Vol 55, No 10 (2019)

Experimental embryology achievements in the century resulted in the birth of the first child conceived artificially. Besides its obvious social significance, the successful solution of the “test-tube babies” provided also the unique chance for direct inspection of human embryos growing in vitro at their earlier stages. New technologies applied for human gametes and earlier embryos studies, combined with high resolution capacities of modern cytogenetic and molecular methods, helped a lot in elaboration of efficient algorithms for assisted reproductive technologies (ART) and also provided a solid background for illumination of many genetic problems of human development before implantation. The later include input of chromosome aberrations and genome imprinting in pathology of early human development, cytogenetic and molecular mechanisms of the primary embryonic differentiation, genome epigenetic changes from fertilization through cleavage and blastulation, and identification of genes responsible for early development and differentiation. Conspicuous achievements in ART also include the creation of three parental embryos as a new step for the treatment of mitochondrial diseases, elaboration of karyomapping technique amenable for the diagnostics of both chromosomal and genetic pathology, and participation of paternal mitochondria delivered by the sperm in human development. A new era in human development genetics and ART was recently mitigated by the genome editing technique. The necessity of strict regulations for the safe implementation of genome editing in human embryonic development has been stressed. The areas of special attention include all studies of genome editing, production of artificial gametes, growing of chimera embryos for the purposes of organ and tissue transplantation, etc. Conspicuous delay of Russian science in the field of human developmental biology and experimental embryology and the necessity of its urgent support from both the fundamental sciences and clinical medicine have to be stressed.

Differential gene expression during development is maintained by complex regulatory epigenetic mechanisms that provide the formation of different specialized cell types. Subsequently, a multicellular organism is a mosaic of cells with differing epigenetic characteristics. It seems likely that exceeding the limits of normal epigenetic variability may cause the occurrence of pathological mosaic states in which one part of the cell population has a normal epigenotype, while the other part carries modified epigenetic information. In this review, using the genomic imprinting as a classical epigenetic phenomenon, for the first time, the prevalence of epigenetic mosaicism and the mechanisms of its origin, as well as its role in the etiology of hereditary disorders, determined by the dysfunction of imprinted genomic loci are summarized.

In recent years, noninvasive prenatal testing (NIPT) for fetal chromosomal abnormalities has come into wide use. NIPT allows detection of fetal chromosomal abnormalities without invasive sampling of fetal material: by analyzing cell-free fetal DNA in maternal blood. Here, we report on the pilot results of using NIPT at the D.O. Ott Research Institute of Obstetrics, Gynecology and Reproductology (St. Petersburg, Russia). The results obtained in 149 blood samples from pregnant women proved the clinical value of NIPT for detection of fetal trisomies 21, 18, and 13. Aneuploidy was detected in 20 out of 149 samples. Among these 20 aneuploid cases, trisomy 21 amounted to 60%, trisomy 18 – to 25%, and trisomy 13 to 5% of cases. In one sample, double aneuploidy involving chromosomes 13 and 21 was detected, and in one case, trisomy X was identified. In 100% of cases, aneuploidies were confirmed by prenatal karyotyping advocating for the absence of false positive NIPT results. The observed high specificity was consistent with the declared test specificity level of >99.9%. The sensitivity of the method was 100%. To summarize, NIPT is a new reliable technique that will probably soon replace the conventional first trimester combined screening. The only disadvantages of implementing NIPT in Russia are its relatively high cost and the lack of coverage by insurance companies. NGS-based NIPT is suitable for clinical practice and will be widely deployed due to a further cost decrease.

The fluorescence in situ hybridization (FISH) technique allows for the estimation of the number of stable chromosomal aberrations (translocations) in human blood T-lymphocytes decades after radiation exposure. Therefore, it is used for retrospective assessment of irradiation doses received by red bone marrow (RBM). Cytogenetic analysis of individuals exposed on the Techa River in the 1950s to ^89,90Sr, locally irradiating RBM, showed that dose assessment based on FISH data led to underestimation of the actual dose estimated from measurements of whole-body ⁹⁰Sr content. The purpose of current study was to evaluate the dose–effect relationship and the frequency of translocations per 1 Gy of RBM irradiation dose and T-lymphocytes dose for donors living in Techa riverside villages (n = 178; translocation yield = 2389; number of genome equivalents GE = 96 446). Irradiation doses were estimated using the latest version of the Techa River dosimetry system and the T-cell irradiation model. Statistical analysis showed that the frequency of translocations per 1000 GE per 1 Gy of RBM dose was 8.0 ± 0.7; this value was statistically significantly lower than the value estimated for Sellafield radiation workers under external exposure (11.6 ± 1.6). At the same time, the use of T-cell and their progenitor doses led to re-evaluation (increase) in the slope of the dose–response curve to 11.8 ± 1.6 per 1 Gy per 1000 GE, which agreed well with the published data. The obtained estimates of the background frequencies of translocations also were close to the published values ​​for unexposed donors. These findings demonstrate the legitimacy of using a model approach for estimation of irradiation doses in T-lymphocytes and their progenitors and the need to take into account complex T-cell dynamics in interpretation of cytogenetic data for the purposes of biodosimetry.

Most common reasons for pregnancy loss are chromosomal anomalies of the fetus. They are found in as much as half of the miscarriages. The standard technique for assessment of chromosomal abnormalities in spontaneously aborted fetuses has been karyotyping, however, it needs cell culture which is the most vulnerable element of a diagnostic process. At present, there are a number of molecular methods, which skip the necessity of cell culture. In this study, we assess retrospectively the diagnostic yield of two commonly used molecular techniques (MLPA and QF-PCR) for aneuploidy detection in miscarriages. A total of 674 samples were analyzed. The QF-PCR assay for chromosomes 13, 15, 16, 18, 21, 22, X and Y was used. Two subtelomeric and subcentromeric probe kits covering all chromosomes were used in MLPA tests. In QF-PCR test, chromosomal abnormalities were found in 49.5% of cases. Trisomies constituted 25.7%, monosomies X— 12.9% and triploidies—10.9%. In the MLPA series, a total of 55.1% samples turned out to carry a chromosomal aberration. Trisomies were found in 43.2% of all good quality samples, chromosome X monosomies accounted for 13.4% of samples, and triploidies were detected in 11.3%. Both QF-PCR and MLPA methods may be successfully implemented as an alternative for standard karyotype in testing material from spontaneous abortion. QF-PCR has lower sensitivity comparing to MLPA in detecting aneuploidies, however, it is an effective tool for the detection of polyploidies. It should be noted, that using these techniques, the maternal cell contamination should be considered as an important issue.

The diagnosis and treatment of patients with hereditary diseases require the creation of efficient methods for the study of individual genomes. The existing approaches either are aimed at searching for a narrow set of genomic variants or are too expensive to use in routine practice. We studied the possibility of detection point mutations and interchromosomal translocations using sequencing of enriched 3C libraries. We demonstrated that enriched 3C libraries are more informative from the point of view of detecting the variants in exons than whole genome libraries, but are inferior to whole exome data. At the same time, translocations significantly change the profile of the chromatin spatial contacts, which makes it possible to detect efficiently such rearrangements when analyzing enriched 3C libraries.

Populations of the indigenous ethnic groups of Northern Eurasia are of considerable interest for population genomics, both because they have been relatively poorly studied with the use of modern genomic technologies and owing to the specificity of their gene pools that developed in various genetic-demographic conditions. We used genotype data on 242 179 autosomal SNPs of 876 individuals to search for regions with runs of homozygosity of more than 1 Mb. For Siberian populations, the number of runs of homozygosity and their total length was higher than for other populations of Northern Eurasia.