Taking too long? Close loading screen.
Connect with us

Science

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

Published

on

The nucleus makes the rules

Single cells continuously experience and react to mechanical challenges in three-dimensional tissues. Spatial constraints in dense tissues, physical activity, and injury all impose changes in cell shape. How cells can measure shape deformations to ensure correct tissue development and homeostasis remains largely unknown (see the Perspective by Shen and Niethammer). Working independently, Venturini et al. and Lomakin et al. now show that the nucleus can act as an intracellular ruler to measure cellular shape variations. The nuclear envelope provides a gauge of cell deformation and activates a mechanotransduction pathway that controls actomyosin contractility and migration plasticity. The cell nucleus thereby allows cells to adapt their behavior to the local tissue microenvironment.

Science, this issue p. eaba2644, p. eaba2894; see also p. 295

Structured Abstract

INTRODUCTION

The human body is a crowded place. This crowding is even more acute when the regulation of cell growth and proliferation fails during the formation of a tumor. Dealing with the lack of space in crowded environments presents cells with a challenge. This is especially true for immune cells, whose task is to patrol tissues, causing them to experience both acute and sustained deformation as they move. Although changes in tissue crowding and associated cell shape alterations have been known by pathologists to be key diagnostic traits of late-stage tumors since the 19th century, the impact of these changes on the biology of cancer and immune cells remains unclear. Moreover, it is not known whether cells can detect and adaptively respond to deformations in densely packed spaces.

RATIONALE

To test the hypothesis that cells possess an ability to detect and respond to environmentally induced changes in their shape, we fabricated artificial microenvironments that mimic the conditions experienced by tumor and immune cells in a crowded tissue. By combining dynamic confinement, force measurements, and live cell imaging, we were able to quantify cell responses to precisely controlled physical perturbations of their shape.

RESULTS

Our results show that, although cells are surprisingly resistant to compressive forces, they monitor their own shape and develop an active contractile response when deformed below a specific height. Notably, we find that this is achieved by cells monitoring the deformation of their largest internal compartment: the nucleus. We establish that the nucleus provides cells with a precise measure of the extent of their deformation. Once cell compression exceeds the size of the nucleus, it causes the bounding nuclear envelope (NE) to unfold and stretch. The onset of the contractile response occurs when the NE reaches a fully unfolded state. This transition in the mechanical state of the NE and its membranes permits calcium release from internal membrane stores and activates the calcium-dependent phospholipase cPLA2, an enzyme known to operate as a molecular sensor of nuclear membrane tension and a critical regulator of signaling and metabolism. Activated cPLA2 catalyzes the formation of arachidonic acid, an omega-6 fatty acid that, among other processes, potentiates the adenosine triphosphatase activity of myosin II. This induces contractility of the actomyosin cortex, which produces pushing forces to resist physical compression and to rapidly squeeze the cell out of its compressive microenvironment in an “evasion reflex” mechanism.

CONCLUSION

Although the nucleus has traditionally been considered a passive storehouse for genetic material, our work identifies it as an active compartment that rapidly convers mechanical inputs into signaling outputs, with a critical role of its envelope in this sensing function. The nucleus is able to detect environmentally imposed compression and respond to it by generating a signal that is used to change cell behaviors. This phenomenon plays a critical role in ensuring that cells, such as the immune cells within a tumor, can adapt, survive, and efficiently move through a crowded and mechanically heterogeneous microenvironment. Characterizing the full spectrum of signals triggered by nuclear compression has the potential to elucidate mechanisms underlying signaling, epigenetic, and metabolic adaptations of cells to their mechanoenvironment and is thus an exciting avenue for future research.

The nuclear ruler and its contribution to the “life cycle” of a confined cell.

(1) Cell confinement below resting nucleus size, leading to nuclear deformation and to unfolding, and stretching of the nuclear envelope. (2) Nuclear membrane tension increase, which triggers calcium release, cPLA2 activation, and arachidonic acid (ARA) production. (3) Actomyosin force (F) generation. (4) Increased cell migratory capacity and escape from confinement.

Abstract

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.

Source

Continue Reading
Advertisement
Click to comment

Leave a Reply

Your email address will not be published. Required fields are marked *

Science

Too bright to breed

Published

on

Night light from coastal cities overpowers natural signals for coral spawning from neighboring reefs.

PHOTO: NOKURO/ALAMY STOCK PHOTO

Most coral species reproduce through broadcast spawning. For such a strategy to be successful, coordination has had to evolve such that gametes across clones are released simultaneously. Over millennia, lunar cycles have facilitated this coordination, but the recent development of bright artificial light has led to an overpowering of these natural signals. Ayalon et al. tested for the direct impact of different kinds of artificial light on different species of corals. The authors found that multiple lighting types, including cold and warm light-emitting diode (LED) lamps, led to loss of synchrony and spawning failure. Further, coastal maps of artificial lighting globally suggest that it threatens to interfere with coral reproduction worldwide and that the deployment of LED lights, the blue light of which penetrates deeper into the water column, is likely to make the situation even worse.

Curr. Biol. 10.1016/j.cub.2020.10.039 (2020).

Source

Continue Reading

Science

SpaceX launches Starlink app and provides pricing and service info to early beta testers

Published

on

SpaceX has debuted an official app for its Starlink satellite broadband internet service, for both iOS and Android devices. The Starlink app allows users to manage their connection – but to take part you’ll have to be part of the official beta program, and the initial public rollout of that is only just about to begin, according to emails SpaceX sent to potential beta testers this week.

The Starlink app provides guidance on how to install the Starlink receiver dish, as well as connection status (including signal quality), a device overview for seeing what’s connected to your network, and a speed test tool. It’s similar to other mobile apps for managing home wifi connections and routers. Meanwhile, the emails to potential testers that CNBC obtained detail what users can expect in terms of pricing, speeds and latency.

The initial Starlink public beta test is called the “Better than Nothing Beta Program,” SpaceX confirms in their app description, and will be rolled out across the U.S. and Canada before the end of the year – which matches up with earlier stated timelines. As per the name, SpaceX is hoping to set expectations for early customers, with speeds users can expect ranging from between 50Mb/s to 150Mb/s, and latency of 20ms to 40ms according to the customer emails, with some periods including no connectivity at all. Even with expectations set low, if those values prove accurate, it should be a big improvement for users in some hard-to-reach areas where service is currently costly, unreliable and operating at roughly dial-up equivalent speeds.

Image Credits: SpaceX

In terms of pricing, SpaceX says in the emails that the cost for participants in this beta program will be $99 per moth, plus a one-time cost of $499 initially to pay for the hardware, which includes the mounting kit and receiver dish, as well as a router with wifi networking capabilities.

The goal eventually is offer reliably, low-latency broadband that provides consistent connection by handing off connectivity between a large constellation of small satellites circling the globe in low Earth orbit. Already, SpaceX has nearly 1,000 of those launched, but it hopes to launch many thousands more before it reaches global coverage and offers general availability of its services.

SpaceX has already announced some initial commercial partnerships and pilot programs for Starlink, too, including a team-up with Microsoft to connect that company’s mobile Azure data centers, and a project with an East Texas school board to connect the local community.

Source

Continue Reading

Science

Erratum for the Report “Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances” by R. Van Klink, D. E. Bowler, K. B. Gongalsky, A. B. Swengel, A. Gentile, J. M. Chase

Published

on

S. Rennie, J. Adamson, R. Anderson, C. Andrews, J. Bater, N. Bayfield, K. Beaton, D. Beaumont, S. Benham, V. Bowmaker, C. Britt, R. Brooker, D. Brooks, J. Brunt, G. Common, R. Cooper, S. Corbett, N. Critchley, P. Dennis, J. Dick, B. Dodd, N. Dodd, N. Donovan, J. Easter, M. Flexen, A. Gardiner, D. Hamilton, P. Hargreaves, M. Hatton-Ellis, M. Howe, J. Kahl, M. Lane, S. Langan, D. Lloyd, B. McCarney, Y. McElarney, C. McKenna, S. McMillan, F. Milne, L. Milne, M. Morecroft, M. Murphy, A. Nelson, H. Nicholson, D. Pallett, D. Parry, I. Pearce, G. Pozsgai, A. Riley, R. Rose, S. Schafer, T. Scott, L. Sherrin, C. Shortall, R. Smith, P. Smith, R. Tait, C. Taylor, M. Taylor, M. Thurlow, A. Turner, K. Tyson, H. Watson, M. Whittaker, I. Woiwod, C. Wood, UK Environmental Change Network (ECN) Moth Data: 1992-2015, NERC Environmental Information Data Centre (2018); .

Source

Continue Reading

Trending