In mammals, the emergence of totipotency after fertilization involves extensive rearrangements of the spatial positioning of the genome1,2. However, the contribution of spatial genome organization to the regulation of developmental programs is unclear3. Here, we have generated high-resolution maps in mouse pre-implantation embryos of genomic interactions with the nuclear lamina, a filamentous meshwork that lines the inner-nuclear membrane. We find that nuclear organisation is not inherited from the maternal germline but is instead established de novo rapidly after fertilisation. The two parental genomes establish lamina-associated domains (LADs4) with different features that converge after the 8-cell stage. We find that the mechanism of LAD establishment is unrelated to DNA replication. Instead, we show that paternal LAD formation in zygotes is prevented by ectopic expression of Kdm5b, suggesting that LAD establishment may be dependent upon remodelling of H3K4 methylation. Together, our data suggest a step-wise assembly model whereby early LAD formation precedes consolidation of Topologically Associating Domains (TADs).
Protein-DNA interactions are critical to the regulation of gene expression, but it remains challenging to define how cell-to-cell heterogeneity in protein-DNA binding influences gene expression variability. Here we report a method for the simultaneous quantification of protein-DNA contacts by combining single-cell DNA adenine methyltransferase identification (DamID) with mRNA sequencing of the same cell (scDam&T-seq). We apply scDam&T-seq to reveal how genome-lamina contacts or chromatin accessibility correlate with gene expression in individual cells. Furthermore, we provide single-cell genome-wide interaction data on a Polycomb-group protein, RING1B, and the associated transcriptome. Our results show that scDam&T-seq is sensitive enough to distinguish mouse embryonic stem cells cultured under different conditions and their different chromatin landscapes. Our method will enable analysis of protein-mediated mechanisms that regulate cell type-specific transcriptional programs in heterogeneous tissues.
Chromosome segregation errors during cell divisions generate aneuploidies and micronuclei, which can undergo extensive chromosomal rearrangements such as chromothripsis1–5. Selective pressures then shape distinct aneuploidy and rearrangement patterns—for example, in cancer6,7—but it is unknown whether initial biases in segregation errors and micronucleation exist for particular chromosomes. Using single-cell DNA sequencing8 after an error-prone mitosis in untransformed, diploid cell lines and organoids, we show that chromosomes have different segregation error frequencies that result in non-random aneuploidy landscapes. Isolation and sequencing of single micronuclei from these cells showed that mis-segregating chromosomes frequently also preferentially become entrapped in micronuclei. A similar bias was found in naturally occurring micronuclei of two cancer cell lines. We find that segregation error frequencies of individual chromosomes correlate with their location in the interphase nucleus, and show that this is highest for peripheral chromosomes behind spindle poles. Randomization of chromosome positions, Cas9-mediated live tracking and forced repositioning of individual chromosomes showed that a greater distance from the nuclear centre directly increases the propensity to mis-segregate. Accordingly, chromothripsis in cancer genomes9 and aneuploidies in early development10 occur more frequently for larger chromosomes, which are preferentially located near the nuclear periphery. Our findings reveal a direct link between nuclear chromosome positions, segregation error frequencies and micronucleus content, with implications for our understanding of tumour genome evolution and the origins of specific aneuploidies during development.
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