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Background In almost all metazoans examined to this respect, the axial patterning system based on canonical Wnt (cWnt) signaling operates throughout the course of development. In most metazoans, gastrulation is polar, and embryos develop morphological landmarks of axial polarity, such as blastopore under control/regulation from cWnt signaling. However, in many cnidarian species, gastrulation is morphologically apolar. The question remains whether cWnt signaling providing the establishment of a body axis controls morphogenetic processes involved in apolar gastrulation. Results In this study, we focused on the embryonic development of Dynamena pumila, a cnidarian species with apolar gastrulation. We thoroughly described cell behavior, proliferation, and ultrastructure and examined axial patterning in the embryos of this species. We revealed that the first signs of morphological polarity appear only after the end of gastrulation, while molecular prepatterning of the embryo does exist during gastrulation. We have shown experimentally that in D. pumila, the direction of the oral-aboral axis is highly robust against perturbations in cWnt activity. Conclusion Our results suggest that morphogenetic processes are uncoupled from molecular axial patterning during gastrulation in D. pumila. Investigation of D. pumila might significantly expand our understanding of the ways in which morphological polarization and axial molecular patterning are linked in Metazoa. This article is protected by copyright. All rights reserved.

The plant cuticle is a multifunctional barrier that separates the organs of the plant from the surrounding environment. Cuticular ridges are microscale wrinkle-like cuticular protrusions that occur on many flower and leaf surfaces. These microscopic ridges can help against pest insects by reducing the frictional forces experienced when they walk on the leaves and might also provide mechanical stability to the growing plant organs. Here, we have studied the development of cuticular ridges on adaxial leaf surfaces of the tropical Araceae Schismatoglottis calyptrata. We used polymer replicas of adaxial leaf surfaces at various ontogenetic stages to study the morphological changes occurring on the leaf surfaces. We characterized the replica surfaces by using confocal laser scanning microscopy and commercial surface analysis software. The development of cuticular ridges is polar and the ridge progression occurs basipetally with a specific inclination to the midrib on Schismatoglottis calyptrata leaves. Using Colorado potato beetles as model species, we performed traction experiments on freshly unrolled and adult leaves and found low walking frictional forces of insects on both of these surfaces. The changes in the micro- and macroscale morphology of the leaves should improve our understanding of the way that plants defend themselves against insect herbivores.

Leaf laminar growth and adaxial–abaxial boundary formation are fundamental outcomes of plant development. Boundary and laminar growth coordinate the further patterning and growth of the leaf, directing the differentiation of cell types within the top and bottom domains and promoting initiation of lateral organs along their adaxial or abaxial axis. Leaf adaxial–abaxial polarity specification and laminar outgrowth are regulated by two transcription factors, REVOLUTA (REV) and KANADI (KAN). ABA INSENSITIVE TO GROWTH 1 (ABIG1) encodes a HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP) class II transcription factor and is a direct target of the adaxial–abaxial regulators REV and KAN. To investigate the role of ABIG1 in leaf development and in the establishment of polarity, we examined the phenotypes of both gain-of-function and loss-of-function mutants. Through genetic interaction analysis with REV and KAN mutants, we determined that ABIG1 plays a role in leaf laminar growth as well as in adaxial–abaxial polarity establishment. Genetic and physical interaction assays showed that ABIG1 interacts with the transcriptional TOPLESS corepressor. This study provides new evidence that ABIG1, another HD-ZIP II, facilitates growth through the corepressor TOPLESS.

Complanadine A and lycodine are representative members of the Lycopodium alkaloids with a characteristic pyridine-containing tetracyclic skeleton. Complanadine A has demonstrated promising neurotrophic activity and potential for persistent pain management. Herein we report a pyrrole strategy enabled by one-carbon insertion and polarity inversion for concise total syntheses of complanadine A and lycodine. The use of a pyrrole as the pyridine precursor allowed the rapid construction of their tetracyclic skeleton via a one-pot Staudinger reduction, amine-ketone condensation, and Mannich-type cyclization. The pyrrole group was then converted to the desired pyridine by the Ciamician-Dennstedt rearrangement via a one-carbon insertion process, which also simultaneously introduced a chloride at C3 for the next C-H arylation. Other key steps include a direct anti-Markovnikov hydroazidation, a Mukaiyama-Michael addition, and a Paal-Knorr pyrrole synthesis. Lycodine and complanadine A were prepared in 8 and 11 steps, respectively, from a readily available known compound.

Loss of polarity protein Par3 promotes breast cancer tumorigenesis and metastasis. The underlying molecular mechanisms of Par3 down-regulation and related prognostic significance in breast cancer remain unclear. Here, we discovered that Par3 down-regulation was associated with shorter relapse-free survival in Luminal A subtype of breast cancer. Par3 knockdown promoted breast cancer cells migration and invasion. Importantly, we identified that transcription factor Sp1 bound to PARD3 promoter region and induced Par3 expression. Breast cancer patients with low Sp1 showed significantly worse RFS and low expression level of Par3. Par3 over-expression partially reversed Sp1 knockdown induced migration and invasion. Together, decreased Sp1 level mediates Par3 down-regulation, which correlated with poor prognosis of ER + breast cancer patients, via reduced binding with PARD3 promoter.

Ionic liquids (ILs), 1-alkyl-3-methylimidazolium alanine [Cnmim][Ala] (n = 2, 4), were synthesized and characterized by 1H NMR and DSC. Then, the average temperature vaporization enthalpy, $$ \Delta _\text{l}^{\text g} H_{\text m}^{\uptheta } $$ (Tav), of [Cnmim][Ala] (n = 2, 4) was determined by thermogravimetric method. The difference in heat capacities of ionic liquids between the vapor phase and the liquid phase, $$ \Delta _{\text l}^{g} C_{\text {p,m}}^{\uptheta } $$ , was calculated and $$ \Delta _\text{l}^{\text g} H_{\text m}^{\uptheta } $$ (Tav) was converted to $$ \Delta _\text{l}^{\text g} H_{\text m}^{\uptheta } $$ (298). In addition, the polarity, δμ, of two ILs was estimated based on the $$ \Delta _\text{l}^{\text g} H_{\text m}^{\uptheta } $$ (298). At the same time, the molar surface Gibbs free energy, gs, was calculated, and the traditional Eotvos equation was improved, and its parameters have clear physical significance. In addition, expression for predicting surface tension, γ, of the ILs is obtained by the combination gs with Lorentz–Lorenz equation, and the results show that both are in good agreement with the experimental values.

We report the successful synthesis and spectroscopic characterization of a novel, water soluble anthanthrene-based derivative, 6,12-bis(TEG)anthanthrene 3. The presence of the two long ethylene glycol side chains gives this large, six-membered polycyclic aromatic compound a high aqueous solubility. It exhibits UV–vis absorption properties similar to those of anthanthrene itself, indicating that the side chains do not have a significant effect on the electronic structure of the central chromophore. The compound exhibits strong, polarity-sensitive fluorescence in aqueous solution in the blue–green region of the spectrum, with a fluorescence quantum yield of 0.13 and a polarity sensitivity factor (PSF) of 2.0. The utility of this new fluorescent molecule as a probe of supramolecular complexation was demonstrated by its inclusion into the molecular host hydroxypropyl-β-cyclodextrin in aqueous solution. Strictly 1:1 inclusion was observed, with a moderately strong binding constant K of 650 M−1. This new fluorescence probe has significant potential applications in fluorescence-based studies of aqueous biochemical and supramolecular systems.

Microtubules establish the directionality of intracellular transport by kinesins and dynein through polarized assembly, but it remains unclear how directed transport occurs along microtubules organized with mixed polarity. We investigated the ability of the plus-end directed kinesin-4 motor KIF21B to navigate mixed polarity microtubules in mammalian dendrites. Reconstitution assays with recombinant KIF21B and engineered microtubule bundles or extracted neuronal cytoskeletons indicate that nucleotide-independent microtubule binding regions of KIF21B modulate microtubule dynamics and promote directional switching on antiparallel microtubules. Optogenetic recruitment of KIF21B to organelles in live neurons induces unidirectional transport in axons but bi-directional transport with a net retrograde bias in dendrites. Removal of the secondary microtubule binding regions of KIF21B or dampening of microtubule dynamics with low concentrations of nocodazole eliminates retrograde bias in live dendrites. Further exploration of the contribution of microtubule dynamics in dendrites to directionality revealed plus-end-out microtubules to be more dynamic than plus-end-in microtubules, with nocodazole preferentially stabilizing the plus-end-out population. We propose a model in which both nucleotide-sensitive and insensitive microtubule binding sites of KIF21B motors contribute to the search and selection of stable plus-end-in microtubules within the mixed polarity microtubule arrays characteristic of mammalian dendrites to achieve net retrograde movement of KIF21B-bound cargos. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text].

A common morphological feature of typical angiosperms is the patterning of lateral organs along primary axes of asymmetry—a proximodistal, a mediolateral, and an adaxial–abaxial axis. Angiosperm leaves usually have distinct adaxial–abaxial identity, which is required for the development of a flat shape. By contrast, many unifacial leaves, consisting of only the abaxial side, show a flattened morphology. This implicates a unique mechanism that allows leaf flattening independent of adaxial–abaxial identity. In this study, we report a role for auxin in outgrowth of unifacial leaves. In two closely related unifacial-leaved species of Juncaceae, Juncus prismatocarpus with flattened leaves, and Juncus wallichianus with transversally radialized leaves, the auxin-responsive gene GLYCOSIDE HYDROLASE3 displayed spatially different expression patterns within leaf primordia. Treatment of J. prismatocarpus seedlings with exogenous auxin or auxin transport inhibitors, which disturb endogenous auxin distribution, eliminated leaf flatness, resulting in a transversally radialized morphology. These treatments did not affect the radialized morphology of leaves of J. wallichianus. Moreover, elimination of leaf flatness by these treatments accompanied dysregulated expression of genetic factors needed to specify the leaf central-marginal polarity in J. prismatocarpus. The findings imply that lamina outgrowth of unifacial leaves relies on proper placement of auxin, which might induce initial leaf flattening and subsequently act to specify leaf polarity, promoting further flattening growth of leaves.

Boron (B) is essential for growth and development, with the B requirement differing depending on the particular organs and tissues, but the molecular mechanisms underlying the preferential distribution of B to different tissues are poorly understood. We investigated the role of a rice gene (OsBOR1) encoding a B efflux transporter in the distribution of B to different tissues under different B supplies. OsBOR1 was highly expressed in the nodes at all growth stages. The OsBOR1 protein shows polar localization at the distal side of bundle sheath cells in nodes and xylem parenchyma cells of elongating leaf sheath, but in the mature leaf sheath and blade at the proximal side of bundle sheath cells. Furthermore, the expression of OsBOR1 was not affected by external B fluctuations, but the OsBOR1 protein was gradually degraded in response to high B. Knockout of this gene altered B distribution, decreasing the distribution of B to new leaves and panicles but increasing B distribution to old leaves. These results indicate that OsBOR1 expressed in nodes and leaf sheath is involved in the preferential distribution of B to different tissues in rice. Furthermore, the OsBOR1 undergoes degradation in response to high B for fine regulation of B distribution to different tissues.

The acquisition of neuronal polarity is a complex molecular process that depends on changes in cytoskeletal dynamics and directed membrane traffic, regulated by the Rho and Rab families of small GTPases, respectively. However, during axon specification, a molecular link that couples these protein families has yet to be identified. In this paper, we describe a new positive feedback loop between Rab8a and Cdc42, coupled by Tuba, a Cdc42-specific guanine nucleotide-exchange factor (GEF), that ensures a single axon generation in rodent hippocampal neurons from embryos of either sex. Accordingly, Rab8a or Tuba gain-of-function generates neurons with supernumerary axons whereas Rab8a or Tuba loss-of-function abrogated axon specification, phenocopying the well-established effect of Cdc42 on neuronal polarity. Although Rab8 and Tuba do not interact physically, the activity of Rab8 is essential to generate a proximal to distal axonal gradient of Tuba in cultured neurons. Tuba-associated and Rab8a-associated polarity defects are also evidencedin vivo, since dominant negative (DN) Rab8a or Tuba knock-down impairs cortical neuronal migration in mice. Our results suggest that Tuba coordinates directed vesicular traffic and cytoskeleton dynamics during neuronal polarization.SIGNIFICANCE STATEMENTThe morphologic, biochemical, and functional differences observed between axon and dendrites, require dramatic structural changes. The extension of an axon that is 1 µm in diameter and grows at rates of up to 500 µm/d, demands the confluence of two cellular processes: directed membrane traffic and fine-tuned cytoskeletal dynamics. In this study, we show that both processes are integrated in a positive feedback loop, mediated by the guanine nucleotide-exchange factor (GEF) Tuba. Tuba connects the activities of the Rab GTPase Rab8a and the Rho GTPase Cdc42, ensuring the generation of a single axon in cultured hippocampal neurons and controlling the migration of cortical neurons in the developing brain. Finally, we provide compelling evidence that Tuba is the GEF that mediates Cdc42 activation during the development of neuronal polarity.

Through the insertion of nonpolar side chains into the bilayer, the hydrophobic effect has long been accepted as a driving force for membrane protein folding. However, how the changing chemical composition of the bilayer affects the magnitude side chain transfer free energieshas historically not been well understood. A particularly challenging region for experimental interrogation is the bilayer interfacial region that is characterized by a steep polarity gradient. In this study we have determined thefor nonpolar side chains as a function of bilayer position using a combination of experiment and simulation. We discovered an empirical correlation between the surface area of nonpolar side chain, the transfer free energies, and the local water concentration in the membrane that allows forto be accurately estimated at any location in the bilayer. Using these water-to-bilayervalues, we calculated the interface-to-bilayer transfer free energy. We find that theare similar to the “biological”, translocon-based transfer free energies, indicating that the translocon energetically mimics the bilayer interface. Together these findings can be applied to increase the accuracy of computational workflows used to identify and design membrane proteins, as well as bring greater insight into our understanding of how disease-causing mutations affect membrane protein folding and function.

A one-pot catalytic method has been developed for the stereoselective synthesis of cyclopropane-fused cyclic amidines using CuBr2/K2S2O8 as an efficient single electron transfer (SET) oxidative system. The generality of this mild method is demonstrated with a wide variety of substrates to furnish pharmaceutically important amidines containing aza-bicyclic and novel aza-tricyclic frameworks in very good yields. A chemoselective reduction of cyclic amidines to 2-/3-azabicyclo[m.n.0]alkanes and octahydroindoles has been developed using a NaBH4/I2 reagent system. The synthetic scope of the chemoselective reduction of the amidine functionality has been exemplified in the stereoselective synthesis of an iminosugar based (±)-epiquinamide analogue.

Desmosomes (DSMs), together with adherens junctions (AJs) and tight junctions (TJs), constitute the apical cell junctional complex (AJC). While the importance of the apical and basolateral polarity machinery in the organization of AJs and TJs is well established, how DSMs are positioned within the AJC is not understood. Here we use highly polarized DLD1 cells as a model to address how DSMs integrate into the AJC. We found that knockout (KO) of the desmosomal ARM protein Pkp3, but not other major DSM proteins, uncouples DSMs from the AJC without blocking DSM assembly. DLD1 cells also exhibit a prominent extraDSM pool of Pkp3, concentrated in tricellular (tC) contacts. Probing distinct apicobasal polarity pathways revealed that neither the DSM's association with AJC nor the extraDSM pool of Pkp3 are abolished in cells with defects in Scrib module proteins responsible for basolateral membrane development. However, a loss of the apical polarity protein, Par3, completely eliminates the extraDSM pool of Pkp3 and disrupts AJC localization of desmosomes, dispersing these junctions along the entire length of cell-cell contacts. Our data are consistent with a model whereby Par3 facilitates DSM assembly within the AJC, controlling the availability of an assembly competent pool of Pkp3 stored in tC contacts.

Neurons are polarized cells of extreme scale and compartmentalization. To fulfill their role in electrochemical signaling, axons must maintain a specific complement of membrane proteins. Despite being subject of considerable attention, the trafficking pathway of axonal membrane proteins is not well understood. Two pathways, direct delivery and transcytosis, have been proposed. Previous studies reached contradictory conclusions about which of these mediates delivery of axonal membrane proteins to their destination, in part because they evaluated long-term distribution changes and not vesicle transport. We developed a novel strategy to selectively label vesicles in different trafficking pathways and determined the trafficking of two canonical axonal membrane proteins, NgCAM and VAMP2. Results from detailed quantitative analyses of transporting vesicles differed substantially from previous studies and found that axonal membrane proteins overwhelmingly undergo direct delivery. Transcytosis plays only a minor role in axonal delivery of these proteins. In addition, we identified a novel pathway by which wayward axonal proteins that reach the dendritic plasma membrane are targeted to lysosomes. These results redefine how axonal proteins achieve their polarized distribution, a crucial requirement for elucidating the underlying molecular mechanisms. [Media: see text] [Media: see text] [Media: see text] [Media: see text].

Significance Many bacteria move across surfaces using type IV pili (T4P). The piliation pattern varies between species; however, the underlying mechanisms governing these patterns remain largely unknown. Here, we demonstrate that in the rod-shaped Myxococcus xanthus cells, the unipolar formation of T4P at the leading cell pole is the result of stimulation by the small GTPase MglA together with the effector protein SgmX, while MglB, the cognate MglA GTPase activating protein (GAP) that localizes to the lagging cell pole, blocks this stimulation at the lagging pole due to its GAP activity. During reversals, MglA/SgmX and MglB switch polarity, laying the foundation for T4P formation at the new leading cell pole and inhibition of T4P formation at the former leading cell pole., Bacteria can move across surfaces using type IV pili (T4P), which undergo cycles of extension, adhesion, and retraction. The T4P localization pattern varies between species; however, the underlying mechanisms are largely unknown. In the rod-shaped Myxococcus xanthus cells, T4P localize at the leading cell pole. As cells reverse their direction of movement, T4P are disassembled at the old leading pole and then form at the new leading pole. Thus, cells can form T4P at both poles but engage only one pole at a time in T4P formation. Here, we address how this T4P unipolarity is realized. We demonstrate that the small Ras-like GTPase MglA stimulates T4P formation in its GTP-bound state by direct interaction with the tetratricopeptide repeat (TPR) domain-containing protein SgmX. SgmX, in turn, is important for polar localization of the T4P extension ATPase PilB. The cognate MglA GTPase activating protein (GAP) MglB, which localizes mainly to the lagging cell pole, indirectly blocks T4P formation at this pole by stimulating the conversion of MglA-GTP to MglA-GDP. Based on these findings, we propose a model whereby T4P unipolarity is accomplished by stimulation of T4P formation at the leading pole by MglA-GTP and SgmX and indirect inhibition of T4P formation at the lagging pole by MglB due to its MglA GAP activity. During reversals, MglA, SgmX, and MglB switch polarity, thus laying the foundation for T4P formation at the new leading pole and inhibition of T4P formation at the new lagging pole.

Transfer cells (TCs) support high nutrient rates into, or at symplasmic discontinuities within, the plant body. Their transport capacity is conferred by an amplified plasma membrane surface area, enriched in nutrient transporters, supported on an intricately invaginated wall labyrinth (WL). Thus, development of the WL is at the heart of TC function. Enquiry has shifted from describing WL architecture and formation to discovering mechanisms regulating WL assembly. Experimental systems used to examine these phenomena are critiqued. Considerable progress has been made in identifying master regulators that commit stem cells to a TC fate (e.g. the maize Myeloblastosis (MYB)-related R1-type transcription factor) and signals that induce differentiated cells to undergo trans-differentiation to a TC phenotype (e.g. sugar, auxin and ethylene). In addition, signals that provide positional information for assembly of the WL include apoplasmic hydrogen peroxide and cytosolic Ca2+ plumes. The former switches on, and specifies the intracellular site for WL construction, while the latter creates subdomains to direct assembly of WL invaginations. Less is known about macromolecule species and their spatial organization essential for WL assembly. Emerging evidence points to a dependency on methyl-esterified homogalacturonan accumulation, unique patterns of cellulose and callose deposition and spatial positioning of arabinogalactan proteins.

Biological membranes present a major obstacle for the delivery of therapeutic agents into cells. Some peptides have been shown to translocate across the membrane spontaneously, and they could be thus used as drug-carriers. However, the advantageous peptide properties for the translocation remain unclear. Of particular interest is the effect of a proline-induced kink in α-helical peptides, because the kink was previously reported to both increase and decrease the antimicrobial activity. The antimicrobial activity of peptides could be related to their translocation across the membrane as is the case of the buforin 2 peptide investigated here. Using computer simulations with two independent models, we consistently showed that the presence of the kink has (1) no effect on the translocation barrier, (2) reduces the peptide affinity to the membrane, and (3) disfavors the transmembrane state. Moreover, we were able to determine that these effects are mainly caused by the peptide increased polarity, not the increased flexibility of the kink. The provided molecular understanding can be utilized for the design of cell-penetrating and drug-carrying peptides.

The evolutionarily conserved Par3/Par6/aPKC complex regulates the polarity establishment of diverse cell types and distinct polarity-driven functions. However, how the Par complex is concentrated beneath the membrane to initiate cell polarization remains unclear. Here we show that the Par complex exhibits cell cycle-dependent condensation in Drosophila neuroblasts, driven by liquid–liquid phase separation. The open conformation of Par3 undergoes autonomous phase separation likely due to its NTD-mediated oligomerization. Par6, via C-terminal tail binding to Par3 PDZ3, can be enriched to Par3 condensates and in return dramatically promote Par3 phase separation. aPKC can also be concentrated to the Par3N/Par6 condensates as a client. Interestingly, activated aPKC can disperse the Par3/Par6 condensates via phosphorylation of Par3. Perturbations of Par3/Par6 phase separation impair the establishment of apical–basal polarity during neuroblast asymmetric divisions and lead to defective lineage development. We propose that phase separation may be a common mechanism for localized cortical condensation of cell polarity complexes., The evolutionarily conserved complex, the Par proteins, regulates cell polarity. Here, the authors show that in Drosophila neuroblasts, the Par complex exhibits liquid–liquid phase separation dependent on the cell cycle.

To determine the role of 3, 3', 5-triiodo-L thyroxine (T3) in the differentiation of Sertoli cells (SCs) and the factors influencing maturity via the Wilms' tumor 1 (WT1)/non-canonical Wnt signaling pathway, high purity SCs were isolated from newborn calves' testes and cultured in vitro. The SCs were stimulated with T3, and co-treated with short interference (si) RNA to knockdown endogenous WT1 and non-canonical Wnt signalling inhibitor Wnt-c59. Our results suggested that the addition of different concentrations (0, 25, 50, and 100 nM) of T3 in the culture medium changed the expression of KRT-18 (SCs immature marker) and accelerated the differentiation of SCs. T3 (100 nM) treatment induced up-regulated expression of WT1 over time (p 0.05), while the expression of polarity proteins (Par3, Par6b, and E-cadherin) and Wnt4 were affected to varying degrees (p 0.05). SCs were treated simultaneously with T3 + Wnt-c59 and T3 + WT1 siRNA, and the results showed that T3 could affect the expression of polarity proteins via WT1/non-canonical Wnt signaling pathway. These data put together indicate that T3 plays a dependent role in the induction of bovine SCs differentiation via WT1/non-canonical Wnt signaling pathway in vitro. This study proposes for the first time that WT1 is a major target for T3.

The symmetry breaking of protein distribution and cytoskeleton organization is an essential aspect for the development of apicobasal polarity. In embryonic cells this process is largely cell autonomous, while differentiated epithelial cells collectively polarize during epithelium formation. Here, we demonstrate that the de novo polarization of mature hepatocytes does not require the synchronized development of apical poles on neighbouring cells. De novo polarization at the single-cell level by mere contact with the extracellular matrix and immobilized cadherin defining a polarizing axis. The creation of these single-cell liver hemi-canaliculi allows unprecedented imaging resolution and control and over the lumenogenesis process. We show that the density and localization of cadherins along the initial cell–cell contact act as key triggers of the reorganization from lateral to apical actin cortex. The minimal cues necessary to trigger the polarization of hepatocytes enable them to develop asymmetric lumens with ectopic epithelial cells originating from the kidney, breast or colon. The polarity of primary hepatocytes has now been shown to be inducible at the single-cell level by passive artificial micro-niches, indicating that the early development of polarity occurs largely independently of the types and response of the neighbouring cells.

Hepatocytes, the main epithelial cells of the liver, organize their polarized membrane domains differently from ductal epithelia. They also differ in their biosynthetic delivery of single-membrane-spanning and glycophosphatidylinositol-anchored proteins to the apical domain. While ductal epithelia target apical proteins to varying degrees from the trans-Golgi network (TGN) to the apical surface directly, hepatocytes target them first to the basolateral domain, from where they undergo basolateral-to-apical transcytosis. How TGN-to-surface transport differs in both scenarios is unknown. Here, we report that the basolateral detour of a hepatocyte apical protein is due, in part, to low RhoA activity at the TGN, which prevents its segregation from basolateral transport carriers. Activating Rho in hepatocytic cells, which switches their polarity from hepatocytic to ductal, also led to apical-basolateral cargo segregation at the TGN as is typical for ductal cells, affirming a central role for Rho-signaling in different aspects of the hepatocytic polarity phenotype. Nevertheless, Rho-induced cargo segregation was not sufficient to target the apical protein directly; thus, failure to recruit apical targeting machinery also contributes to its indirect itinerary.

Defective Kernel 1 (DEK1) is genetically at the nexus of the 3D morphogenesis of land plants. We aimed to localize DEK1 in the moss Physcomitrella patens to decipher its function during this process. To detect DEK1 in vivo, we inserted the tdTomato fluorophore into PpDEK1 gene locus. Confocal microscopy coupled with the use of time-gating allowed the precise DEK1 subcellular localization during 3D morphogenesis. DEK1 localization displays a strong polarized signal, as it is restricted to the plasma membrane domain between recently divided cells during the early steps of 3D growth development as well as during the subsequent vegetative growth. The signal furthermore displays a clear developmental pattern because it is only detectable in recently divided and elongating cells. Additionally, DEK1 localization appears to be independent of its calpain domain proteolytic activity. The DEK1 polar subcellular distribution in 3D tissue developing cells defines a functional cellular framework to explain its role in this developmental phase. Also, the observation of DEK1 during spermatogenesis suggests another biological function for this protein in plants. Finally the DEK1-tagged strain generated here provides a biological platform upon which further investigations into 3D developmental processes can be performed.

International audience; Mitotic spindle orientation has been linked to asymmetric cell divisions, tissue morphogenesis and homeostasis. The canonical pathway to orient the mitotic spindle is composed of the cortical recruitment factor NuMA and the molecular motor dynein, which exerts pulling forces on astral microtubules to orient the spindle. Recent work has defined a novel role for NuMA as a direct contributor to force generation. In addition, the exploration of geometrical and physical cues combined with the study of classical polarity pathways has led to deeper insights into the upstream regulation of spindle orientation. Here, we focus on how cell shape, junctions and mechanical tension act to orient spindle pulling forces in epithelia, and discuss different roles for spindle orientation in epithelia.

In this study, we aimed to study the effect of fluid shear stress on fibroblasts and BMSCs on plane and groove topographies. The results showed that 0.6-Hz stress had the greatest influence on the alignment, polarity, migration and adhesion of fibroblasts on plane by increasing the expression of reoriented actin and vinculin; whereas 1.0-Hz stress promoted differentiation of fibroblasts into myofibroblasts by increasing Col-I and α-SMA expression. Interestingly, under the given frequency stress, the groove structure strengthened the above characteristics of fibroblasts beyond adhesion, and promoted differentiation of BMSCs into myofibroblasts. The above results indicate that 0.6 Hz may improve the implant-tissue sealing, while 1.0-Hz stress probably causes the disordered fiber deposition around implants.

OBJECTIVE To investigate the effect of phase polarity and charge balance of spinal cord stimulation (SCS) waveforms on pain behavior and gene expression in a neuropathic pain rodent model. We hypothesized that differing waveforms will result in diverse behavioral and transcriptomics expression due to unique mechanisms of action. MATERIALS AND METHODS Rats were implanted with a four-contact cylindrical mini-lead and randomly assigned to two control (no-pain and pain model) and five test groups featuring monophasic, as well as charge-unbalanced and charge-balanced biphasic SCS waveforms. Mechanical and cold allodynia were assessed to measure efficacy. The ipsilateral dorsal quadrant of spinal cord adjacent to the lead was harvested post-stimulation and processed to determine gene expression via real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Gene expression, SCS intensity (mA), and behavioral score as percent of baseline (BSPB) were statistically analyzed and used to generate correlograms using R-Studio. Statistical analysis was performed using SPSS22.0, and p

Graphical abstract, Cell migration is a tightly-regulated process that involves protein gradients formed by the Rho family of GTPases, including Rho and Rac. The front (rear) of cells is generally characterized by higher active Rac (Rho) and lower active Rho (Rac) concentrations. Protein clusters, called adhesions, that anchor cells to their external environment have been shown to be dynamic and small (stable and large) at the cell front (rear), forming the force-transmission points necessary for persistent movement. Differences in adhesion sizes and dynamics have been linked to gradients in Rac and Rho activity. Here, we study the effects of Rac activation and gradients in Rac and Rho concentrations and activities on cellular polarity and adhesion size using mathematical and experimental approaches. The former is accomplished by expanding an existing reaction-diffusion model to a 2D domain utilizing stochastic dynamics. The model revealed that a hysteresis between the induced/uninduced states (corresponding to higher/lower Rac concentrations, respectively) along with Rac and Rho activation gradients, generated by chemical cues, were vital for forming polarity. Experimentally, the induced state was generated by increasing the cellular βPIX (a Rac-GEF) level and/or decreasing ROCK (a Rac-GAP effector protein) activity with Y-27632 (a ROCK-inhibitor). In agreement with the simulations, our results showed that cells with elevated RacGTP migrated faster, indicating more robust cellular polarization. However, the directionality of cells was not changed significantly, suggesting that external and/or internal physical or chemical cues were needed. Complementing the faster migration observed, adhesions were smaller, generating the phenotype expected with the induced state.

Calothrix sp. strain PCC 7716 is a filamentous cyanobacterium whose morphology is tapered, with basal-apical polarity. The apical filament shows positive phototropism toward white light or blue light. To elucidate the molecular basis of the phototropism, we determined the complete genome sequence of a spontaneous mutant of this strain that has a thin sheath and is suitable for genomic DNA extraction.

Microtubules are polarised polymers nucleated by multi-protein γ-tubulin ring complexes (γ-TuRCs). Within neurons, microtubule polarity is plus-end-out in axons and mixed or minus-end-out in dendrites. Previously we showed that within the soma of Drosophila sensory neurons γ-tubulin localises asymmetrically to Golgi stacks, Golgi-derived microtubules grow asymmetrically towards the axon, and growing microtubule plus-ends are guided towards the axon and restricted from entering dendrite in a Kinesin-2-dependent manner (Mukerjee et al., 2020). Here we show that depleting γ-TuRCs perturbs the direction of microtubule growth from the Golgi stacks, consistent with a model for asymmetric microtubule nucleation involving γ-TuRCs and other nucleation-promoting factors. We also directly observe microtubule turning along microtubule bundles and show that depleting APC, proposed to link Kinesin-2 to plus ends, reduces microtubule turning and increases plus end growth into dendrites. These results support a model of asymmetric nucleation and guidance within the neuronal soma that helps establish and maintain overall microtubule polarity.

Translation of messenger RNA is regulated through a diverse set of RNA-binding proteins. A significant fraction of RNA-binding proteins contain prion-like domains which form functional prions. This raises the question of how prions can play a role in translational control. Local control of translation in dendritic spines by prions has been invoked in the mechanism of synaptic plasticity and memory. We show how channeling through diffusion and processive translation cooperate in highly ordered mRNA/prion aggregates as well as in less ordered mRNA/protein condensates depending on their sub-structure. We show the direction of translational control, whether it is repressive or activating, depends on the polarity of the mRNA distribution in mRNA/prion assemblies which determines whether vectorial channeling can enhance recycling of ribosomes. Our model also addresses the effect of changes of substrate concentration in assemblies that have been suggested previously to explain translation control by assemblies through the introduction of a potential of mean force biasing diffusion of ribosomes inside the assemblies. The results from the model are compared with the experimental data on translational control by two functional RNA-binding prions, CPEB involved in memory and Rim4 involved in gametogenesis.Significance StatementmRNA/protein assemblies such as functional prions and condensates are involved in locally regulating translation in eukaryotic cells. The mode of regulation depends on the structure of these assemblies. We show that the vectorial processive nature of translation can couple to transport via diffusion so as to repress or activate translation depending on the structure of the RNA protein assembly. We find that multiple factors including diffusivity changes and free energy biases in the assemblies can regulate the translation rate of mRNA by changing the balance between substrate recycling and competition between mRNAs. We mainly focus on the example of CPEB, a functional prion that has been implicated in the mechanism of synaptic plasticity of neurons and in memory.

Zebrafish caudal fin rays are used as a model system for regeneration because of their high regenerative ability, but studies on the regeneration polarity of the fin ray are limited. To investigate this regeneration polarity, we made a hole to excise part of the fin ray and analyzed the regeneration process. We confirmed that the fin rays always regenerated from the proximal margin toward the distal margin, as previously reported, however, regeneration-related genes were expressed at both the proximal and distal edges of the hole in the early stage of regeneration, suggesting that the regenerative response also occurs at the distal edge. One difference between the proximal and distal margins is a sheet-like tissue that is formed on the apical side of the regenerated tissue at the proximal margin. This sheet-like tissue was not observed at the distal edge. To investigate whether the distal margin was also capable of forming this sheet-like tissue and subsequent regeneration, we kept the distal margin separated from the proximal margin by manipulation. Consequently, the sheet-like tissue was formed at the distal margin and regeneration of the fin ray was also induced. The regenerated fin rays from the distal margin protruded laterally from the caudal fin and then bent distally, and their ends showed the same characteristics as those of the normal fin rays. These results suggest that fin rays have an ability to regenerate in both directions, however, under normal conditions, regeneration is restricted to the proximal margin because the sheet-like tissue is preferentially formed on the apical side of the regenerating tissue from the proximal margin.

Cdc42 GTPase rules cell polarity and growth in fission yeast. It is negatively and positively regulated by GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs), respectively. Active Cdc42-GTP localizes to the poles, where it associates with numerous proteins constituting the polarity module. However, little is known about its downregulation. We describe here that oxidative stress causes Sty1-kinase-dependent Cdc42 inactivation at cell poles. Both the amount of active Cdc42 at tips and cell length inversely correlate with Sty1 activity, explaining the elongated morphology of Δsty1 cells. We have created stress-blinded cell poles either by eliminating two Cdc42 GAPs or through the constitutive tethering of Gef1 to cell tips, and we biochemically demonstrate that the GAPs Rga3/6 and the GEF Gef1 are direct substrates of Sty1. We propose that phosphorylation of Rga3/6 and Gef1 mediates the Sty1-dependent inhibition of Cdc42 at cell tips, halting polarized growth during stress adaptation., This work is supported by the Ministerio de Ciencia, Innovación y Universidades (Spain), PLAN E, and FEDER (grant PGC2018-093920-B-I00 to E.H., PGC2018-097248-B-I00 to J.A., and PGC2018-098924-B-100 to P.P.). The Oxidative Stress and Cell Cycle group is also supported by Generalitat de Catalunya (Spain) (2017-SGR-539) and Unidad de Excelencia María de Maeztu, funded by the AEI (Spain) (grant CEX2018-000792-M). P.P. is also supported by Junta de Castilla y León (Escalera de la Excelencia) (grant CLU-2017-03). C.S.-C. was recipient of a María de Maeztu predoctoral fellowship from the Ministerio de Economía y Competitividad (Spain), With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2018-000792-M).

Asymmetric signaling and organization in the stem-cell niche determine stem-cell fates. Here, we investigate the basis of asymmetric signaling and stem-cell organization using the Drosophila wing-disc that creates an adult muscle progenitor (AMP) niche. We show that AMPs extend polarized cytonemes to contact the disc epithelial junctions and adhere themselves to the disc/niche. Niche-adhering cytonemes localize FGF-receptor to selectively adhere to the FGF-producing disc and receive FGFs in a contact-dependent manner. Activation of FGF signaling in AMPs, in turn, reinforces disc-specific cytoneme polarity/adhesion, which maintains their disc-proximal positions. Loss of cytoneme-mediated adhesion promotes AMPs to lose niche occupancy and FGF signaling, occupy a disc-distal position, and acquire morphological hallmarks of differentiation. Discrete AMP organization and diversification patterns are determined by localized expression and presentation patterns of two different FGFs in the wing-disc and their polarized target-specific distribution through niche-adhering cytonemes. Thus, cytonemes are essential for asymmetric signaling and niche-specific AMP organization.

We previously showed the importance of TGFβ signaling in development of the mouse axial skeleton. Here, we provide the first direct evidence that TGFβ signaling is required for resegmentation of the sclerotome using chick embryos. Lipophilic fluorescent tracers, DiO and DiD, were microinjected into adjacent somites of embryos treated with or without TGFβR1 inhibitor, SB431542, at developmental day E2.5 (HH16). Lineage tracing of labeled cells was observed over the course of 4 days until the completion of resegmentation at E6.5 (HH32). Vertebrae were malformed and intervertebral discs were small and misshapen in SB431542 injected embryos. Hypaxial myofibers were also increased in thickness after treatment with the inhibitor. Inhibition of TGFβ signaling resulted in alterations in resegmentation that ranged between full, partial, and slanted shifts in distribution of DiO or DiD labeled cells within vertebrae. Patterning of rostro- caudal markers within sclerotome was disrupted at E3.5 after treatment with SB431542 with rostral domains expressing both rostral and caudal markers. We propose that TGFβ signaling regulates rostro-caudal polarity and subsequent resegmentation in sclerotome during spinal column development.

Maintaining apicobasal polarity (ABP) is crucial for epithelial integrity and homeostasis during tissue development. Although recent studies have greatly advanced our understanding of intracellular mechanisms underlying ABP establishment, it remains largely unknown how the ABP is regulated at the tissue level. Here, we address intercellular mechanisms coordinating ABP using the Drosophila wing imaginal disc. By studying Scribble, a key ABP determinant, we show that ABP is regulated through intercellular alignment, which takes place either progressively or regressively in a context-dependent manner. Cells expressing wild type scribble progressively restore ABP in scribble hypomorphic mutant cells. In contrast, cells with conditional scribble knockdown instigate the regressive loss of polarity in abutting wild type cells. Our data reveal that genetic and physical interactions between Scribble, Septate junction complex and α-Catenin appear to be key for sustaining intercellular network of ABP. Taken together, our findings indicate that the intercellular relay of the status of ABP contributes to the robustness of polarity across the tissue.

Description, The glutamatergic synapses are assembled and maintained by conserved planar cell polarity proteins., Whether there exists a common signaling mechanism that assembles all glutamatergic synapses is unknown. We show here that knocking out Prickle1 and Prickle2 reduced the formation of the PSD-95–positive glutamatergic synapses in the hippocampus and medial prefrontal cortex in postnatal development by 70–80%. Prickle1 and Prickle2 double knockout in adulthood lead to the disassembly of 70 to 80% of the postsynaptic-density(PSD)-95–positive glutamatergic synapses. PSD-95–positive glutamatergic synapses in the hippocampus of Prickle2E8Q/E8Q mice were reduced by 50% at postnatal day 14. Prickle2 promotes synapse formation by antagonizing Vangl2 and stabilizing the intercellular complex of the planar cell polarity (PCP) components, whereas Prickle2 E8Q fails to do so. Coculture experiments show that the asymmetric PCP complexes can determine the presynaptic and postsynaptic polarity. In summary, the PCP components regulate the assembly and maintenance of a large number of glutamatergic synapses and specify the direction of synaptic transmission.

Rivularia sp. strain IAM M-261 is a filamentous cyanobacterium with tapering morphology and basal-apical polarity. The apical filament of this cyanobacterium exhibits positive phototropism toward visible light. To elucidate the molecular basis for this phototropism, we determined the draft genome sequence of this strain.

The transient but pronounced ventral tail bending is found in many chordate embryos and constitutes an interesting model of how tissue interactions control embryo shape (Lu et al., 2020). Here, we identify one key upstream regulator of ventral tail bending in the ascidian Ciona embryo. We show that during early tailbud stage, ventral epidermal cells exhibit a boat-shaped morphology (boat cell) with a narrow apical surface where phosphorylated myosin (pMLC) accumulated. We further show that interfering with the function of the BMP ligand Admp leads to pMLC localizing to the basal instead of the apical side of ventral epidermal cells and a reduced number of boat cells. Finally, we show that cutting ventral epidermal midline cells at their apex using a ultraviolet laser relaxes ventral tail bending. Based on these results, we propose a novel function for Admp in localizing pMLC to the apical side of ventral epidermal cells, which causes the tail to bend ventrally by resisting antero-posterior notochord extension at the ventral side of the tail.Summary StatementAdmp is an upstream regulator of tail bending in the chordate Ciona tailbud embryo, determining tissue polarity of the ventral midline epidermis by localizing phosphorylated myosin.

Arabidopsis root hairs develop as long tubular extensions from the rootward pole of trichoblasts and exert polarized tip growth. The establishment and maintenance of root hair polarity is a complex process involving the local apical production of reactive oxygen species (ROS) generated by NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG PROTEIN C/ROOT HAIR DEFECTIVE 2 (AtRBOHC/RHD2). It has been shown that loss-of-function rhd2 mutants have short root hairs that are unable to elongate by tip growth, and this phenotype was fully complemented by GFP-RHD2 expressed under the RHD2 promoter. However, the spatiotemporal mechanism of AtRBOHC/RHD2 subcellular redistribution and delivery to the plasma membrane (PM) during root hair initiation and tip growth are still unclear. Here, we used advanced microscopy for detailed qualitative and quantitative analysis of vesicular compartments containing GFP-RHD2 and characterization of their movements in developing bulges and growing root hairs. These compartments, identified by an independent marker such as the trans-Golgi network (TGN), deliver GFP-RHD2 to the apical PM domain, the extent of which correlates with the stage of root hair formation. Movements of TGN/early endosomes, but not late endosomes, were affected in the bulging domains of the rhd2-1 mutant. Finally, we reveal that accumulation in the growing tip, docking, and incorporation of TGN compartments containing GFP-RHD2 to the apical PM of root hairs requires structural sterols. These results help clarify the mechanism of polarized AtRBOHC/RHD2 targeting, maintenance, and recycling at the apical PM domain, coordinated with different developmental stages of root hair initiation and growth.One-sentence summaryAdvanced microscopy and quantitative analysis of vesicular TGN compartments revealed that delivering GFP-RHD2 to the apical plasma membrane domains of developing bulges and growing root hairs requires structural sterols.

Hepatocytes display a unique biaxial polarity with shared apical luminal connections between adjacent hepatocytes that merge into a network of bile canaliculi. Belicova et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202103003) discovered that hepatocyte apical membranes generate Rab35-dependent extensions that traverse the lumen and are essential for bile canalicular formation and maintenance.

Myosin Va (myoVa) motors transport membrane-bound cargo through three-dimensional, intracellular actin filament networks. We developed a coarse-grained, in silico model to predict how actin filament density (3-800 filaments) within a randomly oriented actin network affects fluid-like liposome (350nm vs. 1,750nm) transport by myoVa motors. 5,000 simulated liposomes transported within each network adopted one of three states: transport, tug of war, or diffusion. Diffusion due to liposome detachment from actin rarely occurred given at least 10 motors on the liposome surface. However, with increased actin density, liposomes transitioned from primarily directed transport on single actin filaments to an apparent random walk, resulting from a mixture of transport and tug of wars as the probability of encountering additional actin filaments increased. This phase transition arises from a percolation phase transition at a critical number of accessible actin filaments, Nc. Nc, is a geometric property of the actin network that depends only on the position and polarity of the actin filaments and the liposome diameter, as evidenced by a five-fold increase in liposome diameter resulting in a five-fold decrease in Nc. Thus, in cells, actin network density and cargo size may be regulated to match cargo delivery to the cell’s physiological demands.

Belicova et al. report previously unrecognized apical membrane extensions, forming a pattern reminiscent of the bulkheads of boats, that determine the anisotropic expansion of hepatocyte lumina. Loss of the bulkheads caused by Rab35 silencing leads to re-engineering of epithelial polarity and liver tissue architecture., Lumen morphogenesis results from the interplay between molecular pathways and mechanical forces. In several organs, epithelial cells share their apical surfaces to form a tubular lumen. In the liver, however, hepatocytes share the apical surface only between adjacent cells and form narrow lumina that grow anisotropically, generating a 3D network of bile canaliculi (BC). Here, by studying lumenogenesis in differentiating mouse hepatoblasts in vitro, we discovered that adjacent hepatocytes assemble a pattern of specific extensions of the apical membrane traversing the lumen and ensuring its anisotropic expansion. These previously unrecognized structures form a pattern, reminiscent of the bulkheads of boats, also present in the developing and adult liver. Silencing of Rab35 resulted in loss of apical bulkheads and lumen anisotropy, leading to cyst formation. Strikingly, we could reengineer hepatocyte polarity in embryonic liver tissue, converting BC into epithelial tubes. Our results suggest that apical bulkheads are cell-intrinsic anisotropic mechanical elements that determine the elongation of BC during liver tissue morphogenesis., Graphical Abstract

Oriented cell divisions are critical for the formation and maintenance of structured epithelia. Proper mitotic spindle orientation relies on polarised anchoring of force generators to the cell cortex by the evolutionarily conserved Gαi-LGN-NuMA complex. However, the polarity cues that control cortical patterning of this ternary complex remain largely unknown in mammalian epithelia. Here we identify the membrane-associated protein Annexin A1 (ANXA1) as a novel interactor of LGN in mammary epithelial cells. ANXA1 acts independently of Gαito instruct the accumulation of LGN and NuMA at the lateral cortex to ensure cortical anchoring of Dynein-Dynactin and astral microtubules and thereby planar alignment of the mitotic spindle. Loss of ANXA1 randomises mitotic spindle orientation, which in turn disrupts epithelial architecture and luminogenesis in three-dimensional cultures of primary mammary epithelial cells. Our findings establish ANXA1 as an upstream cortical cue that regulates LGN to direct planar cell divisions during mammalian epithelial morphogenesis.

Symmetry establishment is a critical process in the development of multicellular organs and requires careful coordination of polarity axes while cells actively divide within tissues. Formation of the apical style in the Arabidopsis gynoecium involves a bilateral-to-radial symmetry transition, a stepwise process underpinned by the dynamic distribution of the plant morphogen auxin. Here we show that SPATULA (SPT) and the HECATE (HEC) bHLH proteins mediate the final step in the style radialisation process and synergistically control the expression of adaxial-identity genes, HOMEOBOX ARABIDOPSIS THALIANA 3 (HAT3) and ARABIDOPSIS THALIANA HOMEOBOX 4 (ATHB4). HAT3/ATHB4 module drives radialisation of the apical style by promoting basal-to-apical auxin flow and via a negative feedback mechanism that finetune auxin distribution through repression of SPT expression and cytokinin sensitivity. Thus, this work reveals the molecular basis of axes-coordination and hormonal cross-talk during the sequential steps of symmetry transition in the Arabidopsis style., The apical style in Arabidopsis is formed following a bilateral-to-radial symmetry transition in the gynoecium. Here the authors show that the final step in style radialization is coordinated by the adaxial regulators HAT3 and ATHB4, which are induced by the SPT and HEC transcription factors.

Second harmonic generation microscopy (SHG) is now the gold standard technique for in situ visualization of unstained fibrillar collagen in intact tissues [1] . Collagen is the most abundant protein in mammals and is found in many tissues, such as arteries, skin, bone and cornea. The size and the three-dimensional distribution of collagen fibrils are key distinctive features of every tissue that are crucial for its functional behaviour, notably its mechanical properties. In situ characterization of collagen 3D distribution is therefore a major biomedical challenge.

Axons and dendrites are distinguished by microtubule polarity. In Drosophila, dendrites are dominated by minus-end-out microtubules, whereas axons contain plus-end-out microtubules. Local nucleation in dendrites generates microtubules in both orientations. To understand why dendritic nucleation does not disrupt polarity, we used live imaging to analyze the fate of microtubules generated at branch points. We found that they had different rates of success exiting the branch based on orientation: correctly oriented minus-end-out microtubules succeeded in leaving about twice as often as incorrectly oriented microtubules. Increased success relied on other microtubules in a parallel orientation. From a candidate screen, we identified Trim9 and kinesin-5 (Klp61F) as machinery that promoted growth of new microtubules. In S2 cells, Eb1 recruited Trim9 to microtubules. Klp61F promoted microtubule growth in vitro and in vivo, and could recruit Trim9 in S2 cells. In summary, the data argue that Trim9 and kinesin-5 act together at microtubule plus ends to help polymerizing microtubules parallel to pre-existing ones resist catastrophe.

Polarized epithelial cells adhere to each other at apical junctions that connect to the apical F-actin belt. Regulated remodeling of apical junctions supports morphogenesis, while dysregulated remodeling promotes diseases such as cancer. We have documented that branched actin regulator, WAVE, and apical junction protein, Cadherin, assemble together in developing C. elegans embryonic junctions. If WAVE is missing in embryonic epithelia, too much Cadherin assembles at apical membranes, and yet apical F-actin is reduced, suggesting the excess Cadherin is not fully functional. We proposed that WAVE supports apical junctions by regulating the dynamic accumulation of Cadherin at membranes. To test this model, here we examine if WAVE is required for Cadherin membrane enrichment and apical–basal polarity in a maturing epithelium, the post-embryonic C. elegans intestine. We find that larval and adult intestines have distinct apicobasal populations of Cadherin, each with distinct dependence on WAVE branched actin. In vivo imaging shows that loss of WAVE components alters post-embryonic E-cadherin membrane enrichment, especially at apicolateral regions, and alters the lateral membrane. Analysis of a biosensor for PI(4,5)P2 suggests loss of WAVE or Cadherin alters the polarity of the epithelial membrane. EM (electron microscopy) illustrates lateral membrane changes including separations. These findings have implications for understanding how mutations in WAVE and Cadherin may alter cell polarity.

Fibrotic lesions accompany several pathological conditions including tumors. We show that expression of a dominant-active form of the Ras oncogene in Drosophila salivary glands (SGs) leads to redistribution of components of the basement membrane (BM) and fibrotic lesions. Similar to several types of mammalian fibrosis, the disturbed BM attracts clot components including insect transglutaminase and phenoloxidase. SG epithelial cells show reduced apico-basal polarity accompanied by a loss of secretory activity. Both the fibrotic lesions and the reduced cell polarity are alleviated by ectopic expression of the antimicrobial peptide Drosomycin (Drs), which also restores secretory activity of the SGs. In addition to ECM components, both Drs and F-actin localize to fibrotic lesions.

Coordinated polarization of cells in the tissue plane, known as planar cell polarity (PCP), is associated with a signaling pathway critical for the control of morphogenetic processes. Although the segregation of PCP components to opposite cell borders is believed to play a critical role in this pathway, whether PCP derives from egg polarity or preexistent long-range gradient, or forms in response to a localized cue remains a challenging question. Here we investigate the Xenopus neural plate, a tissue that has been previously shown to exhibit PCP. By imaging Vangl2 and Prickle3, we show that PCP is progressively acquired in the neural plate and requires a signal from the posterior region of the embryo. Tissue transplantations indicated that PCP is triggered in the neural plate by a planar cue from the dorsal blastopore lip. The PCP cue did not depend on the orientation of the graft and was distinct from neural inducers. These observations suggest that neuroectodermal PCP is not instructed by a preexisting molecular gradient, but induced by a signal from the dorsal blastopore lip.HighlightsThe Xenopus neural plate progressively acquires PCP in a posterior-to-anterior direction.The dorsal blastopore lip is likely the source of the PCP-instructing signal for the Xenopus neural plate.The PCP cue is distinct from neural inducers and has a planar mode of transmission.

The aim of this paper is to review the present knowledge of the main aspects of differentiation of Acetabularia, a unicellular, eukaryotic organism, and to underline the multiple control pathways modulated by circadian rhythmicity. Growth and morphogenesis are sequentially programmed. Timing of cap differentiation is highly dependent on external conditions. The importance of the sequence of processes is shown by experimental disregulation. The alga is a highly polarized cell, both in morphology and in the relative concentrations of a number of the molecules it contains. Apical cap differentiation is regulated at the post-transcriptional level and could also depend in part on polyamines and on proteolytic activity. Acetabularia displays a number of circadian rhythms (CR). These rhythms form an elaborate biological time structure (also called temporal morphology, or morphology in time as opposed to morphology in space): the distribution in the 24 h cycle of the peaks and troughs of the oscillating functions. The oscillations display fixed relations both with the other functions and with external conditions (such as the transition from dark to light). Interestingly, the CR modulate Acetabularia's development, which is influenced by photoperiod; we present preliminary experiments suggesting that disruption of temporal morphology is deleterious to morphogenesis. Induction of growth and of morphogenesis are totally dependent on blue light. However, blue light receptors in plants arc probably multiple, but we present arguments suggesting that flavin-cytochrome b and the associated KHAM-sensitive molecule are present in Acetabularia plasma membrane and are involved in blue light perception. Agents interfering with different steps of signal perception and transduction show that at least some of these steps are temporally regulated. According to recent experiments from our laboratory, the existence of a redox signalling mechanism appears to be highly probable. The phytohormones (or plant regulators), auxin (indole acetic acid), abscisic acid and ethylene, exert cell-regulatory functions and are involved in Acetabularia differentiation. They also modulate at least some circadian rhythms. Finally, circadian rhythms intervene in differentiation and are proposed to have an integrative function. CONTENTS Summary 1 I. Introduction: the cell cycle and morphology of Acetabularia 2 II. Growth and cap morphogenesis: the developmental programme 3 III. Polarity 5 IV. Temporal morphology 6 V. Induction of growth and cap morphogenesis 9 VI. The plasma membrane 12 VII. Hormones: development and metabolic activity in Acetabularia 12 VIII. Phytohormones receptors and insulin receptors 15 IX. Other possible hormones 16 X. Fundamental role of CR: their intervention in modulating multiple steps in differentiation 16 XI. Conclusions and perspectives 17 Acknowledgements 17 References 17.