair↗
PubMed1992

Effect of 45,X/46,XX mosaicism on root morphology of mandibular premolars.

The effect of X chromosome mosaicism on root morphology of mandibular premolars was studied in 14 females with 45,X/46,XX chromosome constitution. Occurrences of two-rooted premolars and the morphology of the roots were examined from orthopantomograms. Six (43%) of the 45,X/46,XX mosaics had two-rooted mandibular premolars. Two-rooted first premolars were found in four (29%) and second premolars in three (21%); in one, all four mandibular premolars were two-rooted. The results indicate that the frequency of two-rooted mandibular premolars was similar in 45,X/46,XX mosaics and in 45,X females, and in both groups significantly higher than in normal 46,XX females. Compared with 45,X females, the 45,X/46,XX mosaics showed a slight tendency toward more simplified root morphology in the first premolars. The findings suggest that the presence of normal 46,XX cells among the defective 45,X cells does not affect the development of the mandibular premolar roots. Furthermore, the results do not support the earlier proposal that the presence of normal 46,XX cells in 45,X/46,XX mosaic individuals would be reflected in gradual normalization of dental development.

Adult↗
PubMed2006

Detection of hidden Y mosaicism in Turner's syndrome: importance in the prevention of gonadoblastoma.

UNLABELLED: The presence of Y chromosome fragments in patients with Turner's syndrome (TS) is known to increase the risk of gonadoblastoma. The investigation of Y sequences is usually performed only in the presence of marker chromosomes and therefore does not rule out the presence of hidden mosaicism in patients with 45,X TS without any marker. AIMS: 1. To investigate the presence of hidden Y mosaicism in non-mosaic 45,X patients with TS, using samples from different tissues, and its association with the development of gonadoblastoma. STUDY DESIGN: Twenty patients with a 45,X karyotype were studied. The SRY and DYZ3 sequences were amplified by PCR, using genomic DNA from peripheral blood, oral epithelial cells and hair roots. Prophylactic gonadectomy was offered to the Y-positive patients. RESULTS: The analysis of the different tissues revealed that seven (35%) out of the 20 patients studied presented hidden chromosome Y mosaicism. Four of these patients underwent prophylactic gonadectomy, and bilateral gonadoblastoma was found in one of them. CONCLUSIONS: A systematic search for hidden Y chromosome mosaicism in patients with TS and 45,X karyotype is justified by the possibility of developing gonadoblastoma.

Adolescent↗
PubMed2005

Tetraploid/diploid mosaicism with generalized aggressive periodontitis.

BACKGROUND: Changes of chromosome number diploid to triploid or tetraploid states are rare in human pregnancies, where the main clinical features of tetraploidy are delayed growth and/or craniofacial abnormalities. The present report describes the oral features of tetraploid/diploid mosaicism. Although the medical literature described the physical manifestations of this genetic abnormality, the oral features of this disorder were not previously described. METHODS: A 13-year-old patient presented because of his severe periodontal conditions. Clinical, radiological, microbiologic, immunologic, and genetic examinations were conducted. RESULTS: Long eyelashes and mandibular micrognathia were noticeable in his extraoral examination. Intraoral examination revealed significant generalized edema of the gingiva and severe sulcular bleeding on probing. Generalized maxillary and mandibular alveolar destruction was determined with radiographic examination. Actinobacillus actinomycetemcomitans was also detected in his subgingival samples. He was diagnosed as generalized aggressive periodontitis. His medical cytogenetic examination revealed 92,XXYY (25%)/46,XY (75%) karyotype indicating tetraploid/diploid mosaicism. He was given initial and advanced periodontal therapy and he is currently under a routine follow-up period. CONCLUSIONS: This report provides information on the oral characteristics of tetraploid/diploid mosaicism and describes periodontal treatment. Severe periodontal conditions such as aggressive periodontitis may accompany tetraploid/diploid mosaicism subjects and these patients should be frequently seen by their dental practitioners. It is suggested that initial and/or advanced periodontal procedures may be a way of treating tetraploid/diploid mosaicism subjects with aggressive periodontitis. The importance of physical examination and medical consultation is also discussed.

Adolescent↗
PubMed2000

Cell mosaic patterns in the native and regenerated inner retina of zebrafish: implications for retinal assembly.

In part because of its laminar organization and morphologically distinct cell populations, the vertebrate retina has often been used as a system for investigating the assembly of neural structures. The retinas of adult teleost fish, because they grow throughout life and can regenerate following an injury, provide an especially attractive model system for such investigations. In an effort to provide a quantitative foundation for testing hypotheses regarding the mechanisms of pattern formation during growth and regeneration of the vertebrate retina, nearest neighbor and auto-correlation analyses were used to examine the mosaic patterns of eight inner retinal cell groups in the native and regenerated retina of adult zebrafish. In both native and regenerated retina, the mosaic patterns of most inner retinal cells are non-random. However, regenerated mosaics tend toward significantly lower nearest neighbor distances, less orderly patterns, and more variable radial locations than their native retina counterparts. The individual cell groups in both native and regenerated inner retina are likely to be spatially distributed independently. The results support the hypotheses that, in the adult zebrafish: 1) distinct inner retinal cell groups of native retina are also present in regenerated retina; 2) the assembly of inner retinal cell mosaics is controlled by non-random spatial organizing mechanisms during development, growth, and regeneration; and 3) the spatial organization of cell mosaics is disrupted during regeneration. The results suggest that retinal regeneration may represent a spatially disrupted recapitulation of retinal developmental mechanisms.

Animals↗
PubMed2000

Common trisomy mosaicism diagnosed in amniocytes involving chromosomes 13, 18, 20 and 21: karyotype-phenotype correlations.

Karyotype-phenotype correlations of common trisomy mosaicism prenatally diagnosed via amniocentesis was reviewed in 305 new cases from a collaboration of North American cytogenetic laboratories. Abnormal outcome was noted in 10/25 (40%) cases of 47,+13/46, 17/31 (54%) cases of 47,+18/46, 10/152 (6.5%) cases of 47,+20/46, and in 49/97 (50%) cases of 47,+21/46 mosaicism. Risk of abnormal outcome in pregnancies with less than 50% trisomic cells and greater than 50% trisomic cells were: 26% (4/15) versus 60% (6/10) for 47,+13/46, 52% (11/21) versus 75% (6/8) for 47,+18/46, 4.5% (6/132) versus 20% (4/20) 47,+20/46, and 45% (27/60) versus 59% (22/37) for 47,+21/46. Phenotypically normal liveborns were observed with mean trisomic cell lines of 9.3% for 47,+13/46, 8.6% for 47,+18/46, 27% for 47, +20/46, and 17% for 47,+21/46. Cytogenetic confirmation rates were 46% (6/13 cases) for 47,+13/46 mosaicism, 66% (8/12 cases) for 47, +18/46, 10% (10/97 cases) for 47,+20/46, and 44% (24/54 cases) for 47,+21/46. There were higher confirmation rates in pregnancies with abnormal versus normal outcome: 50% versus 44% for 47,+13/46 mosaicism, 100% versus 33% for 47,+18/46, 66% versus 7% for 47, +20/46, and 55% versus 40% for 47,+21/46. Repeat amniocentesis is not helpful in predicting clinical outcome. It may be considered when there is insufficient number of cells or cultures to establish a diagnosis. Fetal blood sampling may have a role in mosaic trisomy 13, 18, and 21 as the risk for abnormal outcome increases with positive confirmation: 1/5 (20%) normal cases versus 5/8 (62%) abnormal cases. High resolution ultrasound examination(s) is recommended for clinical correlation and to facilitate genetic counselling.

Abnormalities, Multiple↗
PubMed2001

[Tissue-specific placental mosaicism for autosomal trisomies in spontaneous human abortuses: mechanisms of formation and phenotypic effects].

The frequencies of autosomal trisomies in extraembryonic human tissues were estimated in the cases of different abnormalities of prenatal development, from the confined placental mosaicism (CPM) with either relatively normal embryogenesis or restricted intrauterine growth to spontaneous abortion. A tissue-specific compartmentalization was found to be characteristic of cell lines with trisomies for individual autosomes. Analysis of various phenotypical effects of chromosomal aberrations associated with mosaicism is necessarily required to understand the mechanisms and factors responsible for tissue chromosomal mosaicism. Based on analysis of the cell karyotype during prenatal diagnosing of chromosome aberrations in tissues of both extraembryonic and embryonic origin, in 1996, Wolstenholme proposed a model of CPM for individual chromosomes. According to the model, the distribution of cell lines with autosomal trisomies between extraembryonic tissues depends on the ratio between meiotic and mitotic mutations early in embryonic development. However, the model cannot be used to study tissue chromosomal mosaicism in spontaneous abortions, because little information is available on cell karyotype in embryonic tissues themselves after intrauterine fetal death. In this work, a model of tissue-specific chromosomal mosaicism was suggested based on the data on cell karyotype determined in extraembryonic tissues alone, which can be helpful in evaluating the contribution of tissue chromosomal differences into the etiology of early intrauterine death. Along with the experimental evidence, comparative analysis of the two models indicated that the meiotic chromosome nondisjunction plays the major role in trisomy formation and the resultant spontaneous arrest of embryonic development. Other factors responsible for tissue-specific distribution of chromosomal aberrations are also discussed. These are differences in cell proliferative activity, as well as changes in compartmentalization and migration of cells with abnormal karyotypes.

Abortion, Spontaneous↗
PubMed2003

[Chromosome 21 mosaicism. A review].

Despite the great efforts contributed to studies on the trisomy 21 etiology, basic mechanisms of nondisjunction are still poorly understood. Even less is known about mosaic variant of trisonomy 21. In this paper, some problems of masaicism are considered: (1) estimation of the prevalence of mosaicism in patients affected with Down syndrome, (2) determination of population rate of parental mosaicism, (3) evaluation of the role of ovarian mosaicism in etiology of Down syndrome, (4) origin of the extra chromosome, (5) mechanisms of production of mosaic lines, (6) phenomenon of skewed sex ratio (female predominance, in fetuses particularly), (7) effect of maternal age.

Chromosomes, Human, Pair 21↗
PubMed1992

Germinal mosaicism and risk calculation in X-linked diseases.

Germinal mosaicism is a major problem in risk estimation for an X-linked disease. A mutation can happen anytime in germ cell development, and the proportion of germ cells bearing the mutated gene is twice the probability of recurrence of the mutation. This proportion could be either very low in late mutations or very high in germinal and somatic mosaicism. When this heterogeneity is taken into consideration, the distribution of the recurrence risk is conveniently represented as a set of discrete classes that may be derived either from models of gametogenesis or from empirical data. A computer program taking into account germinal mosaicism has been devised to calculate the probability of a possible carrier belonging to any of these classes, in order to settle the origin of the mutation of a given family. Germinal mosaicism increases the probability of inheriting the mutation, but this effect is always lowered by the possibility of heterogeneity. When the mother of a possible carrier is not herself a carrier, the risk of her daughter being a carrier is approximately halved, even under the assumption of a high recurrence risk from mosaicism.

Data Interpretation, Statistical↗
PubMed1990

Prenatal diagnosis of chromosome abnormalities. A comparison of the results of various techniques, with special emphasis on mosaicism.

Prenatal diagnosis of chromosome abnormalities can be performed on three different samples; chorion villi (CVS), amniotic fluid (AFS) and fetal blood (FBS). We are presenting data from our own experience on the chromosome analysis of 957 CVS, 1000 AFS and 927 FBS. A total of 69 chromosome abnormalities have been detected in the CVS, 38 in the AFS and 115 in the FBS. The type of abnormalities and their frequencies are compared between the three sampling methods. Our findings are in agreement with published data, and the higher incidence of chromosomal aberrations in the FBS group reflect the greater efficiency with which aneuploidies associated with more severe congenital malformation can be detected by ultrasound. Finally, we reported 18 cases of mosaicism in CVS, 76 in AFS and 31 in FBS. Of these cases, only 10 represented a true mosaicism of the fetus, 98 cases have been classified as pseudomosaicisms and 7 identified as maternal contamination. We have encountered 9 cases of mosaicism confined to the chorionic villi and 1 case limited to the amniotic fluid cells. There appeared to be a similarity between trisomies involved in chorion confined mosaicisms and pseudomosaicism cases of the AFS. The chromosome complement of the placenta may play an important role in the development of the pregnancy, and although a mosaic result in prenatal diagnosis could present difficulties in in the prediction of the fetal karyotype, it might give important information on the general condition of the fetus.

Amniocentesis↗
PubMed1990

[Current interpretation of mosaicism].

The development of cytogenetics and molecular genetics suggests a greater than expected importance of chromosomal, somatic and germ-line mosaicism. Mosaicism may cause varying expressivity of inherited diseases, aggregation of disorders regarded as "new mutations" in ostensibly healthy families, and neoplasia. Detection of latent parental mosaicism may enhance the prevention of abnormal offsprings. In clinical genetics this difficult problem may be solved from two approaches: 1. More thorough cytogenetic investigation of parents of children with chromosome aberrations. 2. Seeking for mild features of congenital disorders. The authors provide examples for these two possibilities from their own findings. Their family investigations suggest that an out-of-phase centromere separation may result in aneuploidy of the offspring even if it occurs in mosaic form in a part of the cells. At the same time, detailed investigation and anthropometric measurements of the parents of 28 children with multiple malformation syndromes revealed characteristic signs in at least one of the parents in 8 families. Among other factors also parental mosaicism should be taken into account, which should be considered in genetic counseling.

Abnormalities, Multiple↗
PubMed1985

Immunological approaches to the purification of putative premalignant hepatocytes from genotypic mosaic rat livers.

Surface-localized rat RT1 alloantigens on isolated hepatocytes have been used to achieve partial purification of putative premalignant liver cells from rats undergoing chemically induced hepatocarcinogenesis. Genotypic mosaic rat livers were constructed by transplantation of carcinogen-altered F-344 (RT1Iv1) or WF (RT1u) donor liver cells into livers of WF X F-344 F1 host rats, whose liver cells bear alloantigens of both parental strains: WF and F-344, RT1u and RT1Iv1, respectively (J. M. Hunt et al., Cancer Res., 42: 227-236, 1982). Donor and host origin hepatocytes were thus distinguishable immunologically with anti-RT1u or anti-RT1Iv1 alloantisera. Donor rats were treated with diethylnitrosamine (200 mg/kg i.p.) followed by an experimental regimen of dietary 2-acetylaminofluorene and partial hepatectomy. Standard host rats received only the 2-acetylaminofluorene-partial hepatectomy regimen. At 10 to 21 days after transplantation, mosaic host rat livers typically contained 7% donor origin hepatocytes, 96% of which were positive histochemically for gamma-glutamyl transpeptidase. Host origin hepatocytes could be effectively purified by affinity chromatography ("panning") of isolated hepatocytes. To obtain donor origin hepatocytes, the putative progenitor cells of liver carcinomas in these mosaic livers, two approaches were used. Alloantibody-mediated rosette formation followed by sedimentation through Ficoll/metrizamide resulted in a 4- to 10-fold enrichment for donor origin hepatocytes isolated from mosaic livers. Similarly, a 5- to 11-fold enrichment for donor origin hepatocytes was achieved by specific alloantibody-mediated cytolysis of host hepatocytes with rabbit complement followed by purification of viable donor origin cells by sedimentation on metrizamide cushions. Hepatocellular carcinomas which developed in the genotypic mosaic host rat livers were excised 17 to 21 months after donor liver cell transplantation and passaged s.c. or i.m. in histocompatible rats. The transplantable tumors were typed for strain of origin by indirect immunofluorescence using rat alloantisera, and five of six tumors displayed antigenicity reflecting donor strain origin. We conclude, therefore, that the transplanted donor liver cell populations contain cellular precursors of hepatocellular carcinomas which may be isolable using combinations of the purification strategies described.

Animals↗
PubMedDate not supplied

[Chromosomal mosaicism after diagnostic chorionic villi biopsy. Subsequent study of the placenta].

Among 311 diagnostic chromosomal analyses after CVS eleven results (mostly chromosomal mosaicism) did not fit completely with the chromosomal sets found in the fetuses and newborns. In all cases chromosomal mosaicism was restricted to the placenta only. All children born after the diagnosis of a chromosomal mosaicism in the placenta were normal. In six cases the investigation of the placenta after termination of pregnancy or birth was possible. In all those cases the mosaicism could be found within the placenta, however, in some cases in a very low percentage. Although occurrence of chromosomal mosaicism in the placenta can hinder chromosomal diagnosis after CVS, the advantages of the method are not neutralized.

Abortion, Eugenic↗
PubMed1984

The origin of mosaic Down syndrome: four cases with chromosome markers.

Four children, a girl and three boys, with diploid/trisomic mosaic Down syndrome were studied for the mechanism of origin of mosaics, using Q- and R-banding heteromorphisms as markers. Three mosaic subjects started as a trisomic zygote followed by the loss of a chromosome 21 at an early mitotic division. Of these, one resulted from a maternal first-meiotic error, another resulted from a paternal first-meiotic event, and the third originated from a first-meiotic error in either parent. The remaining subject could have resulted from either a diploid or a trisomic zygote. These findings, together with a higher proportion of trisomic cells in skin fibroblasts than in peripheral blood lymphocytes in the two patients studied, suggest that the extra chromosome 21 in mosaic Down syndrome patients usually has a meiotic origin. At least two, possibly three, of the diploid cell lines in these mosaics consisted of "uniparental" chromosomes 21, namely, both the homologous members were derived from a parent.

Adult↗
PubMed1984

Investigation of variability among mouse aggregation chimaeras and X-chromosome inactivation mosaics.

Mouse aggregation chimaeras were produced by aggregating C3H/HeH and C3H/HeHa-Pgk-1a/Ws embryos. At mid-term the proportions of the two cell populations in these conceptuses and the X-inactivation mosaic female progeny of C3H/HeH female X C3H/HeHa-Pgk-1a/Ws male matings were estimated using quantitative electrophoresis of phosphoglycerate kinase (PGK-1) allozymes. The percentage of PGK-1B was more variable in the foetus, amnion and yolk sac mesoderm of the chimaeras than in the corresponding tissues of the mosaic conceptuses. Positive correlations were found for the percentage of PGK-1B between these three primitive ectoderm tissues in both chimaeras and mosaics and between the two primitive endoderm tissues (yolk sac endoderm and parietal endoderm) of the chimaeras. There was no significant correlation between the primitive ectoderm and primitive endoderm tissues of the chimaeras. The results suggest that unequal allocation of cell populations to the primitive ectoderm and primitive endoderm considerably increases the variability among chimaeras but variation probably exists before this segregation occurs. The variation that arises before and at this allocation event is present before X-chromosome inactivation occurs in the primitive ectoderm lineage and explains why the proportions of the two cell populations are more variable among chimaeras than mosaics. Additional variation arises within the primitive ectoderm lineage, after X-inactivation. This variation may be greater in chimaeras than mosaics but the evidence is inconclusive. The results also have some bearing on the nature of the allocation of cells to the primitive ectoderm and primitive endoderm lineages and the timing of X-chromosome inactivation in the primitive ectoderm lineage.

Amnion↗
PubMed1995

Molecular studies of chromosomal mosaicism: relative frequency of chromosome gain or loss and possible role of cell selection.

Studies of uniparental disomy and origin of nonmosaic trisomies indicate that both gain and loss of a chromosome can occur after fertilization. It is therefore of interest to determine both the relative frequency with which gain or loss can contribute to chromosomal mosaicism and whether these frequencies are influenced by selective factors. Thirty-two mosaic cases were examined with molecular markers, to try to determine which was the primary and which was the secondary cell line: 16 cases of disomy/trisomy mosaicism (5 trisomy 8, 2 trisomy 13, 1 trisomy 18, 4 trisomy 21, and 4 involving the X chromosome), 14 cases of 45,X/46,XX, and 2 cases of 45,X/47,XXX. Of the 14 cases of mosaic 45,X/46,XX, chromosome loss from a normal disomic fertilization predominated, supporting the hypothesis that 45,X might be compatible with survival only when the 45,X cell line arises relatively late in development. Most cases of disomy/trisomy mosaicism involving chromosomes 13, 18, 21, and X were also frequently associated with somatic loss of one (or more) chromosome, in these cases from a trisomic fertilization. By contrast, four of the five trisomy 8 cases were consistent with a somatic gain of a chromosome 8 during development from a normal zygote. It is possible that survival of trisomy 8 is also much more likely when the aneuploid cell line arises relatively late in development.

Aneuploidy↗
PubMed1992

Chromosomal mosaicism in prenatal diagnosis: a problem still unsolved.

The problems in differentiating chromosomal mosaicism from pseudomosaicism after amniocentesis and CVS are demonstrated in 6 cases. Two cases of true mosaicism (45, X/46, XX and 46, XY/47, XXY) were of clinical relevance. In both cases the aberrant cell line was less expressed in amniotic fluid cells than in fetal blood and cultivated fibroblasts. Two cases of pseudomosaicism (chromosome 2 and chromosome 10 trisomy) originated either from preexisting mutants or from in vitro mutations whereas a case of true chromosome 20 mosaicism indicated the possibility of a mosaic confined to a single fetal tissue. The problems of interpreting mosaicism after CVS is illustrated in a 45, X/46, XY case, in which the abnormal cell line was detectable only in extrembryonic tissue.

Amniocentesis↗
PubMed1998

Trisomy 16 and trisomy 16 Mosaicism: a review.

A review of all prenatal and postnatal diagnoses of trisomy 16 and trisomy 16 mosaicism was carried out in the context of the current understanding of confined placental mosaicism and uniparental disomy (UPD). The prenatal detection of trisomy 16 cells is associated with a high probability of fetal death, preterm delivery, intrauterine growth retardation, and fetal anomalies. Birth defects were typical of those seen in nonmosaic partial duplications of chromosome 16. Surprisingly, anomalies were sometimes limited to a single organ and included some relatively common isolated defects such as a ventricular septal defect, hypospadias, imperforate anus, inguinal hernia, and clubfoot. The risk for abnormality appeared to be higher in those pregnancies in which trisomy 16 cells were identified in amniotic fluid compared to the detection in chorionic villi samples. Contrary to nonmosaic trisomy 16 with an excess of males, mosaic trisomy 16 shows an excess of female karyotypes. Following the prenatal detection of trisomy 16 cells, aneuploid cells are almost never found in fetal or neonatal lymphocytes. Studies on fibroblasts also often fail to confirm the presence of the abnormal cell line even in cases in which multiple anomalies are present. It is likely that trisomy 16 cells are sometimes present in the early developing embryo even though subsequent cytogenetic studies on fetal or neonatal tissues may not detect any aneuploid cells. UPD can be excluded as a mechanism for those anomalies that are common to mosaic trisomy 16 and nonmosaic partial duplications. The term "occult mosaicism" is suggested to describe the situation in which the presence of an abnormal cell line is suspected on the basis of clinical data but unproven by laboratory analysis.

Amniocentesis↗