Temporal and spatial expression of osteoactivin during fracture repair

We previously identified osteoactivin (OA) as a novel secreted osteogenic factor with high expression in developing long bones and calvaria, and that stimulates osteoblast differentiation and matrix mineralization in vitro. In this study, we report on OA mRNA and protein expression in intact long bone and growth plate, and in fracture calluses collected at several time points up to 21 days post‐fracture (PF). OA mRNA and protein were highly expressed in osteoblasts localized in the metaphysis of intact tibia, and in hypertrophic chondrocytes localized in growth plate, findings assessed by in situ hybridization and immunohistochemistry, respectively. Using a rat fracture model, Northern blot analysis showed that expression of OA mRNA was significantly higher in day‐3 and day‐10 PF calluses than in intact rat femurs. Using in situ hybridization, we examined OA mRNA expression during fracture healing and found that OA was temporally regulated, with positive signals seen as early as day‐3 PF, reaching a maximal intensity at day‐10 PF, and finally declining at day‐21 PF. At day‐5 PF, which correlates with chondrogenesis, OA mRNA levels were significantly higher in the soft callus than in intact femurs. Similarly, we detected high OA protein immunoexpression throughout the reparative phase of the hard callus compared to intact femurs. Interestingly, the secreted OA protein was also detected within the newly made cartilage matrix and osteoid tissue. Taken together, these results suggest the possibility that OA plays an important role in bone formation and serves as a positive regulator of fracture healing. J. Cell. Biochem. 111: 295–309, 2010. © 2010 Wiley‐Liss, Inc.     

Molecular Biology of Background K Channels: Insights from K2P Knockout Mice

K_2P channels are a family of cellular proteins that are essential for electrical signaling throughout the body. There are six K_2P channel subfamilies, consisting of 15 distinct mammalian genes. K_2P channels display a remarkable range of regulation by cellular, physical and pharmacologic agents, including protein kinases, intracellular Ca²⁺, changes in internal and external pH, anesthetic agents, heat, stretch and membrane deformers. The molecular and cellular mechanisms underlying this regulation are complex and cooperate at many different levels. Recent research has provided strong evidence that the spatiotemporal-specific expression of K_2P channels are determinants of physiologic selectivity and specificity. In recent years, knockout mice have been generated with inactivated K_2P channel genes. These animals shed new light on the contribution of K_2P channels to normal and abnormal physiology. In this review, we summarize the published data on these mice to broaden the understanding of the role of K_2P channel activity.     

The Desmoglein-Specific Cytoplasmic Region Is Intrinsically Disordered in Solution and Interacts with Multiple Desmosomal Protein Partners

The desmoglein-specific cytoplasmic region (DSCR) is a conserved region of unknown structure and function that uniquely defines the desmoglein family of cell adhesion molecules. It is the site of caspase cleavage during apoptosis, and its mutation is linked to cardiomyopathy. Here, we reveal that a 276-residue DSCR construct of human desmoglein 1 is intrinsically disordered and forms an interaction hub for desmosomal proteins. In solution, it contains 6.5% helical and 10.3% β-strand structure based on circular dichroism spectroscopy. A single monomeric state with a predominantly unfolded structure is found by size-exclusion chromatography and analytical ultracentrifugation. Thermal stability assays and nuclear magnetic resonance spectroscopy reveal a nonglobular structure under a range of solution conditions. However, the introduction of detergent micelles increases structure to 18% helical and 16% β-strand character, suggesting an inducible structure. The DSCR exhibits weak but specific interactions with plakoglobin, the plakin domain of desmoplakin, plakophilin 1, and the cytoplasmic domain of desmocollin 1. The desmoglein 1 membrane proximal region also interacts with all four DSCR ligands, strongly with plakoglobin and plakophilin and more weakly with desmoplakin and desmocollin 1. Thus, the DSCR is an intrinsically disordered functional domain with an inducible structure that, along with the membrane proximal region, forms a flexible scaffold for cytoplasmic assembly at the desmosome.     

A comment on Feldesman's analysis of the distal humerus

It is the combination of anatomy, behavior, and molecular biology that is necessary for the analysis. No one line of evidence is adequate.     

Development of the suprarostral plate of Pipoid Frogs

The rostral region of nonpipoid tadpoles has two sets of cartilages, the cornua trabeculae and the suprarostral cartilages, whereas the rostral region in pipoid larvae is occupied by a single and continuous cartilage, the suprarostral plate. The homology of this region in pipoid and nonpipoids tadpoles has been controversial. We examined the early formation and development of the suprarostral plate using serially cross‐sectioned specimens of Rhinophrynus, Xenopus, and Hymenochirus. We conclude that the cartilaginous structures present in the rostral area of pipoid and nonpipoid larvae are homologous. Furthermore, we found two different developmental patterns among pipoid larvae. The chondrocranium of Hymenochirus boettgeri is described and illustrated to understand its developmental pattern and because of its uniqueness among pipoid chondrocrania. J. Morphol. 240:143–153, 1999. © 1999 Wiley‐Liss, Inc.     

Asymmetric cell division of a triangular halophilic archaebacterium

Abstract The cell division of the halophilic archaebacterium, Haloarcula japonicus , which has a characteristic triangular shape in high salt concentration media, was analysed by time lapse microscopic cinematography. Cell division on an agar medium occured on average every 3.7 h. Cell plates were laid down asymmetrically, generating triangular or rhomboid shape daughter cells which then separated. Cell plate formation was clearly observed because the cells are flat and thin enough to see through using a conventional light microscope.