@article {68633, title = {Specialized actin nanoscale layers control focal adhesion turnover}, journal = {bioRxiv}, year = {2023}, month = {2023 Feb 15}, abstract = {

Focal adhesions (FAs) connect inner workings of the cell to the extracellular matrix to control cell adhesion, migration, and mechanosensing1,2. Previous studies demonstrated that FAs contain three vertical layers, which connect extracellular matrix to the cytoskeleton3,4,5. However, cellular processes rely on precisely-regulated FA turnover, but the molecular machineries that control FA assembly and disassembly have remained elusive. By using super-resolution iPALM microscopy, we identified two unprecedented nanoscale layers within FAs, specified by actin filaments bound to tropomyosin isoforms Tpm1.6 and Tpm3.2. The Tpm1.6-actin filaments beneath the previously identified {\textquoteleft}actin-regulatory layer{\textquoteright} are critical for adhesion maturation and controlled cell motility, whereas the Tpm3.2-actin filament layer towards the bottom of FA facilitates adhesion disassembly. Mechanistically, Tpm3.2 stabilizes KANK-family proteins at adhesions, and hence targets microtubule plus-ends to FAs to catalyse their disassembly. Loss of Tpm3.2 leads to disorganized microtubule network, abnormally stable FAs, and defects in tail retraction during cell migration. Thus, FAs are composed of at least three distinct actin filament layers, each having specific roles in coupling of adhesion to the cytoskeleton, or in controlling adhesion dynamics. In a broader context, these findings demonstrate how distinct actin filament populations can co-exist and perform specific functions within a defined cellular compartment.

}, doi = {10.1101/2023.02.15.528622}, url = {https://doi.org/10.1101/2023.02.15.528622}, author = {Reena Kumari and Katharina Ven and Megan Chastney and Johan Per{\"a}nen and Jesse Aaron and Leonardo Almeida-Souza and Elena Kremneva and Renaud Poincloux and Teng-Leong Chew and Peter W. Gunning and Johanna Ivaska and Pekka Lappalainen} } @article {64998, title = {Superresolution architecture of pluripotency guarding adhesions.}, journal = {bioRxiv}, year = {2018}, month = {2018 Sep 19}, abstract = {

Human pluripotent stem cells (hPSC) can generate almost all adult cell lineages. While it is clear that key transcriptional programmes are important elements for maintaining pluripotency, the equally essential requirement for cell adhesion to specific extracellular matrix components remains poorly defined. Our recent observation that hPSC colonies form unusually large {\textquotedblleft}cornerstone{\textquotedblright} focal adhesions (FA), distinct from parental somatic cells, that are lost following differentiation, emphasises the potential of these atypical FA as gatekeepers of pluripotency. Here, using nanopatterns, we further demonstrate that physical restriction of adhesion size, in hPSC colonies, is sufficient to trigger differentiation. Using superresolution two-colour interfero-metric photo-activated localization microscopy (iPALM), we examined the three-dimensional architecture of these cornerstone adhesions and report vertical lamination of FA proteins with three main structural peculiarities: 1) integrin β5 and talin are present at high density, at the edges of cornerstone FA, adjacent to a vertical kank-rich protein wall. 2) Vinculin localises higher than expected with respect to the substrata and displays a head-above-tail orientation, and 3) surprisingly, actin and α-actinin are present in two discrete layers, a previously undescribed localisation for these proteins. Finally, we report that depletion of kanks diminishes FA patterning, and actin organisation within the colony, indicating a key role for kanks in hPSC colony architecture.

}, doi = {10.1101/402305}, author = {Aki Stubb and Camilo Guzm{\'a}n and Elisa N{\"a}rv{\"a} and Jesse Aaron and Teng-Leong Chew and Markku Saari and Mitro Miihkinen and Guillaume Jacquemet and Johanna Ivaska} }