Biology subjects

Ibar, C.

Publications and source records attributed to Ibar, C..

3 recordsLinked to original sources

bioRxiv2022

Competition between myosin II and βH-Spectrin regulates cytoskeletal tension

Spectrins are membrane cytoskeletal proteins generally thought to function as heterotetramers comprising two -spectrins and two {beta}-spectrins. They influence cell shape and Hippo signaling, but the mechanism by which they influence Hippo signaling has remained unclear. We have investigated the role and regulation of the Drosophila {beta}-heavy Spectrin ({beta}H-Spectrin, encoded by the karst gene) in wing imaginal discs. Our results establish that {beta}H-Spectrin regulates Hippo signaling through the Jub biomechanical pathway due to its influence on cytoskeletal tension. While we find that -Spectrin also regulates Hippo signaling through Jub, unexpectedly, we find that {beta}H-Spectrin localizes and functions independently of -Spectrin. Instead, {beta}H-Spectrin co-localizes with and reciprocally regulates and is regulated by myosin. In vivo and in vitro experiments support a model in which {beta}H-Spectrin and myosin directly compete for binding to apical F-actin. This competition can explain the influence of {beta}H-Spectrin on cytoskeletal tension and myosin accumulation. It also provides new insight into how {beta}H-Spectrin participates in ratcheting mechanisms associated with cell shape change.

cell biology↗

bioRxiv2022

Analysis of the Drosophila Ajuba LIM protein defines functions for distinct LIM domains

The Ajuba LIM protein Jub mediates regulation of Hippo signaling by cytoskeletal tension through interaction with the kinase Warts, and also participates in feedback regulation of junctional tension through regulation of the cytohesin Steppke. To investigate how Jub interacts with and regulates its distinct partners, we investigated the ability of Jub proteins missing different combinations of its three LIM domains to rescue jub phenotypes and to interact with -catenin, Warts and Steppke. Multiple regions of Jub contribute to its ability to bind -catenin and to localize to adherens junctions in Drosophila wing imaginal discs. Co-immunoprecipitation experiments in cultured cells identified a specific requirement for LIM2 for binding to Warts. However, in vivo, both LIM1 and LIM2, but not LIM3, were required for regulation of wing growth, Yorkie activity, and Warts localization. Conversely, LIM2 and LIM3, but not LIM1, were required for regulation of cell shape and Steppke localization in vivo, and for maximal Steppke binding in co-immunoprecipitation experiments. These observations identify distinct functions for the different LIM domains of Jub.

cell biology↗

bioRxiv2017

Tension-dependent regulation of mammalian Hippo signaling through LIMD1

Hippo signaling is regulated by biochemical and biomechanical cues that influence the cytoskeleton, but the mechanisms that mediate this have remained unclear. We show that all three mammalian Ajuba family proteins - AJUBA, LIMD1, and WTIP - exhibit tension-dependent localization to adherens junctions, and that both Lats family proteins, LATS1 and LATS2, exhibit an overlapping tension-dependent junctional localization. This localization of Ajuba and Lats family proteins is also influenced by cell density, and by Rho activation. We establish that junctional localization of Lats kinases requires LIMD1, and that LIMD1 is also specifically required for the regulation of Lats kinases and YAP by Rho. Our results identify a biomechanical pathway that contributes to regulation of mammalian Hippo signaling, establish that this occurs through tension-dependent LIMD1-mediated recruitment and inhibition of Lats kinases in junctional complexes, and identify roles for this pathway in both Rho-mediated and density-dependent regulation of Hippo signaling.

cell biology↗