G protein-coupled receptor/arrestin3 modulation of the endocytic machinery

Nonvisual arrestins (arr) modulate G protein-coupled receptor (GPCR) desensitization and internalization and bind to both clathrin (CL) and AP-2 components of the endocytic coated pit (CP). This raises the possibility that endocytosis of some GPCRs may be a consequence of arr-induced de novo CP formation. To directly test this hypothesis, we examined the behavior of green fluorescent protein (GFP)-arr3 in live cells expressing beta2-adrenergic receptors and fluorescent CL. After agonist stimulation, the diffuse GFP-arr3 signal rapidly became punctate and colocalized virtually completely with preexisting CP spots, demonstrating that activated complexes accumulate in previously formed CPs rather than nucleating new CP formation. After arr3 recruitment, CP appeared larger: electron microscopy analysis revealed an increase in both CP number and in the occurrence of clustered CPs. Mutant arr3 proteins with impaired binding to CL or AP-2 displayed reduced recruitment to CPs, but were still capable of inducing CP clustering. In contrast, though constitutively present in CPs, the COOH-terminal moiety of arr3, which contains CP binding sites but lacks receptor binding, did not induce CP clustering. Together, these results indicate that recruitment of functional arr3-GPCR complexes to CP is necessary to induce clustering. Latrunculin B or 16 degrees C blocked CP rearrangements without affecting arr3 recruitment to CP. These results and earlier studies suggest that discrete CP zones exist on cell surfaces, each capable of supporting adjacent CPs, and that the cortical actin membrane skeleton is intimately involved with both the maintenance of existing CPs and the generation of new structures.     

Occurrence of articulins and epiplasmins in protists

The cortex of ciliates. dinoflagellates, and euglenoids comprises a unique structure called the epiplasm, implicated in pattern-forming processes of the cell cortex and in maintaining cell shape. Articulins, a novel class of cytoskeletal proteins, are major constituents of the epiplasm in the flagellate Euglena gracilis and the ciliate Pseudomicrothorax dubius. The hallmark of articulins is a core domain of repetitive motifs of alternating valine and proline residues, the VPV-motif. The VPV-motif repeats are 12 residues long. Positively and negatively charged residues segregate in register with valine and proline positions. The VPV-motif is unique to articulins. The terminal domains flanking the core are generally hydrophobic and contain a series of hexa- or heptapeptide repeats rich in glycine and hydrophobic residues. Using molecular and immunological tools we show that articulins are also present in the dinoflagellate Amphidinium carterae and the ciliates Paramecium tetraurelia and Paramecium caudatum, Tetrahymena pyriformis, and Euplotes aediculatus. Our analysis further shows that epiplasmins, a group of epiplasmic proteins first characterized in Paramecium, are also present in all these species. Moreover, we present evidence that epiplasmins and articulins represent two distinct classes of cytoskeletal proteins.     

Novel cytoskeletal proteins in the cortex of Tetrahymena

An important unsolved problem lies in the mechanisms that determine overall size, shape, and the localization of subcellular structures in eukaryotic cells. The membrane skeleton must play a central role in these processes in many cell types, and the ciliate membrane skeleton, or epiplasm, offers favorable opportunities for exploring the molecular determinants of cortical organization. Among the ciliates, Tetrahymena is well suited for the application of a wide range of molecular and cellular approaches. Progress has been made in the identification and sequencing of genes and proteins that encode epiplasmic and cortical proteins. The amino acid sequences of these proteins suggest that they define new classes of cytoskeletal proteins, distinct from the articulin and epiplasmin proteins. We will also discuss recent in vivo and in vitro studies of the regulation of assembly of these cortical proteins. This will include information regarding the down-regulation of epiplasmic proteins during cleavage, their topographic regulation in the cell cycle, and the results of in vitro assembly and binding studies of the epiplasmic C protein.     

Myelin basic protein component C1 in increasing concentrations can elicit fusion, aggregation, and fragmentation of myelin-like membranes

Myelin basic protein (MBP) is considered to have a primary role in the formation and maintenance of the myelin sheath. Many studies using artificial vesicle systems of simple lipid composition, and generally small size, have shown that MBP can elicit vesicle fusion, aggregation, or even fragmentation under different conditions. Here, we have studied the effects of increasing concentrations of bovine MBP charge isomer C1 (MBP/C1) on large unilamellar vesicles (LUVs) composed of phosphatidylcholine and phosphatidylserine (92:8 molar ratio), or with a lipid composition similar to that of the myelin membrane in vivo (Cyt-LUVs). Using absorbance spectrophotometry, fluorescence resonance energy transfer, dynamic light scattering and transmission electron microscopy, we have shown that vesicle aggregation and some vesicle fusion occurred upon addition of MBP/C1, and as the molar protein-lipid ratio increased. Fragmentation of Cyt-LUVs was observed at very high protein concentrations. These results showed that the phenomena of vesicle fusion, aggregation, and fragmentation can all be observed in one in vitro system, but were dependent on lipid composition and on the relative proportions of protein and lipid.     

Skeletal development in the Chinese soft‐shelled turtle Pelodiscus sinensis (Testudines: Trionychidae)

We investigated the development of the whole skeleton of the soft‐shelled turtle Pelodiscus sinensis, with particular emphasis on the pattern and sequence of ossification. Ossification starts at late Tokita‐Kuratani stage (TK) 18 with the maxilla, followed by the dentary and prefrontal. The quadrate is the first endoskeletal ossification and appears at TK stage 22. All adult skull elements have started ossification by TK stage 25. Plastral bones are the first postcranial bones to ossify, whereas the nuchal is the first carapacial bone to ossify, appearing as two unstained anlagen. Extensive examination of ossification sequences among autopodial elements reveals much intraspecific variation. Patterns of ossification of cranial dermal elements are more variable than those of endochondral elements, and dermal elements ossify before endochondral ones. Differences in ossification sequences with Apalone spinifera include: in Pelodiscus sinensis the jugal develops relatively early and before the frontal, whereas it appears later in A. spinifera; the frontal appears shortly before the parietal in A. spinifera whereas in P. sinensis the parietal appears several stages before the frontal. Chelydrids exhibit an early development of the postorbital bone and the palatal elements as compared to trionychids. Integration of the onset of ossification data into an analysis of the sequence of skeletal ossification in cryptodirans using the event‐pairing and Parsimov methods reveals heterochronies, some of which reflect the hypothesized phylogeny considered taxa. A functional interpretation of heterochronies is speculative. In the chondrocranium there is no contact between the nasal capsules and planum supraseptale via the sphenethmoid commissurae. The pattern of chondrification of forelimb and hind limb elements is consistent with a primary axis and digital arch. There is no evidence of anterior condensations distal to the radius and tibia. A pattern of quasi‐ simultaneity is seen in the chondrogenesis of the forelimb and the hind limb. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Insights into the role of components of the tumor microenvironment in oral carcinoma call for new therapeutic approaches

The research on oral cancer has focused mainly on the cancer cells, their genetic changes and consequent phenotypic modifications. However, it is increasingly clear that the tumor microenvironment (TME) has been shown to be in a dynamic state of inter-relations with the cancer cells. The TME contains a variety of components including the non-cancerous cells (i.e., immune cells, resident fibroblasts and angiogenic vascular cells) and the ECM milieu [including fibers (mainly collagen and fibronectin) and soluble factors (i.e., enzymes, growth factors, cytokines and chemokines)]. Thus, it is currently assumed that TME is considered a part of the cancerous tissue and the functionality of its key components constitutes the setting on which the hallmarks of the cancer cells can evolve. Therefore, in terms of controlling a malignancy, one should control the growth, invasion and spread of the cancer cells through modifications in the TME components. This mini review focuses on the TME as a diagnostic approach and reports the recent insights into the role of different TME key components [such as carcinoma-associated fibroblasts (CAFs) and inflammation (CAI) cells, angiogenesis, stromal matrix molecules and proteases] in the molecular biology of oral carcinoma. Furthermore, the impact of TME components on clinical outcomes and the concomitant need for development of new therapeutic approaches will be discussed.     

Knockdown of miR-210 decreases hypoxic glioma stem cells stemness and radioresistance

Glioma contains abundant hypoxic regions which provide niches to promote the maintenance and expansion of glioma stem cells (GSCs), which are resistant to conventional therapies and responsible for recurrence. Given the fact that miR-210 plays a vital role in cellular adaption to hypoxia and in stem cell survival and stemness maintenance, strategies correcting the aberrantly expressed miR-210 might open up a new therapeutic avenue to hypoxia GSCs. In the present study, to explore the possibility of miR-210 as an effective therapeutic target to hypoxic GSCs, we employed a lentiviral-mediated anti-sense miR-210 gene transfer technique to knockdown miR-210 expression and analyze phenotypic changes in hypoxic U87s and SHG44s cells. We found that hypoxia led to an increased HIF-2α mRNA expression and miR-210 expression in GSCs. Knockdown of miR-210 decreased neurosphere formation capacity, stem cell marker expression and cell viability, and induced differentiation and G0/G1 arrest in hypoxic GSCs by partially rescued Myc antagonist (MNT) protein expression. Knockdown of MNT could reverse the gene expression changes and the growth inhibition resulting from knockdown of miR-210 in hypoxic GSCs. Moreover, knockdown of miR-210 led to increased apoptotic rate and Caspase-3/7 activity and decreased invasive capacity, reactive oxygen species (ROS) and lactate production and radioresistance in hypoxic GSCs. These findings suggest that miR-210 might be a potential therapeutic target to eliminate GSCs located in hypoxic niches.     

Modular Skeletal Evolution in Sticklebacks Is Controlled by Additive and Clustered Quantitative Trait Loci

Understanding the genetic architecture of evolutionary change remains a long-standing goal in biology. In vertebrates, skeletal evolution has contributed greatly to adaptation in body form and function in response to changing ecological variables like diet and predation. Here we use genome-wide linkage mapping in threespine stickleback fish to investigate the genetic architecture of evolved changes in many armor and trophic traits. We identify >100 quantitative trait loci (QTL) controlling the pattern of serially repeating skeletal elements, including gill rakers, teeth, branchial bones, jaws, median fin spines, and vertebrae. We use this large collection of QTL to address long-standing questions about the anatomical specificity, genetic dominance, and genomic clustering of loci controlling skeletal differences in evolving populations. We find that most QTL (76%) that influence serially repeating skeletal elements have anatomically regional effects. In addition, most QTL (71%) have at least partially additive effects, regardless of whether the QTL controls evolved loss or gain of skeletal elements. Finally, many QTL with high LOD scores cluster on chromosomes 4, 20, and 21. These results identify a modular system that can control highly specific aspects of skeletal form. Because of the general additivity and genomic clustering of major QTL, concerted changes in both protective armor and trophic traits may occur when sticklebacks inherit either marine or freshwater alleles at linked or possible “supergene” regions of the stickleback genome. Further study of these regions will help identify the molecular basis of both modular and coordinated changes in the vertebrate skeleton.     

Evidence of facultative daytime hypothermia in a small passerine wintering at northern latitudes

The use of hypothermia as a means to save energy is well documented in birds. This energy‐saving strategy is widely considered to occur exclusively at night in diurnally active species. However, recent studies suggest that facultative hypothermia may also occur during the day. Here, we document the use of daytime hypothermia in foraging Black‐capped Chickadees Poecile atricapillus wintering in eastern Canada. We measured the body temperature (T_b) of 126 individuals (plus 48 repeated measures) during a single winter and related values to ambient temperature (T_a) at the time of capture. We also tested whether daytime hypothermia was correlated with the size of body reserves (residuals of mass on structural size and fat score) and levels of metabolic performance (basal metabolic rate and maximum thermogenic capacity). We found that T_b of individual birds was lower when captured at low T_a, reaching values as low as 35.5 °C in actively foraging individuals. T_b was unrelated to metabolic performance or measures of body reserves. Therefore, daytime hypothermia does not result from individuals being unable to maintain T_b during cold spells or to a lack of body reserves. Our data also demonstrated a high level of individual variation in the depth of hypothermia, the causes of which remain to be explored.