Altered synthesis of laminin 1 and absence of basement membrane component deposition in β1 integrin-deficient embryoid bodies

Abstract

Basement membranes are the earliest extracellular matrices produced during embryogenesis. They result from synthesis and assembly into a defined supramolecular architecture of several components, including laminins, collagen IV, nidogen, and proteoglycans. In vitro studies have allowed us to propose an assembly model based on the polymerisation of laminin and collagen IV in two separate networks associated together by nidogen. How nucleation of polymers and insolubilisation of the different components into a basement membrane proceed in vivo is, however, unknown. A most important property of several basement membrane components is to provide signals controling the activity of adjacent cells. The transfer of information is mediated by interactions with cell surface receptors, among them integrins. Mouse genetics has demonstrated that the absence of these interactions is not compatible with development as deletion of either laminin (gamma)1 chain or integrin (beta)1 chain lead to lethality of mouse embryos at the peri-implantation stage. We have used embyoid bodies as a model system recapitulating the early steps of embryogenesis to unravel the respective roles of laminin and (beta)1 integrins in basement membrane formation. Our data show that there is formation of a basal lamina in wild-type, but not in (beta)1-integrin deficient, embryoid bodies. Surprisingly, in the absence of (beta)1 integrins, laminin 1 was not secreted in the extracellular space due to a rapid switch off of laminin (alpha)1 chain synthesis which normally drives the secretion of laminin heterotrimers. These results indicate that (beta)1 integrins are required for the initiation of basement membrane formation, presumably by applying a feed-back regulation on the expression of laminin (alpha)1 chain and other components of basement membranes.

ECM-integrin signalling instructs cellular position sensing to pattern the early mouse embryo

“…Our work complements earlier studies in embryonic stem cells that revealed ECM-integrin signals as crucial regulators of the undifferentiated state and cell arrangement ( Aumailley et al, 2000 ; Cattavarayane et al, 2015 ; Li et al, 2002 ). Given the ubiquity and tissue/stage-dependent complexity of the ECM and its receptors, their role in cell fate specification and pattern formation extends beyond early mouse development ( Huang and Ingber, 2005 ; Humphrey et al, 2014 ; Walma and Yamada, 2020 ; Watt and Huck, 2013 ).…”

“…Although laminin itself is a ligand for integrin, integrin β1 is required for the deposition of heterotrimeric laminin into the intercellular space, which, in turn, can bring its cell surface receptors together ( Aumailley et al, 2000 ; Li et al, 2002 ). Accordingly, intercellular laminin, as judged by strand-like laminin γ1 signal in the ICM, was diminished in Itgb1 −/− embryos ( Fig.…”

Opposite roles of Kindlin orthologs in cell survival and proliferation

“…42 K2-deficient fibroblasts featured inhibited proliferation and abnormally upregulated apoptosis in our study, which is a reminder of the defective integrin-deficient embryoid body exhibiting smaller size, lower proliferation rate and irregular shape compared with controls. 43 Similar to our observations, K2 deficiency has been reported to induce apoptosis and restrain proliferation of other anchorage-dependent cells, including chondrocytes, 44 smooth muscle cells, 45 mesenchymal stromal cells 46 and so on. The behaviour of the K2-PXN mutant, at least in part, resembled both K2 and PXN knockouts, characterized by impaired cell adhesion, spreading and migration.…”

“…These conclusions are supported by the detailed structural analysis of the K2‐PXN interaction using point mutations disrupting their binding site 42 . K2‐deficient fibroblasts featured inhibited proliferation and abnormally upregulated apoptosis in our study, which is a reminder of the defective integrin‐deficient embryoid body exhibiting smaller size, lower proliferation rate and irregular shape compared with controls 43 . Similar to our observations, K2 deficiency has been reported to induce apoptosis and restrain proliferation of other anchorage‐dependent cells, including chondrocytes, 44 smooth muscle cells, 45 mesenchymal stromal cells 46 and so on.…”

“…Surprisingly, in contrast to K2KO cells, K3 knockout cells behaved in a completely opposite way to integrin knockout cells. 43 Cellular characteristics of K3 deficiency resembled those of transformed cells. K3-deficient human lymphoma cells grew faster and survived better in our transplantation experiment.…”