The Centralspindlin proteins Pavarotti and Tumbleweed work with WASH to regulate Nuclear Envelope budding

Abstract

Nuclear envelope (NE) budding is a nuclear pore independent nuclear export pathway, analogous to the egress of herpesviruses, and required for protein quality control, synapse development and mitochondrial integrity. The physical formation of NE buds is dependent on the Wiskott-Aldrich Syndrome protein Wash, its regulatory complex (SHRC), and Arp2/3, and requires Wash actin nucleation activity. However, the machinery governing cargo recruitment and organization within the NE bud remains unknown. Here, we identify Pavarotti (Pav) and Tumbleweed (Tum) as new molecular components of NE budding. Pav and Tum interact directly with Wash and define a second nuclear Wash-containing complex required for NE budding. Interestingly, we find that the actin bundling activities of Wash and Pav are required, suggesting a structural role in the physical and/or organizational aspects of NE buds. Thus, Pav and Tum are providing exciting new entry points into the physical machineries of this alternative nuclear export pathway for large cargos during cell differentiation and development.

Nuclear envelope budding: Getting large macromolecular complexes out of the nucleus

“…[ 10 ] ). Previously published super‐resolution images of stained fixed nuclei have shown co‐localization of lamins with foci buds [ 6,10,11 ] (see Figure 2). Viral NE‐budding requires a Nuclear Egress Complex (NEC) consisting of two virally‐encoded proteins that are needed to recruit viral and cellular kinases to its binding sites along the INM that subsequently modify the nuclear lamina.…”

“…[ 58–63 ] More recently, the Drosophila kinesin‐like MKLP1 ortholog Pavarotti (Pav), along with Tumbleweed (Tum; MgcRacGAP), which together form the centralspindlin complex that bundles and moves along microtubules during cytokinesis, [ 64–69 ] have been shown to work with WASH/SHRC proteins and be enriched in NE buds (see Figure 2C). [ 11 ]…”

“…WASH, along with Pav and Tum, is part of a ∼750 KDa complex that plays a structural role and/or is needed for organizational aspects within NE buds. [ 11 ]…”

“…https://doi.org/10.1083/jcb202211074 (2023). [ 11 ] (D) Schematic of NE bud depicting the non‐uniform enrichment of Pav (red) and punctate enrichment of dFz2C (blue). INM: inner nuclear envelope; OMN: outer nuclear envelope.…”

“…In particular, INM‐encapsulated electron‐dense granules have been observed in yeast and Torsin‐deficient HeLa cells that are similar to the dFz2C foci/NE‐buds observed in Drosophila muscle and salivary gland nuclei. [ 6,20,22 ] While the full relationship between NPCs and NE buds is not yet known, an important difference is that the yeast and HeLa nuclear granules observed are much smaller (∼120 nm) than dFz2C foci/NE‐buds observed in larval muscle (∼200 nm) [ 6 ] or larval salivary glands (∼400 to 500 nm) [ 10,11 ] (see Figure 2E‐F). Another difference is that the perinuclear granules visualized by dFz2C in Drosophila did not overlap with NPCs at the light or EM microscopy levels, [ 6 ] nor were several NPC components examined found to localize to NE budding events in yeast cells, [ 12 ] but this does not rule out the possibility of NPC component involvement in specific aspects of NE budding.…”