Assessing Skewed X-Chromosome Inactivation.

We describe a simple and straightforward method for detection and characterization of X-chromosome inactivation in females and/or individuals with more than one X chromosome. The X-chromosome inactivation pattern is visualized on a single-cell level using 5-ethynyl-2-deoxyuridine (EdU) instead of the previously widely applied 5-bromo-2'-deoxyuridine (BUdR). The fluorochrome-labeled nucleoside analog EdU is incorporated into late-replication chromosomal regions of living blood cells in vitro; thus, it can also be used to specifically highlight the inactive X chromosome within a cytogenetic preparation. The EdU-based test for assessing skewed X-chromosome inactivation can only be meaningfully applied if the X chromosome of the index patient can be cytogenetically distinguished under a microscope from the normal one. © 2018 by John Wiley & Sons, Inc.

Comprehensive Analyses of White-Handed Gibbon Chromosomes Enables Access to 92 Evolutionary Conserved Breakpoints Compared to the Human Genome.

Gibbon species (Hylobatidae) impress with an unusually high number of numerical and structural chromosomal changes within the family itself as well as compared to other Hominoidea including humans. In former studies applying molecular cytogenetic methods, 86 evolutionary conserved breakpoints (ECBs) were reported in the white-handed gibbon (Hylobates lar, HLA) with respect to the human genome. To analyze those ECBs in more detail and also to achieve a better understanding of the fast karyotype evolution in Hylobatidae, molecular data for these regions are indispensably necessary. In the present study, we obtained whole chromosome-specific probes by microdissection of all 21 HLA autosomes and prepared them for aCGH. Locus-specific DNA probes were also used for further molecular cytogenetic characterization of selected regions. Thus, we could map 6 yet unreported ECBs in HLA with respect to the human genome. Additionally, in 26 of the 86 previously reported ECBs, the present approach enabled a more precise breakpoint mapping. Interestingly, a preferred localization of ECBs within segmental duplications, copy number variant regions, and fragile sites was observed.

Application of BAC-probes to visualize copy number variants (CNVs).

Copy number variations (CNVs) are structural variations of the human genome. These alterations result in variant copy numbers of certain stretches of DNA. In other words, some regions may be present in more or less copies than in a reference genome; however, these copy number changes do not have any impact on the phenotype. Also, CNVs may be extremely large and cytogenetically detectable or submicroscopic but still spanning several megabasepairs (Mb). In the recent years, array technology has identified especially the latter ones as so-called copy number variant (CNV) polymorphisms. These CNVs are detected in ~12 % of the human genome sequences and may comprise several hundred kilobasepairs. CNVs contribute significantly to the inter-individual differences in humans, and can range between 0.5 and 1.5 Mb amongst different genomes, well within the level of detection using cytogenetics techniques. Thus, they can be visualized by FISH using bacterial artificial chromosomes (BACs) as probes. Here we describe a method that enables discrimination of individual homologous chromosomes at the single cell level based on CNVs in the genome, called parental origin determination fluorescence in situ hybridization (POD-FISH). Possible fields of applications of this single cell-directed approach are in analyses of the parental origin of single chromosomes in inherited and acquired chromosomal aberrations.