Circular RNAs in Hedgehog Signaling Activation and Hedgehog-Mediated Medulloblastoma Tumors

Within the past decade, circular RNAs have largely emerged as novel regulators of human biology, including brain function and cancer development. On the other hand, the Hedgehog pathway has established roles in regulating biological processes, including tumorigenesis. Here, the circular RNA transcriptome, in the context of Hedgehog signaling activation of medulloblastoma Daoy and human embryonic palatal mesenchyme HEPM cells, was determined. In total, 29 out of the 30 selected circular RNAs were validated by Sanger sequencing, with some regulated to a limited extent by Hedgehog signaling. Interestingly, back-spliced junctions, the marker of exonic RNA circles, were also identified at a low frequency within poly (A) mRNAs, reflecting exon repetition events. Thirteen circular RNAs had reduced expression in human medulloblastoma tumors in comparison to normal cerebellum. For seven out of these thirteen RNA circles, the linear mRNAs originating from the same genes did not exhibit a reduced expression. Depletion and/or overexpression of these seven circular RNAs minimally affected medulloblastoma cell proliferation. These findings highlight that differential expression of a gene product may not necessarily elicit an obvious phenotypic impact. Consequently, further analysis is required to determine the possible subtle contributions to the development of this cerebellar tumor.

Cannabinoids modulate associative cerebellar learning via alterations in behavioral state

Cannabinoids are notorious and profound modulators of behavioral state. In the brain, endocannabinoids act via Type 1-cannabinoid receptors (CB1) to modulate synaptic transmission and mediate multiple forms of synaptic plasticity. CB1 knockout (CB1KO) mice display a range of behavioral phenotypes, in particular hypoactivity and various deficits in learning and memory, including cerebellum-dependent delay eyeblink conditioning. Here we find that the apparent effects of CB1 deletion on cerebellar learning are not due to direct effects on CB1-dependent plasticity, but rather, arise as a secondary consequence of altered behavioral state. Hypoactivity of CB1KO mice accounts for their impaired eyeblink conditioning across both animals and trials. Moreover, learning in these mutants is rescued by walking on a motorized treadmill during training. Finally, cerebellar granule-cell-specific CB1KOs exhibit normal eyeblink conditioning, and both global and granule-cell-specific CB1KOs display normal cerebellum-dependent locomotor coordination and learning. These findings highlight the modulation of behavioral state as a powerful independent means through which individual genes contribute to complex behaviors.

Reliable tumor detection by whole-genome methylation sequencing of cell-free DNA in cerebrospinal fluid of pediatric medulloblastoma

Medulloblastoma (MB), the most common form of pediatric brain malignancy, has a low frequency of oncogenic mutations but pronouncedly abnormal DNA methylation changes. Epigenetic analysis of circulating cell-free tumor DNA (ctDNA) by liquid biopsy offers an approach for real-time monitoring of tumor status without tumor dissection. In this study, we identified 6598 differentially methylated CpGs in both MB tumors and the ctDNA isolated from matched cerebrospinal fluid (CSF) compared with normal cerebellum, which could be used to detect MB tumor occurrence and determine its subtype. Furthermore, DNA methylation changes in serial CSF samples could be used to monitor the treatment response and tumor recurrence. Integrating our data with large public datasets, we identified reliable MB DNA methylation signatures in ctDNA that have potential diagnostic and prognostic values. Our study sets the stage for exploiting epigenetic markers in CSF to improve the clinical management of patients with MB.

The stem cell-associated transcription co-factor, ZNF521, interacts with GLI1 and GLI2 and enhances the activity of the Sonic hedgehog pathway

ZNF521 is a transcription co-factor with recognized regulatory functions in haematopoietic, osteo-adipogenic and neural progenitor cells. Among its diverse activities, ZNF521 has been implicated in the regulation of medulloblastoma (MB) cells, where the Hedgehog (HH) pathway, has a key role in the development of normal cerebellum and of a substantial fraction of MBs. Here a functional cross-talk is shown for ZNF521 with the HH pathway, where it interacts with GLI1 and GLI2, the major HH transcriptional effectors and enhances the activity of HH signalling. In particular, ZNF521 cooperates with GLI1 and GLI2 in the transcriptional activation of GLI (glioma-associated transcription factor)-responsive promoters. This synergism is dependent on the presence of the N-terminal, NuRD-binding motif in ZNF521, and is sensitive to HDAC (histone deacetylase) and GLI inhibitors. Taken together, these results highlight the role of ZNF521, and its interaction with the NuRD complex, in determining the HH response at the level of transcription. This may be of particular relevance in HH-driven diseases, especially regarding the MBs belonging to the SHH (sonic HH) subgroup where a high expression of ZNF521 is correlated with that of HH pathway components.

Cannabinoids modulate associative cerebellar learning via alterations in behavioral state

Cannabinoids are notorious and profound modulators of behavioral state. In the brain, endocannabinoids act via Type 1-cannabinoid receptors (CB1) to modulate synaptic transmission and mediate multiple forms of synaptic plasticity. CB1 knockout (CB1KO) mice display a range of behavioral phenotypes, in particular hypoactivity and various deficits in learning and memory, including cerebellumdependent delay eyeblink conditioning. Here we find that the apparent effects of CB1 deletion on cerebellar learning are not due to direct effects on CB1-dependent plasticity, but rather, arise as a secondary consequence of altered behavioral state. Hypoactivity of CB1KO mice accounts for their impaired eyeblink conditioning across both animals and trials. Moreover, learning in these mutants is rescued by walking on a motorized treadmill during training. Finally, cerebellar granule cell-specific CB1KOs exhibit normal eyeblink conditioning, and both global and granule cell-specific CB1KOs display normal cerebellum-dependent locomotor coordination and learning. These findings highlight the modulation of behavioral state as a powerful independent means through which individual genes contribute to complex behaviors.

Age-dependent dormant resident progenitors are stimulated by injury to regenerate Purkinje neurons

Outside of the neurogenic niches of the brain, postmitotic neurons have not been found to undergo efficient regeneration. We demonstrate that mouse Purkinje cells (PCs), which are born at midgestation and are crucial for development and function of cerebellar circuits, are rapidly and fully regenerated following their ablation at birth. New PCs are produced from immature FOXP2+ Purkinje cell precursors (iPCs) that are able to enter the cell cycle and support normal cerebellum development. The number of iPCs and their regenerative capacity, however, diminish soon after birth and consequently PCs are poorly replenished when ablated at postnatal day five. Nevertheless, the PC-depleted cerebella reach a normal size by increasing cell size, but scaling of neuron types is disrupted and cerebellar function is impaired. Our findings provide a new paradigm in the field of neuron regeneration by identifying a population of immature neurons that buffers against perinatal brain injury in a stage-dependent process.

Age-dependent dormant resident progenitors are stimulated by injury to regenerate Purkinje neurons

Outside of the neurogenic niches of the brain, postmitotic neurons have not been found to undergo efficient regeneration. Here we demonstrate that Purkinje cells (PCs), which are born at midgestation and are crucial for both development and function of cerebellar circuits, are rapidly and fully regenerated following their ablation at birth. New PCs are produced by a previously unidentified progenitor population and support normal cerebellum development. The number of PC progenitors and their regenerative capacity, however, diminish soon after birth, and consequently PCs are poorly replenished when ablated at postnatal day 5. Nevertheless, the PC-depleted cerebella reach a normal size by increasing cell size, but scaling of neuron types is disrupted and cerebellar function is impaired. Our findings thus provide a new paradigm in the field of neuron regeneration by identifying a unipotent neural progenitor that buffers against perinatal brain injury in a stage-dependent process.One sentence summaryInjury induces a dormant progenitor population present at birth to regenerate cerebellar neurons in a time-dependent manner.

Encephalocele development from a congenital meningocele: case report

A fetal MRI study obtained at 21 weeks’ gestation revealed a suboccipital meningocele without hydrocephalus. One day after term birth, MRI demonstrated an acquired cerebellar encephalocele, and MRI obtained 5 months later showed progressive enlargement of the encephalocele, still without obvious hydrocephalus. The patient underwent an operation in which an external ventricular drain was placed, the grossly normal cerebellum was reduced into the posterior fossa without resection, and the dural defect was closed. The drain was weaned out over 5 days, and no ventriculoperitoneal shunt was placed. Postoperative MR images revealed normal cerebellum and no hydrocephalus. The patient is developmentally normal. Meningocele and encephalocele are embryologically distinct. An acquired encephalocele could develop from hydrocephalus (which was not present in this case), or secondary to the lower resistance to expansion into the dural defect of the meningocele relative to the resistance to expansion of the fetal skull. The cerebellar tissue was normal in this case, and was thus preserved. The developmental prognosis is excellent. To the authors’ knowledge, this is the first reported case of this occurrence. It is important to differentiate between congenital and acquired encephalocele etiologies, because resection of the cerebellar tissue in an acquired encephalocele (as is routinely done in cases of congenital encephalocele) would be expected to result in neurological deficits.

Neuropsychological Profiles of Children with Aqueductal Stenosis and Spina Bifida Myelomeningocele

We compared neuropsychological profiles in children with shunted hydrocephalus secondary to aqueductal stenosis (AS), a rare form of congenital hydrocephalus, and spina bifida myelomeningocele (SBM), a common form of congenital hydrocephalus. Participants were 180 children with shunted hydrocephalus grouped according to etiology: SBM (n = 151), AS (n = 29), and typically developing (TD; n = 60) individuals. The group with AS performed below the TD group on all tasks except for reading, and their overall performance was higher than the group with SBM, who had the lowest performance in the sample. Both clinical groups significantly differed from the TD group on tasks of spatial function, concept formation, motor function, and memory. Performance of the subgroup of AS children with normal cerebellum status approximated that of the TD group, while those with cerebellar anomalies performed lower than others with AS. Cerebellar abnormalities (present in the whole SBM group and in a subset of the AD group) are associated with more compromise of cognitive as well as motor function. (JINS, 2012, 18, 1–10)