Insights into the origin of metazoan filopodia and microvilli.

Filopodia are fine actin-based cellular projections used for both environmental sensing and cell motility, and they are essential organelles for metazoan cells. In this study, we reconstruct the origin of metazoan filopodia and microvilli. We first report on the evolutionary assembly of the filopodial molecular toolkit and show that homologs of many metazoan filopodial components, including fascin and myosin X, were already present in the unicellular or colonial progenitors of metazoans. Furthermore, we find that the actin crosslinking protein fascin localizes to filopodia-like structures and microvilli in the choanoflagellate Salpingoeca rosetta. In addition, homologs of filopodial genes in the holozoan Capsaspora owczarzaki are upregulated in filopodia-bearing cells relative to those that lack them. Therefore, our findings suggest that proteins essential for metazoan filopodia and microvilli are functionally conserved in unicellular and colonial holozoans and that the last common ancestor of metazoans bore a complex and specific filopodial machinery.

Narrow-band imaging in the evaluation of villous morphology: a feasibility study assessing a simplified classification and observer agreement.

BACKGROUND AND STUDY AIMS: To determine the utility of narrow-band imaging with optical magnification (NBI-Z) in the evaluation of villous morphology. PATIENTS AND METHODS: Patients considered at risk of having celiac disease were invited. After standard endoscopy, they underwent further evaluation with NBI-Z which was digitally recorded. Targeted biopsies of each area videoed with NBI-Z were performed and tissue sent for histopathological analysis. Two expert endoscopists then selected the best representative videos (developmental phase). Next, 41 representative images of these videos were classified as follows: villous patterns present (N) or absent (A). Images showing absence of villi were then classified as cerebriform (C) or flat (F), corresponding to partial or total villous atrophy respectively. Three NBI-Z-naïve endoscopists then graded the videos. They underwent an interactive training session (learning phase) with video and images from a digital library before embarking on the actual assessment. To test for reproducibility, all videos were randomly reordered and graded again after a week. RESULTS: Forty-one videos (10 celiac disease, 31 normal) from 21 patients (3 celiac disease, 18 normal) were analyzed. The overall sensitivity and specificity in correctly distinguishing the presence or absence of villi were 93.3% and 97.8% respectively, with interobserver and intraobserver agreement (kappa, κ) at 0.82 and 0.86. The sensitivity and specificity in differentiating partial from total villous atrophy were 83.3% and 100%, κ at 0.73 and 0.68 respectively. CONCLUSIONS: Using a simplified classification, we demonstrated the feasibility of using NBI-Z to detect villous atrophy in patients presenting with suspected celiac disease.

Lipid rafts in epithelial brush borders: atypical membrane microdomains with specialized functions.

Epithelial cells that fulfil high-throughput digestive/absorptive functions, such as small intestinal enterocytes and kidney proximal tubule cells, are endowed with a dense apical brush border. It has long been recognized that the microvillar surface of the brush border is organized in cholesterol/sphingolipid-enriched membrane microdomains commonly known as lipid rafts. More recent studies indicate that microvillar rafts, in particular those of enterocytes, have some unusual properties in comparison with rafts present on the surface of other cell types. Thus, microvillar rafts are stable rather than transient/dynamic, and their core components include glycolipids and the divalent lectin galectin-4, which together can be isolated as "superrafts", i.e., membrane microdomains resisting solubilization with Triton X-100 at physiological temperature. These glycolipid/lectin-based rafts serve as platforms for recruitment of GPI-linked and transmembrane digestive enzymes, most likely as an economizing effort to secure and prolong their digestive capability at the microvillar surface. However, in addition to microvilli, the brush border surface also consists of membrane invaginations between adjacent microvilli, which are the only part of the apical surface sterically accessible for membrane fusion/budding events. Many of these invaginations appear as pleiomorphic, deep apical tubules that extend up to 0.5-1 microm into the underlying terminal web region. Their sensitivity to methyl-beta-cyclodextrin suggests them to contain cholesterol-dependent lipid rafts of a different type from the glycolipid-based rafts at the microvillar surface. The brush border is thus an example of a complex membrane system that harbours at least two different types of lipid raft microdomains, each suited to fulfil specialized functions. This conclusion is in line with an emerging, more varied view of lipid rafts being pluripotent microdomains capable of adapting in size, shape, and content to specific cellular functions.