Vertebrate eye development has been an excellent model system to investigate basic concepts of developmental biology ranging from mechanisms of tissue induction to the complex patterning and ...bidimensional orientation of the highly specialized retina. Recent advances have shed light on the interplay between numerous transcriptional networks and growth factors that are involved in the specific stages of retinogenesis, optic nerve formation, and topographic mapping. In this review, we summarize this recent progress on the molecular mechanisms underlying the development of the eye, visual system, and embryonic tumors that arise in the optic system.
Cerebellar development is regulated by a coordinated spatiotemporal interplay between granule neuron progenitors (GNPs), Purkinje neurons, and glia. Abnormal development can trigger motor deficits, ...and more recent data indicate important roles in aspects of memory, behavior, and autism spectrum disorders (ASDs). Germline mutation in the NF1 tumor suppressor gene underlies Neurofibromatosis type 1, a complex disease that enhances susceptibility to certain cancers and neurological disorders, including intellectual deficits and ASD. The NF1 gene encodes for neurofibromin, a RAS GTPase-activating protein, and thus negatively regulates the RAS signaling pathway. Here, using mouse models to direct conditional NF1 ablation in either embryonic cerebellar progenitors or neonatal GNPs, we show that neurofibromin is required for appropriate development of cerebellar folia layering and structure. Remarkably, neonatal administration of inhibitors of the ERK pathway reversed the morphological defects. Thus, our findings establish a critical cell-autonomous role for the NF1-RAS-ERK pathway in the appropriate regulation of cerebellar development and provide a basis for using neonatal ERK inhibitor-based therapies to treat NF1-induced cerebellar disorders.
Schwann cells are highly plastic cells that dedifferentiate to a progenitor-like state following injury. However, deregulation of this plasticity, may be involved in the formation of neurofibromas, ...mixed-cell tumors of Schwann cell (SC) origin that arise upon loss of NF1. Here, we show that adult myelinating SCs (mSCs) are refractory to Nf1 loss. However, in the context of injury, Nf1-deficient cells display opposing behaviors along the wounded nerve; distal to the injury, Nf1−/− mSCs redifferentiate normally, whereas at the wound site Nf1−/− mSCs give rise to neurofibromas in both Nf1+/+ and Nf1+/− backgrounds. Tracing experiments showed that distinct cell types within the tumor derive from Nf1-deficient SCs. This model of neurofibroma formation demonstrates that neurofibromas can originate from adult SCs and that the nerve environment can switch from tumor suppressive to tumor promoting at a site of injury. These findings have implications for both the characterization and treatment of neurofibromas.
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•Adult myelinating Schwann cells can be the cell of origin for neurofibromas•The nerve is tumor suppressive, given that Nf1−/− SCs remyelinate normally after injury•At the site of injury, Nf1−/− adult myelinating Schwann cells form tumors•Tumor cells are mostly S100− and some resemble the “perineurial-like” cells of tumors
Neurofibromas are mixed-cell tumors of Schwann cell (SC) origin that arise upon loss of NF1. Here, Lloyd and colleagues show that adult myelinating SCs (mSCs) are insensitive to NF1 loss. However, when nerves are injured, NF1-deficient mSCs display opposing behavior along the wounded nerve, forming tumors at the injury site while redifferentiating normally along the rest of the nerve. This demonstrates that the nerve environment can switch from tumor suppressive to tumor promoting at a site of injury.
Stem cells are under strict regulation by both intrinsic factors and the microenvironment. There is increasing evidence that many cancers initiate through acquisition of genetic mutations (loss of ...intrinsic control) in stem cells or their progenitors, followed by alterations of the surrounding microenvironment (loss of extrinsic control). In neurofibromatosis type 1 (NF1), deregulation of Ras signaling results in development of multiple neurofibromas, complex tumors of the peripheral nerves. Neurofibromas arise from the Schwann cell lineage following loss of function at the NF1 locus, which initiates a cascade of interactions with other cell types in the microenvironment and additional cell autonomous modifications. In this study, we sought to identify whether a temporal "window of opportunity" exists during which cells of the Schwann cell lineage can give rise to neurofibromas following loss of NF1. We showed that acute loss of NF1 in both embryonic and adult Schwann cells can lead to neurofibroma formation. However, the embryonic period when Schwann cell precursors and immature Schwann cells are most abundant coincides with enhanced susceptibility to plexiform neurofibroma tumorigenesis. This model has important implications for understanding early cellular events that dictate neurofibroma development, as well as for the development of novel therapies targeting these tumors.
Subependymal nodules (SENs) and subependymal giant cell astrocytomas (SEGAs) are common brain lesions found in patients with tuberous sclerosis complex (TSC). These brain lesions present a mixed ...glioneuronal phenotype and have been hypothesized to originate from neural stem cells. However, this hypothesis has not been tested empirically. Here, we report that loss of Tsc1 in mouse subventricular zone (SVZ) neural stem/progenitor cells (NSPCs) results in formation of SEN- and SEGA-like structural abnormalities in the lateral ventricle, the consequence of abnormal migration of NSPCs following Tsc1 loss.
Highlights ► PTEN is a negative regulator of the PI3K/AKT pathway, and Pten germline mutations are found in a small subset of autism patients. ► Loss of PTEN function in the brain has profound and ...multiple effects on neuronal cells. ► The TSC/mTORC1 signaling pathway is a major PI3K/PTEN/AKT downstream pathway that mediates cellular and behavioral effects in the nervous system. ► The PTEN pathway can synergize with other signaling pathways to control social behavior.
Neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), are associated with the physiology of the striatum and the loss of its normal functioning under pathological conditions. The ...role of BDNF and its downstream signaling in regulating the development of the striatum has not been fully investigated, however. Here we report that ablation of Bdnf in both the cortex and substantia nigra depletes BDNF in the striatum, and leads to impaired striatal development, severe motor deficits, and postnatal lethality. Furthermore, striatal-specific ablation of TrkB , the gene encoding the high-affinity receptor for BDNF, is sufficient to elicit an array of striatal developmental abnormalities, including decreased anatomical volume, smaller neuronal nucleus size, loss of dendritic spines, reduced enkephalin expression, diminished nigral dopaminergic projections, and severe deficits in striatal dopamine signaling through DARPP32. In addition, TrkB ablation in striatal neurons elicits a non–cell-autonomous reduction of tyrosine hydroxylase protein level in the axonal projections of substantia nigral dopaminergic neurons. Thus, our results establish an essential function for TrkB in regulating the development of striatal neurons.
We previously reported that central nervous system (CNS) inactivation of Nf1 and p53 tumor suppressor genes in mice results in the development of low-grade to high-grade progressive astrocytomas. ...When the tumors achieve high grade, they are frequently accompanied by Akt activation, reminiscent of the frequent association of PTEN mutations in human high-grade glioma. In the present study, we introduced CNS heterozygosity of Pten into the Nf1/p53 astrocytoma model. Resulting mice had accelerated morbidity, shortened survival, and full penetrance of high-grade astrocytomas. Haploinsufficiency of Pten accelerated formation of grade 3 astrocytomas, whereas loss of Pten heterozygosity and Akt activation coincided with progression into grade 4 tumors. These data suggest that successive loss of each Pten allele may contribute to de novo formation of high-grade astrocytoma and progression into glioblastoma, respectively, thus providing insight into the etiology of primary glioblastoma. The presence of ectopically migrating neural stem/progenitor lineage cells in presymptomatic Pten-deficient mutant brains supports the notion that these tumors may arise from stem/progenitor cells.
Neurofibromatosis type 1 (NF1) is one of the most prevalent dominantly inherited genetic diseases of the nervous system. NF1 encodes a tumor suppressor whose functional loss results in the ...development of benign neurofibromas that can progress to malignancy. Neurofibromas are complex tumors composed of axonal processes, Schwann cells, fibroblasts, perineurial cells, and mast cells. Through use of a conditional (cre/lox) allele, we show that loss of NF1 in the Schwann cell lineage is sufficient to generate tumors. In addition, complete NF1-mediated tumorigenicity requires both a loss of NF1 in cells destined to become neoplastic as well as heterozygosity in non-neoplastic cells. The requirement for a permissive haploinsufficient environment to allow tumorigenesis may have therapeutic implications for NF1 and other familial cancers.
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