ASD/OCD-Linked Protocadherin-10 Regulates Synapse, But Not Axon, Development in the Amygdala and Contributes to Fear- and Anxiety-Related Behaviors.

The Protocadherin-10 (PCDH10) gene is associated with autism spectrum disorder (ASD), obsessive-compulsive disorder (OCD), and major depression (MD). The PCDH10 protein is a homophilic cell adhesion molecule that belongs to the δ2-protocadherin family. PCDH10 is highly expressed in the developing brain, especially in the basolateral nucleus of the amygdala (BLA). However, the role of PCDH10 in vivo has been debatable: one paper reported that a Pcdh10 mutant mouse line showed changes in axonal projections; however, another Pcdh10 mutant mouse line was reported to have failed to detect axonal phenotypes. Therefore, the actual roles of PCDH10 in the brain remain to be elucidated. We established a new Pcdh10 KO mouse line using the CRISPR/Cas9 system, without inserting gene cassettes to avoid nonspecific effects, examined the roles of PCDH10 in the brain, and studied the behavioral consequences of Pcdh10 inactivation. Here, we show that Pcdh10 KO mice do not show defects in axonal development. Instead, we find that Pcdh10 KO mice exhibit impaired development of excitatory synapses in the dorsal BLA. We further demonstrate that male Pcdh10 KO mice exhibit reduced anxiety-related behaviors, impaired fear conditioning, decreased stress-coping responses, and mildly impaired social recognition and communication. These results indicate that PCDH10 plays a critical role in excitatory synapse development, but not axon development, in the dorsal BLA and that PCDH10 regulates anxiety-related, fear-related, and stress-related behaviors. Our results reveal the roles of PCDH10 in the brain and its relationship to relevant psychiatric disorders such as ASD, OCD, and MD.SIGNIFICANCE STATEMENTProtocadherin-10 (PCDH10) encodes a cell adhesion molecule and is implicated in autism spectrum disorder (ASD), obsessive-compulsive disorder (OCD), and major depression (MD). PCDH10 is highly expressed in the basolateral nucleus of the amygdala (BLA). However, the phenotypes of previously published Pcdh10 mutant mice are debatable, and some are possibly because of the nonspecific effects of the LacZ/Neo cassette inserted in the mice. We have generated a new Pcdh10 mutant mouse line without the LacZ/Neo cassette. Using our new mouse line, we reveal the roles of PCDH10 for excitatory synapse development in the BLA. The mutant mice exhibit anxiety-related, fear-related, and stress-related behaviors, which are relevant to ASD, OCD, and MD, suggesting a possible treatment strategy for such psychiatric disorders.

Regulation of CCR4-NOT complex deadenylase activity and cellular responses by MK2-dependent phosphorylation of CNOT2.

CCR4-NOT complex-mediated mRNA deadenylation serves critical functions in multiple biological processes, yet how this activity is regulated is not fully understood. Here, we show that osmotic stress induces MAPKAPK-2 (MK2)-mediated phosphorylation of CNOT2. Programmed cell death is greatly enhanced by osmotic stress in CNOT2-depleted cells, indicating that CNOT2 is responsible for stress resistance of cells. Although wild-type (WT) and non-phosphorylatable CNOT2 mutants reverse this sensitivity, a phosphomimetic form of CNOT2, in which serine at the phosphorylation site is replaced with glutamate, does not have this function. We also show that mRNAs have elongated poly(A) tails in CNOT2-depleted cells and that introduction of CNOT2 WT or a non-phosphorylatable mutant, but not phosphomimetic CNOT2, renders their poly(A) tail lengths comparable to those in control HeLa cells. Consistent with this, the CCR4-NOT complex containing phosphomimetic CNOT2 exhibits less deadenylase activity than that containing CNOT2 WT. These data suggest that CCR4-NOT complex deadenylase activity is regulated by post-translational modification, yielding dynamic control of mRNA deadenylation.

Female-specific synaptic dysfunction and cognitive impairment in a mouse model of PCDH19 disorder.

Protocadherin-19 (PCDH19) mutations cause early-onset seizures and cognitive impairment. The PCDH19 gene is on the X-chromosome. Unlike most X-linked disorders, PCDH19 mutations affect heterozygous females (PCDH19HET♀ ) but not hemizygous males (PCDH19HEMI♂ ); however, the reason why remains to be elucidated. We demonstrate that PCDH19, a cell-adhesion molecule, is enriched at hippocampal mossy fiber synapses. Pcdh19HET♀ but not Pcdh19HEMI♂ mice show impaired mossy fiber synaptic structure and physiology. Consistently, Pcdh19HET♀ but not Pcdh19HEMI♂ mice exhibit reduced pattern completion and separation abilities, which require mossy fiber synaptic function. Furthermore, PCDH19 appears to interact with N-cadherin at mossy fiber synapses. In Pcdh19HET♀ conditions, mismatch between PCDH19 and N-cadherin diminishes N-cadherin-dependent signaling and impairs mossy fiber synapse development; N-cadherin overexpression rescues Pcdh19HET♀ phenotypes. These results reveal previously unknown molecular and cellular mechanisms underlying the female-specific PCDH19 disorder phenotype.

Optimizing Nervous System-Specific Gene Targeting with Cre Driver Lines: Prevalence of Germline Recombination and Influencing Factors.

The Cre-loxP system is invaluable for spatial and temporal control of gene knockout, knockin, and reporter expression in the mouse nervous system. However, we report varying probabilities of unexpected germline recombination in distinct Cre driver lines designed for nervous system-specific recombination. Selective maternal or paternal germline recombination is showcased with sample Cre lines. Collated data reveal germline recombination in over half of 64 commonly used Cre driver lines, in most cases with a parental sex bias related to Cre expression in sperm or oocytes. Slight differences among Cre driver lines utilizing common transcriptional control elements affect germline recombination rates. Specific target loci demonstrated differential recombination; thus, reporters are not reliable proxies for another locus of interest. Similar principles apply to other recombinase systems and other genetically targeted organisms. We hereby draw attention to the prevalence of germline recombination and provide guidelines to inform future research for the neuroscience and broader molecular genetics communities.

Differential expression of axon-sorting molecules in mouse olfactory sensory neurons.

In the mouse olfactory system, the axons of olfactory sensory neurons that express the same type of odorant receptor (OR) converge to a specific set of glomeruli in the olfactory bulb (OB). It is widely accepted that expressed OR molecules instruct glomerular segregation by regulating the expression of axon-sorting molecules. Although the relationship between the expression of axon-sorting molecules and OR types has been analyzed in detail, those between the expressions of axon-sorting molecules remain to be elucidated. Here we collected the expression profiles of four axon-sorting molecules from a large number of glomeruli in the OB. These molecules demonstrated position-independent mosaic expressions, but their patterns were not identical in the OB. Comparing their expressions identified positive and negative correlations between several pairs of genes even though they showed various expressions. Furthermore, the principal component analysis revealed that the factor loadings in the principal component 1, which explain the largest amount of variation, were most likely to reflect the degree of the cyclic nucleotide-gated (CNG) channel dependence on the expression of axon-sorting molecules. Thus, neural activity generated through the CNG channel is a major component in the generation of a wide variety of expressions of axon-sorting molecules in glomerular segregation.

LMTK3 deficiency causes pronounced locomotor hyperactivity and impairs endocytic trafficking.

LMTK3 belongs to the LMTK family of protein kinases that are predominantly expressed in the brain. Physiological functions of LMTK3 and other members of the LMTK family in the CNS remain unknown. In this study, we performed a battery of behavioral analyses using Lmtk3(-/-) mice and showed that these mice exhibit abnormal behaviors, including pronounced locomotor hyperactivity, reduced anxiety behavior, and decreased depression-like behavior. Concurrently, the dopamine metabolite levels and dopamine turnover rate are increased in the striata of Lmtk3(-/-) mice compared with wild-type controls. In addition, using cultured primary neurons from Lmtk3(-/-) mice, we found that LMTK3 is involved in the endocytic trafficking of N-methyl-d-aspartate receptors, a type of ionotropic glutamate receptor. Altered membrane traffic of the receptor in Lmtk3(-/-) neurons may underlie behavioral abnormalities in the mutant animals. Together, our data suggest that LMTK3 plays an important role in regulating locomotor behavior in mice.

Protocadherin 17 regulates presynaptic assembly in topographic corticobasal Ganglia circuits.

Highly topographic organization of neural circuits exists for the regulation of various brain functions in corticobasal ganglia circuits. Although neural circuit-specific refinement during synapse development is essential for the execution of particular neural functions, the molecular and cellular mechanisms for synapse refinement are largely unknown. Here, we show that protocadherin 17 (PCDH17), one of the nonclustered δ2-protocadherin family members, is enriched along corticobasal ganglia synapses in a zone-specific manner during synaptogenesis and regulates presynaptic assembly in these synapses. PCDH17 deficiency in mice causes facilitated presynaptic vesicle accumulation and enhanced synaptic transmission efficacy in corticobasal ganglia circuits. Furthermore, PCDH17(-/-) mice exhibit antidepressant-like phenotypes that are known to be regulated by corticobasal ganglia circuits. Our findings demonstrate a critical role for PCDH17 in the synaptic development of specific corticobasal ganglia circuits and suggest the involvement of PCDH17 in such circuits in depressive behaviors.

NYAP: a phosphoprotein family that links PI3K to WAVE1 signalling in neurons.

The phosphoinositide 3-kinase (PI3K) pathway has been extensively studied in neuronal function and morphogenesis. However, the precise molecular mechanisms of PI3K activation and its downstream signalling in neurons remain elusive. Here, we report the identification of the Neuronal tYrosine-phosphorylated Adaptor for the PI 3-kinase (NYAP) family of phosphoproteins, which is composed of NYAP1, NYAP2, and Myosin16/NYAP3. The NYAPs are expressed predominantly in developing neurons. Upon stimulation with Contactin5, the NYAPs are tyrosine phosphorylated by Fyn. Phosphorylated NYAPs interact with PI3K p85 and activate PI3K, Akt, and Rac1. Moreover, the NYAPs interact with the WAVE1 complex which mediates remodelling of the actin cytoskeleton after activation by PI3K-produced PIP(3) and Rac1. By simultaneously interacting with PI3K and the WAVE1 complex, the NYAPs bridge a PI3K-WAVE1 association. Disruption of the NYAP genes in mice affects brain size and neurite elongation. In conclusion, the NYAPs activate PI3K and concomitantly recruit the downstream effector WAVE complex to the close vicinity of PI3K and regulate neuronal morphogenesis.

Transcriptional repressor TIEG1 regulates Bmal1 gene through GC box and controls circadian clockwork.

The circadian clock controls daily rhythms in many physiologic processes, and the clock oscillation is regulated by external time cues such as light, temperature, and feeding. In mammals, the transcriptional regulation of clock genes underlies the clock oscillatory mechanism, which is operative even in cultured fibroblasts. We previously demonstrated that glucose treatment of rat-1 fibroblasts evokes circadian expression of clock genes with a rapid induction of Tieg1 transcript encoding a transcriptional repressor. Here, we found diurnal variation of both Tieg1 mRNA and nuclear TIEG1 protein levels in the mouse liver with their peaks at day/night transition and midnight, respectively. In vitro experiments showed that TIEG1 bound to Bmal1 gene promoter and repressed its transcriptional activity through two juxtaposed GC boxes near the transcription initiation site. The GC box/TIEG1-mediated repression of Bmal1 promoter was additive to RORE-dependent repression by REV-ERBalpha, a well-known repressor of Bmal1 gene. In cell-based real-time assay, siRNA-mediated knock-down of TIEG1 caused period shortening of cellular bioluminescence rhythms driven by Bmal1-luciferase and Per2-luciferase reporters. These findings highlight an active role of TIEG1 in the normal clock oscillation and GC box-mediated regulation of Bmal1 transcription.

Focal adhesion kinase regulates laminin-induced oligodendroglial process outgrowth.

In the central nervous system (CNS), myelination of axons occurs when oligodendrocyte progenitor cells undergo terminal differentiation, and initiate process formation and axonal ensheathment. Although Fyn, a member of the Src-family kinases (SFKs), plays an important role in this differentiation process, the substrates of Fyn in oligodendrocytes are largely unknown. Using mass spectrometric analysis, we identified focal adhesion kinase (FAK) as a tyrosine-phosphorylated protein in the rat-derived CG4 oligodendrocyte cell line. Tyrosine phosphorylation of FAK was enhanced during differentiation of CG4 cells in a Fyn-dependent manner. In addition, phosphorylation of FAK was stimulated by laminin, one of the ligands for integrin. Knockdown of FAK expression in CG4 cells suppressed process outgrowth on laminin. Rac1 and Cdc42 activities, which are required for oligodendrocyte process formation, were down-regulated in FAK-knockdown cells. Expression of wild-type (WT) FAK in FAK-knockdown CG4 cells restored outgrowth of processes, but the Y397F mutant lacking the autophosphorylation site did not. These results suggest that FAK/Fyn-mediated activation of Rac1 and Cdc42 is critical for laminin-induced outgrowth of oligodendrocyte processes.

Phosphorylation at Tyr-694 of Nogo-A by Src-family kinases.

Nogo-A is a neurite outgrowth inhibitor protein associated with myelin in the central nervous system. Unexpectedly, targeted disruption of Nogo-A in mice results in little or no improvement of axonal regeneration, suggesting that Nogo-A has other functions and/or receives complex regulations to exert its inhibitory functions. Here, we have found that Nogo-A becomes phosphorylated at Tyr-694 in the N-terminal region. The phosphorylation is mediated co-operatively by Src-family tyrosine kinases, which play many important roles in the nervous system. Levels of tyrosine phosphorylation of Nogo-A seem to be irrelevant to developmental stages of oligodendrocytes, and might be regulated by specific extracellular stimuli. Identification of tyrosine phosphorylation of Nogo-A will introduce an additional level of complexity into Nogo-A functions.