Oligodendrocyte Nf1 Controls Aberrant Notch Activation and Regulates Myelin Structure and Behavior

The RASopathy neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant genetic disorders. In NF1 patients, neurological issues may result from damaged myelin, and mice with a neurofibromin gene (Nf1) mutation show white matter (WM) defects including myelin decompaction. Using mouse genetics, we find that altered Nf1 gene-dose in mature oligodendrocytes results in progressive myelin defects and behavioral abnormalities mediated by aberrant Notch activation. Blocking Notch, upstream mitogen-activated protein kinase (MAPK), or nitric oxide signaling rescues myelin defects in hemizygous Nf1 mutants, and pharmacological gamma secretase inhibition rescues aberrant behavior with no effects in wild-type (WT) mice. Concomitant pathway inhibition rescues myelin abnormalities in homozygous mutants. Notch activation is also observed in Nf1+/− mouse brains, and cells containing active Notch are increased in NF1 patient WM. We thus identify Notch as an Nf1 effector regulating myelin structure and behavior in a RASopathy and suggest that inhibition of Notch signaling may be a therapeutic strategy for NF1

Human Dendritic Cell Activity against Histoplasma capsulatum Is Mediated via Phagolysosomal Fusion

Histoplasma capsulatum is a fungal pathogen that requires the induction of cell-mediated immunity (CMI) for host survival. We have demonstrated that human dendritic cells (DC) phagocytose H. capsulatum yeasts and, unlike human macrophages (Mø) that are permissive for intracellular growth, DC killed and degraded the fungus. In the present study, we sought to determine whether the mechanism(s) by which DC kill Histoplasma is via lysosomal hydrolases, via the production of toxic oxygen metabolites, or both. Phagosome-lysosome fusion (PL-fusion) was quantified by using fluorescein isothiocyanate-dextran and phase and fluorescence microscopy and by electron microscopy with horseradish peroxidase colloidal gold to label lysosomes. Unlike Mφ, Histoplasma-infected DC exhibited marked PL-fusion. The addition of suramin to Histoplasma-infected DC inhibited PL-fusion and DC fungicidal activity. Incubation of Histoplasma-infected DC at 18°C also concomitantly reduced PL-fusion and decreased the capacity of DC to kill and degrade H. capsulatum yeasts. Further, culture of Histoplasma-infected DC in the presence of bafilomycin, an inhibitor of the vacuolar ATPase, did not block DC anti-Histoplasma activity, indicating that phagosome acidification was not required for lysosome enzyme activity. In contrast, culture of Histoplasma-infected DC in the presence of inhibitors of the respiratory burst or inhibitors of NO synthase had little to no effect on DC fungicidal activity. These data suggest that the major mechanism by which human DC mediate anti-Histoplasma activity is through the exposure of yeasts to DC lysosomal hydrolases. Thus, DC can override one of the strategies used by H. capsulatum yeasts to survive intracellularly within Mø

Synapse Formation in Monosynaptic Sensory–Motor Connections Is Regulated by Presynaptic Rho GTPase Cdc42

Spinal reflex circuit development requires the precise regulation of axon trajectories, synaptic specificity, and synapse formation. Of these three crucial steps, the molecular mechanisms underlying synapse formation between group Ia proprioceptive sensory neurons and motor neurons is the least understood. Here, we show that the Rho GTPase Cdc42 controls synapse formation in monosynaptic sensory–motor connections in presynaptic, but not postsynaptic, neurons. In mice lacking Cdc42 in presynaptic sensory neurons, proprioceptive sensory axons appropriately reach the ventral spinal cord, but significantly fewer synapses are formed with motor neurons compared with wild-type mice. Concordantly, electrophysiological analyses show diminished EPSP amplitudes in monosynaptic sensory–motor circuits in these mutants. Temporally targeted deletion of Cdc42 in sensory neurons after sensory–motor circuit establishment reveals that Cdc42 does not affect synaptic transmission. Furthermore, addition of the synaptic organizers, neuroligins, induces presynaptic differentiation of wild-type, but not Cdc42-deficient, proprioceptive sensory neurons in vitro. Together, our findings demonstrate that Cdc42 in presynaptic neurons is required for synapse formation in monosynaptic sensory–motor circuits

Perinatal or Adult \u3cem\u3eNf1\u3c/em\u3e Inactivation using Tamoxifen-inducible PlpCre Each Cause Neurofibroma Formation

OBJECTIVES Neurofibromas are tumors initiated by biallelic mutation of the NF1 tumor suppressor gene in the Schwann cell lineage. One idea within the field suggests that Nf1loss must occur within progenitor cells present within a critical window during Schwann cell development in order for neurofibromas to form. To test this hypothesis and to examine whethermyelinating Schwann cells can serve as aneurofibroma cell of origin, Nf1 loss was induced at perinatal or adult timepoints using a tamoxifen-inducible Plp-CreERT driver. RESULTS Perinatal loss of Nf1 resulted in small neurofibromas late in life, while adult loss caused large neurofibromas and morbidity beginning 4 months after onset of Nf1loss. PLP-CreERT recombination (EGFP+ cells) occurred in: satellite cells, S100β+ myelinating Schwann cells, and p75+ cells. Plp-CreERTnerves and neurofibromas contained cells with Remak bundle disruption; however, no recombination within GFAP+ non-myelinating Schwann cells was identified. Extramedullarylympho-hematopoietic expansion that contained EGFP+/Sca-1+ stromal cells amongst EGFP-negative lympho-hematopoietic cells was also observed. CONCLUSIONS/SIGNIFICANCE Neurofibroma formation is not restricted to loss of Nf1 in embryonic life, but can be triggered by Nf1 loss throughout life.Although all neurofibroma models and human samples have Remak bundle disruption (leading to the assumption that Nf1 loss within the non-myelinating Schwann cell may be vital for tumor formation), there was no EGFP+ recombination within GFAP+ non-myelinating Schwann cells – eliminating the GFAP+ non-myelinating Schwann cell as the cell of origin for neurofibroma formation

Perinatal or Adult \u3cem\u3eNf1\u3c/em\u3e Inactivation using Tamoxifen-inducible PlpCre Each Cause Neurofibroma Formation

OBJECTIVES Neurofibromas are tumors initiated by biallelic mutation of the NF1 tumor suppressor gene in the Schwann cell lineage. One idea within the field suggests that Nf1loss must occur within progenitor cells present within a critical window during Schwann cell development in order for neurofibromas to form. To test this hypothesis and to examine whethermyelinating Schwann cells can serve as aneurofibroma cell of origin, Nf1 loss was induced at perinatal or adult timepoints using a tamoxifen-inducible Plp-CreERT driver. RESULTS Perinatal loss of Nf1 resulted in small neurofibromas late in life, while adult loss caused large neurofibromas and morbidity beginning 4 months after onset of Nf1loss. PLP-CreERT recombination (EGFP+ cells) occurred in: satellite cells, S100β+ myelinating Schwann cells, and p75+ cells. Plp-CreERTnerves and neurofibromas contained cells with Remak bundle disruption; however, no recombination within GFAP+ non-myelinating Schwann cells was identified. Extramedullarylympho-hematopoietic expansion that contained EGFP+/Sca-1+ stromal cells amongst EGFP-negative lympho-hematopoietic cells was also observed. CONCLUSIONS/SIGNIFICANCE Neurofibroma formation is not restricted to loss of Nf1 in embryonic life, but can be triggered by Nf1 loss throughout life.Although all neurofibroma models and human samples have Remak bundle disruption (leading to the assumption that Nf1 loss within the non-myelinating Schwann cell may be vital for tumor formation), there was no EGFP+ recombination within GFAP+ non-myelinating Schwann cells – eliminating the GFAP+ non-myelinating Schwann cell as the cell of origin for neurofibroma formation

Perinatal or Adult \u3cem\u3eNf1\u3c/em\u3e Inactivation using Tamoxifen-Inducible PlpCre each cause Neurofibroma Formation

Plexiform neurofibromas are peripheral nerve sheath tumors initiated by biallelic mutation of the NF1 tumor suppressor gene in the Schwann cell lineage. To understand whether neurofibroma formation is possible after birth, we induced Nf1 loss of function with an inducible proteolipid protein Cre allele. Perinatal loss of Nf1 resulted in the development of small plexiform neurofibromas late in life, whereas loss in adulthood caused large plexiform neurofibromas and morbidity beginning 4 months after onset of Nf1 loss. A conditional EGFP reporter allele identified cells showing recombination, including peripheral ganglia satellite cells, peripheral nerve S100β+ myelinating Schwann cells, and peripheral nerve p75+ cells. Neurofibromas contained cells with Remak bundle disruption but no recombination within GFAP+ nonmyelinating Schwann cells. Extramedullary lympho-hematopoietic expansion was also observed in PlpCre;Nf1fl/fl mice. These tumors contained EGFP+/Sca-1+ stromal cells among EGFP-negative lympho-hematopoietic cells indicating a noncell autonomous effect and unveiling a role of Nf1-deleted microenvironment on lympho-hematopoietic proliferation in vivo. Together these findings define a tumor suppressor role for Nf1 in the adult and narrow the range of potential neurofibroma-initiating cell populations

Perinatal or Adult \u3cem\u3eNf1\u3c/em\u3e Inactivation using Tamoxifen-Inducible PlpCre each cause Neurofibroma Formation

Plexiform neurofibromas are peripheral nerve sheath tumors initiated by biallelic mutation of the NF1 tumor suppressor gene in the Schwann cell lineage. To understand whether neurofibroma formation is possible after birth, we induced Nf1 loss of function with an inducible proteolipid protein Cre allele. Perinatal loss of Nf1 resulted in the development of small plexiform neurofibromas late in life, whereas loss in adulthood caused large plexiform neurofibromas and morbidity beginning 4 months after onset of Nf1 loss. A conditional EGFP reporter allele identified cells showing recombination, including peripheral ganglia satellite cells, peripheral nerve S100β+ myelinating Schwann cells, and peripheral nerve p75+ cells. Neurofibromas contained cells with Remak bundle disruption but no recombination within GFAP+ nonmyelinating Schwann cells. Extramedullary lympho-hematopoietic expansion was also observed in PlpCre;Nf1fl/fl mice. These tumors contained EGFP+/Sca-1+ stromal cells among EGFP-negative lympho-hematopoietic cells indicating a noncell autonomous effect and unveiling a role of Nf1-deleted microenvironment on lympho-hematopoietic proliferation in vivo. Together these findings define a tumor suppressor role for Nf1 in the adult and narrow the range of potential neurofibroma-initiating cell populations

Identification of epithelial label-retaining cells at the transition between the anal canal and the rectum in mice

In certain regions of the body, transition zones exist where stratified squamous epithelia directly abut against other types of epithelia. Certain transition zones are especially prone to tumorigenesis an example being the anorectal junction, although the reason for this is not known. One possibility is that the abrupt transition of the simple columnar epithelium of the colon to the stratified squamous epithelium of the proximal portion of the anal canal may contain a unique stem cell niche. We investigated whether the anorectal region contained cells with stem cell properties relative to the adjacent epithelium. We utilized a tetracycline-regulatable histone H2B-GFP transgenic mice model, previously used to identify hair follicle stem cells, to fluorescently label slow-cycling anal epithelial cells (e.g., prospective stem cells) in combination with a panel of putative stem cell markers. We identified a population of long-term GFP label-retaining cells concentrated at the junction between the anal canal and the rectum. These cells are BrdU-retaining cells and expressed the stem cell marker CD34. Moreover, tracking the fate of the anal label-retaining cells in vivo revealed that the slow-cycling cells only gave rise to progeny of the anal epithelium. In conclusion, we identified a unique population of cells at the anorectal junction which can be separated from the other basal anal epithelial cells based upon the expression of the stem cell marker CD34 and integrin α6, and thus represent a putative anal stem cell population