Precise regulation of RNA metabolism is crucial for dynamic gene expression and controlling cellular functions. In the nervous system, defects in RNA metabolism are implicated in disturbing brain homeostasis and development. Here we report that deubiquitinating enzyme, ubiquitin specific peptidase 15 (USP15), deubiquitinates terminal uridylyl transferase 1 (TUT1) and changes global RNA metabolism. We found that the expression of USP15 redistributes TUT1 from nucleolus to nucleoplasm, resulting in the stabilization of U6-snRNA. We also found that lack of the Usp15 gene induces impairment in motor ability with the unconventional cerebellar formation. Moreover, inhibition of the USP15-TUT1 cascade triggered mild and chronic endoplasmic reticulum (ER) stress. Therefore, our results suggest that USP15 is crucial for mRNA metabolism and maintains a healthy brain. These findings provide a possibility that disturbance of the USP15-TUT1 cascade may induce chronic and mild ER stress, leading to an acceleration of neurodegenerative phenotype.

No abstract

Hevin is a secreted extracellular matrix protein that is encoded by the SPARCL1 gene. Recent studies have shown that Hevin plays an important role in regulating synaptogenesis and synaptic plasticity. Mutations in the SPARCL1 gene increase the risk of autism spectrum disorder (ASD). However, the molecular basis of how mutations in SPARCL1 increase the risk of ASD is not been fully understood. In this study, we show that one of the SPARCL1 mutations associated with ASD impairs normal Hevin secretion. We identified Hevin mutants lacking the EF-hand motif through analyzing ASD-related mice with vulnerable spliceosome functions. Hevin deletion mutants accumulate in the endoplasmic reticulum (ER), leading to the activation of unfolded protein responses. We also found that a single amino acid substitution of Trp647 with Arg in the EF-hand motif associated with a familial case of ASD causes a similar phenotype in the EF-hand deletion mutant. Importantly, molecular dynamics (MD) simulation revealed that this single amino acid substitution triggers exposure of a hydrophobic amino acid to the surface, increasing the binding of Hevin with molecular chaperons, BIP. Taken together, these data suggest that the integrity of the EF-hand motif in Hevin is crucial for proper folding and that ASD-related mutations impair the export of Hevin from the ER. Our data provide a novel mechanism linking a point mutation in the SPARCL1 gene to the molecular and cellular characteristics involved in ASD.

Microglia are resident macrophages that are critical for brain development and homeostasis. Microglial morphology is dynamically changed during postnatal stages, leading to regulating synaptogenesis and synapse pruning. Moreover, it has been well known that the shape of microglia is also altered in response to the detritus of the apoptotic cells and pathogens such as bacteria and viruses. Although the morphologic changes are crucial for acquiring microglial functions, the exact mechanism which controls their morphology is not fully understood. Here, we report that the FAT atypical cadherin family protein, FAT3, regulates the morphology of microglial cell line, BV2. We found that the shape of BV2 becomes elongated in a high-nutrient medium. Using microarray analysis, we identified that FAT3 expression is induced by culturing with a high-nutrient medium. In addition, we found that purinergic analog, hypoxanthine, promotes FAT3 expression in BV2 and mouse primary microglia. FAT3 expression induced by hypoxanthine extends the time of sustaining the elongated forms in BV2. These data suggest that the hypoxanthine-FAT3 axis is a novel pathway associated with microglial morphology. Our data provide a possibility that FAT3 may control microglial transitions involved in their morphologic changes during the postnatal stages in vivo .

The central nervous system (CNS) plays a crucial role in regulating bodily functions by sensing and integrating environmental cues and maintaining proper physiological conditions. Recent research has revealed that CNS functions are closely coordinated with the immune system. As even minor disturbances of the immune system in the CNS can lead to various dysfunctions, diseases, or even death, it is highly specialized and segregated from that in peripheral regions. Microglia in the parenchyma and macrophages at the interface between the CNS and peripheral regions are essential immune cells in the CNS that monitor environmental changes. Recent omics analyses have revealed that these cells exhibit highly heterogeneous populations. In this review, we summarize the functions and diversity of microglia in the brain parenchyma and those of macrophages in the border regions, such as the meninges, perivascular spaces, and choroid plexus.

Hevin is a secreted extracellular matrix protein that is encoded by SPARCL1 gene. Recent studies show that Hevin plays an important role in regulating synaptogenesis and synaptic plasticity. Mutations in SPARCL1 gene increase the risk of autism spectrum disorder (ASD). However, the molecular basis of how mutations in SPARCL1 increase the risk of ASD has not been fully understood. In this study, we show that one of SPARCL1 mutations associated with ASD impairs normal Hevin secretion. We identified Hevin mutants lacking the EF-hand motif through analyzing ASD-related mice with vulnerable spliceosome functions. Hevin deletion mutants accumulate in the ER, leading to the activation of unfolded protein responses. We also found that a single amino acid substitution of Trp647 with Arg in the EF-hand motif associated with a familial case of ASD causes a similar phenotype with the EF-hand deletion mutant. Importantly, molecular dynamics (MD) simulation revealed that this single amino acid substitution triggers exposure of hydrophobic amino acid to the surface, increasing the binding of Hevin with a molecular chaperon, BIP. Taken together, these data suggest that the integrity of EF-hand motif in Hevin is crucial for proper folding and ASD-related mutation impairs an export of Hevin from the endoplasmic reticulum (ER). Our data provide a novel mechanism linking a point mutation in SPARCL1 gene to the molecular and cellular characteristics involved in ASD.

No abstract

Mammals are thermostatic animals and can regulate their body temperature within a precise range, irrespective of ambient temperature conditions. However, the mechanisms of how a body temperature is controlled in cold environments are still unclear. Here, we report that RNA binding motif protein 3 (RBM3) is crucial for maintaining body temperature in response to cold stimulation. RBM3, the RNA binding protein that stabilizes the target mRNA, is one of the significant proteins induced by cold stimulation. The Rbm3 knockout (Rbm3-/-) juvenile mice are sensitive to cold exposure and cannot maintain their body temperature. Notably,Rbm3-/-mice decreased the expression level of UCP1 and UCP3, pivotal for thermogenesis in brown adipose tissue (BAT) and skeletal muscle, respectively. We also found that a defect in RBM3 increases the size of lipid droplets in the BAT. Additionally, UCP1 expression is canceled by cold stimulation inRbm3-/-BAT. On the other hand, RBM3 deficiency has little effect on cold-induced UCP3 expression in skeletal muscle. These data suggest that RBM3 prevents body temperature reduction induced by cold stimulation via expressing UCP1 in BAT. Our findings provide a possibility that RBM3 is a crucial regulator of thermogenesis in juvenile mice with unstable body temperature regulation.