MECP2 Mutation Interrupts Nucleolin–mTOR–P70S6K Signaling in Rett Syndrome Patients

Rett syndrome (RTT) is a severe and rare neurological disorder that is caused by mutations in the X-linked MECP2 (methyl CpG-binding protein 2) gene. MeCP2 protein is an important epigenetic factor in the brain and in neurons. In Mecp2-deficient neurons, nucleoli structures are compromised. Nucleoli are sites of active ribosomal RNA (rRNA) transcription and maturation, a process mainly controlled by nucleolin and mechanistic target of rapamycin (mTOR)–P70S6K signaling. Currently, it is unclear how nucleolin–rRNA–mTOR–P70S6K signaling from RTT cellular model systems translates into human RTT brain. Here, we studied the components of nucleolin–rRNA–mTOR–P70S6K signaling in the brain of RTT patients with common T158M and R255X mutations. Immunohistochemical examination of T158M brain showed disturbed nucleolin subcellular localization, which was absent in Mecp2-deficient homozygous male or heterozygote female mice, compared to wild type (WT). We confirmed by Western blot analysis that nucleolin protein levels are altered in RTT brain, but not in Mecp2-deficient mice. Further, we studied the expression of rRNA transcripts in Mecp2-deficient mice and RTT patients, as downstream molecules that are controlled by nucleolin. By data mining of published ChIP-seq studies, we showed MeCP2-binding at the multi-copy rRNA genes in the mouse brain, suggesting that rRNA might be a direct MeCP2 target gene. Additionally, we observed compromised mTOR–P70S6K signaling in the human RTT brain, a molecular pathway that is upstream of rRNA–nucleolin molecular conduits. RTT patients showed significantly higher phosphorylation of active mTORC1 or mTORC2 complexes compared to age- and sex-matched controls. Correlational analysis of mTORC1/2–P70S6K signaling pathway identified multiple points of deviation from the control tissues that may result in abnormal ribosome biogenesis in RTT brain. To our knowledge, this is the first report of deregulated nucleolin–rRNA–mTOR–P70S6K signaling in the human RTT brain. Our results provide important insight toward understanding the molecular properties of human RTT brain

Role of DNA Methyl-CpG-Binding Protein MeCP2 in Rett Syndrome Pathobiology and Mechanism of Disease

Rett Syndrome (RTT) is a severe, rare, and progressive developmental disorder with patients displaying neurological regression and autism spectrum features. The affected individuals are primarily young females, and more than 95% of patients carry de novo mutation(s) in the Methyl-CpG-Binding Protein 2 (MECP2) gene. While the majority of RTT patients have MECP2 mutations (classical RTT), a small fraction of the patients (atypical RTT) may carry genetic mutations in other genes such as the cyclin-dependent kinase-like 5 (CDKL5) and FOXG1. Due to the neurological basis of RTT symptoms, MeCP2 function was originally studied in nerve cells (neurons). However, later research highlighted its importance in other cell types of the brain including glia. In this regard, scientists benefitted from modeling the disease using many different cellular systems and transgenic mice with loss- or gain-of-function mutations. Additionally, limited research in human postmortem brain tissues provided invaluable findings in RTT pathobiology and disease mechanism. MeCP2 expression in the brain is tightly regulated, and its altered expression leads to abnormal brain function, implicating MeCP2 in some cases of autism spectrum disorders. In certain disease conditions, MeCP2 homeostasis control is impaired, the regulation of which in rodents involves a regulatory microRNA (miR132) and brain-derived neurotrophic factor (BDNF). Here, we will provide an overview of recent advances in understanding the underlying mechanism of disease in RTT and the associated genetic mutations in the MECP2 gene along with the pathobiology of the disease, the role of the two most studied protein variants (MeCP2E1 and MeCP2E2 isoforms), and the regulatory mechanisms that control MeCP2 homeostasis network in the brain, including BDNF and miR132

Yolk Sac Tumor Of Vagina

Malignant germ-cell tumors (MGCT) are rare tumors of childhood accounting for less than 3% of pediatric malignancies. Endodermal sinus tumor (EST) forms the most common histologic subtype of MGCT. The vagina is an extremely rare site for GCTs. An 8-month-old female was admitted with a short history of vaginal bleeding, and a mass protruding from the vagina. She was pale and a mass was palpable anteriorly on rectal examination. Computed tomography (CT) showed a tumor mass posterior to the bladder. A biopsy revealed a vaginal EST. The serum alpha-fetoprotein (AFP) was elevated. Vaginohysterectomy was done. The patient was subsequently referred to the oncologist for further management. EST is the most common GCT in children. In females, it is usually encountered in the ovary. EST of the vagina is a rare, highly malignant GCT that exclusively involves children less than 3 years of age. The diagnosis is based on histology and raised AFP. Vaginal EST is both locally aggressive and capable of metastasis. The serum AFP level is a useful marker for diagnosis and monitoring the recurrence of vaginal EST in infants

Vertebral Malacoplakia

Malacoplakia is a rare chronic inflammatory disease associated with infection and immunosuppression, and very few occurrences have been reported in the bone. The authors describe the case of a 22-year-old woman with paraplegia and urinary and fecal incontinence whose thoracic spine Magnetic Resonance Imaging suggested a tumoral or extensive inflammatory process in the body of the 8th, 9th and 10th thoracic vertebrae.On histology,however,the area turned out to be malacoplakia of bone.Although microbiologic cultures and polymerase chain reaction were negative for Mycobacterium tuberculosis, the lesion demonstrated regression following treatment with anti-TB regimen which had been started because of clinical suspicion.

Yolk Sac Tumor of Vagina

Malignant germ-cell tumors (MGCT) are rare tumors of childhood accounting for less than 3% of pediatric malignancies.Endodermal sinus tumor(EST)forms the most common histologic subtype of MGCT.The vagina is an extremely rare site for GCTs. An 8-month-old female was admitted with a short history of vaginal bleeding,and a mass protruding from the vagina.She was pale and a mass was palpable anteriorly on rectal examination.Computed tomography (CT) showed a tumor mass posterior to the bladder.A biopsy revealed a vaginal EST. The serum alpha-fetoprotein(AFP)was elevated.Vaginohysterectomy was done.The patient was subsequently referred to the oncologist for further management.EST is the most common GCT in children.In females,itis usually encountered in the ovary.EST of the vagina is a rare,highly malignant GCT that exclusively involves children less than 3years of age.The diagnosis is based on histology and raised AFP.Vaginal EST is both locally aggressive and capable of metastasis. The serum AFP level is a useful marker for diagnosis and monitoring the recurrence of vaginal EST in infants

Differential Sensitivity of the Protein Translation Initiation Machinery and mTOR Signaling to <i>MECP2</i> Gain- and Loss-of-Function Involves MeCP2 Isoform-Specific Homeostasis in the Brain

Eukaryotic gene expression is controlled at multiple levels, including gene transcription and protein translation initiation. One molecule with key roles in both regulatory mechanisms is methyl CpG binding protein 2 (MeCP2). MECP2 gain- and loss-of-function mutations lead to Rett Syndrome and MECP2 Duplication Syndrome, respectively. To study MECP2 gain-of-function, we generated stably transduced human brain cells using lentiviral vectors for both MECP2E1 and MECP2E2 isoforms. Stable overexpression was confirmed by Western blot and immunofluorescence. We assessed the impact of MeCP2E1-E2 gain-of-function on the MeCP2 homeostasis regulatory network (MECP2E1/E2-BDNF/BDNF-miR-132), mTOR-AKT signaling, ribosome biogenesis, markers of chromatin structure, and protein translation initiation. We observed that combined co-transduction of MeCP2 isoforms led to protein degradation of MeCP2E1. Proteosome inhibition by MG132 treatment recovered MeCP2E1 protein within an hour, suggesting its induced degradation through the proteosome pathway. No significant change was detected for translation initiation factors as a result of MeCP2E1, MeCP2E2, or combined overexpression of both isoforms. In contrast, analysis of human Rett Syndrome brains tissues compared with controls indicated impaired protein translation initiation, suggesting that such mechanisms may have differential sensitivity to MECP2 gain- and loss-of-function. Collectively, our results provide further insight towards the dose-dependent functional role of MeCP2 isoforms in the human brain