Immuno-fluorescent Labeling of Microtubules and Centrosomal Proteins in Ex Vivo Intestinal Tissue and 3D In Vitro Intestinal Organoids

MCC is a centrosomal protein that relocalizes to non-centrosomal apical sites during intestinal cell differentiation

The gene mutated in colorectal cancer (MCC) encodes a coiled-coil protein implicated, as its name suggests, in the pathogenesis of hereditary human colon cancer. To date, however, the contributions of MCC to intestinal homeostasis and disease remain unclear. Here, we examine the subcellular localization of MCC, both at the mRNA and protein levels, in the adult intestinal epithelium. Our findings reveal that Mcc transcripts are restricted to proliferating crypt cells, including Lgr5+ stem cells, where the Mcc protein is distinctly associated with the centrosome. Upon intestinal cellular differentiation, Mcc is redeployed to the apical domain of polarized villus cells where non-centrosomal microtubule organizing centers (ncMTOCs) are positioned. Using intestinal organoids, we show that the shuttling of the Mcc protein depends on phosphorylation by casein kinases 1δ and ε, which are critical modulators of WNT signaling. Together, our findings support a role for MCC in establishing and maintaining the cellular architecture of the intestinal epithelium as a component of both the centrosome and ncMTOC.

Mutational inactivation of Apc in the intestinal epithelia compromises cellular organisation

The adenomatous polyposis coli (Apc) protein regulates diverse effector pathways essential for tissue homeostasis. Truncating oncogenic mutations in Apc removing its Wnt pathway and microtubule regulatory domains drives intestinal epithelia tumorigenesis. Exuberant cell proliferation is one well-established consequence of oncogenic Wnt pathway activity; however, the contribution of other deregulated molecular circuits to tumorigenesis has not been fully examined. Using in vivo and organoid models of intestinal epithelial tumorigenesis we found that Wnt pathway activity controls intestinal epithelial villi and crypt structure, morphological features lost upon Apc inactivation. Although the Wnt pathway target gene c-Myc (also known as Myc) has critical roles in regulating cell proliferation and tumorigenesis, Apc specification of intestinal epithelial morphology is independent of the Wnt-responsive Myc-335 (also known as Rr21) regulatory element. We further demonstrate that Apc inactivation disrupts the microtubule cytoskeleton and consequently localisation of organelles without affecting the distribution of the actin cytoskeleton and associated components. Our data indicates the direct control over microtubule dynamics by Apc through an independent molecular circuit. Our study stratifies three independent Apc effector pathways in the intestinal epithelial controlling: (1) proliferation, (2) microtubule dynamics and (3) epithelial morphology.This article has an associated First Person interview with the first author of the paper.

Super-resolution imaging and quantification of megakaryocytes and platelets

Recent advances in super-resolution (sub-diffraction limited) microscopy have yielded remarkable insights into the nanoscale architecture and behavior of cells. In addition to the capacity to provide sub 100 nm resolution, these technologies offer unique quantitative opportunities with particular relevance to platelet and megakaryocyte biology. In this review, we provide a short introduction to modern super-resolution microscopy, its applications in the field of platelet and megakaryocyte biology, and emerging quantitative approaches which will allow for unprecedented insights into the biology of these unique cell types.

Labeling and Characterization of Human GLP-1-Secreting L-cells in Primary Ileal Organoid Culture

Glucagon-like peptide-1 (GLP-1) from intestinal L-cells stimulates insulin secretion and reduces appetite after food ingestion, and it is the basis for drugs against type-2 diabetes and obesity. Drugs targeting L- and other enteroendocrine cells are under development, with the aim to mimic endocrine effects of gastric bypass surgery, but they are difficult to develop without human L-cell models. Human ileal organoids, engineered by CRISPR-Cas9, express the fluorescent protein Venus in the proglucagon locus, enabling maintenance of live, identifiable human L-cells in culture. Fluorescence-activated cell sorting (FACS)-purified organoid-derived L-cells, analyzed by RNA sequencing (RNA-seq), express hormones, receptors, and ion channels, largely typical of their murine counterparts. L-cells are electrically active and exhibit membrane depolarization and calcium elevations in response to G-protein-coupled receptor ligands. Organoids secrete hormones in response to glucose and other stimuli. The ability to label and maintain human L-cells in organoid culture opens avenues to explore L-cell function and develop drugs targeting the human enteroendocrine system.

Centering and Shifting of Centrosomes in Cells

Centrosomes have a nonrandom localization in the cells: either they occupy the centroid of the zone free of the actomyosin cortex or they are shifted to the edge of the cell, where their presence is justified from a functional point of view, for example, to organize additional microtubules or primary cilia. This review discusses centrosome placement options in cultured and in situ cells. It has been proven that the central arrangement of centrosomes is due mainly to the pulling microtubules forces developed by dynein located on the cell cortex and intracellular vesicles. The pushing forces from dynamic microtubules and actomyosin also contribute, although the molecular mechanisms of their action have not yet been elucidated. Centrosomal displacement is caused by external cues, depending on signaling, and is drawn through the redistribution of dynein, the asymmetrization of microtubules through the capture of their plus ends, and the redistribution of actomyosin, which, in turn, is associated with basal-apical cell polarization.