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Metabotropic glutamate receptor 2 (GRM2) is highly expressed in hippocampal dentate granule cells (DGCs), regulating synaptic transmission and hippocampal functions. Newborn DGCs are continuously generated throughout life and express GRM2 when they are mature. However, it remained unclear whether and how GRM2 regulates the development and integration of these newborn neurons. We discovered that the expression of GRM2 in adult-born DGCs increased with neuronal development in mice of both sexes. Lack of GRM2 caused developmental defects of DGCs and impaired hippocampus-dependent cognitive functions. Intriguingly, our data showed that knockdown ofGrm2resulted in decreased b/c-Raf kinases and paradoxically led to an excessive activation of MEK/ERK1/2 pathway. Inhibition of MEK ameliorated the developmental defects caused byGrm2knockdown. Together, our results indicate that GRM2 is necessary for the development and functional integration of newborn DGCs in the adult hippocampus through regulating the phosphorylation and activation state of MEK/ERK1/2 pathway.SIGNIFICANCE STATEMENTMetabotropic glutamate receptor 2 (GRM2) is highly expressed in mature dentate granule cells (DGCs) in the hippocampus. It remains unclear whether GRM2 is required for the development and integration of adult-born DGCs. We providedin vivoandin vitroevidence to show that GRM2 regulates the development of adult-born DGCs and their integration into existing hippocampal circuits. Lack of GRM2 in a cohort of newborn DGCs impaired object-to-location memory in mice. Moreover, we revealed that GRM2 knockdown paradoxically upregulated MEK/ERK1/2 pathway by suppressing b/c-Raf in developing neurons, which is likely a common mechanism underlying the regulation of the development of neurons expressing GRM2. Thus, Raf/MEK/ERK1/2 pathway could be a potential target for brain diseases related to GRM2 abnormality.

Protein quality control (PQC) is essential for maintaining protein homeostasis and guarding the accuracy of neurodevelopment. Previously, we found that a conserved EBAX-type CRL regulates the protein quality of SAX-3/ROBO guidance receptors in Caenorhabditis elegans. Here, we report that ZSWIM8, the mammalian homolog of EBAX-1, is essential for developmental stability of mammalian brains. Conditional deletion of Zswim8 in the embryonic nervous system causes global cellular stress, partial perinatal lethality and defective migration of neural progenitor cells. CRISPR-mediated knockout of ZSWIM8 impairs spine formation and synaptogenesis in hippocampal neurons. Mechanistic studies reveal that ZSWIM8 controls protein quality of Disabled 1 (Dab1), a key signal molecule for brain development, thus protecting the signaling strength of Dab1. As a ubiquitin ligase enriched with intrinsically disordered regions (IDRs), ZSWIM8 specifically recognizes IDRs of Dab1 through a “disorder targets misorder” mechanism and eliminates misfolded Dab1 that cannot be properly phosphorylated. Adult survivors of ZSWIM8 CKO show permanent hippocampal abnormality and display severely impaired learning and memory behaviors. Altogether, our results demonstrate that ZSWIM8-mediated PQC is critical for the stability of mammalian brain development.

Hippocampal neurogenesis declines with aging. Wnt ligands and antagonists within the hippocampal neurogenic niche regulate the proliferation of neural progenitor cells and the development of new neurons, and the changes of their levels in the niche mediate aging-associated decline of neurogenesis. We found that RNA-binding protein Lin28a remained existent in neural progenitor cells and granule neurons in the adult hippocampus, and decreased with aging. Loss of Lin28a inhibited the responsiveness of neural progenitor cells to niche Wnt agonist and reduced neurogenesis, thus impairing pattern separation. Overexpression of Lin28a increased the proliferation of neural progenitor cells, promoted the functional integration of newborn neurons, restored neurogenesis in Wnt-deficient dentate gyrus, and rescued the impaired pattern separation in aging mice. Our data suggest that Lin28a regulates adult hippocampal neurogenesis as an intracellular mechanism by responding to niche Wnt signals, and its decrease is involved in aging-associated decline of hippocampal neurogenesis as well as related cognitive functions.

Aiming at the problems of low optimization accuracy, poor optimization effect, and long running time in current teaching optimization algorithms, a multiclass interactive martial arts teaching optimization method based on the Euclidean distance is proposed. Using the K-means algorithm, the initial population is divided into several subgroups based on the Euclidean distance, so as to effectively use the information of the population neighborhood and strengthen the local search ability of the algorithm. Imitating the school's selection of excellent teachers to guide students with poor performance, after the “teaching” stage, the worst individual in each subgroup will learn from the best individual in the population, and the information interaction in the evolutionary process will be enhanced, so that the poor individuals will quickly move closer to the best individuals. According to different learning levels and situations of students, different teaching stages and contents are divided, mainly by grade, supplemented by different types of learning groups in the form of random matching, so as to improve the learning ability of members with weak learning ability in each group, which effectively guarantees the diversity of the population and realizes multiclass interactive martial arts teaching optimization. Experimental results show that the optimization effect of the proposed method is better, which can effectively improve the accuracy of algorithm optimization and shorten the running time of the algorithm.

Microglia modulate memories Synaptic reorganization and circuit rewiring leads to loss or weakening of connections between neurons and may result in the erasure of previously formed memories. Microglia eliminate excessive synapses in the developing brain and regulate the dynamics of synaptic connections between neurons throughout life. However, it is still unclear whether forgetting is related to microglia activity and how microglia regulate memory erasure in the adult brain. Wang et al. discovered that microglia eliminated synaptic components in the adult hippocampus and that depleting microglia or inhibiting phagocytosis of microglia prevented forgetting. Synapse elimination by microglia may thus lead to degradation of memory engrams and forgetting of previously learned contextual fear memory. Science , this issue p. 688