Brush borders of intestinal epithelial cells are mandatory for nutrient uptake. Yet, which actin nucleators are crucial for forming the F-actin bundles supporting microvilli and the actin filaments of the terminal web, in which microvilli are rooted, is unknown. We show that mice lacking the actin nucleator cobl surprisingly did not display reduced microvilli densities or changes in microvillar f-actin bundles or microvilli diameter but particularly in the duodenum displayed increased microvillar length. Interestingly, Cobl-deficient mice furthermore showed a significant widening of the terminal web. Quantitative analyses of high-resolution cryo-scanning electron microscopy (eM) of deep-etched duodenum samples revealed that Cobl is specifically important for the formation of fine filaments in the central terminal web that connect the apical structure of the terminal web underlying the plasma membrane, the microvilli rootlets and the basal structure of the terminal web with each other. Thus, the actin nucleator cobl is critically involved in generating one of the cellular structures of the brush borderdecorated apical cortex of enterocytes representing the absorptive intestinal surface. Surface extensions of epithelial cells (enterocytes) by microvilli are mandatory for nutrient uptake in the gut. New-borns with reduced length of microvilli, as it e.g. occurs in the inherited microvillar inclusion disease, thus usually die during their early infancy 1,2. Yet, despite this importance, it is still unknown which actin nucleators are crucial for forming the F-actin bundles supporting microvilli and the actin filaments of the terminal web, in which microvilli are rooted 3-5. Microvilli are uniform membrane protrusions that are structurally supported by a dense bundle of unbranched actin filaments, that are organised in a very dense, almost hexagonal packing by actin-crosslinking proteins and that show very uniform length in brush borders. This length differs along the intestinal tract with about 1300-1400 nm in the small intestine and only 800 nm in the colon 6. The minus ends of microvillar F-actin bundles reach into the cells as rootlets and are anchored-presumably by plastin 1 (fimbrin) interlinking them with the keratin network 7-in the terminal web, which spans the entire apical cortex of enterocytes 8,9. Although a variety of F-actin-binding proteins including e.g. myosins, tropomyosin, villin, spectrin, ezrin and espin have been identified in biochemical isolations of microvilli and attached terminal web structures 3 , loss-of-function data identifying the actin nucleator(s) that give rise to the F-actin structures in microvilli and/or in the terminal web is lacking. Despite significant scientific efforts during several decades, also microvilli formation and length control in intestinal brush borders still are poorly understood, as i) intestine tissues are not well accessible for molecular manipulations, ii) enterocytes in the murine gut only have a lifespan of a few days and iii) once intestinal microvilli are ...

Ischemic stroke is a major cause of death and long-term disability. We demonstrate that middle cerebral artery occlusion (MCAO) in mice leads to a strong decline in dendritic arborization of penumbral neurons. These defects were subsequently repaired by an ipsilateral recovery process requiring the actin nucleator Cobl. Ischemic stroke and excitotoxicity, caused by calpain-mediated proteolysis, significantly reduced Cobl levels. In an apparently unique manner among excitotoxicity-affected proteins, this Cobl decline was rapidly restored by increased mRNA expression and Cobl then played a pivotal role in poststroke dendritic arbor repair in peri-infarct areas. In Cobl knockout (KO) mice, the dendritic repair window determined to span day 2 to 4 poststroke in wild type (WT) strikingly passed without any dendritic regrowth. Instead, Cobl KO penumbral neurons of the primary motor cortex continued to show the dendritic impairments caused by stroke. Our results thereby highlight a powerful poststroke recovery process and identified causal molecular mechanisms critical during poststroke repair.

Ischemic stroke is a major cause of death and long-term disability. We demonstrate that middle cerebral artery occlusion in mice leads to a strong decline in dendritic arborization of penumbral neurons. These defects were subsequently repaired by an ipsilateral recovery process requiring the actin nucleator Cobl. Ischemic stroke and excitotoxicity, caused by calpain-mediated proteolysis, significantly reduced Cobl levels. In an apparently unique manner among excitotoxicity-affected proteins, this Cobl decline was rapidly restored by increased mRNA expression and Cobl then played a pivotal role in post-stroke dendritic arbor repair in peri-infarct areas. In Cobl KO mice, the dendritic repair window determined to span day 2-4 post-stroke in WT strikingly passed without any dendritic regrowth. Instead, Cobl KO penumbral neurons of the primary motor cortex continued to show the dendritic impairments caused by stroke. Our results thereby highlight a powerful post-stroke recovery process and identified causal molecular mechanisms critical during post-stroke repair.