SUMMARY N6-methyladenosine (m6A), installed by the Mettl3/Mettl14 methyltransferase complex, is the most prevalent internal mRNA modification. Whether m6A regulates mammalian brain development is unknown. Here we show that m6A depletion by Mettl14 knockout in embryonic mouse brains prolongs cell cycle of radial glia cells and extends cortical neurogenesis into postnatal stages. m6A depletion by Mettl3 knockdown also leads to prolonged cell cycle and maintenance of radial glia cells. m6A-sequencing of embryonic mouse cortex reveals enrichment of mRNAs related to transcription factors, neurogenesis, cell cycle and neuronal differentiation, and m6A-tagging promotes their decay. Further analysis uncovers previously unappreciated transcriptional pre-patterning in cortical neural stem cells. m6A signaling also regulates human cortical neurogenesis in forebrain organoids. Comparison of m6A-mRNA landscapes between mouse and human cortical neurogenesis reveals enrichment of human-specific m6A-tagging of transcripts related to brain disorder risk genes. Our study identifies an epitranscriptomic mechanism in heightened transcriptional coordination during mammalian cortical neurogenesis.

Dysregulation of cyclin-dependent kinase 5 (cdk5) per relative concentrations of its activators p35 and p25 is implicated in neurodegenerative diseases. P35 has a short t ½ and undergoes rapid proteasomal degradation in its membrane-bound myristoylated form. P35 is converted by calpain to p25, which, along with an extended t ½ , promotes aberrant activation of cdk5 and causes abnormal hyperphosphorylation of tau, thus leading to the formation of neurofibrillary tangles. The sigma-1 receptor (Sig-1R) is an endoplasmic reticulum chaperone that is implicated in neuronal survival. However, the specific role of the Sig-1R in neurodegeneration is unclear. Here we found that Sig-1Rs regulate proper tau phosphorylation and axon extension by promoting p35 turnover through the receptor's interaction with myristic acid. In Sig-1R-KO neurons, a greater accumulation of p35 is seen, which results from neither elevated transcription of p35 nor disrupted calpain activity, but rather to the slower degradation of p35. In contrast, Sig-1R overexpression causes a decrease of p35. Sig-1R-KO neurons exhibit shorter axons with lower densities. Myristic acid is found here to bind Sig-1R as an agonist that causes the dissociation of Sig-1R from its cognate partner binding immunoglobulin protein. Remarkably, treatment of Sig-1R-KO neurons with exogenous myristic acid mitigates p35 accumulation, diminishes tau phosphorylation, and restores axon elongation. Our results define the involvement of Sig-1Rs in neurodegeneration and provide a mechanistic explanation that Sig-1Rs help maintain proper tau phosphorylation by potentially carrying and providing myristic acid to p35 for enhanced p35 degradation to circumvent the formation of overreactive cdk5/p25.A xons are structurally and functionally distinct protrusions of neurons that modulate neurotransmitter release and neural function. Malfunction of axonal maintenance, regeneration, and target recognition contribute to CNS disorders such as Alzheimer's disease (AD), Parkinson's disease, stroke, and spinal cord injuries (1-3). Cyclin-dependent kinase (Cdk) 5 activities within the axon play a significant role in the cytoskeletal dynamics of microtubules and actin neurofilaments (NFs), which determine axonal path and length. Specifically, cdk5 active complexes phosphorylate proteins that contribute to the stabilization or destabilization of microtubules, formation of neurofibrillary tangles, and axonal pathfinding (4-6).Cdk5 is a ubiquitously expressed enzyme; however, its activator, p35, is almost exclusively expressed in neurons (7,8). Cdk5 signaling supports neurite projection and proper neuronal migration (9-11). Dysregulation of cdk5 activity leads to hyperphosphorylation of several substrates, including NF proteins and tau, which causes the formation of neurofibrillary tangles (6, 12). Although the kinetics of cdk5 activity when in complex with p35 or p25 are the same, cdk5/p25 complexes are proposed to be responsible for neurodegenerative pathophysiology because of their longer duration o...

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A large fraction of human cancers contain genetic alterations within the Mitogen Activated Protein Kinase (MAPK) signaling network that promote unpredictable phenotypes. Previous studies have shown that the temporal patterns of MAPK activity (i.e. signaling dynamics) differentially regulate cell behavior. However, the role of signaling dynamics in mediating the effects of cancer driving mutations has not been systematically explored. Here, we show that oncogene expression leads to either pulsatile or sustained ERK activity that correlate with opposing cellular behaviors (i.e. proliferation vs. cell cycle arrest, respectively). Moreover, sustained–but not pulsatile–ERK activity triggers ERK activity waves in unperturbed neighboring cells that depend on the membrane metalloprotease ADAM17 and EGFR activity. Interestingly, the ADAM17-EGFR signaling axis coordinates neighboring cell migration toward oncogenic cells and is required for oncogenic cell extrusion. Overall, our data suggests that the temporal patterns of MAPK activity differentially regulate cell autonomous and non-cell autonomous effects of oncogene expression.

Introduction Sigma-1 receptors (Sig-1Rs) are molecular chaperones that reside mainly in the endoplasmic reticulum (ER) but exist also in the proximity of the plasma membrane. Sig-1Rs are highly expressed in the CNS and are involved in many cellular processes including cell differentiation, neuritogenesis, microglia activation, protein quality control, calcium-mediated ER stress and ion channel modulation. Disturbance in any of the above cellular processes can accelerate the progression of many neurological disorders; therefore, the Sig-1R has been implicated in several neurological diseases. Areas covered This review broadly covers the functions of Sig-1Rs including several neurodegenerative disorders in humans and drug addiction-associated neurological disturbance in the case of HIV infection. We discuss how several Sig-1R ligands could be utilized in therapeutic approaches to treat those disorders. Expert opinion Emerging understanding of the cellular functions of this unique transmembrane chaperone may lead to the use of new agents or broaden the use of certain available ligands as therapeutic targets in those neurological disorders.

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12Epithelial tissues are constantly challenged by individual cell fate decisions while 13 maintaining barrier function. During oncogenesis, mutant and normal cells also differ in their 14 signaling states and cellular behaviors creating competitive interactions that are poorly 15 understood. Here we show that the temporal patterns of MAPK activity are decoded by the 16 ADAM17-EGFR paracrine signaling axis to coordinate migration of neighboring cells and promote 17 extrusion of aberrantly-signaling cells. Concurrently, neighboring cells increase proliferation to 18 maintain cell density while oncogene expressing cells undergo cell cycle arrest. Moreover, the 19 stress MAPK p38 elicits the same paracrine signaling and extrusion response, suggesting that 20 the ADAM17-EGFR pathway constitutes a quality control mechanism to eliminate and replace 21 unfit cells from epithelial tissues. Overall, we show that the temporal patterns of MAPK activity 22 coordinates both single and collective cell behaviors to maintain tissue homeostasis. 23 24 27 cancers 1 . In normal conditions the ERK pathway promotes proliferation, differentiation, survival 28 and cell migration 2 . Conversely, during oncogenesis mutations or amplification of ERK pathway 29 components can also promote oncogene-induced senescence 3 (OIS) or cellular extrusion from 30 epithelial monolayers 4,5 . The mechanisms underlying dose dependent effects of ERK signaling 31 have been intensely studied using bulk cell population assays. However, the advent of single cell 32 analysis has shown that single cells often behave qualitatively different than bulk populations. In 33 fact, in vivo and in vitro studies have now shown that pulsatile or sustained ERK activity have 34 different effects on cell fate 6-12 . Whether oncogenic perturbations also have different functional 35 outcomes depending on downstream signaling dynamics remains unknown. To address this 36 question, an isogenic single-cell approach with temporal control of oncogene expression is 37 needed. 38 39 Recent in vivo studies revealed that oncogene expression can trigger cell-cell competition and 40 tissue level responses involving normal neighboring cells 13-16 . During these events, the 41 mechanistic basis of competition and the signaling events involved in recognition between normal 42 and diseased cells are poorly understood. Coincidentally, propagating ERK signaling waves that 43 depend on the sheddase ADAM17 have been observed in mouse epidermis and intestinal 44 organoids, but the physiological role of these collective signaling events in homeostasis remains 45 unclear 7,8,17 . Understanding of the context-dependent mechanisms of paracrine signaling and cell-46 cell competition upon oncogene expression holds the key to unlocking new therapeutic strategies. 47 48 Here we combine live cell imaging of signaling biosensors with inducible expression of oncogenes 49 to study the cell autonomous and non-cell autonomous effects of oncogene expression in 50 epithelial monolayers. Our data shows that pulsa...

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