Abnormality of Apico-Basal Polarity in Adenocarcinoma

Apico–basal polarity is a fundamental property of the epithelium that functions as a barrier, holds cells together, and determines the directions of absorption and secretion. Apico–basal polarity is regulated by extracellular matrix‐integrin binding and downstream signaling pathways, including focal adhesion kinase, rouse‐sarcoma oncogene (SRC), and RHO/RHO‐associated kinase (ROCK). Loss of epithelial cell polarity plays a critical role in the progression of cancer cells. However, in differentiated carcinomas, polarity is not completely lost but dysregulated. Recent progress with a three‐dimensional culture of primary cancer cells allowed for studies of the mechanism underlying the abnormality of polarity in differentiated cancers, including flexible switching of polarity status in response to the microenvironment. Invasive micropapillary carcinoma (MPC) is one of the histopathological phenotypes of adenocarcinoma, which is characterized by inverted polarity. Aberrant activation of RHO–ROCK signaling plays a critical role in the MPC phenotype. Establishing in vitro models will contribute to future drug targeting of the abnormal polarity status in cancer.

Rosiglitazone affects lumen formation in MDCKII cell through regulating apico-basal polarity

This study aimed to investigate the potential mechanisms underlying the effects of Rosiglitazone on the apico-basal polarity in renal epithelial cells. 3D-MDCK model was used to study the lumen formation and localization of polarity proteins at the early stage of the establishment of the apico-basal polarity. The calcium switch model, immunofluorescence staining and measurement of transmembrane electrical impedance are employed to investigate the epithelial apico-basal polarity including the development and maintenance of apical domains and the formation of tight junction. MDCKII cells were cultured with 20 uM rosiglitazone or DMSO. Results showed Rosiglitazone reduced the percentage of single central lumen cysts, but the percentage of multiple lumen cysts increased. At the early stage of MDCKII cysts (2-5 cells), Rosiglitazone induced mislocalization of apical and basolateral membrane proteins. In the repolarization process of MDCKII cell induced by a calcium switch (CS), Rosiglitazone delayed the apical membrane domain development in the early phase of cell polarization; while during the maintenance phase of cell polarity, the apical domain retention was significantly affected by Rosiglitazone. Rosiglitazone significantly delayed the formation of tight junctions (TJs); 24 h after CS, however, there were no apparent differences between control group and Rosiglitazone group; the development of transepithelial electrical resistance (TER) was significantly disturbed in Rosiglitazone group. This study shows Rosiglitazone may affect the development and maintenance of apical domains and the formation of TJs disturbs apical protein delivery to the plasma membrane, eventually leading to the abnormal apico-basal polarity, which affects lumen formation in MDCKII cells.

Polarity and morphogenesis of the eye epithelium requires the adhesion junction associated adaptor protein Traf4

During development, neuroepithelial progenitors acquire apico-basal polarity and adhere to one another via apically located tight and adherens junction complexes. This polarized neuroepithelium must continue to integrate cells arising through cell divisions and intercalation, and allow for cell movements, at the same time as undergoing morphogenesis. Cell proliferation, migration and intercalation all occur in the morphing embryonic eye. To understand how eye development might depend on dynamic epithelial adhesion, we investigated the function of a known regulator of junctional plasticity, Tumour necrosis factor receptor-associated factor 4 (Traf4). traf4a mRNA is expressed in the developing eye vesicle over the period of optic cup morphogenesis, and Traf4a loss leads to disrupted evagination and elongation of the eye vesicles, and aberrant organization and apico-basal polarity of the eye epithelium. We propose a model whereby Traf4a regulates apical junction plasticity in nascent eye epithelium, allowing for its polarization and morphogenesis. Symbols and Abbreviations: AB: apico-basal; aPKC: atypical protein kinase-C; CRISPR: clustered regularly-interspaced short palindromic repeats; GFP: green fluorescent protein; hpf: hours post-fertilization; MO: antisense morpholino oligonucleotide; pHH3: phospho histone H3; ss: somite stage; Traf4: Tumour necrosis factor receptor-associated factor 4; ZO-1: zona occludens-1.

SHIP2 Regulates Lumen Generation, Cell Division, and Ciliogenesis through the Control of Basolateral to Apical Lumen Localization of Aurora A and HEF 1

Lumen formation during epithelial morphogenesis requires the creation of a luminal space at cell interfaces named apical membrane-initiation sites (AMISs). This is dependent upon integrated signaling from mechanical and biochemical cues, vesicle trafficking, cell division, and processes tightly coupled to ciliogenesis. Deciphering relationships between polarity determinants and lumen or cilia generation remains a fundamental issue. Here, we report that Src homology 2 domain-containing inositol 5-phosphatase 2 (SHIP2), a basolateral determinant of polarity, regulates RhoA-dependent actin contractility and cell division to form AMISs. SHIP2 regulates mitotic spindle alignment. SHIP2 is expressed in G1 phase, whereas Aurora A kinase is enriched in mitosis. SHIP2 binds Aurora A kinase and the scaffolding protein HEF1 and promotes their basolateral localization at the expense of their luminal expression connected with cilia resorption. Furthermore, SHIP2 expression increases cilia length. Thus, our findings offer new insight into the relationships among basolateral proteins, lumen generation, and ciliogenesis.

Apico-basal Polarity Determinants Encoded by crumbs Genes Affect Ciliary Shaft Protein Composition, IFT Movement Dynamics, and Cilia Length

One of the most obvious manifestations of polarity in epithelia is the subdivision of the cell surface by cell junctions into apical and basolateral domains. crumbs genes are among key regulators of this form of polarity. Loss of crumbs function disrupts the apical cell junction belt and crumbs overexpression expands the apical membrane size. Crumbs proteins contain a single transmembrane domain and localize to cell junction area at the apical surface of epithelia. In some tissues, they are also found in cilia. To test their role in ciliogenesis, we investigated mutant phenotypes of zebrafish crumbs genes. In zebrafish, mutations of three crumbs genes, oko meduzy/crb2a, crb3a, and crb2b, affect cilia length in a subset of tissues. In oko meduzy (ome), this is accompanied by accumulation of other Crumbs proteins in the ciliary compartment. Moreover, intraflagellar transport (IFT) particle components accumulate in the ciliary shaft of ome;crb3a double mutants. Consistent with the above, Crb3 knockdown in mammalian cells affects the dynamics of IFT particle movement. These findings reveal crumbs-dependent mechanisms that regulate the localization of ciliary proteins, including Crumbs proteins themselves, and show that crumbs genes modulate intraflagellar transport and cilia elongation.

The Apical Domain Is Required and Sufficient for the First Lineage Segregation in the Mouse Embryo

Mammalian development begins with segregation of the extra-embryonic trophectoderm from the embryonic lineage in the blastocyst. While cell polarity and adhesion play key roles, the decisive cue driving this lineage segregation remains elusive. Here, to study symmetry breaking, we use a reduced system in which isolated blastomeres recapitulate the first lineage segregation. We find that in the 8-cell stage embryo, the apical domain recruits a spindle pole to ensure its differential distribution upon division. Daughter cells that inherit the apical domain adopt trophectoderm fate. However, the fate of apolar daughter cells depends on whether their position within the embryo facilitates apical domain formation by Cdh1-independent cell contact. Finally, we develop methods for transplanting apical domains and show that acquisition of this domain is not only required but also sufficient for the first lineage segregation. Thus, we provide mechanistic understanding that reconciles previous models for symmetry breaking in mouse development.

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A reduced system was established to study symmetry breaking in mouse development

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8-cell stage blastomeres acquire the capacity to self-organize the apical domain

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The apical domain is required and sufficient for the first lineage segregation

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Contact asymmetry specifies cell fate, leading to self-organized embryo patterning

Reversible Optogenetic Control of Subcellular Protein Localization in a Live Vertebrate Embryo

We demonstrate the utility of the phytochrome system to rapidly and reversibly recruit proteins to specific subcellular regions within specific cells in a living vertebrate embryo. Light-induced heterodimerization using the phytochrome system has previously been used as a powerful tool to dissect signaling pathways for single cells in culture but has not previously been used to reversibly manipulate the precise subcellular location of proteins in multicellular organisms. Here we report the experimental conditions necessary to use this system to manipulate proteins in vivo. As proof of principle, we demonstrate that we can manipulate the localization of the apical polarity protein Pard3 with high temporal and spatial precision in both the neural tube and the embryo’s enveloping layer epithelium. Our optimizations of optogenetic component expression and chromophore purification and delivery should significantly lower the barrier for establishing this powerful optogenetic system in other multicellular organisms.

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The phytochrome system has been optimized for use within multicellular organisms

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Protein recruitment can be tightly controlled to a specific subcellular region

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Protein recruitment occurs with high binding and reversal kinetics

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The subcellular localization of the apical polarity protein Pard3 is manipulated

N-cadherin-based adherens junction regulates the maintenance, proliferation, and differentiation of neural progenitor cells during development

This review addresses our current understanding of the regulatory mechanism by which N-cadherin, a classical cadherin, affects neural progenitor cells (NPCs) during development. N-cadherin is responsible for the integrity of adherens junctions (AJs), which develop in the sub-apical region of NPCs in the neural tube and brain cortex. The apical domain, which contains the sub-apical region, is involved in the switching from symmetric proliferative division to asymmetric neurogenic division of NPCs. In addition, N-cadherin-based AJ is deeply involved in the apico-basal polarity of NPCs and the regulation of Wnt-β-catenin, hedgehog (Hh), and Notch signaling. In this review, we discuss the roles of N-cadherin in the maintenance, proliferation, and differentiation of NPCs through components of AJ, β-catenin and αE-catenin.

ArhGEF18 regulated Rho signaling in vertebrate retina development

Epithelia consisting of highly polarized columnar cells contribute to many organs during development, including the central nervous system. Epithelial organization is essential for proliferation and differentiation of progenitor cells and subsequent organ morphology and function. Small GTPases of the Rho family are important regulators of cellular morphology and polarity. We recently identified ArhGEF18 as a key regulator of RhoA-Rock2 signaling that is crucial for maintenance of polarity in the vertebrate retinal epithelium. ArhGEF18 is required to maintain apico-basal polarity, localization of tight junctions and cortical actin, thus shaping cellular morphology. Loss of ArhGEF18 activity results in increased proliferation and reduced cell cycle exit. Together, these perturbations result in a severely misshaped embryonic eye, where the stereotype arrangement of retinal cell types is randomized. Our findings reveal an important role for RhoA-Rock2 signaling to maintain apico-basal polarity in retinal progenitor cells, which is essential for subsequent cellular differentiation, morphology and eventually organ function.