Membrane-less organelles (MLOs) are liquid-like subcellular compartments that form through phase separation of proteins and RNA. While their biophysical properties are increasingly understood, their regulation and the consequences of perturbed MLO states for cell physiology are less clear. To study the regulatory networks, we targeted 1,354 human genes and screened for morphological changes of nucleoli, Cajal bodies, splicing speckles, PML nuclear bodies (PML-NBs), cytoplasmic processing bodies, and stress granules. By multivariate analysis of MLO features we identified hundreds of genes that control MLO homeostasis. We discovered regulatory crosstalk between MLOs, and mapped hierarchical interactions between aberrant MLO states and cellular properties. We provide evidence that perturbation of pre-mRNA splicing results in stress granule formation and reveal that PML-NB abundance influences DNA replication rates and that PML-NBs are in turn controlled by HIP kinases. Together, our comprehensive dataset is an unprecedented resource for deciphering the regulation and biological functions of MLOs.

Stress granules are mRNA-protein assemblies formed from nontranslating mRNAs. Stress granules are important in the stress response and may contribute to some degenerative diseases. Here, we describe the stress granule transcriptome of yeast and mammalian cells through RNA-sequencing (RNA-seq) analysis of purified stress granule cores and single-molecule fluorescence in situ hybridization (smFISH) validation. While essentially every mRNA, and some noncoding RNAs (ncRNAs), can be targeted to stress granules, the targeting efficiency varies from <1% to >95%. mRNA accumulation in stress granules correlates with longer coding and UTR regions and poor translatability. Quantifying the RNA-seq analysis by smFISH reveals that only 10% of bulk mRNA molecules accumulate in mammalian stress granules and that only 185 genes have more than 50% of their mRNA molecules in stress granules. These results suggest that stress granules may not represent a specific biological program of messenger ribonucleoprotein (mRNP) assembly, but instead form by condensation of nontranslating mRNPs in proportion to their length and lack of association with ribosomes.