Unconventional Myosins,Actin Dynamics and Endocytosis: A Ménage à Trois?

Ever since the discovery of class I myosins, the first nonmuscle myosins, about 30 years ago, the history of unconventional myosins has been linked to the organization and working of actin filaments. It slowly emerged from studies of class I myosins in lower eukaryotes that they are involved in mechanisms of endocytosis. Most interestingly, a flurry of recent findings assign a more active role to class I myosins in regulating the spatial and temporal organization of actin filament nucleation and elongation. The results highlight the multiple links between class I myosins and the major actin nucleator, the Arp2/3 complex, and its newly described activators. Two additional types of unconventional myosins, myosinIX, and Dictyostelium discoideum MyoM, have recently been tied to the signaling pathways controlling actin cytoskeleton remodeling. The present review surveys the links between these three classes of molecular motors and the complex cellular processes of endocytosis and actin dynamics, and concentrates on a working model accounting for the function of class I myosins via recruitment of the machinery responsible for actin nucleation and elongation .     

Werner syndrome protein,the MRE11 complex and ATR: menage‐à‐trois in guarding genome stability during DNA replication?

The correct execution of the DNA replication process is crucially import for the maintenance of genome integrity of the cell. Several types of sources, both endogenous and exogenous, can give rise to DNA damage leading to the DNA replication fork arrest. The processes by which replication blockage is sensed by checkpoint sensors and how the pathway leading to resolution of stalled forks is activated are still not completely understood. However, recent emerging evidence suggests that one candidate for a sensor of replication stress is ATR and that, together with a member of RecQ family helicases, Werner syndrome protein (WRN) and MRE11 complex, can collaborate to promote the restarting of DNA synthesis through the resolution of stalled replication forks. Here, we discuss how WRN, the MRE11 complex and the ATR kinase could work together in response to replication blockage to avoid DNA replication fork collapse and genome instability.     

Quelle est la signification des anomalies observées en scintigraphie osseuse ?: Retour sur les mécanismes de fixation des bisphosphonates-(99mTc)

Likely, but still controversial, mechanisms of uptake of bisphosphonates-(^99mTc) are recalled: uptake on organic phase, on mineral phase and/or cellular internalization (osteoclasts and osteoblasts). These hypotheses are critically reviewed in the light of recent progress in pathophysiology of malignant (bone metastases, myeloma) and benign (Paget's disease of bone, fibrous dysplasia) disorders at tissular, cellular and molecular levels, from pharmacology of therapeutic bisphosphonates. Such knowledge improvements have been allowed through in vitro studies, animal models and clinical cases in multimodality imaging (radiology, scintigraphy, pathology).