Torsin ATPases influence chromatin interaction of the Torsin regulator LAP1

Abstract

The inner nuclear membrane is functionalized by diverse transmembrane proteins that associate with nuclear lamins and/or chromatin. When cells enter mitosis, membrane-chromatin contacts must be broken to allow for proper chromosome segregation; yet how this occurs remains ill-understood. Unexpectedly, we observed that an imbalance in the levels of the lamina-associated polypeptide 1 (LAP1), an activator of ER-resident Torsin AAA+-ATPases, causes a failure in membrane removal from mitotic chromatin, accompanied by chromosome segregation errors and changes in post-mitotic nuclear morphology. These defects are dependent on a hitherto unknown chromatin-binding region of LAP1 that we have delineated. LAP1-induced NE abnormalities are efficiently suppressed by expression of wild-type but not ATPase-deficient Torsins. Furthermore, a dominant-negative Torsin induces chromosome segregation defects in a LAP1-dependent manner. These results indicate that association of LAP1 with chromatin in the nucleus can be modulated by Torsins in the perinuclear space, shedding new light on the LAP1-Torsin interplay.

LAP1 supports nuclear plasticity during constrained migration

“…We found that mitochondria presenting HA-LAP1B NT or HA-LAP1B uNT on their surface could be strongly relocalised to the GFP-Lamin positive NE, whereas mitochondria expressing HA-LAP1C NT were less able to be relocated (Fig.6b, c). Consistent with the presence of a chromatin-binding domain in LAP1 B’s NT 40 , mitochondria presenting this region were strongly relocalised to the chromatin periphery. In all cases, expression of the HA-LAP1 N-termini on mitochondria induced their clustering, but mitochondria that did not relocalise to the NE were able to strongly recruit GFP-Lamin B1, but not GFP-Lamin A/C.…”

“…In all cases, expression of the HA-LAP1 N-termini on mitochondria induced their clustering, but mitochondria that did not relocalise to the NE were able to strongly recruit GFP-Lamin B1, but not GFP-Lamin A/C. We suggest that as well as containing a chromatin binding region 40 , the unique NT of LAP1B encodes a dominant lamin-binding domain that displays preference for B-type lamins.…”

“…These data suggested that LAP1B might be involved in stronger protein-protein interactions with the nuclear lamina. Nuclear lamins are key nuclear mechanosensors 18 The NT of LAP1 interacts with lamin A/C and lamin B1 39 and Luithle et al, have recently demonstrated the existence of two distinct lamin-binding regions in LAP1’s NT: 1-72 (present in the unique region of LAP1B) and 184-337 (present in both LAP1B and LAP1C) 40 We hypothesised that the different length of the N-termini of LAP1 isoforms might encode differential lamin-binding properties.…”

Embedded Microbubbles for Acoustic Manipulation of Single Cells and Microfluidic Applications

“…We expand the investigation of our device by demonstrating its application for two diverse applications, i.e., single-cell manipulation as well as microfluidic mixing. HeLa cells are a prominent model organism for biomedical as well as genetic research 29,30 and their controlled manipulation exposes great potential to allow for further insights on a single cell level. 3 The image sequence in Figure 4 solid-structure-based acoustic mixers.…”

A CTDNEP1-lipin 1-mTOR regulatory network restricts ER membrane biogenesis to enable chromosome motions necessary for mitotic fidelity

“…Some evidence also suggests that the ER surrounding spindle MTs serves as part of an organelle-exclusion 'spindle envelope' that spatially confines mitotic proteins to the spindle region (Schweizer et al, 2015). Persistent ER membrane contacts with mitotic chromosomes, but not with spindle MTs, have been associated with higher incidences of chromosome missegregation (Champion et al, 2019;Luithle et al, 2020;Schlaitz et al, 2013;Smyth et al, 2012). These studies suggest that the physical removal of ER membranes from mitotic chromosomes is necessary for accurate chromosome segregation; however, how the spatial reorganization of ER membranes and its clearance from the spindle region contributes to mitotic fidelity remains unknown.…”