Open Collections

Abstract

Positioning of cells within three dimensional tissues requires regulation and maintenance of cell adhesion. Cells adhere to the extracellular matrix (ECM) via the integrin adhesion complex, which binds to the ECM ligands outside the cell and the actin cytoskeleton inside the cell. The large cytoplasmic protein talin is an essential component of the adhesion complex and provides a direct link between the integrins and the cytoskeleton. Talin is required for cell-ECM adhesion and plays a role in integrin regulation. Integrins are normally in a low-affinity binding state and can undergo conformational changes to increase the affinity for their ligand, a process known as integrin activation. Mutations in the talin protein can block integrin activation. While these mutations, and thus the role of integrin activation, have been characterized in certain systems such as blood clotting and lymphocyte extravasation, their role in early mouse development has not been elucidated. We show that integrin activation by talin is required for early mammalian development. The integrin activation mutants are lethal around E8.5-9.5. They show no gross defects in embryonic patterning, specifically in the mesoderm and the endoderm, as well as in patterning of the extracellular matrix. Integrin activation mutants display increased apoptosis and decreased cell proliferation at E7.5. Embryonic stem cells isolated from the integrin activation mutants show fewer focal adhesions and a reduction in adhesion strength. Thus, our results show the inside-out integrin activation by talin is required for early mammalian development. Additionally, our lab has previously generated a point mutation that blocks talin autoinhibition, Tln1ᴱ¹⁷⁷⁰ᴬ, which shows increases integrin activation in fibroblasts. Tln1ᴱ¹⁷⁷⁰ᴬ mutant mice display defective hemostasis; furthermore, platelets isolated from Tln1ᴱ¹⁷⁷⁰ᴬ mice exhibit disrupted aggregation, delayed clot retraction and decreased platelet spreading area. Thus, talin autoinhibition is an important regulatory mechanism in platelets during hemostasis. Together, my research provides insight into the regulation of integrin function, specifically the role of integrin activation during mammalian development and hemostasis.