Tissue Mechanics Regulate Mitotic Nuclear Dynamics during Epithelial Development

1. Download : Download high-res image (217KB)
2. Download : Download full-size image

     

Genetic analysis of auditory neuropathy spectrum disorder in the Korean population

Auditory neuropathy spectrum disorder (ANSD) is caused by dys-synchronous auditory neural response as a result of impairment of the functions of the auditory nerve or inner hair cells, or synapses between inner hair cells and the auditory nerve. To identify a causative gene causing ANSD in the Korean population, we conducted gene screening of the OTOF, DIAPH3, and PJVK genes in 19 unrelated Korean patients with ANSD. A novel nonsense mutation (p.Y1064X) and a known pathogenic mutation (p.R1939Q) of the OTOF gene were identified in a patient as compound heterozygote. Pedigree analysis for these mutations showed co-segregation of mutation genotype and the disease in the family, and it supported that the p.Y1064X might be a novel genetic cause of autosomal recessive ANSD. A novel missense variant p.K1017R (c.3050A>G) in the DIAPH3 gene was also identified in the heterozygous state. In contrast, no mutation was detected in the PJVK gene. These results indicate that no major causative gene has been reported to date in the Korean population and that pathogenic mutations in undiscovered candidate genes may have an effect on ANSD.     

Mechanical regulation of signaling pathways in bone

A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.     

High-resolution structural analysis of mammalian profilin 2a complex formation with two physiological ligands: the formin homology 1 domain of mDia1 and the proline-rich domain of VASP

Profilins are small proteins capable of binding actin, poly-l-proline and other proline-rich sequences, and phosphatidylinositol (4,5)-bisphosphate. A number of proline-rich ligands for profilin have been characterised, including proteins of the Ena/VASP and formin families. We have determined the high-resolution crystal structures of mouse profilin 2a in complex with peptides from two functionally important ligands from different families, VASP and mDia1. The structures show that the binding mode of the peptide ligand is strongly affected by the non-proline residues in the sequence, and the peptides from VASP and mDia1 bind to profilin 2a in distinct modes. The high resolution of the crystallographic data allowed us to detect conserved CH-π hydrogen bonds between the peptide and profilin in both complexes. Furthermore, both peptides, which are shown to have micromolar affinity, induced the dimerisation of profilin, potentially leading to functionally different ligand-profilin-actin complexes. The peptides did not significantly affect actin polymerisation kinetics in the presence or in the absence of profilin 2a. Mutant profilins were tested for binding to poly-l-proline and the VASP and mDia1 peptides, and the F139A mutant bound proline-rich ligands with near-native affinity. Peptide blotting using a series of designed peptides with profilins 1 and 2a indicates differences between the two profilins towards proline-rich peptides from mDia1 and VASP. Our data provide structural insights into the mechanisms of mDia1 and VASP regulated actin polymerisation.     

Cell polarization: From epithelial cells to odontoblasts

Cell polarity identifies the asymmetry of a cell. Various types of cells, including odontoblasts and epithelial cells, polarize to fulfil their destined functions. Odontoblast polarization is a prerequisite and fundamental step for tooth development and tubular dentin formation. Current knowledge of odontoblast polarization, however, is very limited, which greatly impedes the development of novel approaches for regenerative endodontics. Compared to odontoblasts, epithelial cell polarization has been extensively studied over the last several decades. The knowledge obtained from epithelia polarization has been found applicable to other cell types, which is particularly useful considering the remarkable similarities of the morphological and compositional features between polarized odontoblasts and epithelia. In this review, we first discuss the characteristics, the key regulatory factors, and the process of epithelial polarity. Next, we compare the known facts of odontoblast polarization with epithelial cells. Lastly, we clarify knowledge gaps in odontoblast polarization and propose the directions for future research to fill the gaps, leading to the advancement of regenerative endodontics.     

Differing and isoform-specific roles for the formin DIAPH3 in plasma membrane blebbing and filopodia formation

Plasma membrane (PM) blebs are dynamic actin-rich cell protrusions that occur, e.g., during cytokinesis, amoeboid cell motility and cell attachment. Using a targeted siRNA screen against 21 actin nucleation factors, we identify a novel and essential role of the human diaphanous formin DIAPH3 in PM blebbing during cell adhesion. Suppression of DIAPH3 inhibited blebbing to promote rapid cell spreading involving β1-integrin. Multiple isoforms of DIAPH3 were detected on the mRNA and protein level of which isoforms 3 and 7 were the largest and most abundant isoforms that however did not induce formation of actin-rich protrusions. Rather, PM blebbing specifically involved the low abundance isoform 1 of DIAPH3 and activation of isoform 7 by deletion of the diaphanous-autoregulatory domain caused the formation of filopodia. Dimerization and actin assembly activity were essential for induction of specific cell protrusions by DIAPH3 isoforms 1 and 7. Our data suggest that the N-terminal region comprising the GTPase-binding domain determined the subcellular localization of the formin as well as its protrusion activity between blebs and filopodia. We propose that isoform-selective actin assembly by DIAPH3 exerts specific and differentially regulated functions during cell adhesion and motility.     

Rho 1 participates in parasitoid wasp eggs maturation and host cellular immunity inhibition

Endoparasitoid wasps introduce venom into their host insects during the egg-laying stage. Venom proteins play various roles in the host physiology, development, immunity, and behavior manipulation and regulation. In this study, we identified a venom protein, MmRho1, a small guanine nucleotide-binding protein derived from ovary in the endoparasitoid wasp Microplitis mediator and found that knockdown of its expression by RNA interference caused down-regulation of vitellogenin and juvenile hormone, egg production, and cocoons formation in the female wasps. We demonstrated that MmRho1 entered the cotton bollworm's (host) hemocytes and suppressed cellular immune responses after parasitism using immunofluorescence staining. Furthermore, wasp MmRho1 interacted with the cotton bollworm's actin cytoskeleton rearrangement regulator diaphanous by yeast 2-hybrid and glutathione s-transferase pull-down. In conclusion, this study indicates that MmRho1 plays dual roles in wasp development and the suppression of the host insect cellular immune responses.