Differential recruitment of Dishevelled provides signaling specificity in the planar cell polarity and Wingless signaling pathways

In Drosophila, planar cell polarity (PCP) signaling is mediated by the receptor Frizzled (Fz) and transduced by Dishevelled (Dsh). Wingless (Wg) signaling also requires Dsh and may utilize DFz2 as a receptor. Using a heterologous system, we show that Dsh is recruited selectively to the membrane by Fz but not DFz2, and this recruitment depends on the DEP domain but not the PDZ domain in Dsh. A mutation in the DEP domain impairs both membrane localization and the function of Dsh in PCP signaling, indicating that translocation is important for function. Further genetic and molecular analyses suggest that conserved domains in Dsh function differently during PCP and Wg signaling, and that divergent intracellular pathways are activated. We propose that Dsh has distinct roles in PCP and Wg signaling. The PCP signal may selectively result in focal Fz activation and asymmetric relocalization of Dsh to the membrane, where Dsh effects cytoskeletal reorganization to orient prehair initiation.     

Maintenance and modulation of T cell polarity

As T cells move through the lymphatics and tissues, chemokine receptors, adhesion molecules, costimulatory molecules and antigen receptors engage their ligands in the microenvironment and contribute to establishing and maintaining cell polarity. Cytoskeletal assemblies, surface proteins and vesicle traffic are essential components of polarity and probably stabilize the activity of lymphocytes that must negotiate their 'noisy' environment. An additional component of polarity is a family of polarity proteins in T cells that includes Dlg, Scrib and Lgl, as well as a complex of partitioning-defective proteins. Ultimately, the strength of a T cell response may rely on correct T cell polarization. Therefore, loss of polarity regulators or guidance cues may interfere with T cell activation.     

The role of segment polarity genes during Drosophila neurogenesis

Segment polarity genes in Drosophila are required for the proper formation of epidermal pattern within each segment. Here we show that certain segment polarity genes are also critical for the determination of specific neuronal identities in the developing central nervous system (CNS) of the Drosophila embryo. For several mutants, however, the pattern defects do not simply parallel their cuticular phenotypes. In fused, armadillo, and cubitus interruptus Dominant mutants, much of the CNS appears relatively normal. In hedgehog mutants, the CNS is highly disorganized, but this disruption may occur secondary to the initial events of neurogenesis. The specific cellular defects in patched mutants suggests that this gene specifies a subset of neuroblasts and neural progeny underlying the region of epidermal pattern defect. gooseberry mutants display a complex series of alterations in neuronal identity both underlying and outside of the region of epidermal modification. Neuronal identities of a set of cells along the midline appear to be changed in Cell mutants. The phenotype of wingless mutants is the most restricted and may be due to improper communication between sibling neurons. Thus, in addition to their functions in epidermal pattern formation, at least four of the segment polarity genes (gooseberry, patched, Cell, and wingless) appear to have specific roles in the control of cell fates during neurogenesis.     

Cystic kidney diseases and planar cell polarity signaling

Renal cystic diseases are a major clinical concern as they are the most common genetic cause of end-stage renal disease. While many of the genes causing cystic disease have been identified in recent years, knowing the molecular nature of the mutations has not clarified the mechanisms underlying cyst formation. Recent research in model organisms has suggested that cyst formation may be because of defective planar cell polarity (PCP) and/or ciliary defects. In this review, we first outline the clinical features of renal cystic diseases and then discuss current research linking our understanding of cystic kidney disease to PCP and cilia.     

Sex- and stage-specific reporter gene expression in Plasmodium falciparum

For malaria transmission, Plasmodium parasites must successfully complete gametocytogenesis in the vertebrate host. Differentiation into mature male or female Plasmodium falciparum gametocytes takes 9-12 days as the parasites pass through five distinct morphologic stages (I-V). To evaluate the signals controlling the initiation of stage- and/or sex-specific expression, reporter constructs containing the 5'-flanking regions (FR) of seven genes with distinct expression patterns through gametogenesis were developed. The regulatory information present in the 5'-FR of each selected gene was found to be sufficient to drive appropriate sex- and stage-specific reporter gene expression. The transformed parasite lines also provide in vivo markers to identify gametocytes at specific stages, including a subpopulation of schizonts that express early gametocyte markers.     

Lipid signaling and the modulation of surface charge during phagocytosis

Summary:  Phagocytosis is an important component of innate and adaptive immunity. The formation of phagosomes and the subsequent maturation that capacitates them for pathogen elimination and antigen presentation are complex processes that involve signal transduction, cytoskeletal reorganization, and membrane remodeling. Lipids are increasingly appreciated to play a crucial role in these events. Sphingolipids, cholesterol, and glycerophospholipids, notably the phosphoinositides, are required for the segregation of signaling microdomains and for the generation of second messengers. They are also instrumental in the remodeling of the actin cytoskeleton and in directing membrane traffic. They accomplish these feats by congregating into liquid-ordered domains, by generating active metabolites that activate receptors, and by recruiting and anchoring specific protein ligands to the membrane, often altering their conformation and catalytic activity. A less appreciated role of acidic phospholipids is their contribution to the negative surface charge of the inner leaflet of the plasmalemma. The unique negativity of the inner aspect of the plasma membrane serves to attract and anchor key signaling and effector molecules that are required to initiate phagosome formation. Conversely, the loss of charge that accompanies phospholipid metabolism as phagosomes seal facilitates the dissociation of proteins and the termination of signaling and cytoskeleton assembly. In this manner, lipids provide a binary electrostatic switch to control phagocytosis.     

Redox modulation of insulin signaling and endothelial function

Reactive oxygen and nitrogen species (ROS and RNS) recently emerged as critical signaling molecules in cardiovascular research. Several studies over the past decade have shown that physiological effects of vasoactive factors are mediated by these reactive species and, conversely, that altered redox mechanisms are implicated in the occurrence of metabolic and cardiovascular diseases. Oxidant stress occurs when ROS and/or RNS production exceeds the cell natural antioxidant systems, and pathological events ensue. Cardiovascular risk factors are associated with an imbalance of the redox equilibrium toward oxidative stress, leading to endothelial activation and proinflammatory processes implicated in atherogenesis and metabolic disorders. Recent studies indicate that insulin and insulin-sensitizing drugs activate antiinflammatory pathways that may limit oxidant stress in insulin target tissues. The main goal of this brief review is to discuss recent progress in the field of cellular redox signaling as it pertains to insulin modulation of vascular endothelial function in cardiovascular diseases.     

Redox modulation of cellular metabolism through targeted degradation of signaling proteins by the proteasome

Under conditions of oxidative stress, the 20S proteasome plays a critical role in maintaining cellular homeostasis through the selective degradation of oxidized and damaged proteins. This adaptive stress response is distinct from ubiquitin-dependent pathways in that oxidized proteins are recognized and degraded in an ATP-independent mechanism, which can involve the molecular chaperone Hsp90. Like the regulatory complexes 19S and 11S REG, Hsp90 tightly associates with the 20S proteasome to mediate the recognition of aberrant proteins for degradation. In the case of the calcium signaling protein calmodulin, proteasomal degradation results from the oxidation of a single surface exposed methionine (i.e., Met145); oxidation of the other eight methionines has a minimal effect on the recognition and degradation of calmodulin by the proteasome. Since cellular concentrations of calmodulin are limiting, the targeted degradation of this critical signaling protein under conditions of oxidative stress will result in the downregulation of cellular metabolism, serving as a feedback regulation to diminish the generation of reactive oxygen species. The targeted degradation of critical signaling proteins, such as calmodulin, can function as sensors of oxidative stress to downregulate global rates of metabolism and enhance cellular survival.     

Diversity of immunoglobulin heavy chain gene segment rearrangement in B lymphoblastoid cell lines from X-linked agammaglobulinemia patients

X-linked agammaglobulinemia (XLA) is characterized by an arrest in early B lymphocyte differentiation. Precursor B cells are present in the bone marrow (BM), whereas peripheral blood B cell numbers are severely decreased. A series of Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) was established from peripheral blood of three XLA patients belonging to one pedigree. These BLCL manifested productive VHDJH rearrangements and a random utilization of the VH families. The CDR3 regions of the rearrangements varied in length from 12 to 47 nucleotides and included N regions in all cases. The results supported the conclusion that the few B lymphocytes in peripheral blood of XLA patients exhibit all mechanisms that generate immunoglobulin (Ig) heavy (H) chain diversity. However, no evidence for somatic mutation was found. Within the VH3 family 50% of the expressed VH gene segments belonged to a single subgroup and within the VH4 family a preferential utilization of one VH4 gene element was observed. The utilization of H chain joining (HH) elements was biased to JH4 and JH6 and a high percentage of the CDR3 regions was found to be generated by unconventional mechanisms, such as multiple D usage and the fusion of D elements to D segments with irregular recombination recognition signals. These unique features of the recombined and expressed VHDJH regions in XLA may explain the inability of XLA patients to respond to a variety of antigens. Alternatively, they could be secondary to a B lymphocyte maturation defect in XLA.     

Templated insertions in the rearranged chicken IgL V gene segment arise by intrachromosomal gene conversion

Chickens create a repertoire for their immunoglobulin light-chain gene by a novel process of sequence substitution within a unique rearranged V gene segment (VL1) during B-cell development in the bursa of Fabricius. Sequence analysis has shown that these nucleotide substitutions are not random. Potential donors for observed sequence substitutions are present within the 25 psi VL segments located 5' of the VL1 gene. In this report, we demonstrate that VL1 sequence substitutions: (1) are derived from the psi VL donor segment templates in cis, (2) do not result in reciprocal transfer of VL1 gene sequences to the psi VL segments, and (3) lead to the rapid disappearance of cells with nondiversified rearranged VL1 genes during B-cell development in the bursa of Fabricius. Together, these data provide evidence that VL1 sequence diversity arises as a result of intrachromosomal gene conversion.