Madeleine Gross

Early Embryonic Chromosome Instability Results in Stable Mosaic Pattern in Human Tissues

The discovery of copy number variations (CNV) in the human genome opened new perspectives on the study of the genetic causes of inherited disorders and the aetiology of common diseases. Here, a single-cell-level investigation of CNV in different human tissues led us to uncover the phenomenon of mitotically derived genomic mosaicism, which is stable in different cell types of one individual. The CNV mosaic ratios were different between the 10 individuals studied. However, they were stable in the T lymphocytes, immortalized B lymphoblastoid cells, and skin fibroblasts analyzed in each individual. Because these cell types have a common origin in the connective tissues, we suggest that mitotic changes in CNV regions may happen early during embryonic development and occur only once, after which the stable mosaic ratio is maintained throughout the differentiated tissues. This concept is further supported by a unique study of immortalized B lymphoblastoid cell lines obtained with 20 year difference from two subjects. We provide the first evidence of somatic mosaicism for CNV, with stable variation ratios in different cell types of one individual leading to the hypothesis of early embryonic chromosome instability resulting in stable mosaic pattern in human tissues. This concept has the potential to open new perspectives in personalized genetic diagnostics and can explain genetic phenomena like diminished penetrance in autosomal dominant diseases. We propose that further genomic studies should focus on the single-cell level, to better understand the aetiology of aging and diseases mediated by somatic mutations.

Multicolor fluorescence in situ hybridization (FISH) applied to FISH-banding

During the last decade not only multicolor fluorescence in situ hybridization (FISH) using whole chromosome paints as probes, but also numerous chromosome banding techniques based on FISH have been developed for the human and for the murine genome. This review focuses on such FISH-banding techniques, which were recently defined as ‘any kind of FISH technique, which provide the possibility to characterize simultaneously several chromosomal subregions smaller than a chromosome arm. FISH-banding methods fitting that definition may have quite different characteristics, but share the ability to produce a DNA-specific chromosomal banding’. While the standard chromosome banding techniques like GTG lead to a protein-related black and white banding pattern, FISH-banding techniques are DNA-specific, more colorful and, thus, more informative. For some, even high-resolution FISH-banding techniques the development is complete and they can be used for whole genome hybridizations in one step. Other FISH-banding methods are only available for selected chromosomes and/or are still under development. FISH-banding methods have successfully been applied in research in evolution- and radiation-biology, as well as in studies on the nuclear architecture. Moreover, their suitability for diagnostic purposes has been proven in prenatal, postnatal and tumor cytogenetics, indicating that they are an important tool with the potential to partly replace the conventional banding techniques in the future.

The Human Genome Puzzle - the Role of Copy Number Variation in Somatic Mosaicism

The discovery of copy number variations (CNV) in the human genome opened new perspectives in the study of the genetic causes of inherited disorders and the etiology of common diseases. Differently patterned instances of somatic mosaicism in CNV regions have been shown to be present in monozygotic twins and throughout different tissues within an individual. A single-cell-level investigation of CNV in different human cell types led us to uncover mitotically derived genomic mosaicism, which is stable in different cell types of one individual. A unique study of immortalized B-lymphoblastoid cell lines obtained with 20 year interval from the same two subjects shows that mitotic changes in CNV regions may happen early during embryonic development and seem to occur only once, as levels of mosaicism remained stable. This finding has the potential to change our concept of dynamic human genome variation. We propose that further genomic studies should focus on the single-cell level, to understand better the etiology and physiology of aging and diseases mediated by somatic variations.

Altered tissue distribution of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-DNA adducts in mice transgenic for human sulfotransferases 1A1 and 1A2

Soluble sulfotransferases (SULTs) generate electrophilically reactive metabolites from numerous food-borne compounds, environmental contaminants and drugs, often resulting in mutagenicity and carcinogenicity. Substrate specificity, regulation and tissue distribution of SULTs show large interspecies differences. In humans, therefore, SULTs may be involved in the induction of cancer in different tissues than in standard animal models. To construct a rodent model taking some species differences into account, we transferred a 68.5 kb human (h) genomic sequence that comprised the transcribed and long flanking regions of SULT1A1 and 1A2 into murine oocytes. This approach resulted in several mouse lines expressing these human genes in a copy number-dependent manner with a tissue distribution similar to that in humans. In previous in vitro studies, we had demonstrated that human SULT1A1 and 1A2 efficiently catalyze the terminal activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to a mutagen. The transgenic mice were used to study the hSULT1A1/1A2-mediated activation. Tissue distribution and levels of DNA adducts were determined in hSULT1A1/1A2 transgenic and wild-type mice after an oral dosage of PhIP. Transgenic mice exhibited significantly elevated PhIP-DNA adduct levels compared with the wild-type in liver (13-fold), lung (3.8-fold), colon (2-fold), kidney (1.6-fold) and cecum (1.5-fold). Moreover, among the eight tissues examined, liver was the one with the lowest and highest adduct levels in wild-type and transgenic mice, respectively. Hence, expression of hSULT1A1/1A2 not only enhanced the genotoxicity but also substantially changed the organotropism of PhIP.

Complex rearranged small supernumerary marker chromosomes (sSMC), three new cases; evidence for an underestimated entity?

BackgroundSmall supernumerary marker chromosomes (sSMC) are present ~2.6 × 106 human worldwide. sSMC are a heterogeneous group of derivative chromosomes concerning their clinical consequences as well as their chromosomal origin and shape. Besides the sSMC present in Emanuel syndrome, i.e. der(22)t(11;22)(q23;q11), only few so-called complex sSMC are reported.ResultsHere we report three new cases of unique complex sSMC. One was a de novo case with a dic(13 or 21;22) and two were maternally derived: a der(18)t(8;18) and a der(13 or 21)t(13 or 21;18). Thus, in summary, now 22 cases of unique complex sSMC are available in the literature. However, this special kind of sSMC might be under-diagnosed among sSMC-carriers.ConclusionMore comprehensive characterization of sSMC and approaches like reverse fluorescence in situ hybridization (FISH) or array based comparative genomic hybridization (array-CGH) might identify them to be more frequent than only ~0.9% among all sSMC.

A molecular cytogenetic study of chromosome evolution in chimpanzee

We applied multitude multicolor banding (mMCB) in combination with a novel FISH DNA probe set including subcentromeric, subtelomeric and whole chromosome painting probes (subCTM) to characterize a Pan paniscus (PPA) cell line. These powerful techniques allowed us to refine the breakpoints of a pericentric inversion on chimpanzee chromosome 4, and discovered a novel cryptic pericentric inversion in chimpanzee chromosome 11. mMCB provided a starting point for mapping and high resolution analysis of breakpoints on PPA chromosome 4, which are within a long terminal repeat (LTR) and surrounded by segmental duplications, as well as the integration/expansion sites of the interstitial heterochromatin on chimpanzee chromosomes 6 and 14. Moreover, we found evidence at hand for different types of heterochromatin in the chimpanzee genome. Finally, shedding new light on the human/chimpanzee speciation, karyotypes of three members of the genus Pan were studied by mMCB and no cytogenetic differences were found although the phylogenetic distance between these subspecies is suggested to be 2.5 million years.

Banding and molecular cytogenetic studies detected a CBFB-MYH11 fusion gene that appeared as abnormal chromosomes 1 and 16 in a baby with acute myeloid leukemia FAB M4-Eo.

The acute myeloid leukemia (AML) subtype M4Eo occurs in 5% of all AML cases and is usually associated with either an inv(16)(p13.1q22) or a t(16;16)(p13.1;q22) chromosomal abnormality. At the molecular level, these abnormalities generate a CBFB-MYH11 fusion gene. Patients with this genetic alteration are usually assigned to a low-risk group and thus receive standard chemotherapy. AML-M4Eo is rarely found in infants. We describe clinical, conventional banding, and molecular cytogenetic data for a 12-month-old baby with AML-M4Eo and a chimeric CBFB-MYH11 fusion gene masked by a novel rearrangement between chromosomes 1 and 16. This rearrangement characterizes a new type of inv(16)(p13.1q22) masked by a chromosome translocation.

Multicolor-FISH applied to resolve complex chromosomal changes in a case of T-ALL (FAB L2).

We report on a patient with a clinically diagnosed acute lymphoblastic leukemia (ALL) with partial unrecorded complex translocation events especially involving chromosomes 5, 9 and 18. At the GTG-band level the karyotype was abnormal in 20% of the analyzed cells. The complex karyotype was studied in more detail by spectral karyotyping (SKY) and multicolor banding (MCB) to characterize it in more detail. Thus, the karyotype could be described very accurately and in summary three different clones were detected, reflecting a high rate of karyotypic evolution in this patient.