A tissue-specific knockout reveals that Gata1 is not essential for Sertoli cell function in the mouse

The transcription factor Gata1 is essential for the development of erythroid cells. Consequently, Gata1 null mutants die in utero due to severe anaemia. Outside the haematopoietic system, Gata1 is only expressed in the Sertoli cells of the testis. To elucidate the function of Gata1 in the testis, we made a Sertoli cell-specific knockout of the Gata1 gene in the mouse. We deleted a normally functioning 'floxed' Gata1 gene in pre-Sertoli cells in vivo through the expression of Cre from a transgene driven by the Desert Hedgehog promoter. Surprisingly, Gata1 null testes developed to be morphologically normal, spermatogenesis was not obviously affected and expression levels of putative Gata1 target genes, and other Gata factors, were not altered. We conclude that expression of Gata1 in Sertoli cells is not essential for testis development or spermatogenesis in the mouse

Dynamin 2 mutations in Charcot-Marie-Tooth neuropathy highlight the importance of clathrin-mediated endocytosis in myelination

Mutations in dynamin 2 (DNM2) lead to dominant intermediate Charcot-Marie-Tooth neuropathy type B, while a different set of DNM2 mutations cause autosomal dominant centronuclear myopathy. In this study, we aimed to elucidate the disease mechanisms in dominant intermediate Charcot-Marie-Tooth neuropathy type B and to find explanations for the tissue-specific defects that are associated with different DNM2 mutations in dominant intermediate Charcot-Marie-Tooth neuropathy type B versus autosomal dominant centronuclear myopathy. We used tissue derived from Dnm2-deficient mice to establish an appropriate peripheral nerve model and found that dominant intermediate Charcot-Marie-Tooth neuropathy type B-associated dynamin 2 mutants, but not autosomal dominant centronuclear myopathy mutants, impaired myelination. In contrast to autosomal dominant centronuclear myopathy mutants, Schwann cells and neurons from the peripheral nervous system expressing dominant intermediate Charcot-Marie-Tooth neuropathy mutants showed defects in clathrin-mediated endocytosis. We demonstrate that, as a consequence, protein surface levels are altered in Schwann cells. Furthermore, we discovered that myelination is strictly dependent on Dnm2 and clathrin-mediated endocytosis function. Thus, we propose that altered endocytosis is a major contributing factor to the disease mechanisms in dominant intermediate Charcot-Marie-Tooth neuropathy type

Zeb2 is essential for Schwann cell differentiation, myelination and nerve repair

Schwann cell development and peripheral nerve myelination require the serial expression of transcriptional activators, such as Sox10, Oct6 (also called Scip or Pou3f1) and Krox20 (also called Egr2). Here we show that transcriptional repression, mediated by the zinc-finger protein Zeb2 (also known as Sip1), is essential for differentiation and myelination. Mice lacking Zeb2 in Schwann cells develop a severe peripheral neuropathy, caused by failure of axonal sorting and virtual absence of myelin membranes. Zeb2-deficient Schwann cells continuously express repressors of lineage progression. Moreover, genes for negative regulators of maturation such as Sox2 and Ednrb emerge as Zeb2 target genes, supporting its function as an inhibitor of inhibitors in myelination control. When Zeb2 is deleted in adult mice, Schwann cells readily dedifferentiate following peripheral nerve injury and become repair cells. However, nerve regeneration and remyelination are both perturbed, demonstrating that Zeb2, although undetectable in adult Schwann cells, has a latent function throughout life

LGI3/2-ADAM23 interactions cluster Kv1 channels in myelinated axons to regulate refractory period

Along myelinated axons, Shaker-type potassium channels (Kv1) accumulate at high density in the juxtaparanodal region, directly adjacent to the paranodal axon-glia junctions that flank the nodes of Ranvier. However, the mechanisms that control the clustering of Kv1 channels, as well as their function at this site, are still poorly understood. Here we demonstrate that axonal ADAM23 is essential for both the accumulation and stability of juxtaparanodal Kv1 complexes. The function of ADAM23 is critically dependent on its interaction with its extracellular ligands LGI2 and LGI3. Furthermore, we demonstrate that juxtaparanodal Kv1 complexes affect the refractory period, thus enabling high-frequency burst firing of action potentials. Our findings not only reveal a previously unknown molecular pathway that regulates Kv1 channel clustering, but they also demonstrate that the juxtaparanodal Kv1 channels that are concealed below the myelin sheath, play a significant role in modifying axonal physiology

HDAC1 and HDAC2 control the transcriptional program of myelination and the survival of Schwann cells

Histone deacetylases (HDACs) are major epigenetic regulators. We show that HDAC1 and HDAC2 functions are critical for myelination of the peripheral nervous system. Using mouse genetics, we have ablated Hdac1 and Hdac2 specifically in Schwann cells, resulting in massive Schwann cell loss and virtual absence of myelin in mutant sciatic nerves. Expression of Sox10 and Krox20, the main transcriptional regulators of Schwann cell myelination, was greatly reduced. We demonstrate that in Schwann cells, HDAC1 and HDAC2 exert specific primary functions: HDAC2 activates the transcriptional program of myelination in synergy with Sox10, whereas HDAC1 controls Schwann cell survival by regulating the levels of active beta-catenin

Chemical corrector treatment ameliorates increased seizure susceptibility in a mouse model of familial epilepsy

Epilepsy is one of the most common and intractable brain disorders. Mutations in the human gene LGI1, encoding a neuronal secreted protein, cause autosomal dominant lateral temporal lobe epilepsy (ADLTE). However, the pathogenic mechanisms of LGI1 mutations remain unclear. We classified 22 reported LGI1 missense mutations as either secretion defective or secretion competent, and we generated and analyzed two mouse models of ADLTE encoding mutant proteins representative of the two groups. The secretion-defective LGI1(E383A) protein was recognized by the ER quality-control machinery and prematurely degraded, whereas the secretable LGI1(S473L) protein abnormally dimerized and was selectively defective in binding to one of its receptors, ADAM22. Both mutations caused a loss of function, compromising intracellular trafficking or ligand activity of LGI1 and converging on reduced synaptic LGI1-ADAM22 interaction. A chemical corrector, 4-phenylbutyrate (4PBA), restored LGI1(E383A) folding and binding to ADAM22 and ameliorated the increased seizure susceptibility of the LGI 1(E383A) model mice. This study establishes LGI1-related epilepsy as a conformational disease and suggests new therapeutic options for human epilepsy

Novel Foxo1-dependent transcriptional programs control T-reg cell function

Regulatory T (T-reg) cells, characterized by expression of the transcription factor forkhead box P3 (Foxp3), maintain immune homeostasis by suppressing self-destructive immune responses(1-4). Foxp3 operates as a late-acting differentiation factor controlling T-reg cell homeostasis and function(5), whereas the early T-reg-cell-lineage commitment is regulated by the Akt kinase and the forkhead box O (Foxo) family of transcription factors(6-10). However, whether Foxo proteins act beyond the T-reg-cell-commitment stage to control T-reg cell homeostasis and function remains largely unexplored. Here we show that Foxo1 is a pivotal regulator of T-reg cell function. T-reg cells express high amounts of Foxo1 and display reduced T-cell-receptor-induced Akt activation, Foxo1 phosphorylation and Foxo1 nuclear exclusion. Mice with T-reg-cell-specific deletion of Foxo1 develop a fatal inflammatory disorder similar in severity to that seen in Foxp3-deficient mice, but without the loss of T-reg cells. Genome-wide analysis of Foxo1 binding sites reveals similar to 300 Foxo1-bound target genes, including the pro-inflammatory cytokine Ifng, that do not seem to be directly regulated by Foxp3. These findings show that the evolutionarily ancient Akt-Foxo1 signalling module controls a novel genetic program indispensable for T-reg cell function

Dicer in Schwann cells is required for myelination and axonal integrity

Dicer is responsible for the generation of mature micro-RNAs (miRNAs) and loading them into RNA-induced silencing complex (RISC). RISC functions as a probe that targets mRNAs leading to translational suppression and mRNA degradation. Schwann cells (SCs) in the peripheral nervous system undergo remarkable differentiation both in morphology and gene expression patterns throughout lineage progression to myelinating and nonmyelinating phenotypes. Gene expression in SCs is particularly tightly regulated and critical for the organism, as highlighted by the fact that a 50% decrease or an increase to 150% of normal gene expression of some myelin proteins, like PMP22, results in peripheral neuropathies. Here, we selectively deleted Dicer and consequently gene expression regulation by mature miRNAs from Mus musculus SCs. Our results show that in the absence of Dicer, most SCs arrest at the promyelinating stage and fail to start forming myelin. At the molecular level, the promyelinating transcription factor Krox20 and several myelin proteins [including myelin associated glycoprotein (MAG) and PMP22] were strongly reduced in mutant sciatic nerves. In contrast, the myelination inhibitors SOX2, Notch1, and Hes1 were increased, providing an additional potential basis for impaired myelination. A minor fraction of SCs, with some peculiar differences between sensory and motor fibers, overcame the myelination block and formed unusually thin myelin, in line with observed impaired neuregulin and AKT signaling. Surprisingly, we also found signs of axonal degeneration in Dicer mutant mice. Thus, our data indicate that miRNAs critically regulate Schwann cell gene expression that is required for myelination and to maintain axons via axon- glia interactions. Copyrigh