Diet effects on female reproduction in high growth (hg/hg) mice that are deficient in the Socs-2 gene

The detrimental effect of larger body size on reproductive performance has been well documented in mouse models of overgrowth, such as Growth Hormone (GH) transgenics. This study describes the reproductive performance of the High Growth (HG) mouse model of overgrowth. The HG mouse model exhibits overgrowth due to a partially recessive autosomal mutation that increases growth rate and mature body size. The HG phenotype results from the lack of expression of Socs-2, which negatively regulates GH signaling. C57BL/6J (C57) and congenic C57BL/6J-hg/hg (HG) female mice were fed four diets differing in protein and energy content, starting at 8 weeks of age. A complete reproductive cycle from mating to weaning was evaluated. HG mice were 40% larger than C57 and had a higher feed intake throughout the experiment. Significant genotype x diet interactions were detected for growth, body composition and reproductive traits. HG females showed poor reproductive performance compared to controls as demonstrated by their lower fertility during mating, which was not overcome by changes in the diet. No differences were detected in litter size, but HG animals exhibited a longer gestation length and heavier pup weaning weights compared to controls. Reproductive impairment in HG seems to be the consequence of the lack of Socs-2 independent of the effects of increased body size on reproduction.     

Sema4C-Plexin B2 signalling modulates ureteric branching in developing kidney

Semaphorins, originally identified as axon guidance molecules, have also been implicated in angiogenesis, function of the immune system and cancerous growth. Here we show that deletion of Plexin B2 (Plxnb2), a semaphorin receptor that is expressed both in the pretubular aggregates and the ureteric epithelium in the developing kidney, results in renal hypoplasia and occasional double ureters. The rate of cell proliferation in the ureteric epithelium and consequently the number of ureteric tips are reduced in the kidneys lacking Plexin B2 (Plxnb2-/-). Semaphorin 4C, a ligand for Plexin B2, stimulates branching of the ureteric epithelium in wild type and Plxnb2+/- kidney explants, but not in Plxnb2-/- explants. As shown by co-immunoprecipitation Plexin B2 interacts with the Ret receptor tyrosine kinase, the receptor of Glial-cell-line-derived neurotrophic factor (Gdnf), in embryonic kidneys. Isolated Plxnb2-/- ureteric buds fail to respond to Gdnf by branching, but this response is rescued by Fibroblast growth factor 7 and Follistatin as well as by the metanephric mesenchyme. The differentiation of the nephrogenic mesenchyme, its morphology and the rate of apoptosis in the Plxnb2-/- kidneys are normal. Plexin B2 is co-expressed with Plexin B1 (Plxnb1) in the kidney. The double homozygous Plxnb1-Plxnb2-deficient mice show high embryonic lethality prior to onset of nephrogenesis. The only double homozygous embryo surviving to E12 showed hypoplastic kidneys with ureteric branches and differentiating mesenchyme. Taken together, our results show that Sema4C-Plexin B2 signalling regulates ureteric branching, possibly through modulation of Gdnf signalling by interaction with Ret, and suggest non-redundant roles for Plexin B1 and Plexin B2 in kidney development.     

Socs-1 inhibits TEL-JAK2-mediated transformation of hematopoietic cells through inhibition of JAK2 kinase activity and induction of proteasome-mediated degradation

TEL-JAK2 fusion proteins, which are a result of t(9;12)(p24;p13) translocations associated with human leukemia, activate Stat5 in vitro and in vivo and cause a myelo- and lymphoproliferative disease in a murine bone marrow transplant model. We report that Socs-1, a member of the SOCS family of endogenous inhibitors of JAKs and STATs, inhibits transformation of Ba/F3 cells by TEL-JAK2 but has no effect on Ba/F3 cells transformed by BCR-ABL, TEL-ABL, or TEL-platelet-derived growth factor receptor beta. TEL-JAK2, in addition to activating Stat5, associates with Shc and Grb2 and induces activation of Erk2, and expression of Socs-1 inhibits engagement of each of these signaling molecules. TEL-JAK2 kinase activity is inhibited by Socs-1, as assessed by in vitro kinase assays. In addition, Socs-1 induces proteasomal degradation of TEL-JAK2. Mutational analysis indicates that the SOCS box of Socs-1 is required for proteasomal degradation and for abrogation of growth of TEL-JAK2-transformed cells. Furthermore, murine bone marrow transplant assays demonstrate that expression of Socs-1 prolongs latency of TEL-JAK2-mediated disease in vivo. Collectively, these data indicate that Socs-1 inhibits TEL-JAK2 in vitro and in vivo through inhibition of kinase activity and induction of TEL-JAK2 protein degradation.     

Drosophila Plexin B is a Sema-2a receptor required for axon guidance

Plexin receptors play a crucial role in the transduction of axonal guidance events elicited by semaphorin proteins. In Drosophila, Plexin A (PlexA) is a receptor for the transmembrane semaphorin semaphorin-1a (Sema-1a) and is required for motor and central nervous system (CNS) axon guidance in the developing embryonic nervous system. However, it remains unknown how PlexB functions during neural development and which ligands serve to activate this receptor. Here, we show that plexB, like plexA, is robustly expressed in the developing CNS and is required for motor and CNS axon pathfinding. PlexB and PlexA serve both distinct and shared neuronal guidance functions. We observe a physical association between these two plexin receptors in vivo and find that they can utilize common downstream signaling mechanisms. PlexB does not directly bind to the cytosolic semaphorin signaling component MICAL (molecule that interacts with CasL), but requires MICAL for certain axonal guidance functions. Ligand binding and genetic analyses demonstrate that PlexB is a receptor for the secreted semaphorin Sema-2a, suggesting that secreted and transmembrane semaphorins in Drosophila use PlexB and PlexA, respectively, for axon pathfinding during neural development. These results establish roles for PlexB in central and peripheral axon pathfinding, define a functional ligand for PlexB, and implicate common signaling events in plexin-mediated axonal guidance.     

New Eukaryotic Semaphorins with Close Homology to Semaphorins of DNA Viruses

Semaphorins were initially described as a family of repulsive guidance molecules in embryonal development. Their basic structure consists of an N-terminal signal sequence, the defining semaphorin domain ofapproximately 500 amino acids, an Ig-like domain,and a variable carboxy-terminus. We recently described a viral semaphorin homologue encoded by the alcelaphine herpesvirus type 1. Less conserved, truncated homologues were also identified in poxviruses. Here we describe new human and murine semaphorin homologues. The respective genes were cloned and sequenced, and they were termed H-Sema-L and M-Sema-L (HGMW-approved symbols SEMAL and Semal, respectively). A multiply spliced mRNA of 3.2 kb is expressed in human placenta, spleen, thymus, and gonadal tissue. H-Sema-L maps to chromosome 15q22.3–q23 and M-Sema-L to the homologous locus 9A3.3-B in the mouse genome. The expression patterns and the presence of related genes in large DNA viruses suggest that this new semaphorin has a relevant function in the immune system.     

The vesicular SNARE Synaptobrevin is required for Semaphorin 3A axonal repulsion

Attractive and repulsive molecules such as Semaphorins (Sema) trigger rapid responses that control the navigation of axonal growth cones. The role of vesicular traffic in axonal guidance is still largely unknown. The exocytic vesicular soluble N-ethylmaleimide sensitive fusion protein attachment protein receptor (SNARE) Synaptobrevin 2 (Syb2) is known for mediating neurotransmitter release in mature neurons, but its potential role in axonal guidance remains elusive. Here we show that Syb2 is required for Sema3A-dependent repulsion but not Sema3C-dependent attraction in cultured neurons and in the mouse brain. Syb2 associated with Neuropilin 1 and Plexin A1, two essential components of the Sema3A receptor, via its juxtatransmembrane domain. Sema3A receptor and Syb2 colocalize in endosomal membranes. Moreover, upon Sema3A treatment, Syb2-deficient neurons failed to collapse and transport Plexin A1 to cell bodies. Reconstitution of Sema3A receptor in nonneuronal cells revealed that Sema3A further inhibited the exocytosis of Syb2. Therefore, Sema3A-mediated signaling and axonal repulsion require Syb2-dependent vesicular traffic.     

Analysis of zebrafish sidetracked mutants reveals a novel role for Plexin A3 in intraspinal motor axon guidance

One of the earliest guidance decisions for spinal cord motoneurons occurs when pools of motoneurons orient their growth cones towards a common, segmental exit point. In contrast to later events, remarkably little is known about the molecular mechanisms underlying intraspinal motor axon guidance. In zebrafish sidetracked (set) mutants, motor axons exit from the spinal cord at ectopic positions. By single-cell labeling and time-lapse analysis we show that motoneurons with cell bodies adjacent to the segmental exit point properly exit from the spinal cord, whereas those farther away display pathfinding errors. Misguided growth cones either orient away from the endogenous exit point, extend towards the endogenous exit point but bypass it or exit at non-segmental, ectopic locations. Furthermore, we show that sidetracked acts cell autonomously in motoneurons. Positional cloning reveals that sidetracked encodes Plexin A3, a semaphorin guidance receptor for repulsive guidance. Finally, we show that sidetracked (plexin A3) plays an additional role in motor axonal morphogenesis. Together, our data genetically identify the first guidance receptor required for intraspinal migration of pioneering motor axons and implicate the well-described semaphorin/plexin signaling pathway in this poorly understood process. We propose that axonal repulsion via Plexin A3 is a major driving force for intraspinal motor growth cone guidance.     

Proteomics computational analyses suggest that the carboxyl terminal glycoproteins of Bunyaviruses are class II viral fusion protein (beta-penetrenes)

The Bunyaviridae family of enveloped RNA viruses includes five genuses, orthobunyaviruses, hantaviruses, phleboviruses, nairoviruses and tospoviruses. It has not been determined which Bunyavirus protein mediates virion:cell membrane fusion. Class II viral fusion proteins (beta-penetrenes), encoded by members of the Alphaviridae and Flaviviridae, are comprised of three antiparallel beta sheet domains with an internal fusion peptide located at the end of domain II. Proteomics computational analyses indicate that the carboxyl terminal glycoprotein (Gc) encoded by Sandfly fever virus (SAN), a phlebovirus, has a significant amino acid sequence similarity with envelope protein 1 (E1), the class II fusion protein of Sindbis virus (SIN), an Alphavirus. Similar sequences and common structural/functional motifs, including domains with a high propensity to interface with bilayer membranes, are located collinearly in SAN Gc and SIN E1. Gc encoded by members of each Bunyavirus genus share several sequence and structural motifs. These results suggest that Gc of Bunyaviridae, and similar proteins of Tenuiviruses and a group of Caenorhabditis elegans retroviruses, are class II viral fusion proteins. Comparisons of divergent viral fusion proteins can reveal features essential for virion:cell fusion, and suggest drug and vaccine strategies.     

Molecular characterization of a bacteriophage (Chp2) from Chlamydia psittaci

Comparisons of the proteome of abortifacient Chlamydia psittaci isolates from sheep by two-dimensional gel electrophoresis identified a novel abundant protein with a molecular mass of 61.4 kDa and an isoelectric point of 6.41. C-terminal sequence analysis of this protein yielded a short peptide sequence that had an identical match to the viral coat protein (VP1) of the avian chlamydiaphage Chp1. Electron microscope studies revealed the presence of a 25-nm-diameter bacteriophage (Chp2) with no apparent spike structures. Thin sections of chlamydia-infected cells showed that Chp2 particles were located to membranous structures surrounding reticulate bodies (RBs), suggesting that Chp2 is cytopathic for ovine C. psittaci RBs. Chp2 double-stranded circular replicative-form DNA was purified and used as a template for DNA sequence analysis. The Chp2 genome is 4,567 bp and encodes up to eight open reading frames (ORFs); it is similar in overall organization to the Chp1 genome. Seven of the ORFs (1 to 5, 7, and 8) have sequence homologies with Chp1. However, ORF 6 has a different spatial location and no cognate partner within the Chp1 genome. Chlamydiaphages have three viral structural proteins, VP1, VP2, and VP3, encoded by ORFs 1 to 3, respectively. Amino acid residues in the phiX174 procapsid known to mediate interactions between the viral coat protein and internal scaffolding proteins are conserved in the Chp2 VP1 and VP3 proteins. We suggest that VP3 performs a scaffolding-like function but has evolved into a structural protein.     

Plexin‐B1 is a GTPase activating protein for M‐Ras,remodelling dendrite morphology

Plexins are receptors for axonal guidance molecules known as semaphorins. We recently reported that the semaphorin 4D (Sema4D) receptor, Plexin‐B1, induces axonal growth cone collapse by functioning as an R‐Ras GTPase activating protein (GAP). Here, we report that Plexin‐B1 shows GAP activity for M‐Ras, another member of the Ras family of GTPases. In cortical neurons, the expression of M‐Ras was upregulated during dendritic development. Knockdown of endogenous M‐Ras—but not R‐Ras—reduced dendritic outgrowth and branching, whereas overexpression of constitutively active M‐Ras, M‐Ras(Q71L), enhanced dendritic outgrowth and branching. Sema4D suppressed M‐Ras activity and reduced dendritic outgrowth and branching, but this reduction was blocked by M‐Ras(Q71L). M‐Ras(Q71L) stimulated extracellular signal‐regulated kinase (ERK) activation, inducing dendrite growth, whereas Sema4D suppressed ERK activity and down‐regulation of ERK was required for a Sema4D‐induced reduction of dendrite growth. Thus, we conclude that Plexin‐B1 is a dual functional GAP for R‐Ras and M‐Ras, remodelling axon and dendrite morphology, respectively.