Methylmercury sexual dimorphism in the mouse

Summary 5–8 days after a single nontoxic dose of radioactive methylmercury chloride adult male mouse kidneys contain twice as much radioactive mercury per unit wet wt as do kidneys of similarly dosed adult females.This investigation was supported in part by NSF (RANN) grants (GI-30097 and AEN75-14889), by Program Project grant (ES-01248) and Center grant (ES-01247) from the NIEHS, and in part by the US Department of Energy at the University of Rochester Department of Radiation Biology and Biophysics and has been assigned Report No. UR-3490-1308.     

Mutations in the gene encoding the basal body protein RPGRIP1L, a nephrocystin-4 interactor, cause Joubert syndrome

Protein-protein interaction analyses have uncovered a ciliary and basal body protein network that, when disrupted, can result in nephronophthisis (NPHP), Leber congenital amaurosis, Senior-L?ken syndrome (SLSN) or Joubert syndrome (JBTS). However, details of the molecular mechanisms underlying these disorders remain poorly understood. RPGRIP1-like protein (RPGRIP1L) is a homolog of RPGRIP1 (RPGR-interacting protein 1), a ciliary protein defective in Leber congenital amaurosis. We show that RPGRIP1L interacts with nephrocystin-4 and that mutations in the gene encoding nephrocystin-4 (NPHP4) that are known to cause SLSN disrupt this interaction. RPGRIP1L is ubiquitously expressed, and its protein product localizes to basal bodies. Therefore, we analyzed RPGRIP1L as a candidate gene for JBTS and identified loss-of-function mutations in three families with typical JBTS, including the characteristic mid-hindbrain malformation. This work identifies RPGRIP1L as a gene responsible for JBTS and establishes a central role for cilia and basal bodies in the pathophysiology of this disorder.     

The VASE exon downregulates the neurite growth-promoting activity of NCAM 140.

Axonal growth, guidance and synapse formation are controlled by receptors on neuronal growth cones that can recognize positive and inhibitory cues in the local microenvironment. Four well characterized receptor systems are known that recognize the growth-promoting activities associated with the extracellular matrix and the membranes of cells such as astrocytes, muscle cells and Schwann cells; these are the integrins and the homophilically binding cell adhesion molecules neural-cell adhesion molecule (NCAM), N-cadherin and L1 (refs 5-12). Alternative splicing generates 20-30 isoforms of NCAM and these can also be differentially glycosylated. There are two sites where alternative splicing changes the extracellular structure of membrane-bound NCAM and one of these (the MSD1 region) does not obviously affect function. Here we report that the variable alternatively spliced exon (VASE) in immunoglobulin domain 4 downregulates the neurite outgrowth-promoting activity of NCAM. The high level of VASE expression in the adult central as compared with peripheral nervous system could contribute to the poor regenerative capacity of the former.     

The lipid phosphatase SHIP2 controls insulin sensitivity

Insulin is the primary hormone involved in glucose homeostasis, and impairment of insulin action and/or secretion has a critical role in the pathogenesis of diabetes mellitus. Type-II SH2-domain-containing inositol 5-phosphatase, or 'SHIP2', is a member of the inositol polyphosphate 5-phosphatase family. In vitro studies have shown that SHIP2, in response to stimulation by numerous growth factors and insulin, is closely linked to signalling events mediated by both phosphoinositide-3-OH kinase and Ras/mitogen-activated protein kinase. Here we report the generation of mice lacking the SHIP2 gene. Loss of SHIP2 leads to increased sensitivity to insulin, which is characterized by severe neonatal hypoglycaemia, deregulated expression of the genes involved in gluconeogenesis, and perinatal death. Adult mice that are heterozygous for the SHIP2 mutation have increased glucose tolerance and insulin sensitivity associated with an increased recruitment of the GLUT4 glucose transporter and increased glycogen synthesis in skeletal muscles. Our results show that SHIP2 is a potent negative regulator of insulin signalling and insulin sensitivity in vivo.     

A threshold effect of the major isoforms of NCAM on neurite outgrowth

Interactions between recognition molecules on the surface of neuronal growth cones and guidance cues present in the local cellular environment are thought to account for the growth of neurites in the highly stereospecific manner that contributes to correct target cell innervation. In vitro assays have been used to identify candidate molecular components of this system, either directly by demonstrating their ability to promote neurite outgrowth, or indirectly by the ability of specific antibodies to inhibit neurite outgrowth. The role of the neural cell adhesion molecule (NCAM) in pathway finding is not fully understood. Some immunological studies support a positive role; others do not, and it has been reported that purified NCAM does not support neurite outgrowth. We have previously shown that an arbitrary biochemical index of neurite outgrowth, the relative level of immunoreactive neurofilament protein, is increased when human and rat dorsal root ganglion neurons are cultured on monolayers of cells expressing transfected human NCAM. But, the complexity of growth precluded a simple morphological analysis and we did not determine the 'dose-response' relationship between NCAM expression and neuronal response. Here, we report on the morphology of rat cerebellar neurons cultured on monolayers of 3T3 cells transfected with complementary DNAs encoding all of the main NCAM isoforms found in cells such as astrocytes, Schwann cells and skeletal muscle. The data indicate that both transmembrane and glycosyl-phosphatidylinositol linked NCAM isoforms are potent substrates for neurite extension. A critical threshold value of NCAM expression is required for increased neurite outgrowth. Above this threshold, small increases in NCAM induce substantial increases in neurite outgrowth.     

A human natural killer cell subset provides an innate source of IL-22 for mucosal immunity

Natural killer (NK) cells are classically viewed as lymphocytes that provide innate surveillance against virally infected cells and tumour cells through the release of cytolytic mediators and interferon (IFN)-gamma. In humans, blood CD56(dim) NK cells specialize in the lysis of cell targets. In the lymph nodes, CD56(bright) NK cells secrete IFN-gamma cooperating with dendritic cells and T cells in the generation of adaptive responses. Here we report the characterization of a human NK cell subset located in mucosa-associated lymphoid tissues, such as tonsils and Peyer's patches, which is hard-wired to secrete interleukin (IL)-22, IL-26 and leukaemia inhibitory factor. These NK cells, which we refer to as NK-22 cells, are triggered by acute exposure to IL-23. In vitro, NK-22-secreted cytokines stimulate epithelial cells to secrete IL-10, proliferate and express a variety of mitogenic and anti-apoptotic molecules. NK-22 cells are also found in mouse mucosa-associated lymphoid tissues and appear in the small intestine lamina propria during bacterial infection, suggesting that NK-22 cells provide an innate source of IL-22 that may help constrain inflammation and protect mucosal sites.     

CEP41 is mutated in Joubert syndrome and is required for tubulin glutamylation at the cilium

Tubulin glutamylation is a post-translational modification that occurs predominantly in the ciliary axoneme and has been suggested to be important for ciliary function. However, its relationship to disorders of the primary cilium, termed ciliopathies, has not been explored. Here we mapped a new locus for Joubert syndrome (JBTS), which we have designated as JBTS15, and identified causative mutations in CEP41, which encodes a 41-kDa centrosomal protein. We show that CEP41 is localized to the basal body and primary cilia, and regulates ciliary entry of TTLL6, an evolutionarily conserved polyglutamylase enzyme. Depletion of CEP41 causes ciliopathy-related phenotypes in zebrafish and mice and results in glutamylation defects in the ciliary axoneme. Our data identify CEP41 mutations as a cause of JBTS and implicate tubulin post-translational modification in the pathogenesis of human ciliary dysfunction.