Clustering of neuronal potassium channels is independent of their interaction with PSD-95

Voltage-dependent potassium channels regulate membrane excitability and cell–cell communication in the mammalian nervous system, and are found highly localized at distinct neuronal subcellular sites. Kv1 (mammalian Shaker family) potassium channels and the neurexin Caspr2, both of which contain COOH-terminal PDZ domain binding peptide motifs, are found colocalized at high density at juxtaparanodes flanking nodes of Ranvier of myelinated axons. The PDZ domain–containing protein PSD-95, which clusters Kv1 potassium channels in heterologous cells, has been proposed to play a major role in potassium channel clustering in mammalian neurons. Here, we show that PSD-95 colocalizes precisely with Kv1 potassium channels and Caspr2 at juxtaparanodes, and that a macromolecular complex of Kv1 channels and PSD-95 can be immunopurified from mammalian brain and spinal cord. Surprisingly, we find that the high density clustering of Kv1 channels and Caspr2 at juxtaparanodes is normal in a mutant mouse lacking juxtaparanodal PSD-95, and that the indirect interaction between Kv1 channels and Caspr2 is maintained in these mutant mice. These data suggest that the primary function of PSD-95 at juxtaparanodes lies outside of its accepted role in mediating the high density clustering of Kv1 potassium channels at these sites

The SH3 domain of postsynaptic density 95 mediates inflammatory pain through phosphatidylinositol-3-kinase recruitment

Sensitization to inflammatory pain is a pathological form of neuronal plasticity that is poorly understood and treated. Here we examine the role of the SH3 domain of postsynaptic density 95 (PSD95) by using mice that carry a single amino-acid substitution in the polyproline-binding site. Testing multiple forms of plasticity we found sensitization to inflammation was specifically attenuated. The inflammatory response required recruitment of phosphatidylinositol-3-kinase-C2α to the SH3-binding site of PSD95. In wild-type mice, wortmannin or peptide competition attenuated the sensitization. These results show that different types of behavioural plasticity are mediated by specific domains of PSD95 and suggest novel therapeutic avenues for reducing inflammatory pain

Pathogenetics of alveolar capillary dysplasia with misalignment of pulmonary veins.

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is a lethal lung developmental disorder caused by heterozygous point mutations or genomic deletion copy-number variants (CNVs) of FOXF1 or its upstream enhancer involving fetal lung-expressed long noncoding RNA genes LINC01081 and LINC01082. Using custom-designed array comparative genomic hybridization, Sanger sequencing, whole exome sequencing (WES), and bioinformatic analyses, we studied 22 new unrelated families (20 postnatal and two prenatal) with clinically diagnosed ACDMPV. We describe novel deletion CNVs at the FOXF1 locus in 13 unrelated ACDMPV patients. Together with the previously reported cases, all 31 genomic deletions in 16q24.1, pathogenic for ACDMPV, for which parental origin was determined, arose de novo with 30 of them occurring on the maternally inherited chromosome 16, strongly implicating genomic imprinting of the FOXF1 locus in human lungs. Surprisingly, we have also identified four ACDMPV families with the pathogenic variants in the FOXF1 locus that arose on paternal chromosome 16. Interestingly, a combination of the severe cardiac defects, including hypoplastic left heart, and single umbilical artery were observed only in children with deletion CNVs involving FOXF1 and its upstream enhancer. Our data demonstrate that genomic imprinting at 16q24.1 plays an important role in variable ACDMPV manifestation likely through long-range regulation of FOXF1 expression, and may be also responsible for key phenotypic features of maternal uniparental disomy 16. Moreover, in one family, WES revealed a de novo missense variant in ESRP1, potentially implicating FGF signaling in the etiology of ACDMPV

A case-control association study and family-based expression analysis of the bipolar disorder candidate gene PI4K2B

Bipolar disorder, schizophrenia and recurrent major depression are complex psychiatric illnesses with a substantial, yet unknown genetic component. Linkage of bipolar disorder and recurrent major depression with markers on chromosome 4p15–p16 has been identified in a large Scottish family and three smaller families. Analysis of haplotypes in the four chromosome 4p-linked families, identified two regions, each shared by three of the four families, which are also supported by a case-control association study. The candidate gene phosphatidylinositol 4-kinase type-II beta (PI4K2B) lies within one of these regions. PI4K2B is a strong functional candidate as it is a member of the phosphatidylinositol pathway, which is targeted by lithium for therapeutic effect in bipolar disorder. Two approaches were undertaken to test the PI4K2B candidate gene as a susceptibility factor for psychiatric illness. First, a case-control association study, using tagging SNPs from the PI4K2B genomic region, in bipolar disorder (n = 368), schizophrenia (n = 386) and controls (n = 458) showed association with a two-marker haplotype in schizophrenia but not bipolar disorder (rs10939038 and rs17408391, global P = 0.005, permuted global P = 0.039). Second, expression studies at the allele-specific mRNA and protein level using lymphoblastoid cell lines from members of the large Scottish family, which showed linkage to 4p15–p16 in bipolar disorder and recurrent major depression, showed no difference in expression differences between affected and non-affected family members. There is no evidence to suggest that PI4K2B is contributing to bipolar disorder in this family but a role for this gene in schizophrenia has not been excluded