The makings of anisosomes: Phase separation of proteins within the cell can produce a liquid-inside-a-liquid phase resembling oil droplets in water. Yu et al. now report that an RNA-binding protein called TDP-43, in which mutation and aggregation are linked to amyotrophic lateral sclerosis and frontotemporal dementia, phase separates into complex droplets, which they named anisosomes. This process occurred when TDP-43 lost its ability to bind RNA through disease-causing mutation or posttranslational acetylation. Anisosomes have spherical shells of TDP-43 (with properties of a liquid crystal) surrounding centers of the protein chaperone HSP70. Chaperone activity was required to maintain liquidity. Anisosomes formed in neurons in vivo when proteasome activity was inhibited and were converted into aggregates when adenosine triphosphate (ATP) levels fell. Science , this issue p. eabb4309

The double membrane nuclear envelope (NE), which is contiguous with the ER, contains nuclear pore complexes (NPCs) – the channels for nucleocytoplasmic transport, and the nuclear lamina (NL) – a scaffold for NE and chromatin organization. Since numerous human diseases linked to NE proteins occur in mesenchyme-derived cells, we used proteomics to characterize NE and other subcellular fractions isolated from mesenchymal stem cells and from adipocytes and myocytes. Based on spectral abundance, we calculated enrichment scores for proteins in the NE fractions. We demonstrated by quantitative immunofluorescence microscopy that five little-characterized proteins with high enrichment scores are substantially concentrated at the NE, with Itprip exposed at the outer nuclear membrane, Smpd4 enriched at the NPC, and Mfsd10, Tmx4, and Arl6ip6 likely residing in the inner nuclear membrane. These proteins provide new focal points for studying the functions of the NE. Moreover, our datasets provide a resource for evaluating additional potential NE proteins.