Microglia-mediated demyelination protects against CD8+ T cell-driven axon degeneration in mice carrying PLP defects.

Axon degeneration and functional decline in myelin diseases are often attributed to loss of myelin but their relation is not fully understood. Perturbed myelinating glia can instigate chronic neuroinflammation and contribute to demyelination and axonal damage. Here we study mice with distinct defects in the proteolipid protein 1 gene that develop axonal damage which is driven by cytotoxic T cells targeting myelinating oligodendrocytes. We show that persistent ensheathment with perturbed myelin poses a risk for axon degeneration, neuron loss, and behavioral decline. We demonstrate that CD8+ T cell-driven axonal damage is less likely to progress towards degeneration when axons are efficiently demyelinated by activated microglia. Mechanistically, we show that cytotoxic T cell effector molecules induce cytoskeletal alterations within myelinating glia and aberrant actomyosin constriction of axons at paranodal domains. Our study identifies detrimental axon-glia-immune interactions which promote neurodegeneration and possible therapeutic targets for disorders associated with myelin defects and neuroinflammation.

Developmental control of nuclear size and shape by Kugelkern and Kurzkern.

BACKGROUND: The shape of a nucleus depends on the nuclear lamina, which is tightly associated with the inner nuclear membrane and on the interaction with the cytoskeleton. However, the mechanism connecting the differentiation state of a cell to the shape changes of its nucleus are not well understood. We investigated this question in early Drosophila embryos, where the nuclear shape changes from spherical to ellipsoidal together with a 2.5-fold increase in nuclear length during cellularization. RESULTS: We identified two genes, kugelkern and kurzkern, required for nuclear elongation. In kugelkern- and kurzkern-depleted embryos, the nuclei reach only half the length of the wild-type nuclei at the end of cellularization. The reduced nuclear size affects chromocenter formation as marked by Heterochromatin protein 1 and expression of a specific set of genes, including early zygotic genes. kugelkern contains a putative coiled-coil domain in the N-terminal half of the protein, a nuclear localization signal (NLS), and a C-terminal CxxM-motif. The carboxyterminal CxxM motif is required for the targeting of Kugelkern to the inner nuclear membrane, where it colocalizes with lamins. Depending on the farnesylation motif, expression of kugelkern in Drosophila embryos or Xenopus cells induces overproliferation of nuclear membrane. CONCLUSIONS: Kugelkern is so far the first nuclear protein, except for lamins, that contains a farnesylation site. Our findings suggest that Kugelkern is a rate-determining factor for nuclear size increase. We propose that association of farnesylated Kugelkern with the inner nuclear membrane induces expansion of nuclear surface area, allowing nuclear growth.

The Drosophila melanogaster LEM-domain protein MAN1.

Here we describe the Drosophila melanogaster LEM-domain protein encoded by the annotated gene CG3167 which is the putative ortholog to vertebrate MAN1. MAN1 of Drosophila (dMAN1) and vertebrates have the following properties in common. Firstly, both molecules are integral membrane proteins of the inner nuclear membrane (INM) and share the same structural organization comprising an N-terminally located LEM motif, two transmembrane domains in the middle of the molecule, and a conserved RNA recognition motif in the C-terminal region. Secondly, dMAN1 has similar targeting domains as it has been reported for the human protein. Thirdly, immunoprecipitations with dMAN1-specific antibodies revealed that this Drosophila LEM-domain protein is contained in protein complexes together with lamins Dm0 and C. It has been previously shown that human MAN1 binds to A- and B-type lamins in vitro. During embryogenesis and early larval development LEM-domain proteins dMAN1 and otefin show the same expression pattern and are much more abundant in eggs and the first larval instar than in later larval stages and young pupae whereas the LEM-domain protein Bocksbeutel is uniformly expressed in all developmental stages. dMAN1 is detectable in the nuclear envelope of embryonic cells including the pole cells. In mitotic cells of embryos at metaphase and anaphase, LEM-domain proteins dMAN1, otefin and Bocksbeutel were predominantly localized in the region of the two spindle poles whereas the lamin B receptor and lamin Dm0 were more homogeneously distributed. Downregulation of dMAN1 by RNA interference (RNAi) in Drosophila cultured Kc167 cells has no obvious effect on nuclear architecture, viability of RNAi-treated cells and the intracellular distribution of the LEM-domain proteins Bocksbeutel and otefin. In contrast, the localization of dMAN1, Bocksbeutel and otefin at the INM is supported by lamin Dm0. We conclude that the dMAN1 protein is not a limiting component of the nuclear architecture in Drosophila cultured cells.

A polymorphism in the human cytotoxic T-lymphocyte antigen 4 ( CTLA4) gene (exon 1 +49) alters T-cell activation.

The cytotoxic T-lymphocyte antigen 4 (CTLA4) is an important modifier of T-cell activation with down-regulatory properties upon B7 engagement. An allelic polymorphism in exon 1 of the CTLA4 gene coding for the peptide leader sequence of CTLA4 was recently described. This polymorphism was detected in association with several autoimmune diseases. In this study, we investigated the functional impact of the CTLA4 exon 1 +49 A/G dimorphism on T-cell activation and cellular localization. We examined the T-cell response from healthy donors either homozygous for A or G at position +49 of the exon 1. Under suboptimal stimulation conditions we found a greater proliferative response of cells from donors homozygous for G at position +49. FACS analysis of CTLA4 expression revealed a reduced up-regulation of CTLA4 from G/G donors upon T-cell activation, if compared with wild-type cells. Intracellular CTLA4 distribution demonstrated qualitatively different staining patterns between the two genotypes as determined using confocal fluorescence microscopy. Our results suggest that the G allele at position +49 of exon 1 affects the CTLA4-driven down-regulation of T-cell activation and may be an important factor in the pathogenesis of autoimmune diseases.