Gastrulation: Wnts signal constriction. Curr Biol. 2006;16:R874-R876. [PMID: 17055968 DOI: 10.1016/j.cub.2006.09.028]

Terminal alpha-d-mannosides are critical during sea urchin gastrulation

The sea urchin embryo is a United States National Institutes of Health (NIH) designated model system to study mechanisms that may be involved in human health and disease. In order to examine the importance of high-mannose glycans and polysaccharides in gastrulation, Lytechinus pictus embryos were incubated with Jack bean α-mannosidase (EC 3.2.1.24), an enzyme that cleaves terminal mannose residues that have α1-2-, α1-3-, or α1-6-glycosidic linkages. The enzyme treatment caused a variety of morphological deformations in living embryos, even with α-mannosidase activities as low as 0.06 U/ml. Additionally, formaldehyde-fixed, 48-hour-old L. pictus embryos were microdissected and it was demonstrated that the adhesion of the tip of the archenteron to the roof of the blastocoel in vitro is abrogated by treatment with α-mannosidase. These results suggest that terminal mannose residues are involved in the adhesion between the archenteron and blastocoel roof, perhaps through a lectin-like activity that is not sensitive to fixation.

Intestinal stem cell marker LGR5 expression during gastric carcinogenesis

AIM: To investigate the differential expression of leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) in gastric cancer tissues and its significance related to tumor growth and spread.

METHODS: Formalin-fixed biopsy specimens of intestinal metaplasia (n = 90), dysplasia (n = 53), gastric adenocarcinoma (n = 180), metastases in lymph nodes and the liver (n = 15), and lesion-adjacent normal gastric mucosa (controls; n = 145) were obtained for analysis from the Peking University Cancer Hospital’s Department of Pathology and Gastrointestinal Surgery tissue archives (January 2003 to December 2011). The biopsied patients’ demographic and clinicopathologic data were retrieved from the hospital’s medical records database. Each specimen was subjected to histopathological typing to classify the tumor node metastasis (TNM) stage and to immunohistochemistry staining to detect the expression of the cancer stem cell marker LGR5. The intergroup differences in LGR5 expression were assessed by Spearman’s rank correlation analysis, and the relationship between LGR5 expression level and the patients’ clinicopathological characteristics was evaluated by the χ² test or Fisher’s exact test.

RESULTS: Significantly more gastric cancer tissues showed LGR5⁺ staining than normal control tissues (all P < 0.01), with immunoreactivity detected in 72.2% (65/90) and 50.9% (27/53) of intestinal metaplasia and dysplasia specimens, respectively, 52.8% (95/180) of gastric adenocarcinoma specimens, and 73.3%% (11/15) of metastasis specimens, but 26.9% (39/145) of lesion-adjacent normal gastric mucosa specimens. Comparison of the intensity of LGR5⁺ staining showed an increasing trend that generally followed increasing dedifferentiation and tumor spread (normal tissue < dysplasia, < gastric adenocarcinoma < metastasis; all P < 0.001), with the exception of expression level detected in intestinal metaplasia which was higher than that in normal gastric tissues (P < 0.001). Moreover, gastric cancer-associated enhanced expression of LGR5 was found to be significantly associated with age, tumor differentiation, Lauren type and TNM stage (I + II vs III + IV) (all P < 0.05), but not with sex, tumor site, location, size, histology, lymphovascular invasion, depth of invasion, lymph node metastasis or distant metastasis. Patients with LGR5⁺ gastric cancer specimens and without signs of metastasis from the original biopsy experienced more frequent rates of recurrence or metastasis during follow-up than patients with LGR5^- specimens (P < 0.05).

CONCLUSION: Enhanced LGR5 is related to progressive dedifferentiation and metastasis of gastric cancer, indicating the potential of this receptor as an early diagnostic and prognostic biomarker.

Wasf2: a novel target of intermittent parathyroid hormone administration

Systemic intermittent administration of parathyroid hormone (PTH) stimulates bone formation in animals and humans, and recombinant human PTH1-34 (teriparatide) is used clinically for the treatment of osteoporosis. In this study, we investigated the regulation of gene expression by intermittent PTH administration in MC3T3-E1 osteoblastic cells. We found that intermittent PTH1-34 administration downregulated Wiskott-Aldrich syndrome protein family member (Wasf) 2 mRNA expression. Wnt inhibitor, IWP-2, and protein kinase C inhibitor, Go6976, inhibited this downregulation. However, continuous PTH did not affect Wasf2 expression. Transfection of Wasf2 siRNA reduced bone sialoprotein (BSP) mRNA expression in a similar manner following intermittent PTH administration in MC3T3-E1 cells. These results identify Wasf2 as a novel target of intermittent PTH administration via the Wnt and phosphoinositide-dependent protein kinase signaling pathways, and the resulting regulation of BSP expression may contribute to the anabolic effects of PTH.

Early development of cephalochordates (amphioxus)

The Phylum Chordata includes three groups--Vertebrata, Tunicata, and Cephalochordata. In cephalochordates, commonly called amphioxus or lancelets, which are basal in the Chordata, the eggs are small and relatively non-yolky. As in vertebrates, cleavage is indeterminate with cell fates determined gradually as development proceeds. The oocytes are attached to the ovarian follicle at the animal pole, where the oocyte nucleus is located. The cytoplasm at the opposite side of the egg, the vegetal pole, contains the future germ plasm or pole plasm, which includes determinants of the germline. After fertilization, additional asymmetries are established by movements of the egg and sperm nuclei, resulting in a concentration of mitochondria at one side of the animal hemisphere. This may be related to establishment of the dorsal/ventral axis. Patterning along the embryonic axes is mediated by secreted signaling proteins. Dorsal identity is specified by Nodal/Vg1 signaling, while during the gastrula stage, opposition between Nodal/Vg1 and BMP signaling establishes dorsal/anterior (i.e., head) and ventral/posterior (i.e., trunk/tail) identities, respectively. Wnt/β-catenin signaling specifies posterior identity while retinoic acid signaling specifies positions along the anterior/posterior axis. These signals are further modulated by a number of secreted antagonists. This fundamental patterning mechanism is conserved, with some modifications, in vertebrates.

A comprehensive model of the spatio-temporal stem cell and tissue organisation in the intestinal crypt

We introduce a novel dynamic model of stem cell and tissue organisation in murine intestinal crypts. Integrating the molecular, cellular and tissue level of description, this model links a broad spectrum of experimental observations encompassing spatially confined cell proliferation, directed cell migration, multiple cell lineage decisions and clonal competition.

Using computational simulations we demonstrate that the model is capable of quantitatively describing and predicting the dynamic behaviour of the intestinal tissue during steady state as well as after cell damage and following selective gain or loss of gene function manipulations affecting Wnt- and Notch-signalling. Our simulation results suggest that reversibility and flexibility of cellular decisions are key elements of robust tissue organisation of the intestine. We predict that the tissue should be able to fully recover after complete elimination of cellular subpopulations including subpopulations deemed to be functional stem cells. This challenges current views of tissue stem cell organisation.

In the murine small intestine there are more than a million organized groups of proliferating cells, the crypts, each of which contains about 250–300 cells. About 60% of these cells are in rapid cycle. The functional stem cells of this tissue have been demonstrated to reside at defined positions at the lower third of the crypt and to give rise to four different cell types. Considering this simple structure the murine intestine is an ideal system to study general aspects of tissue organization. Here, we introduce a comprehensive and predictive computer model of the spatio-temporal organization of the murine intestine which describes how cell production and cell fate decisions could be organized in steady state as well as under perturbations. The model is based on single cells acting as individual agents, updating their status within a certain set of options governed by some active rules and on signals received from the environment. This kind of self-organization enables effective tissue regeneration without assuming an explicit stem cell population that maintains itself by asymmetric division. Thus, the model offers a novel systems biological view on crypt stem cell and tissue organisation.

SAX-7/L1CAM and HMR-1/cadherin function redundantly in blastomere compaction and non-muscle myosin accumulation during Caenorhabditis elegans gastrulation

Gastrulation is the first major morphogenetic movement in development and requires dynamic regulation of cell adhesion and the cytoskeleton. Caenorhabditis elegans gastrulation begins with the migration of the two endodermal precursors, Ea and Ep, from the surface of the embryo into the interior. Ea/Ep migration provides a relatively simple system to examine the intersection of cell adhesion, cell signaling, and cell movement. Ea/Ep ingression depends on correct cell fate specification and polarization, apical myosin accumulation, and Wnt activated actomyosin contraction that drives apical constriction and ingression (Lee et al., 2006; Nance et al., 2005). Here, we show that Ea/Ep ingression also requires the function of either HMR-1/cadherin or SAX-7/L1CAM. Both cadherin complex components and L1CAM are localized at all sites of cell-cell contact during gastrulation. Either system is sufficient for Ea/Ep ingression, but loss of both together leads to a failure of apical constriction and ingression. Similar results are seen with isolated blastomeres. Ea/Ep are properly specified and appear to display correct apical-basal polarity in sax-7(eq1);hmr-1(RNAi) embryos. Significantly, in sax-7(eq1);hmr-1(RNAi) embryos, Ea and Ep fail to accumulate myosin (NMY-2Colon, two colonsGFP) at their apical surfaces, but in either sax-7(eq1) or hmr-1(RNAi) embryos, apical myosin accumulation is comparable to wild type. Thus, the cadherin and L1CAM adhesion systems are redundantly required for localized myosin accumulation and hence for actomyosin contractility during gastrulation. We also show that sax-7 and hmr-1 function are redundantly required for Wnt-dependent spindle polarization during division of the ABar blastomere, indicating that these cell surface proteins redundantly regulate multiple developmental events in early embryos.

Mechanical control of tissue and organ development

Many genes and molecules that drive tissue patterning during organogenesis and tissue regeneration have been discovered. Yet, we still lack a full understanding of how these chemical cues induce the formation of living tissues with their unique shapes and material properties. Here, we review work based on the convergence of physics, engineering and biology that suggests that mechanical forces generated by living cells are as crucial as genes and chemical signals for the control of embryological development, morphogenesis and tissue patterning.

Wnt to build a tube: contributions of Wnt signaling to epithelial tubulogenesis

Epithelial tubes are crucial to the function of organ systems including the cardiovascular system, pulmonary system, gastrointestinal tract, reproductive organ systems, excretory system, and auditory system. Using a variety of animal model systems, recent studies have substantiated the role of Wnt signaling via the canonical/beta-catenin-mediated trajectory, the non-canonical Wnt trajectories, or both, in forming epithelial tubular tissues. This review focuses on the involvement of the Wnt pathways in the induction, specification, proliferation, and morphogenesis involved in tubulogenesis within tissues including the lungs, kidneys, ears, mammary glands, gut, and heart. The ultimate goal is to describe the developmental processes forming the various tubulogenic organ systems to determine the relationships between these processes.

Gastrointestinal stem cells in development and cancer

An enormous body of knowledge about the biology of stem cells and their role in development, tissue homeostasis and cancer formation has been gained in the last 20 years. This review gives a comprehensive overview on knowledge about localization and regulation of normal gastrointestinal stem cells and links it to our understanding of gastrointestinal tumourigenesis and malignant progression in the light of the cancer stem cell concept. The focus is on intestinal stem cells and newly identified stem cell factors, such as the beta-catenin target gene Lgr5. The basis of intestinal stem cell regulation is a permanent crosstalk between epithelial and underlying mesenchymal cells in the intestinal stem cell niche. This crosstalk is mediated by crucial pathways, including the Wnt, Hedgehog (HH), Notch, PI3K and BMP pathways. Disturbances in this fine-regulated interaction can both initiate intestinal tumours and, in association with additional genetic alterations or environmental activation of embryonic processes such as epithelial-mesenchymal transition (EMT), lead to tumour invasion and metastasis.

The Wnt signal transduction pathway in stem cells and cancer cells: influence on cellular invasion

The regulative network conducting adult stem cells in endogenous tissue repair is of prime interest for understanding organ regeneration as well as preventing degenerative and malignant diseases. One major signal transduction pathway which is involved in the control of these (patho)physiological processes is the Wnt pathway. Recent results obtained in our laboratories showed for the first time that canonical Wnt signaling is critically involved in the control of the migration/invasion behaviour of human mesenchymal stem cells (hMSC). In the first part of this review, we describe that the regenerative state is closely linked to the activation of the Wnt pathway. Central hallmarks of activated stem cells are recapitulated in a similar way also in cancer metastasis, where the acquisition of an invasive cancer stem cell phenotype is associated with the induction of Wnt-mediated epithelial to mesenchymal transition (EMT). In the second part, the influence of proinflammatory cytokines such as transforming growth factor (TGF-)beta1, interleukin (Il-)1beta, and tumor necrosis factor (TNF-)alpha is discussed with regard to the invasive characteristics of hMSC. In this context, special attention has been paid on the role of matrix metalloproteinases (MMPs), such as MMP-2, MMP-9 and membrane type 1 (MT1)-MMP, as well as on the tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2. Putative cross-talks between different signal transduction pathways that may amplify the invasive capacity of this stem cell population are also discussed. Finally, the consequences towards future drug-mediated therapeutical modifications of Wnt signaling in stem cells and tumor cells are highlighted.

Control of morphogenetic cell movements in the early zebrafish myotome

As the vertebrate myotome is generated, myogenic precursor cells undergo extensive and coordinated movements as they differentiate into properly positioned embryonic muscle fibers. In the zebrafish, the "adaxial" cells adjacent to the notochord are the first muscle precursors to be specified. After initially differentiating into slow-twitch myosin-expressing muscle fibers, these cells have been shown to undergo a remarkable radial migration through the lateral somite, to populate the superficial layer of slow-twitch muscle of the mature myotome. Here we characterize an earlier set of adaxial cell behaviors; the transition from a roughly 4x5 array of cuboidal cells to a 1x20 stack of elongated cells, prior to the migration event. We find that adaxial cells display a highly stereotypical series of behaviors as they undergo this rearrangement. Furthermore, we show that the actin regulatory molecule, Cap1, is specifically expressed in adaxial cells and is required for the progression of these behaviors. The requirement of Cap1 for a cellular apical constriction step is reminiscent of similar requirements of Cap during apical constriction in Drosophila development, suggesting a conservation of gene function for a cell biological event critical to many developmental processes.