Biology subjects

Roeper, K.

Publications and source records attributed to Roeper, K..

4 recordsLinked to original sources

bioRxiv2021

Toll-like receptor signalling via IRAK4 confers epithelial integrity and tightness through regulation of junctional tension

Toll-like receptors (TLRs) in mammalian systems are well characterised for their role in innate immunity. In addition, TLRs also fulfil crucial functions outside immunity, including the dorso-ventral patterning function of the original Toll receptor in Drosophila and neurogenesis in mice. Recent discoveries in flies suggested key roles for TLRs in epithelial cells in patterning of cytoskeletal activity near epithelial junctions. Here we address the function of TLRs and the downstream key signal transduction component IRAK4 (interleukin-1 receptor associated kinase 4) in human epithelial cells. Using differentiated human Caco-2 cells as a model for the intestinal epithelium, we show that these cells exhibit baseline TLR signalling as revealed by p-IRAK4 and that blocking IRAK4 function leads to a loss of epithelial tightness involving key changes at tight junctions and adherens junctions. These changes correlate with a loss of epithelial tension and changes in junctional actomyosin. Knock-down of IRAK4 and certain TLRs phenocopies the inhibitor treatment. These data suggest a model whereby TLR receptors near epithelial junctions might be involved in a continuous sensing of the epithelial state to promote epithelial tightness and integrity.

cell biology↗

bioRxiv2020

A release-and-capture mechanism generates an essential non-centrosomal microtubule array during tube budding

Non-centrosomal microtubule arrays serve crucial functions in cells, yet the mechanisms of their generation are poorly understood. During budding of the epithelial tubes of the salivary glands in the Drosophila embryo, we previously demonstrated that the activity of pulsatile apical-medial actomyosin depends on a longitudinal non-centrosomal microtubule array. Here we uncover that the exit from the last embryonic division cycle of the epidermal cells of the salivary gland placode leads to the mother centrosome in the cells losing all microtubule-nucleation capacity. This restriction of nucleation activity to the daughter centrosome is key for proper morphogenesis. Furthermore, the microtubule-severing protein Katanin and the minus-end-binding protein Patronin accumulate in an apical-medial position only in placodal cells. Loss of either in the placode prevents formation of the longitudinal microtubule array and leads to loss of apical-medial actomyosin and apical constriction. We thus propose a mechanism whereby Katanin-severing at the single active centrosome releases microtubule minus-ends that are then anchored by apical-medial Patronin to promote formation of the longitudinal microtubule array crucial for apical constriction and tube formation.

developmental biology↗

bioRxiv2019

Rho-kinase planar polarisation at tissue boundaries depends on phospho-regulation of membrane residence time

Rho-kinase (Rok) is a major myosin II activator during morphogenesis. In the Drosophila embryonic salivary gland placode Rok is planar polarised at the tissue boundary, through a negative regulation by the apical polarity protein Crumbs that is anisotropically localised at the boundary. However, in inner cells of the placode both Crumbs and Rok are isotropically enriched at junctions. We propose a model that reconciles both behaviours through modulation of Rok membrane residence time by Crumbs and downstream effectors. Using FRAP in embryos expressing endogenously-tagged Rok combined with in silico simulations, we find that the lower membrane dissociation rate (koff) of Rok at the tissue boundary, where Crumbs membrane levels are lower, explains this boundary-specific effect. The S/T-kinase Pak1 negatively affects Rok membrane association in vivo within the epidermis, and in vitro can phosphorylate Rok near the PH domain that mediates membrane association. Pak1 is recruited to the membrane by Cdc42 which, like its binding partner Crumbs, shows anisotropic localisation at the boundary. These data reveal an important mechanism of modulation of Rok membrane residence time via affecting the koff that may be widely employed during tissue morphogenesis.

developmental biology↗

bioRxiv2018

Radially-patterned cell behaviours during tube budding from an epithelium

The budding of tubular organs from flat epithelial sheets is a vital morphogenetic process. Cell behaviours that drive such processes are only starting to be unraveled. Using live imaging and novel morphometric methods we show that in addition to apical constriction, radially oriented directional intercalation of placodal cells plays a major contribution to the early stages of invagination of the salivary gland tube in the Drosophila embryo. Extending analyses in 3D, we find that near the pit of invagination, isotropic apical constriction leads to strong cell wedging, and further from the pit cells interleave circumferentially, suggesting apically driven behaviours. Supporting this, junctional myosin is enriched in, and neighbour exchanges biased towards the circumferential orientation. In a mutant failing pit specification, neither are biased due to an inactive pit. Thus, tube budding depends on a radially polarised pattern of apical myosin leading to radially oriented 3D cell behaviours, with a close mechanical interplay between invagination and intercalation.

developmental biology↗