@article {2110, title = {Cortical neurons derived from human pluripotent stem cells lacking FMRP display altered spontaneous firing patterns.}, journal = {Mol Autism}, volume = {11}, year = {2020}, month = {2020 Jun 19}, pages = {52}, abstract = {

BACKGROUND: Fragile X syndrome (FXS), a neurodevelopmental disorder, is a leading monogenetic cause of intellectual disability and autism spectrum disorder. Notwithstanding the extensive studies using rodent and other pre-clinical models of FXS, which have provided detailed mechanistic insights into the pathophysiology of this disorder, it is only relatively recently that human stem cell-derived neurons have been employed as a model system to further our understanding of the pathophysiological events that may underlie FXS. Our study assesses the physiological properties of human pluripotent stem cell-derived cortical neurons lacking fragile X mental retardation protein (FMRP).

METHODS: Electrophysiological whole-cell voltage- and current-clamp recordings were performed on two control and three FXS patient lines of human cortical neurons derived from induced pluripotent stem cells. In addition, we also describe the properties of an isogenic pair of lines in one of which FMR1 gene expression has been silenced.

RESULTS: Neurons lacking FMRP displayed bursts of spontaneous action potential firing that were more frequent but shorter in duration compared to those recorded from neurons expressing FMRP. Inhibition of large conductance Ca-activated K currents and the persistent Na current in control neurons phenocopies action potential bursting observed in neurons lacking FMRP, while in neurons lacking FMRP pharmacological potentiation of voltage-dependent Na channels phenocopies action potential bursting observed in control neurons. Notwithstanding the changes in spontaneous action potential firing, we did not observe any differences in the intrinsic properties of neurons in any of the lines examined. Moreover, we did not detect any differences in the properties of miniature excitatory postsynaptic currents in any of the lines.

CONCLUSIONS: Pharmacological manipulations can alter the action potential burst profiles in both control and FMRP-null human cortical neurons, making them appear like their genetic counterpart. Our studies indicate that FMRP targets that have been found in rodent models of FXS are also potential targets in a human-based model system, and we suggest potential mechanisms by which activity is altered.

}, issn = {2040-2392}, doi = {10.1186/s13229-020-00351-4}, author = {Das Sharma, Shreya and Pal, Rakhi and Reddy, Bharath Kumar and Selvaraj, Bhuvaneish T and Raj, Nisha and Samaga, Krishna Kumar and Srinivasan, Durga J and Ornelas, Loren and Sareen, Dhruv and Livesey, Matthew R and Bassell, Gary J and Svendsen, Clive N and Kind, Peter C and Chandran, Siddharthan and Chattarji, Sumantra and Wyllie, David J A} } @article {2063, title = {N-terminal variant Asp14Asn of the human p70 S6 Kinase 1 enhances translational signaling causing different effects in developing and mature neuronal cells.}, journal = {Neurobiol Learn Mem}, volume = {171}, year = {2020}, month = {2020 May}, pages = {107203}, abstract = {

The ribosomal p70 S6 Kinase 1 (S6K1) has been implicated in the etiology of complex neurological diseases including autism, depression and dementia. Though no major gene disruption has been reported in humans in RPS6KB1, single nucleotide variants (SNVs) causing missense mutations have been identified, which have not been assessed for their impact on protein function. These S6K1 mutations have the potential to influence disease progression and treatment response. We mined the Simon Simplex Collection (SSC) and SPARK autism database to find inherited SNVs in S6K1 and characterized the effect of two missense SNVs, Asp14Asn (allele frequency\ =\ 0.03282\%) and Glu44Gln (allele frequency\ =\ 0.0008244\%), on S6K1 function in HEK293, human ES cells and primary neurons. Expressing Asp14Asn in HEK293 cells resulted in increased basal phosphorylation of downstream targets of S6K1 and increased de novo translation. This variant also showed blunted response to the specific S6K1 inhibitor, FS-115. In human embryonic cell line Shef4, Asp14Asn enhanced spontaneous neural fate specification in the absence of differentiating growth factors. In addition to enhanced translation, neurons expressing Asp14Asn exhibited impaired dendritic arborization and increased levels of phosphorylated ERK 1/2. Finally, in the SSC families tracked, Asp14Asn segregated with lower IQ scores when found in the autistic individual rather than the unaffected sibling. The Glu44Gln mutation showed a milder, but opposite phenotype in HEK cells as compared to Asp14Asn. Although the Glu44Gln mutation displayed increased neuronal translation, it had no impact on neuronal morphology. Our results provide the first characterization of naturally occurring human S6K1 variants on cognitive phenotype, neuronal morphology and maturation, underscoring again the importance of translation control in neural development and plasticity.

}, issn = {1095-9564}, doi = {10.1016/j.nlm.2020.107203}, author = {Venkatasubramani, Janani Priya and Subramanyam, Prakash and Pal, Rakhi and Reddy, Bharath K and Srinivasan, Durga Jeyalakshmi and Chattarji, Sumantra and Iossifov, Ivan and Klann, Eric and Bhattacharya, Aditi} } @article {1598, title = {FMRP Interacts with C/D Box snoRNA in the Nucleus and Regulates Ribosomal RNA Methylation.}, journal = {iScience}, volume = {9}, year = {2018}, month = {2018 Nov 30}, pages = {399-411}, abstract = {

FMRP is an RNA-binding protein that is known to localize in the cytoplasm and in the nucleus. Here, we have identified an interaction of FMRP with a specific set of C/D box snoRNAs in the nucleus. C/D box snoRNAs guide 2{\textquoteright}O methylations of ribosomal RNA (rRNA) on defined sites, and this modification regulates rRNA folding and assembly of ribosomes. 2{\textquoteright}O methylation of rRNA is partial on several sites in human embryonic stem cells, which results in ribosomes with differential methylation patterns. FMRP-snoRNA interaction affects rRNA methylation on several of these sites, and in the absence of FMRP, differential methylation pattern of rRNA is significantly altered. We found that FMRP recognizes ribosomes carrying specific methylation patterns on rRNA and the recognition of methylation pattern by FMRP may potentially determine the translation status of its target mRNAs. Thus, FMRP integrates its function in the nucleus and in the cytoplasm.

}, issn = {2589-0042}, doi = {10.1016/j.isci.2018.11.007}, author = {D{\textquoteright}Souza, Michelle Ninochka and Gowda, Naveen Kumar Chandappa and Tiwari, Vishal and Babu, Rosana Ottakandathil and Anand, Praveen and Dastidar, Sudhriti Ghosh and Singh, Randhir and James, Owen G and Selvaraj, Bhuvaneish and Pal, Rakhi and Ramesh, Arati and Chattarji, Sumantra and Chandran, Siddharthan and Gulyani, Akash and Palakodeti, Dasaradhi and Muddashetty, Ravi S} }