RhoA Recruits Ect2 and Anillin to the Cortex where they interact to Maintain Furrow Ingression during Cytokinesis.

Cytokinesis is the division of one cell into two genetically identical daughter cells due to the ingression of an actin-myosin based contractile ring. Cytokinesis failure can lead to genomic instability and cancer. In human cells, contractile ring formation and ingression depends on active RhoA, which forms in a discrete region of the cortex during anaphase. Signals from the mitotic spindle shape the zone of active RhoA, but the mechanism is still poorly understood. We investigate how this discrete zone of active RhoA is formed to establish the division plane. Ect2, the guanine nucleotide exchange factor for RhoA, localizes to the anaphase spindle and activates RhoA after anaphase onset. We found that Ect2 is also recruited to the equatorial cortex in a RhoA-dependent manner, suggesting a positive feedback loop reinforces the activation of RhoA in the division plane. Ect2’s cortical interaction is essential for its activity, and one hypothesis is that cortical Ect2 is more active vs. Ect2 in other locations of the cell. Furthermore, Ect2 can interact with anillin, a conserved scaffold protein that also localizes to the cell cortex during anaphase and is essential for cytokinesis. In anillin-depleted cells, the cortical pool of Ect2 is lost, which could lead to decreased localization of active RhoA and unstable furrowing. We hypothesize that in human cells, the Ect2-anillin interaction anchors anaphase spindle microtubules to the equatorial cortex to generate active RhoA in a discrete zone to form the contractile ring and maintain its ingression in the correct plane

Portable x-ray fluorescence spectrometer for coating thickness measurement

peer reviewedA handheld x-ray spectrometer has been realized and tested. The purpose of the device is to measure the thickness of coated samples in the range of 1-1500 nm in an industrial environment. Accuracy of similar to 3% has been achieved in this range with a measurement time of 1 min. Automated software has been implemented to allow utilization by a nonspecialist operator. An automated calibration procedure, based on measurements of reference samples, is used. (C) 2007 American Institute of Physics

Muscle RANK is a key regulator of calcium storage, SERCA activity, and function of fast-twitch skeletal muscles

Receptor-activator of nuclear factor kB (RANK), its ligand RANKL and the soluble decoy receptor osteoprotegerin (OPG)are the key regulators of osteoclast differentiation and bone remodeling. Here we show that RANK is also expressed in fully differentiated myotubes and skeletal muscle. Muscle RANK deletion (RANKmko) has inotropic effects in denervated, but not in sham, extensor digitorum longus (EDL) muscle preventing the loss of maximum specific force while promoting muscle atrophy, fatigability and increased proportion of fast-twitch fibers. In denervated EDL muscles, RANK deletion markedly increased stromal interaction molecule 1 (Stim1) content, a calcium sensor, and altered activity of the sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) modulating Ca2+ storage. Muscle RANK deletion had no significant effects on the sham or denervated slow-twitch soleus (Sol) muscles. These data identify a novel role for RANK as a key regulator of calcium storage and SERCA activity, ultimately affecting denervated skeletal muscle function

Assessment of atomic layer deposited TiO2 photocatalytic self-cleaning by quartz crystal microbalance

The self-cleaning properties emerging from photocatalytic effects consist in the elimination of an organic contamination layer by light-induced redox reactions. Quartz crystal microbalances (QCMs), monitoring the contaminant mass loss under UV illumination, were used to investigate this effect and its efficiency. A new setup dedicated to such purpose is introduced along with the results of a self-cleaning experiment performed with a 20-nm TiO2 thin film coated on a QCM by atomic layer deposition. In particular, a 10-nm paraffin oil thin film deposited under vacuum is shown to be degraded down to its complete removal according to a zeroth order photocatalytic reaction. Finally, the experimental opportunities offered by the new setup, such as a controlled environment composition, are presented.Peer reviewe

Bone marrow CD169+ macrophages promote the retention of hematopoietic stem and progenitor cells in the mesenchymal stem cell niche

Hematopoietic stem cells (HSCs) reside in specialized bone marrow (BM) niches regulated by the sympathetic nervous system (SNS). Here, we have examined whether mononuclear phagocytes modulate the HSC niche. We defined three populations of BM mononuclear phagocytes that include Gr-1hi monocytes (MOs), Gr-1lo MOs, and macrophages (MΦ) based on differential expression of Gr-1, CD115, F4/80, and CD169. Using MO and MΦ conditional depletion models, we found that reductions in BM mononuclear phagocytes led to reduced BM CXCL12 levels, the selective down-regulation of HSC retention genes in Nestin+ niche cells, and egress of HSCs/progenitors to the bloodstream. Furthermore, specific depletion of CD169+ MΦ, which spares BM MOs, was sufficient to induce HSC/progenitor egress. MΦ depletion also enhanced mobilization induced by a CXCR4 antagonist or granulocyte colony-stimulating factor. These results highlight two antagonistic, tightly balanced pathways that regulate maintenance of HSCs/progenitors in the niche during homeostasis, in which MΦ cross talk with the Nestin+ niche cell promotes retention, and in contrast, SNS signals enhance egress. Thus, strategies that target BM MΦ hold the potential to augment stem cell yields in patients that mobilize HSCs/progenitors poorly