The nucleus acts as a ruler tailoring cell responses to spatial constraints.

The microscopic environment inside a metazoan organism is highly crowded. Whether individual cells can tailor their behavior to the limited space remains unclear. In this study, we found that cells measure the degree of spatial confinement by using their largest and stiffest organelle, the nucleus. Cell confinement below a resting nucleus size deforms the nucleus, which expands and stretches its envelope. This activates signaling to the actomyosin cortex via nuclear envelope stretch-sensitive proteins, up-regulating cell contractility. We established that the tailored contractile response constitutes a nuclear ruler-based signaling pathway involved in migratory cell behaviors. Cells rely on the nuclear ruler to modulate the motive force that enables their passage through restrictive pores in complex three-dimensional environments, a process relevant to cancer cell invasion, immune responses, and embryonic development.

ESCRT III repairs nuclear envelope ruptures during cell migration to limit DNA damage and cell death.

In eukaryotic cells, the nuclear envelope separates the genomic DNA from the cytoplasmic space and regulates protein trafficking between the two compartments. This barrier is only transiently dissolved during mitosis. Here, we found that it also opened at high frequency in migrating mammalian cells during interphase, which allowed nuclear proteins to leak out and cytoplasmic proteins to leak in. This transient opening was caused by nuclear deformation and was rapidly repaired in an ESCRT (endosomal sorting complexes required for transport)-dependent manner. DNA double-strand breaks coincided with nuclear envelope opening events. As a consequence, survival of cells migrating through confining environments depended on efficient nuclear envelope and DNA repair machineries. Nuclear envelope opening in migrating leukocytes could have potentially important consequences for normal and pathological immune responses.

Preferential retroviral-mediated transduction of EBV- and CMV-specific T cells after polyclonal T-cell activation.

Graft-versus-host disease, resulting from the T cells present in allogeneic hematopoietic stem cell (HSC) inoculums, can potentially be treated if a suicide gene has been introduced into the donor T cells. However, the diversity and functionality of the transfused T-cell population, including EBV- (EBV-T) and CMV-specific (CMV-T) CD8+ T cells, which are particularly important for immunosuppressed individuals undergoing HSC transplants, are often modified by the gene transfer protocol. Here, we show that following polyclonal T-cell activation, EBV-T and CMV-T cells are preferentially transduced by oncoretroviral vectors, as compared to the bulk CD8+ T-cell population. This preferential transduction is associated with higher surface levels of PiT-2, the receptor for the amphotropic envelope with which the virions are pseudotyped. Moreover, EBV-T and CMV-T cells proliferate more extensively as compared to bulk CD8+ T cells. Thus, retroviral-mediated transduction can be biased toward a given antigenic specificity, even under conditions of polyclonal stimulation.