Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, Faculty of Mathematics & Science, The Edmond J. Safra Campus, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
Department of Genetics, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem, 91904, Israel.
Nat Commun. 2023 Aug 12;14(1):4885. doi: 10.1038/s41467-023-40647-6.
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.
荧光蛋白（FP）常用于研究细胞内的蛋白质。在高级荧光显微镜中，FPs 可以报告其他细胞内变量。一个变量是 FP 附近的局部密度，这在研究细胞生物凝聚物内的密度时很有用。在这里，我们表明常见的单体 FP 的荧光寿命的减少报告了局部密度的增加水平。我们展示了这种基于荧光的变量在早期分化前后用于报告在小鼠胚胎干细胞（ESC）中异染色质蛋白 1α（HP1α）内局部密度的分布。我们发现，在多能 ESC 中的 HP1α凝聚物内的局部密度是异质的，不能用单一的液相来解释。然而，早期分化诱导了局部密度的分布朝着更均匀的方向变化，可以解释为类似液体的相。总之，我们提供了一种基于荧光的方法来报告增加的局部密度，并应用它来区分生物凝聚物内的均匀和不均匀的局部密度。
