Cytoskeleton reorganization and FAK phosphorylation are involved in lanthanum(Ⅲ)-promoted proliferation and differentiation in rat osteoblasts

The effect of lanthanum ion(La3+)on osteoblast function and cytoskeleton is assessed in vitro. Osteoblasts were isolated from Snraeuo-tjawiey tetai neonatal rats.Cell proliferation and gene expression levels of cbfa-1,alkaline phosphatase(ALP),osteocalcin(OC),bone sialo-protein(BSP)and osteopontin(OPN)were examined by cell counting and RT-PCR.Cytoskeleton F-actin was stained with rhodamine-con-jugated phalloidin and was visualized by a confocal microscope.As the results,10-8-10-4M La3+-induced osteoblast proliferation on day2.Data from the RT-PCR assay revealed that 10-6 M La3+ up-regulated the expression levels of ALP,BSP,and cbfa-lon day 4,while it enhanced the expressions of OC and OPN on day 21.The F-actin cytoskeleton was strengthened and reorganized under the exposure of La3+.In addition,the phosphorylation of focal adhesion kinase(FAK)was significantly promoted in 24 h evaluated by Western blot analysis.These findings indi-sate that La 3+ promotes osteoblast activity through the phosphorylation of F AK and reorganization of the cytoskeleton.     

Creep effect on cellular uptake of viral particles

Receptor diffusion on cell membrane is usually believed as a major factor that controls how fast a virus can enter into host cell via endocytosis. However, when receptors are densely distributed around the binding site so that receptor recruiting through diffusion is no longer energetically favorable, we thus hypothesize that another effect, the creep deformation of cytoskeleton, might turn to play the dominant role in relaxing the engulfing process. In order to deeply understand this mechanism, we propose a viscoelastic model to investigate the dynamic process of virus engulfment retarded by the creep deformation of cytoskeleton and driven by the binding of ligand-receptor bonds after overcoming resistance from elastic deformation of lipid membrane and cytoskeleton. Based on this new model, we predict the lower bound of the ligand density and the range of virus size that allows the complete engulfment, and an optimal virus size corresponding to the smallest wrapping time. Surprisingly, these predictions can be reduced to the previous predictions based on simplified membrane models by taking into account statistical thermodynamic effects. The results presented in this study may be of interest to toxicologists, nanotechnologists, and virologists.     

Molecular basis of morphogenesis during vertebrate gastrulation

Gastrulation is a crucial step in early embryogenesis. During gastrulation, a set of morphogenetic processes takes place leading to the establishment of the basic body plan and formation of primary germ layers. A rich body of knowledge about these morphogenetic processes has been accumulated over decades. The understanding of the molecular mechanism that controls the complex cell movement and inductive processes during gastrulation remains a challenge. Substantial progress has been made recently to identify and characterize pathways and molecules implicated in the modulation of morphogenesis during vertebrate gastrulation. Here, we summarize recent findings in the analysis of signaling pathways implicated in gastrulation movements, with the aim to generalize the basic molecular principles of vertebrate morphogenesis.     

Cytoskeleton reorganization and FAK phosphorylation are involved in lanthanum （Ⅲ）-promoted proliferation and differentiation in rat osteoblasts

The effect of lanthanum ion (La³⁺) on osteoblast function and cytoskeleton is assessed in vitro. Osteoblasts were isolated from Sprague-Dawley fetal neonatal rats. Cell proliferation and gene expression levels of cbfa-1, alkaline phosphatase (ALP), osteocalcin (OC), bone sialoprotein (BSP) and osteopontin (OPN) were examined by cell counting and RT-PCR. Cytoskeleton F-actin was stained with rhodamine-conjugated phalloidin and was visualized by a confocal microscope. As the results, 10⁻⁸-10⁻⁴ M La³⁺-induced osteoblast proliferation on day 2. Data from the RT-PCR assay revealed that 10⁻⁶ M La³⁺ up-regulated the expression levels of ALP, BSP, and cbfa-1 on day 4, while it enhanced the expressions of OC and OPN on day 21. The F-actin cytoskeleton was strengthened and reorganized under the exposure of La³⁺. In addition, the phosphorylation of focal adhesion kinase (FAK) was significantly promoted in 24 h evaluated by Western blot analysis. These findings indicate that La³⁺ promotes osteoblast activity through the phosphorylation of FAK and reorganization of the cytoskeleton.     

Rheological behavior of mammalian cells

Rheological properties of living cells determine how cells interact with their mechanical microenvironment and influence their physiological functions. Numerous experimental studies have show that mechanical contractile stress borne by the cytoskeleton and weak power-law viscoelasticity are governing principles of cell rheology, and that the controlling physics is at the level of integrative cytoskeletal lattice properties. Based on these observations, two concepts have emerged as leading models of cytoskeletal mechanics. One is the tensegrity model, which explains the role of the contractile stress in cytoskeletal mechanics, and the other is the soft glass rheology model, which explains the weak power-law viscoelasticity of cells. While these two models are conceptually disparate, the phenomena that they describe are often closely associated in living cells for reasons that are largely unknown. In this review, we discuss current understanding of cell rheology by emphasizing the underlying biophysical mechanism and critically evaluating the existing rheological models. Received 25 May 2008; received after revision 19 June 2008; accepted 1 July 2008     

ER-to-Golgi transport and cytoskeletal interactions in animal cells

The endoplasmic reticulum (ER)-Golgi system has been studied using biochemical, genetic, electron and light microscopic techniques. We now understand many aspects of trafficking from the ER to the Golgi apparatus, including some of the signals and mechanisms for selective retention and retrieval of ER resident proteins and export of cargo proteins. Proteins that leave the ER emerge in export complexes or ER exit sites and accumulate in pleiomorphic transport carriers referred to sometimes as VTCs or intermediate compartments. These structures then transit from the ER to the Golgi apparatus along microtubules using the dynein/dynactin motor and fuse with the cis cisterna of the Golgi apparatus. Many proteins (including vSNAREs, ERGIC53/p58 and the KDEL receptor) must cycle back to the ER from pre-Golgi intermediates or the Golgi. We will discuss both the currently favored model that this cycling occurs via 50-nm COPI-coated vesicles and in vivo evidence that suggests retrograde trafficking may occur via tubular structures.