Polarity Cues Research Articles

Ca2+–calpains axis regulates Yki stability and activity in Drosophila

Yorkie (Yki) is a key effector of the Hippo pathway that activates the expression of targets by associating with the transcription factor Scalloped. Various upstream signals, such as cell polarity and mechanical cues, control transcriptional programs by regulating Yki activity. Searching for Yki regulatory factors has far-reaching significance for studying the Hippo pathway in development and human diseases. In this study, we identify Calpain-A (CalpA) and Calpain-B (CalpB), two calcium (Ca2+)-dependent modulatory proteases of the calpain family, as critical regulators of Yki in Drosophila that interact with Yki, respectively. Ca2+ induces Yki cleavage in a CalpA/CalpB-dependent manner, and the protease activity of CalpA/CalpB is pivotal for the cleavage. Furthermore, overexpression of CalpA or CalpB in Drosophila partially restores the large wing phenotype caused by Yki overexpression, and F98 of Yki is an important cleavage site by the Ca2+–calpains axis. Our study uncovers a unique mechanism whereby the Ca2+–calpain axis modulates Yki activity through protein cleavage.

Exploiting Polarized Material Cues for Robust Car Detection

Car detection is an important task that serves as a crucial prerequisite for many automated driving functions. The large variations in lighting/weather conditions and vehicle densities of the scenes pose significant challenges to existing car detection algorithms to meet the highly accurate perception demand for safety, due to the unstable/limited color information, which impedes the extraction of meaningful/discriminative features of cars. In this work, we present a novel learning-based car detection method that leverages trichromatic linear polarization as an additional cue to disambiguate such challenging cases. A key observation is that polarization, characteristic of the light wave, can robustly describe intrinsic physical properties of the scene objects in various imaging conditions and is strongly linked to the nature of materials for cars (e.g., metal and glass) and their surrounding environment (e.g., soil and trees), thereby providing reliable and discriminative features for robust car detection in challenging scenes. To exploit polarization cues, we first construct a pixel-aligned RGB-Polarization car detection dataset, which we subsequently employ to train a novel multimodal fusion network. Our car detection network dynamically integrates RGB and polarization features in a request-and-complement manner and can explore the intrinsic material properties of cars across all learning samples. We extensively validate our method and demonstrate that it outperforms state-of-the-art detection methods. Experimental results show that polarization is a powerful cue for car detection. Our code is available at https://github.com/wind1117/AAAI24-PCDNet.

Imaging and Analysis of Drosophila Neural Stem Cell Asymmetric Division.

Cell division is a conserved process among eukaryotes. It is designed to segregate chromosomes into future daughter cells and involves a complex rearrangement of the cytoskeleton, including microtubules and actin filaments. An additional level of complexity is present in asymmetric dividing stem cells because cytoskeleton elements are also regulated by polarity cues. The neural stem cell system of the fruit fly represents a simple model to dissect the mechanisms that control cytoskeleton reorganization during asymmetric division. In this chapter, we propose to describe protocols that allow accurate analysis of microtubule reorganization during cell division in this model.

PI-NLOS: polarized infrared non-line-of-sight imaging.

Passive non-line-of-sight (NLOS) imaging is a promising technique to enhance visual perception for the occluded object hidden behind the wall. Here we present a data-driven NLOS imaging framework by using polarization cue and long-wavelength infrared (LWIR) images. We design a dual-channel input deep neural network to fuse the intensity features from polarized LWIR images and contour features from polarization degree images for NLOS scene reconstruction. To train the model, we create a polarized LWIR NLOS dataset which contains over ten thousand images. The paper demonstrates the passive NLOS imaging experiment in which the hidden people is approximate 6 meters away from the relay wall. It is an exciting finding that even the range is further than that in the prior works. The quantitative evaluation metric of PSNR and SSIM show that our method as an advance over state-of-the-art in passive NLOS imaging.

IPNet: Polarization-based Camouflaged Object Detection via dual-flow network

Camouflaged Object Detection (COD) is a critical task in a variety of domains, such as medicine and military applications. The main challenge in COD is accurately detecting and extracting the concealed object from the complex background. The similarity between the camouflaged objects and their background significantly reduces the accuracy of object extraction. Polarization information can provide valuable insights into the characteristics of objects with different material properties and surface roughness. It reflects the difference in polarization information between the object and the background, which increases the contrast between the two and improves the object detection accuracy even under complex scenes. In this paper, we propose IPNet, an efficient cross-modal fusion network that utilizes both RGB intensity and linear polarization cues to generate scene representation with high contrast. Our novel network architecture dynamically fuses RGB intensity and polarization cues using an efficient cross-modal fusion module, leveraging cross-level contextual information to achieve robust detection. For training and evaluating the proposed network, we construct a polarization-based PCOD_1200 dataset that contains 89 subclasses and 1200 samples. A comprehensive set of experiments demonstrates the effectiveness of IPNet to fuse polarization and RGB intensity information and shows that our approach outperforms state-of-the-art methods.

Synthetic Par polarity induces cytoskeleton asymmetry in unpolarized mammalian cells

Polarized cells rely on a polarized cytoskeleton to function. Yet, how cortical polarity cues induce cytoskeleton polarization remains elusive. Here, we capitalized on recently established designed 2D protein arrays to ectopically engineer cortical polarity of virtually any protein of interest during mitosis in various cell types. This enables direct manipulation of polarity signaling and the identification of the cortical cues sufficient for cytoskeleton polarization. Using this assay, we dissected the logic of the Par complex pathway, a key regulator of cytoskeleton polarity during asymmetric cell division. We show that cortical clustering of any Par complex subunit is sufficient to trigger complex assembly and that the primary kinetic barrier to complex assembly is the relief of Par6 autoinhibition. Further, we found that inducing cortical Par complex polarity induces two hallmarks of asymmetric cell division in unpolarized mammalian cells: spindle orientation, occurring via Par3, and central spindle asymmetry, depending on aPKC activity.

Multi‐cues underwater image restoration algorithm combined with light field technology

AbstractUnderwater images suffer from color distortion, low clarity and halos problems due to light absorption, particle scattering and non‐uniform illumination. To address these degradation issues, a multi‐cues underwater image restoration algorithm combined with light field technology is proposed. First, based on Epipolar Plane Image, the light field cue transmittance containing depth information is calculated. Then, according to the turbidity of the underwater image, the light field cue transmittance and the polarization cue transmittance are fused to obtain the multi‐cues transmittance, which can effectively reduce the effect of particle scattering and color bias. Finally, the background light is estimated through the all‐focus operation, which can effectively overcome the distortion of an underwater single image and simultaneously reduce the halo phenomenon. Experimental results show that the method achieves the best results evaluated by UCIQE, UIQM, PSNR, and SSIM, and the restored color under the method is closer to the actual image than other underwater restoration methods.

Drosophila Adducin facilitates phase separation and function of a conserved spindle orientation complex.

Asymmetric cell division (ACD) allows stem cells to generate differentiating progeny while simultaneously maintaining their own pluripotent state. ACD involves coupling mitotic spindle orientation with cortical polarity cues to direct unequal segregation of cell fate determinants. In Drosophila neural stem cells (neuroblasts; NBs), spindles orient along an apical-basal polarity axis through a conserved complex of Partner of Inscuteable (Pins; human LGN) and Mushroom body defect (Mud; human NuMA). While many details of its function are well known, the molecular mechanics that drive assembly of the cortical Pins/Mud complex remain unclear, particularly with respect to the mutually exclusive Pins complex formed with the apical scaffold protein Inscuteable (Insc). Here we identify Hu li tai shao (Hts; human Adducin) as a direct Mud-binding protein, using an aldolase fold within its head domain (HtsHEAD) to bind a short Mud coiled-coil domain (MudCC) that is adjacent to the Pins-binding domain (MudPBD). Hts is expressed throughout the larval central brain and apically polarizes in mitotic NBs where it is required for Mud-dependent spindle orientation. In vitro analyses reveal that Pins undergoes liquid-liquid phase separation with Mud, but not with Insc, suggesting a potential molecular basis for differential assembly mechanics between these two competing apical protein complexes. Furthermore, we find that Hts binds an intact Pins/Mud complex, reduces the concentration threshold for its phase separation, and alters the liquid-like property of the resulting phase separated droplets. Domain mapping and mutational analyses implicate critical roles for both multivalent interactions (via MudCC oligomerization) and protein disorder (via an intrinsically disordered region in Hts; HtsIDR) in phase separation of the Hts/Mud/Pins complex. Our study identifies a new component of the spindle positioning machinery in NBs and suggests that phase separation of specific protein complexes might regulate ordered assembly within the apical domain to ensure proper signaling output.

Length limitation of astral microtubules orients cell divisions in murine intestinal crypts

Planar spindle orientation is critical for epithelial tissue organization and is generally instructed by the long cell-shape axis or cortical polarity domains. We introduced mouse intestinal organoids in order to study spindle orientation in a monolayered mammalian epithelium. Although spindles were planar, mitotic cells remained elongated along the apico-basal (A-B) axis, and polarity complexes were segregated to basal poles, so that spindles oriented in an unconventional manner, orthogonal to both polarity and geometric cues. Using high-resolution 3D imaging, simulations, and cell-shape and cytoskeleton manipulations, we show that planar divisions resulted from a length limitation in astral microtubules (MTs) which precludes them from interacting with basal polarity, and orient spindles from the local geometry of apical domains. Accordingly, lengthening MTs affected spindle planarity, cell positioning, and crypt arrangement. We conclude that MT length regulation may serve as a key mechanism for spindles to sense local cell shapes and tissue forces to preserve mammalian epithelial architecture.

Branched-chain actin dynamics polarizes vesicle trajectories and partitions apicobasal epithelial membrane domains.

In prevailing epithelial polarity models, membrane- and junction-based polarity cues such as the partitioning-defective PARs specify the positions of apicobasal membrane domains. Recent findings indicate, however, that intracellular vesicular trafficking can determine the position of the apical domain, upstream of membrane-based polarity cues. These findings raise the question of how vesicular trafficking becomes polarized independent of apicobasal target membrane domains. Here, we show that the apical directionality of vesicle trajectories depends on actin dynamics during de novo polarized membrane biogenesis in the C. elegans intestine. We find that actin, powered by branched-chain actin modulators, determines the polarized distribution of apical membrane components, PARs, and itself. Using photomodulation, we demonstrate that F-actin travels through the cytoplasm and along the cortex toward the future apical domain. Our findings support an alternative polarity model where actin-directed trafficking asymmetrically inserts the nascent apical domain into the growing epithelial membrane to partition apicobasal membrane domains.

The biosynthetic-secretory pathway, supplemented by recycling routes, determines epithelial membrane polarity.

In prevailing epithelial polarity models, membrane-based polarity cues (e.g., the partitioning-defective PARs) position apicobasal cellular membrane domains. Intracellular vesicular trafficking expands these domains by sorting polarized cargo toward them. How the polarity cues themselves are polarized in epithelia and how sorting confers long-range apicobasal directionality to vesicles is still unclear. Here, a systems-based approach using two-tiered C. elegans genomics-genetics screens identifies trafficking molecules that are not implicated in apical sorting yet polarize apical membrane and PAR complex components. Live tracking of polarized membrane biogenesis indicates that the biosynthetic-secretory pathway, linked to recycling routes, is asymmetrically oriented toward the apical domain during this domain's biosynthesis, and that this directionality is regulated upstream of PARs and independent of polarized target membrane domains. This alternative mode of membrane polarization could offer solutions to open questions in current models of epithelial polarity and polarized trafficking.

Deciphering the roles of cell shape and Fat and Dachsous planar polarity in arranging the Drosophila apical microtubule network through quantitative image analysis.

In epithelial cells, planar polarization of subapical microtubule networks is thought to be important for both breaking cellular symmetry and maintaining the resulting cellular polarity. Studies in the Drosophila pupal wing and other tissues have suggested two alternative mechanisms for specifying network polarity. On one hand, mechanical strain and/or cell shape have been implicated as key determinants; on the other hand, the Fat-Dachsous planar polarity pathway has been suggested to be the primary polarizing cue. Using quantitative image analysis in the pupal wing, we reassess these models. We found that cell shape was a strong predictor of microtubule organization in the developing wing epithelium. Conversely, Fat-Dachsous polarity cues do not play any direct role in the organization of the subapical microtubule network, despite being able to weakly recruit the microtubule minus-end capping protein Patronin to cell boundaries. We conclude that any effect of Fat-Dachsous on microtubule polarity is likely to be indirect, via their known ability to regulate cell shape.

Annexin A1 is a polarity cue that directs mitotic spindle orientation during mammalian epithelial morphogenesis

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 protein complex formed by the Gαi subunit of heterotrimeric G proteins, the Leucine-Glycine-Asparagine repeat protein (LGN) and the nuclear mitotic apparatus protein. 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 an interactor of LGN in mammary epithelial cells. Annexin A1 acts independently of Gαi to instruct the accumulation of LGN and nuclear mitotic apparatus protein at the lateral cortex to ensure cortical anchoring of Dynein-Dynactin and astral microtubules and thereby planar alignment of the mitotic spindle. Loss of Annexin A1 randomises mitotic spindle orientation, which in turn disrupts epithelial architecture and luminogenesis in three-dimensional cultures of primary mammary epithelial cells. Our findings establish Annexin A1 as an upstream cortical cue that regulates LGN to direct planar cell divisions during mammalian epithelial morphogenesis.

Shape From Polarization With Distant Lighting Estimation.

This article presents a new approach for surface normal recovery from polarization images under an unknown distant light. Polarization provides rich cues of object geometry and material, but it is also influenced by different lighting conditions. Different from previous Shape-from-Polarization (SfP) methods, which rely on handcrafted or data-driven priors, we analytically investigate the benefits of estimating distant lighting for resolving the ambiguity in normal estimation from SfP using the polarimetric Bidirectional Reflectance Distribution Function (pBRDF) based image formation model. We then propose a two-stage learning framework that first effectively exploits polarization and shading cues to estimate the reflectance and lighting information and then optimizes the initial normal as the geometric prior. Leveraging the normal prior with the polarization cues from the input images, our network further generates the surface normal with more details in the second stage. We also present a data generation pipeline derived from the pBRDF model enabling model training and create a real dataset for evaluation of SfP approaches. Extensive ablation studies show the effectiveness of our designed architecture, and our approach outperforms existing methods in quantitative and qualitative experiments on real data.

Depth Recovery With Large-Area Data Loss Guided by Polarization Cues for Time-of-Flight Imaging

Time-of-Flight imaging is one of the quintessential techniques in three-dimensional reconstruction. However, depth missing is a common problem in Time-of-Flight imaging, which can be classified into structure-based depth loss and large-area one according to various reasons. Large-area depth loss generally occurs due to close-range overexposure resulting in limited dynamic range in depth sensing. Compared to structure-based depth loss, the recovery of large-area depth missing is more challenging and has been rarely studied. In this paper, a large-area depth recovery framework guided by polarization cues is proposed stemmed from a solid physical basic concerning depth and polarization, to realize high dynamic range in applications. Inspired by RGB-D system and shape-from-polarization technique, a dual camera system is utilized including infrared Time-of-Flight camera and visible polarized camera. A physical model between depth map and polarization cues, specifically depth-gradient and degree-of-polarization, is investigated and established. Based on the physical basics, a corresponding polarization-guided depth recovery algorithm with statistical analysis and image processing approach is introduced. Experimental results towards different targets demonstrate the effectiveness of the proposed method qualitatively and quantitatively, accompanied with outcome analysis and detailed discussions about strengths and future works, which indicates a great potential for the applications of high-quality three-dimensional reconstruction and depth sensing.

Notch-dependent Abl signaling regulates cell motility during ommatidial rotation in Drosophila.

A collective cell motility event that occurs during Drosophila eye development, ommatidial rotation (OR), serves as a paradigm for signaling-pathway-regulated directed movement of cell clusters. OR is instructed by the EGFR and Notch pathways and Frizzled/planar cell polarity (Fz/PCP) signaling, all of which are associated with photoreceptor R3 and R4 specification. Here, we show that Abl kinase negatively regulates OR through its activity in the R3/R4 pair. Abl is localized to apical junctional regions in R4, but not in R3, during OR, and this apical localization requires Notch signaling. We demonstrate that Abl and Notch interact genetically during OR, and Abl co-immunoprecipitates in complexes with Notch in eye discs. Perturbations of Abl interfere with adherens junctional organization of ommatidial preclusters, which mediate the OR process. Together, our data suggest that Abl kinase acts directly downstream of Notch in R4 to fine-tune OR via its effect on adherens junctions.

550 aPKC regulates the spindle orientation machinery to promote planar cell divisons

Oriented cell division is a key regulator of cell fate and linked to the positioning of the spindle in mitosis. However, in mammals the cues that determine planar versus perpendicular positioning of the spindle remain largely unclear. One candidate is the polarity protein atypical protein kinase C (aPKC)l, which regulates cell fate and spindle orientation in vivo in the epidermis. To study how aPKC controls mitotic spindle orientation, we developed a minimal keratinocyte culture system in which planar spindle positioning occurs in the absence of intercellular adhesive polarity cues.

The basement membrane in epidermal polarity, stemness, and regeneration.

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

PIN-FORMED1 polarity in the plant shoot epidermis is insensitive to the polarity of neighboring cells

SummaryAt the Arabidopsis shoot apex, epidermal cells are planar-polarized along an axis marked by the asymmetric localization patterns of several proteins including PIN-FORMED1 (PIN1), which facilitates the directional efflux of the plant hormone auxin to pattern phyllotaxis. While PIN1 polarity is known to be regulated non-cell autonomously via the MONOPTEROS (MP) transcription factor, how this occurs has not been determined. Here, we use mosaic expression of the serine threonine kinase PINOID (PID) to test whether PIN1 polarizes according to the polarity of neighboring cells. Our findings reveal that PIN1 is insensitive to the polarity of PIN1 in neighboring cells arguing against auxin flux or extracellular auxin concentrations acting as a polarity cue, in contrast to previous model proposals.

Polarization-based approach for multipath interference mitigation in time-of-flight imaging.

The existence of nearby obstruction causes significant errors in depth sensing for time-of-flight cameras, namely multipath interference. A polarized time-of-flight system is established for multipath interference mitigation. Based on polarization cues and the phasor representation of time-of-flight imaging, the proposed method acquires depth maps in high accuracy when specular dominant obstruction is in path. Both rough and smooth targets are applicable in our approach even though they have distinct polarization characteristics. Several experiments with different types of targets and various obstructions confirm the effectiveness of our method qualitatively and quantitatively.