Calculating RNA degradation rates using large-scale normalization in mouse embryonic stem cells.

Data normalization is critical to the process of estimating RNA degradation by analyzing RNA levels when transcription is blocked. Here, we present a protocol for measuring mRNA degradation rates, optimized for mouse embryonic stem cells, using α-amanitin inhibitor. We describe steps for a time course α-amanitin treatment, RNA-seq, and alignment; we then detail procedures for analyzing data and sequence enrichment. Our method relies on large-scale normalization of stable transcripts in genomic RNA-seq measurements, providing reliable readouts. For complete details on the use and execution of this protocol, please refer to Viegas et al.1.

Fluorescent protein lifetimes report densities and phases of nuclear condensates during embryonic stem-cell differentiation.

Fluorescent proteins (FP) are frequently used for studying proteins inside cells. In advanced fluorescence microscopy, FPs can report on additional intracellular variables. One variable is the local density near FPs, which can be useful in studying densities within cellular bio-condensates. Here, we show that a reduction in fluorescence lifetimes of common monomeric FPs reports increased levels of local densities. We demonstrate the use of this fluorescence-based variable to report the distribution of local densities within heterochromatin protein 1α (HP1α) in mouse embryonic stem cells (ESCs), before and after early differentiation. We find that local densities within HP1α condensates in pluripotent ESCs are heterogeneous and cannot be explained by a single liquid phase. Early differentiation, however, induces a change towards a more homogeneous distribution of local densities, which can be explained as a liquid-like phase. In conclusion, we provide a fluorescence-based method to report increased local densities and apply it to distinguish between homogeneous and heterogeneous local densities within bio-condensates.