Direct binding of Talin to Rap1 is required for cell-ECM adhesion in Drosophila.

Attachment of cells to the extracellular matrix (ECM) via integrins is essential for animal development and tissue maintenance. The cytoplasmic protein Talin (encoded by rhea in flies) is necessary for linking integrins to the cytoskeleton, and its recruitment is a key step in the assembly of the adhesion complex. However, the mechanisms that regulate Talin recruitment to sites of adhesion in vivo are still not well understood. Here, we show that Talin recruitment to, and maintenance at, sites of integrin-mediated adhesion requires a direct interaction between Talin and the GTPase Rap1. A mutation that blocks the direct binding of Talin to Rap1 abolished Talin recruitment to sites of adhesion and the resulting phenotype phenocopies that seen with null alleles of Talin. Moreover, we show that Rap1 activity modulates Talin recruitment to sites of adhesion via its direct binding to Talin. These results identify the direct Talin-Rap1 interaction as a key in vivo mechanism for controlling integrin-mediated cell-ECM adhesion.

The talin head domain reinforces integrin-mediated adhesion by promoting adhesion complex stability and clustering.

Talin serves an essential function during integrin-mediated adhesion in linking integrins to actin via the intracellular adhesion complex. In addition, the N-terminal head domain of talin regulates the affinity of integrins for their ECM-ligands, a process known as inside-out activation. We previously showed that in Drosophila, mutating the integrin binding site in the talin head domain resulted in weakened adhesion to the ECM. Intriguingly, subsequent studies showed that canonical inside-out activation of integrin might not take place in flies. Consistent with this, a mutation in talin that specifically blocks its ability to activate mammalian integrins does not significantly impinge on talin function during fly development. Here, we describe results suggesting that the talin head domain reinforces and stabilizes the integrin adhesion complex by promoting integrin clustering distinct from its ability to support inside-out activation. Specifically, we show that an allele of talin containing a mutation that disrupts intramolecular interactions within the talin head attenuates the assembly and reinforcement of the integrin adhesion complex. Importantly, we provide evidence that this mutation blocks integrin clustering in vivo. We propose that the talin head domain is essential for regulating integrin avidity in Drosophila and that this is crucial for integrin-mediated adhesion during animal development.

Out-of-hospital management of unresponsive, apneic, witnessed opioid overdoses: a case series from a supervised consumption site.

OBJECTIVES: There are conflicting recommendations for lay rescuer management of patients who are unresponsive and apneic due to opioid overdose. We evaluated the management of such patients at an urban supervised consumption site. METHODS: At a single urban supervised consumption site in Vancouver, BC, we conducted a retrospective chart review and administrative database linkage of consecutive patients who were unresponsive and apneic following witnessed opioid overdose between January 1, 2012 and December 31, 2017. We linked these visits with regional hospital records to define the entire care episode, which concluded when the patient was discharged from the supervised consumption site, ED, or hospital, or died. The primary outcome was successful resuscitation, defined as alive and neurologically intact (ambulatory and speaking coherently, or alert and oriented, or Glasgow Coma Scale 15) at the conclusion of the care episode. Secondary outcomes included mortality and predefined complications of resuscitation. RESULTS: We collected 767 patients, with a median age of 43 and 81.6% male, with complete follow-up on 763 patients (99.5%). All patients were managed with oxygen and ventilation (100%, 95% CI 0.995-1.0); 715 (93.2%, 95% CI 0.911-0.949) received naloxone; no patients underwent chest compressions (0%, 95% CI 0-0.005). All patients with complete follow-up were alive and neurologically intact at the end of their care episode (100%, 95% CI 0.994-1.0). Overall, 191 (24.9%) patients were transported to hospital, and 15 (2.0%) patients required additional naloxone after leaving the supervised consumption site; 16 (2.1%) developed complications, and 1 patient was admitted to hospital. CONCLUSIONS: At an urban supervised consumption site, all unresponsive, apneic patients with witnessed opioid overdose were successfully resuscitated with oxygen and/or naloxone. No patients required chest compressions.

RéSUMé: OBJECTIFS: Il existe des recommandations contradictoires concernant la prise en charge par des secouristes non professionnels des patients qui ne réagissent pas et sont apnéiques en raison d'une surdose d'opioïdes. Nous avons évalué la prise en charge de ces patients dans un site urbain de consommation supervisée. MéTHODES: Dans un seul site de consommation supervisée urbain à Vancouver, en Colombie-Britannique, nous avons effectué un examen rétrospectif des dossiers et un couplage de bases de données administratives de patients consécutifs qui étaient insensibles et apnéiques après avoir été témoins d'une surdose d'opioïdes entre le 1er janvier 2012 et le 31 décembre 2017. Le résultat primaire était la réussite de la réanimation, définie comme étant vivante et neurologiquement intacte (ambulatoire et parlant de manière cohérente, ou alerte et orientée, ou échelle de coma de Glasgow 15) à la fin de l'épisode de soins. Les résultats secondaires comprenaient la mortalité et les complications prédéfinies de la réanimation. RéSULTATS: Nous avons recueilli 767 patients, avec un âge médian de 43 ans et 81,6 % d'hommes, avec un suivi complet de 763 patients (99,5 %). Tous les patients ont été pris en charge avec de l'oxygène et la ventilation (100 %, IC à 95 % : 0,995-1,0) ; 715 (93,2 %, IC à 95 % : 0,911-0,949) ont reçu de la naloxone ; aucun patient n'a subi de compressions thoraciques (0 %, IC à 95 % : 0-0,005). Tous les patients ayant fait l'objet d'un suivi complet étaient vivants et intacts sur le plan neurologique à la fin de leur épisode de soins (100 %, IC à 95 % : 0,994-1,0). Dans l'ensemble, 191 (24,9 %) patients ont été transportés à l'hôpital, et 15 (2,0 %) patients ont eu besoin de naloxone supplémentaire après avoir quitté le site de consommation supervisée ; 16 (2,1 %) ont développé des complications, et 1 patient a été admis à l'hôpital. CONCLUSIONS: Dans un centre de consommation supervisée urbain, tous les patients apnéiques non réceptifs ayant été témoins d'une surdose d'opioïdes ont été réanimés avec succès avec de l'oxygène et/ou de la naloxone. Aucun patient n'a eu besoin de compressions thoraciques.

Cell-cell and cell-extracellular matrix adhesions cooperate to organize actomyosin networks and maintain force transmission during dorsal closure.

Tissue morphogenesis relies on the coordinated action of actin networks, cell-cell adhesions, and cell-extracellular matrix (ECM) adhesions. Such coordination can be achieved through cross-talk between cell-cell and cell-ECM adhesions. Drosophila dorsal closure (DC), a morphogenetic process in which an extraembryonic tissue called the amnioserosa contracts and ingresses to close a discontinuity in the dorsal epidermis of the embryo, requires both cell-cell and cell-ECM adhesions. However, whether the functions of these two types of adhesions are coordinated during DC is not known. Here we analyzed possible interdependence between cell-cell and cell-ECM adhesions during DC and its effect on the actomyosin network. We find that loss of cell-ECM adhesion results in aberrant distributions of cadherin-mediated adhesions and actin networks in the amnioserosa and subsequent disruption of myosin recruitment and dynamics. Moreover, loss of cell-cell adhesion caused up-regulation of cell-ECM adhesion, leading to reduced cell deformation and force transmission across amnioserosa cells. Our results show how interdependence between cell-cell and cell-ECM adhesions is important in regulating cell behaviors, force generation, and force transmission critical for tissue morphogenesis.

Basal Cell-Extracellular Matrix Adhesion Regulates Force Transmission during Tissue Morphogenesis.

Tissue morphogenesis requires force-generating mechanisms to organize cells into complex structures. Although many such mechanisms have been characterized, we know little about how forces are integrated across developing tissues. We provide evidence that integrin-mediated cell-extracellular matrix (ECM) adhesion modulates the transmission of apically generated tension during dorsal closure (DC) in Drosophila. Integrin-containing adhesive structures resembling focal adhesions were identified on the basal surface of the amnioserosa (AS), an extraembryonic epithelium essential for DC. Genetic modulation of integrin-mediated adhesion results in defective DC. Quantitative image analysis and laser ablation experiments reveal that basal cell-ECM adhesions provide resistance to apical cell displacements and force transmission between neighboring cells in the AS. Finally, we provide evidence for integrin-dependent force transmission to the AS substrate. Overall, we find that integrins regulate force transmission within and between cells, thereby playing an essential role in transmitting tension in developing tissues.