Mauro, M. | bioRxiv Science

bioRxiv2019

Local regulation of lipid synthesis controls ER sheet insertion into nuclear envelope holes to complete nuclear closure

The nuclear permeability barrier depends on closure of holes in the nuclear envelope (NE). Here, we use meiotic C. elegans oocytes to demonstrate that local control of glycerophospholipid synthesis by CNEP-1/CTDNEP1 regulates the insertion of ER sheets into NE holes and functions independently of ESCRT-III to ensure NE closure. Deletion of CNEP-1 causes excess incorporation of ER membranes into NE holes and a defective NE permeability barrier. ESCRT-III components accumulate at the NE opening surrounding the meiotic spindle, and loss of NE adaptors for ESCRT-III exacerbates NE sealing defects in cnep-1 mutants. Limiting ER sheet production by restoring glycerophospholipid synthesis in cnep-1 mutants rescued NE permeability defects. 3D analysis showed that membrane sheets feed into and narrow NE holes occluded by meiotic spindle microtubules supporting a role for ER sheet insertion in NE closure. Thus, feeding of ER sheets into NE holes must be coordinated with production of ER sheets near the NE to promote NE closure.

cell biology↗

bioRxiv2017

Dynein Pulling Forces On Ruptured Nuclei Counteract Lamin-Mediated Nuclear Envelope Repair Mechanisms In Vivo

Recent work done exclusively in tissue culture cells revealed that the nuclear envelope (NE) undergoes ruptures leading to transient mixing of nuclear and cytoplasmic components. The duration of transient NE ruptures depends on lamins, however the underlying mechanisms and the relevance to in vivo events is not known. Here, we use C. elegans embryos to show that dynein forces that position nuclei increase the severity of lamin-induced NE ruptures in vivo. In the absence of dynein forces, lamin prevents nuclear-cytoplasmic mixing caused by NE ruptures. By monitoring the dynamics of NE rupture events, we demonstrate that lamin is required for a distinct step in NE recovery that restricts nucleocytoplasmic mixing prior to the full restoration of NE rupture sites. We show that laser-induced puncture of the NE recapitulates phenotypes associated with NE recovery in wild type cells. Surprisingly, we find that embryonic lethality does not correlate with the incidence of NE rupture events suggesting that embryos survive transient losses of NE compartmentalization during early embryogenesis. In addition to presenting the first mechanistic analysis of transient NE ruptures in vivo, this work demonstrates that lamin controls the duration of NE ruptures by opposing dynein forces on ruptured nuclei to allow reestablishment of the NE permeability barrier and subsequent restoration of NE rupture sites.

developmental biology↗