RNA-seq Mouse 2-cell 1,6-Hexanediol

The majority of our genome is composed of repeated DNA sequences, which assemble into heterochromatin, a highly compacted structure that constrains their mutational potential. How heterochromatin forms during development and how its structure is maintained is not fully understood. Here, we show that mouse heterochromatin phase separates after fertilization, during the earliest stages of mammalian embryogenesis. Using high resolution, quantitative imaging and molecular biology approaches we show that pericentromeric heterochromatin displays liquid-like properties at the 2-cell stage, but it transitions into a more solid-like or gel-like state at the 4-cell stage, when chromocenters mature and heterochromatin becomes silent. Disrupting the condensates results in altered transcript levels of pericentromeric heterochromatin, suggesting a functional role for phase separation in heterochromatin function. Thus, our work shows that mouse heterochromatin forms membrane-less compartments with biophysical properties that change during development and provides new insights into the self-organization of chromatin domains during mammalian embryogenesis. Overall design: Mouse 2-cell stage treated for 1 hour with 1.6-hexanediol and subjected to single-embryo Smart-seq2