Complex biology of constitutional ring chromosomes structure and (in)stability revealed by somatic cell reprogramming

Abstract

Human ring chromosomes are often unstable during mitosis, and daughter cells can be partially or completely aneuploid. We studied the mitotic stability of four ring chromosomes, 8, 13, 18, and 22, in long-term cultures of skin fibroblasts and induced pluripotent stem cells (iPSCs) by GTG karyotyping and aCGH. Ring chromosome loss and secondary aberrations were observed in all fibroblast cultures except for r(18). We found monosomy, fragmentation, and translocation of indexed chromosomes. In iPSCs, aCGH revealed striking differences in mitotic stability both between iPSC lines with different rings and, in some cases, between cell lines with the same ring chromosome. We registered the spontaneous rescue of karyotype 46,XY,r(8) to 46,XY in all six iPSC lines through ring chromosome loss and intact homologue duplication with isoUPD(8)pat occurrence, as proven by SNP genotype distribution analysis. In iPSCs with other ring chromosomes, karyotype correction was not observed. Our results suggest that spontaneous correction of the karyotype with ring chromosomes in iPSCs is not universal and that pluripotency is compatible with a wide range of derivative karyotypes. We conclude that marked variability in the frequency of secondary rearrangements exists in both fibroblast and iPSC cultures, expanding the clinical significance of the constitutional ring chromosome.

From contemplation to classification of chromosomal mosaicism in human preimplantation embryos

“…Using IPSCs as analogs of embryonic stem cells (ESCs) makes it possible to simulate the segregation of chromosomes between daughter cells during early postzygotic mitotic cell division and in the ICM, which affects the subsequent status of the chromosomal mosaicism of different germ layers and tissues that are usually unavailable for cytogenetic analysis of preimplantation embryos, fetuses during prenatal diagnosis or patients with chromosomal abnormalities. The culturing of IPSCs and their subsequent directed differentiation into the target cell types or even into 3D organoids (gastruloids, or blastocyst-like structures and human iBlastoids) [74,[100][101][102][103] provide opportunities to trace step by step the dynamics of chromosomal mosaicism, including karyotype self-correction, in IPSCs derived from somatic cells with different chromosomal abnormalities, which can be obtained from carriers of aneuploidy, balanced and unbalanced translocations, Robertsonian translocations, inversions, and unstable chromosome aberrations, such as ring chromosomes [104,105].…”

Prenatal Diagnosis of Small Supernumerary Marker Chromosome 10 by Array-Based Comparative Genomic Hybridization and Microdissected Chromosome Sequencing

“…Data obtained indicate that the ring nature of the sSMC should be considered separately during genetic counselling, taking into account the possibility of ring chromosome secondary rearrangements and inherent instability [20]. The precise determination of the localization of the breakpoint during formation of the ring sSMC does not always allow us to accurately describe its composition and changes in structure and gene content between different cell clones due to dynamic mosaicism.…”

iPSC reprogramming-mediated aneuploidy correction in autosomal trisomy syndromes

“…Spontaneous karyotype correction was observed after reprogramming of skin fibroblasts from Miller–Dieker syndrome patients with ring chromosome 17 or 13. iPSCs generated from patient cells had lost a ring chromosome and had two intact chromosomes by dynamic mosaicism and compensatory uniparental disomy (UPD) [ 12 ] . Another group reprogrammed four fibroblast lines, one each with different ring chromosomes 8, 13, 18, and 22, and found spontaneous correction for ring chromosome 8 [ 13 ] . We established a total of 57 iPSC clones whose trisomy was rescued upon cell reprogramming.…”