FLN-1/filamin is required to anchor the actomyosin cytoskeleton and for global organization of sub-cellular organelles in a contractile tissue

A mutation in F-actin polymerization factor suppresses the distal arthrogryposis type 5 PIEZO2 pathogenic variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole-genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]), significantly increased brood size and ovulation rate, as well as alleviating the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Expression of GEX-3 in the soma is required to rescue the brood size defects in pezo-1(R2405P) animals. Actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the PIEZO coordinates with the cytoskeleton regulator to maintain the F-actin network and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

Mutation in F-actin Polymerization Factor Suppresses Distal Arthrogryposis Type 5 (DA5) PIEZO2 Pathogenic Variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]) , significantly restored the small brood size and low ovulation rate, as well as alleviated the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Auxin-inducible degradation of GEX-3 revealed that only somatic-specific degradation of GEX-3 restored the reduced brood size in the pezo-1(R2405P) mutants. Additionally, actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the cytoskeleton plays an important role in regulating PIEZO channel activity and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

An integrin binding motif in TLN-1/talin plays a minor role in motility and ovulation

TLN-1/talin is a conserved focal adhesion protein that forms part of the linkage between the cytoplasmic tail of integrin and the actin cytoskeleton. In C. elegans , TLN-1 is expressed strongly in striated muscle and the gonadal sheath cells. Here, we report that a CRISPR-generated TLN-1 allele TLN-1(W387A), predicted to affect binding of talin to integrins, results in mild phenotypes, including motility defects and ovulation defects. The arrangement of the actin cytoskeleton in the body wall muscles, spermatheca, and sheath appears identical in wild type and TLN-1(W387A) animals. This analysis suggests that W387 in TLN-1 does not have a major effect on the binding of talin to integrin in vivo .

Tension-dependent RHGF-1 recruitment to stress fibers drives robust spermathecal tissue contraction

Contractile epithelial tubes are found in various organs, such as lung airways and blood capillaries. Their ability to sense luminal pressure and respond with adequate contractility is essential for their physiology, and its mis-regulation results in diseases such as asthma and hypertension. Here, we describe a mechanoresponsive regulatory pathway downstream of tissue stretching that controls contraction of the C. elegans spermatheca, a tubular structure where fertilization occurs. Using live-imaging, we show that ovulation-induced stretching of spermathecal cells leads to recruitment of the RhoGEF RHGF-1 to stress fibers, which activates RHO-1 and myosin II in a positive feedback loop. Through deletion analysis, we identified the PDZ domain of RHGF-1 as responsible for F-actin binding, and genetic epistasis analysis with the RhoGAP spv-1 demonstrated that tension-dependent recruitment of RHGF-1 to F-actin is required for robust spermathecal contractility. Our study illustrates how mechanosensitive regulators of Rho GTPases provide epithelial tubes the ability to tune their contractility in response to internal pressure.

ZYX-1/Zyxin plays a minor role in oocyte transit through the spermatheca in C. elegans

In C. elegans, oocytes are ovulated into the spermatheca, where they are fertilized before being pushed into the uterus. Contraction in the C. elegans spermatheca is driven by circumferential acto-myosin fibers. The C. elegans zyxin homolog, zyx-1, is expressed in the body wall muscle, pharynx and spermatheca. To our surprise, a CRISPR-generated zyx-1 deletion allele results in no overt developmental phenotypes, and the spermathecal actin cytoskeleton appears wild type, however, oocyte transit through the spermatheca is slower than in wild type animals. This suggests ZYX-1/Zyxin may regulate spermathecal contraction magnitude or timing of spermathecal bag contraction and/or spermathecal-uterine valve dilation.

Nonmuscle Myosin II in cancer cell migration and mechanotransduction

Cell migration is a key step of cancer metastasis, immune-cell navigation, homing of stem cells and development. What adds complexity to it is the heterogeneity of the tissue environment that gives rise to a vast diversity of migratory mechanisms utilized by cells. A majority of cell motility mechanisms reported elsewhere largely converge in depicting the importance of the activity and complexity of actomyosin networks in the cell. In this review, we highlight the less discussed functional diversity of these actomyosin complexes and describe in detail how the major cellular actin-binding molecular motor proteins, nonmuscle myosin IIs are regulated and how they participate and mechanically reciprocate to changes in the microenvironment during cancer cell migration and tumor progression. Understanding the role of nonmuscle myosin IIs in the cancer cell is important for designing efficient therapeutic strategies to prevent cancer metastasis.

Survey of cancer cell anatomy in nonadhesive confinement reveals a role for filamin-A and fascin-1 in leader bleb-based migration

Cancer cells migrating in confined microenvironments exhibit plasticity of migration modes. Confinement of contractile cells in a nonadhesive environment drives “leader bleb–based migration” (LBBM), morphologically characterized by a long bleb that points in the direction of movement separated from a cell body by a contractile neck. Although cells undergoing LBBM have been visualized within tumors, the organization of organelles and actin regulatory proteins mediating LBBM is unknown. We analyzed the localization of fluorescent organelle-specific markers and actin-associated proteins in human melanoma and osteosarcoma cells undergoing LBBM. We found that organelles from the endolysosomal, secretory, and metabolic systems as well as the vimentin and microtubule cytoskeletons localized primarily in the cell body, with some endoplasmic reticulum, microtubules, and mitochondria extending into the leader bleb. Overexpression of fluorescently tagged actin regulatory proteins showed that actin assembly factors localized toward the leader bleb tip, contractility regulators and cross-linkers in the cell body cortex and neck, and cross-linkers additionally throughout the leader bleb. Quantitative analysis showed that excess filamin-A and fascin-1 increased migration speed and persistence, while their depletion by small interfering RNA indicates a requirement in promoting cortical tension and pressure to drive LBBM. This indicates a critical role of specific actin crosslinkers in LBBM.