Involvement of headless myosin X in the motility of immortalized gonadotropin-releasing hormone neuronal cells

A Novel Netrin-1-Derived Peptide Enhances Protection against Neuronal Death and Mitigates of Intracerebral Hemorrhage in Mice

It has been reported that Netrin-1 is involved in neuroprotection following injury to the central nervous system. However, the minimal functional domain of Netrin-1 which can preserve the neuroprotection but avoid the major side effects of Netrin remains elusive. Here, we investigated the neuroprotective effect of a peptide E1 derived from Netrin-1′s EGF3 domain (residues 407–422). We found that it interacts with deleted colorectal carcinoma (DCC) to activate focal adhesion kinase phosphorylation exhibiting neuroprotection. The administration of the peptide E1 was able to improve functional recovery through reduced apoptosis in an experimental murine model of intracerebral hemorrhage (ICH). In summary, we reveal a functional sequence of Netrin-1 that is involved in the recovery process after ICH and identify a candidate peptide for the treatment of ICH.

Myosins: Domain Organisation, Motor Properties, Physiological Roles and Cellular Functions

Myosins are cytoskeletal motor proteins that use energy derived from ATP hydrolysis to generate force and movement along actin filaments. Humans express 38 myosin genes belonging to 12 classes that participate in a diverse range of crucial activities, including muscle contraction, intracellular trafficking, cell division, motility, actin cytoskeletal organisation and cell signalling. Myosin malfunction has been implicated a variety of disorders including deafness, hypertrophic cardiomyopathy, Usher syndrome, Griscelli syndrome and cancer. In this chapter, we will first discuss the key structural and kinetic features that are conserved across the myosin family. Thereafter, we summarise for each member in turn its unique functional and structural adaptations, cellular roles and associated pathologies. Finally, we address the broad therapeutic potential for pharmacological interventions that target myosin family members.

Myosin X regulates neuronal radial migration through interacting with N-cadherin

Proper brain function depends on correct neuronal migration during development, which is known to be regulated by cytoskeletal dynamics and cell-cell adhesion. Myosin X (Myo10), an uncharacteristic member of the myosin family, is an important regulator of cytoskeleton that modulates cell motilities in many different cellular contexts. We previously reported that Myo10 was required for neuronal migration in the developing cerebral cortex, but the underlying mechanism was still largely unknown. Here, we found that knockdown of Myo10 expression disturbed the adherence of migrating neurons to radial glial fibers through abolishing surface Neuronal cadherin (N-cadherin) expression, thereby impaired neuronal migration in the developmental cortex. Next, we found Myo10 interacted with N-cadherin cellular domain through its FERM domain. Furthermore, we found knockdown of Myo10 disrupted N-cadherin subcellular distribution and led to localization of N-cadherin into Golgi apparatus and endosomal sorting vesicle. Taking together, these results reveal a novel mechanism of Myo10 interacting with N-cadherin and regulating its cell-surface expression, which is required for neuronal adhesion and migration.

A Fluorescent Live Imaging Screening Assay Based on Translocation Criteria Identifies Novel Cytoplasmic Proteins Implicated in G Protein-coupled Receptor Signaling Pathways

Several cytoplasmic proteins that are involved in G protein-coupled receptor signaling cascades are known to translocate to the plasma membrane upon receptor activation, such as beta-arrestin2. Based on this example and in order to identify new cytoplasmic proteins implicated in the ON-and-OFF cycle of G protein-coupled receptor, a live-imaging screen of fluorescently labeled cytoplasmic proteins was performed using translocation criteria. The screening of 193 fluorescently tagged human proteins identified eight proteins that responded to activation of the tachykinin NK2 receptor by a change in their intracellular localization. Previously we have presented the functional characterization of one of these proteins, REDD1, that translocates to the plasma membrane. Here we report the results of the entire screening. The process of cell activation was recorded on videos at different time points and all the videos can be visualized on a dedicated website. The proteins BAIAP3 and BIN1, partially translocated to the plasma membrane upon activation of NK2 receptors. Proteins ARHGAP12 and PKM2 translocated toward membrane blebs. Three proteins that associate with the cytoskeleton were of particular interest : PLEKHH2 rearranged from individual dots located near the cell-substrate adhesion surface into lines of dots. The speriolin-like protein, SPATC1L, redistributed to cell-cell junctions. The Chloride intracellular Channel protein, CLIC2, translocated from actin-enriched plasma membrane bundles to cell-cell junctions upon activation of NK2 receptors. CLIC2, and one of its close paralogs, CLIC4, were further shown to respond with the same translocation pattern to muscarinic M3 and lysophosphatidic LPA receptors. This screen allowed us to identify potential actors in signaling pathways downstream of G protein-coupled receptors and could be scaled-up for high-content screening.

Myo10 is required for neurogenic cell adhesion and migration

Myosin X (Myo10), an untraditional member of myosin superfamily, is characterized as an actin-based molecular motor, which plays a critical role in diverse cellular motile events. Previous research by our group has found that Myo10 influenced neuronal radial migration in developing neocortex, but the underlying mechanism is still largely unknown. In this study, we found that knockdown of endogenous Myo10 in a normal gonadotropin-releasing hormone (GnRH) neuronal cell line transfected with the large T antigen (NLT) induced the impairment of cell motility and orientation. In the wound healing assay, with the Golgi complex staining to display cell polarity, Myo10 knockdown cells were randomly oriented compared to the control. Furthermore, suppressing the expression of Myo10 decreased the ability of cell-matrix adhesion. N-cadherin, a calcium-dependent classical cell adhesion molecule, rescued the migration deficiency caused by Myo10 knockdown in cell aggregates and collagen gel assay. These results suggest that Myo10 is required for neurogenic cell migration through N-cadherin mediated cell adhesion.

Cloning, characterization, and promoter analysis of mouse Myo10 gene

Myosin X (Myo10) is an unconventional myosin associated with filopodia motility. Recent studies show that in addition to full-length Myo10, brain expresses a shorter form of Myo10 that lacks a myosin motor domain named headless Myo10. Herein, we analyzed and cloned 2-kb of the 5'-upstream sequences of mouse full-length Myo10 (fMyo10) and headless Myo10 (hMyo10) to understand the transcriptional regulation of the Myo10 gene. The putative transcription factor binding sites and CpG island were analyzed by a bioinformatic approach. Luciferase reporter assays showed that the 2-kb of 5'-upstream sequences of both fMyo10 and hMyo10 had promoter activities.

Myo10 is a key regulator of TNT formation in neuronal cells

Cell-to-cell communication is essential in multicellular organisms. Tunneling nanotubes (TNTs) have emerged as a new type of intercellular spreading mechanism allowing the transport of various signals, organelles and pathogens. Here, we study the role of the unconventional molecular motor myosin-X (Myo10) in the formation of functional TNTs within neuronal CAD cells. Myo10 protein expression increases the number of TNTs and the transfer of vesicles between co-cultured cells. We also show that TNT formation requires both the motor and tail domains of the protein, and identify the F2 lobe of the FERM domain within the Myo10 tail as necessary for TNT formation. Taken together, these results indicate that, in neuronal cells, TNTs can arise from a subset of Myo10-driven dorsal filopodia, independent of its binding to integrins and N-cadherins. In addition our data highlight the existence of different mechanisms for the establishment and regulation of TNTs in neuronal cells and other cell types.

Both Myosin-10 isoforms are required for radial neuronal migration in the developing cerebral cortex

During embryonic development of the mammalian cerebral cortex, postmitotic cortical neurons migrate radially from the ventricular zone to the cortical plate. Proper migration involves the correct orientation of migrating neurons and the transition from a multipolar to a mature bipolar morphology. Herein, we report that the 2 isoforms of Myosin-10 (Myo10) play distinct roles in the regulation of radial migration in the mouse cortex. We show that the full-length Myo10 (fMyo10) isoform is located in deeper layers of the cortex and is involved in establishing proper migration orientation. We also demonstrate that fMyo10-dependent orientation of radial migration is mediated at least in part by the netrin-1 receptor deleted in colorectal cancer. Moreover, we show that the headless Myo10 (hMyo10) isoform is required for the transition from multipolar to bipolar morphologies in the intermediate zone. Our study reveals divergent functions for the 2 Myo10 isoforms in controlling both the direction of migration and neuronal morphogenesis during radial cortical neuronal migration.

Headless Myo10 is a negative regulator of full-length Myo10 and inhibits axon outgrowth in cortical neurons

Myo10 is an unconventional myosin that localizes to and induces filopodia, structures that are critical for growing axons. In addition to the ~240-kDa full-length Myo10, brain expresses a ~165 kDa isoform that lacks a functional motor domain and is known as headless Myo10. We and others have hypothesized that headless Myo10 acts as an endogenous dominant negative of full-length Myo10, but this hypothesis has not been tested, and the function of headless Myo10 remains unknown. We find that cortical neurons express both headless and full-length Myo10 and report the first isoform-specific localization of Myo10 in brain, which shows enrichment of headless Myo10 in regions of proliferating and migrating cells, including the embryonic ventricular zone and the postnatal rostral migratory stream. We also find that headless and full-length Myo10 are expressed in embryonic and neuronal stem cells. To directly test the function of headless and full-length Myo10, we used RNAi specific to each isoform in mouse cortical neuron cultures. Knockdown of full-length Myo10 reduces axon outgrowth, whereas knockdown of headless Myo10 increases axon outgrowth. To test whether headless Myo10 antagonizes full-length Myo10, we coexpressed both isoforms in COS-7 cells, which revealed that headless Myo10 suppresses the filopodia-inducing activity of full-length Myo10. Together, these results demonstrate that headless Myo10 can function as a negative regulator of full-length Myo10 and that the two isoforms of Myo10 have opposing roles in axon outgrowth.

Myosin-X: a MyTH-FERM myosin at the tips of filopodia

Myosin-X (Myo10) is an unconventional myosin with MyTH4-FERM domains that is best known for its striking localization to the tips of filopodia and its ability to induce filopodia. Although the head domain of Myo10 enables it to function as an actin-based motor, its tail contains binding sites for several molecules with central roles in cell biology, including phosphatidylinositol (3,4,5)-trisphosphate, microtubules and integrins. Myo10 also undergoes fascinating long-range movements within filopodia, which appear to represent a newly recognized system of transport. Myo10 is also unusual in that it is a myosin with important roles in the spindle, a microtubule-based structure. Exciting new studies have begun to reveal the structure and single-molecule properties of this intriguing myosin, as well as its mechanisms of regulation and induction of filopodia. At the cellular and organismal level, growing evidence demonstrates that Myo10 has crucial functions in numerous processes ranging from invadopodia formation to cell migration.