Dynein directs prophase centrosome migration to control the stem cell division axis in the developing Caenorhabditis elegans epidermis.

The microtubule motor dynein is critical for the assembly and positioning of mitotic spindles. In Caenorhabditis elegans, these dynein functions have been extensively studied in the early embryo but remain poorly explored in other developmental contexts. Here, we use a hypomorphic dynein mutant to investigate the motor's contribution to asymmetric stem cell-like divisions in the larval epidermis. Live imaging of seam cell divisions that precede formation of the seam syncytium shows that mutant cells properly assemble but frequently misorient their spindle. Misoriented divisions misplace daughter cells from the seam cell row, generate anucleate compartments due to aberrant cytokinesis, and disrupt asymmetric cell fate inheritance. Consequently, the seam becomes disorganized and populated with extra cells that have lost seam identity, leading to fatal epidermal rupture. We show that dynein orients the spindle through the cortical GOA-1Gα-LIN-5NuMA pathway by directing the migration of prophase centrosomes along the anterior-posterior axis. Spindle misorientation in the dynein mutant can be partially rescued by elongating cells, implying that dynein-dependent force generation and cell shape jointly promote correct asymmetric division of epithelial stem cells.

Alzheimer's disease: Insights and new prospects in disease pathophysiology, biomarkers and disease-modifying drugs.

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases that affect millions of people worldwide, with both prevalence and incidence increasing with age. It is characterized by cognitive decline associated, specifically, with degeneration of cholinergic neurons. The problem of this disease is even more fundamental as the available therapies remain fairly limited and mainly focused on symptoms' relief. Although the aetiology of the disease remains elusive, two main pathological hallmarks are described: i) presence of neurofibrillary tangles formed by unfolded protein aggregates (hyperphosphorylated Tau protein) and ii) presence of extracellular aggregates of amyloid-beta peptide. Given the complexity surrounding the pathogenesis of the disease, several potential targets have been highlighted and interrelated upon its progression, such as oxidative stress and the accumulation of metal ions. Thus, advances have been made on the development of innovative multitarget therapeutical compounds to delay the disease progression and restore cell function. This review focuses the ongoing research on new insights and emerging disease-modifying drugs for AD treatment. Furthermore, classical and novel potential biomarkers for early diagnosis of the disease, and their role in assisting on the improvement of targeted therapies will also be approached.

JIP3 interacts with dynein and kinesin-1 to regulate bidirectional organelle transport.

The MAP kinase and motor scaffold JIP3 prevents excess lysosome accumulation in axons of vertebrates and invertebrates. How JIP3's interaction with dynein and kinesin-1 contributes to organelle clearance is unclear. We show that human dynein light intermediate chain (DLIC) binds the N-terminal RH1 domain of JIP3, its paralog JIP4, and the lysosomal adaptor RILP. A point mutation in RH1 abrogates DLIC binding without perturbing the interaction between JIP3's RH1 domain and kinesin heavy chain. Characterization of this separation-of-function mutation in Caenorhabditis elegans shows that JIP3-bound dynein is required for organelle clearance in the anterior process of touch receptor neurons. Unlike JIP3 null mutants, JIP3 that cannot bind DLIC causes prominent accumulation of endo-lysosomal organelles at the neurite tip, which is rescued by a disease-associated point mutation in JIP3's leucine zipper that abrogates kinesin light chain binding. These results highlight that RH1 domains are interaction hubs for cytoskeletal motors and suggest that JIP3-bound dynein and kinesin-1 participate in bidirectional organelle transport.

Plastin and spectrin cooperate to stabilize the actomyosin cortex during cytokinesis.

Cytokinesis, the process that partitions the mother cell into two daughter cells, requires the assembly and constriction of an equatorial actomyosin network. Different types of non-motor F-actin crosslinkers localize to the network, but their functional contribution remains poorly understood. Here, we describe a synergy between the small rigid crosslinker plastin and the large flexible crosslinker spectrin in the C. elegans one-cell embryo. In contrast to single inhibitions, co-inhibition of plastin and the ßH-spectrin (SMA-1) results in cytokinesis failure due to progressive disorganization and eventual collapse of the equatorial actomyosin network. Cortical localization dynamics of non-muscle myosin II in co-inhibited embryos mimic those observed after drug-induced F-actin depolymerization, suggesting that the combined action of plastin and spectrin stabilizes F-actin in the contractile ring. An in silico model predicts that spectrin is more efficient than plastin at stabilizing the ring and that ring formation is relatively insensitive to ßH-spectrin length, which is confirmed in vivo with a sma-1 mutant that lacks 11 of its 29 spectrin repeats. Our findings provide the first evidence that spectrin contributes to cytokinesis and highlight the importance of crosslinker interplay for actomyosin network integrity.

Dynein-dynactin segregate meiotic chromosomes in C. elegans spermatocytes.

The microtubule motor cytoplasmic dynein 1 (dynein) and its essential activator dynactin have conserved roles in spindle assembly and positioning during female meiosis and mitosis, but their contribution to male meiosis remains poorly understood. Here, we characterize the G33S mutation in the C. elegans dynactin subunit DNC-1, which corresponds to G59S in human p150Glued that causes motor neuron disease. In spermatocytes, dnc-1(G33S) delays spindle assembly and penetrantly inhibits anaphase spindle elongation in meiosis I, which prevents the segregation of homologous chromosomes. By contrast, chromosomes segregate without errors in the early dnc-1(G33S) embryo. Deletion of the DNC-1 N-terminus shows that defective meiosis in dnc-1(G33S) spermatocytes is not due to the inability of DNC-1 to interact with microtubules. Instead, our results suggest that the DNC-1(G33S) protein, which is aggregation prone in vitro, is less stable in spermatocytes than the early embryo, resulting in different phenotypic severity in the two dividing tissues. Thus, the dnc-1(G33S) mutant reveals that dynein-dynactin drive meiotic chromosome segregation in spermatocytes and illustrates that the extent to which protein misfolding leads to loss of function can vary significantly between cell types.

A transient helix in the disordered region of dynein light intermediate chain links the motor to structurally diverse adaptors for cargo transport.

All animal cells use the motor cytoplasmic dynein 1 (dynein) to transport diverse cargo toward microtubule minus ends and to organize and position microtubule arrays such as the mitotic spindle. Cargo-specific adaptors engage with dynein to recruit and activate the motor, but the molecular mechanisms remain incompletely understood. Here, we use structural and dynamic nuclear magnetic resonance (NMR) analysis to demonstrate that the C-terminal region of human dynein light intermediate chain 1 (LIC1) is intrinsically disordered and contains two short conserved segments with helical propensity. NMR titration experiments reveal that the first helical segment (helix 1) constitutes the main interaction site for the adaptors Spindly (SPDL1), bicaudal D homolog 2 (BICD2), and Hook homolog 3 (HOOK3). In vitro binding assays show that helix 1, but not helix 2, is essential in both LIC1 and LIC2 for binding to SPDL1, BICD2, HOOK3, RAB-interacting lysosomal protein (RILP), RAB11 family-interacting protein 3 (RAB11FIP3), ninein (NIN), and trafficking kinesin-binding protein 1 (TRAK1). Helix 1 is sufficient to bind RILP, whereas other adaptors require additional segments preceding helix 1 for efficient binding. Point mutations in the C-terminal helix 1 of Caenorhabditis elegans LIC, introduced by genome editing, severely affect development, locomotion, and life span of the animal and disrupt the distribution and transport kinetics of membrane cargo in axons of mechanosensory neurons, identical to what is observed when the entire LIC C-terminal region is deleted. Deletion of the C-terminal helix 2 delays dynein-dependent spindle positioning in the one-cell embryo but overall does not significantly perturb dynein function. We conclude that helix 1 in the intrinsically disordered region of LIC provides a conserved link between dynein and structurally diverse cargo adaptor families that is critical for dynein function in vivo.

Dynactin binding to tyrosinated microtubules promotes centrosome centration in C. elegans by enhancing dynein-mediated organelle transport.

The microtubule-based motor dynein generates pulling forces for centrosome centration and mitotic spindle positioning in animal cells. How the essential dynein activator dynactin regulates these functions of the motor is incompletely understood. Here, we dissect the role of dynactin's microtubule binding activity, located in the p150 CAP-Gly domain and an adjacent basic patch, in the C. elegans zygote. Analysis of p150 mutants engineered by genome editing suggests that microtubule tip tracking of dynein-dynactin is dispensable for targeting the motor to the cell cortex and for generating robust cortical pulling forces. Instead, mutations in p150's CAP-Gly domain inhibit cytoplasmic pulling forces responsible for centration of centrosomes and attached pronuclei. The centration defects are mimicked by mutations of α-tubulin's C-terminal tyrosine, and both p150 CAP-Gly and tubulin tyrosine mutants decrease the frequency of early endosome transport from the cell periphery towards centrosomes during centration. Our results suggest that p150 GAP-Gly domain binding to tyrosinated microtubules promotes initiation of dynein-mediated organelle transport in the dividing one-cell embryo, and that this function of p150 is critical for generating cytoplasmic pulling forces for centrosome centration.

Molecular mechanism of dynein recruitment to kinetochores by the Rod-Zw10-Zwilch complex and Spindly.

The molecular motor dynein concentrates at the kinetochore region of mitotic chromosomes in animals to accelerate spindle microtubule capture and to control spindle checkpoint signaling. In this study, we describe the molecular mechanism used by the Rod-Zw10-Zwilch complex and the adaptor Spindly to recruit dynein to kinetochores in Caenorhabditis elegans embryos and human cells. We show that Rod's N-terminal ß-propeller and the associated Zwilch subunit bind Spindly's C-terminal domain, and we identify a specific Zwilch mutant that abrogates Spindly and dynein recruitment in vivo and Spindly binding to a Rod ß-propeller-Zwilch complex in vitro. Spindly's N-terminal coiled-coil uses distinct motifs to bind dynein light intermediate chain and the pointed-end complex of dynactin. Mutations in these motifs inhibit assembly of a dynein-dynactin-Spindly complex, and a null mutant of the dynactin pointed-end subunit p27 prevents kinetochore recruitment of dynein-dynactin without affecting other mitotic functions of the motor. Conservation of Spindly-like motifs in adaptors involved in intracellular transport suggests a common mechanism for linking dynein to cargo.

Small bowel tumors detection in capsule endoscopy by Gaussian modeling of color curvelet covariance coefficients.

This paper is concerned with the classification of tumoral tissue in the small bowel by using capsule endoscopic images. The followed approach is based on texture classification. Texture descriptors are derived from selected scales of the Discrete Curvelet Transform (DCT). The goal is to take advantage of the high directional sensitivity of the DCT (16 directions) when compared with the Discrete Wavelet Transform (DWT) (3 directions). Second order statistics are then computed in the HSV color space and named Color Curvelet Covariance (3C) coefficients. Finally, these coefficients are modeled by a Gaussian Mixture Model (GMM). Sensitivity of 99% and specificity of 95.19% are obtained in the testing set.

Automatic detection of small bowel tumors in capsule endoscopy based on color curvelet covariance statistical texture descriptors.

Traditional endoscopic methods do not allow the visualization of the entire Gastrointestinal (GI) tract. Wireless Capsule Endoscopy (CE) is a diagnostic procedure that overcomes this limitation of the traditional endoscopic methods. The CE video frames possess rich information about the condition of the stomach and intestine mucosa, encoded as color and texture patterns. It is known for a long time that human perception of texture is based in a multi-scale analysis of patterns, which can be modeled by multi-resolution approaches. Furthermore, modeling the covariance of textural descriptors has been successfully used in classification of colonoscopy videos. Therefore, in the present paper it is proposed a frame classification scheme based on statistical textural descriptors taken from the Discrete Curvelet Transform (DCT) domain, a recent multi-resolution mathematical tool. The DCT is based on an anisotropic notion of scale and high directional sensitivity in multiple directions, being therefore suited to characterization of complex patterns as texture. The covariance of texture descriptors taken at a given detail level, in different angles, is used as classification feature, in a scheme designated as Color Curvelet Covariance. The classification step is performed by a multilayer perceptron neural network. The proposed method has been applied in real data taken from several capsule endoscopic exams and reaches 97.2% of sensitivity and 97.4% specificity. These promising results support the feasibility of the proposed method.

Detection of small bowel tumors in capsule endoscopy frames using texture analysis based on the discrete wavelet transform.

Capsule endoscopy is an important tool to diagnose tumor lesions in the small bowel. The capsule endoscopic images possess vital information expressed by color and texture. This paper presents an approach based in the textural analysis of the different color channels, using the wavelet transform to select the bands with the most significant texture information. A new image is then synthesized from the selected wavelet bands, trough the inverse wavelet transform. The features of each image are based on second-order textural information, and they are used in a classification scheme using a multilayer perceptron neural network. The proposed methodology has been applied in real data taken from capsule endoscopic exams and reached 98.7% sensibility and 96.6% specificity. These results support the feasibility of the proposed algorithm.