Adult neurogenesis occurs throughout life in discrete regions of the adult mammalian brain. Little is known about the mechanism governing the sequential developmental process that leads to integration of new neurons from adult neural stem cells into the existing circuitry. Here, we investigated roles of Disrupted-In-Schizophrenia 1 (DISC1), a schizophrenia susceptibility gene, in adult hippocampal neurogenesis. Unexpectedly, downregulation of DISC1 leads to accelerated neuronal integration, resulting in aberrant morphological development and mispositioning of new dentate granule cells in a cell-autonomous fashion. Functionally, newborn neurons with DISC1 knockdown exhibit enhanced excitability and accelerated dendritic development and synapse formation. Furthermore, DISC1 cooperates with its binding partner NDEL1 in regulating adult neurogenesis. Taken together, our study identifies DISC1 as a key regulator that orchestrates the tempo of functional neuronal integration in the adult brain and demonstrates essential roles of a susceptibility gene for major mental illness in neuronal development, including adult neurogenesis.

BACKGROUND Common variable immunodeficiency (CVID) is characterized by late-onset hypogammaglobulinemia in the absence of predisposing factors. The genetic cause is unknown in the majority of cases, and less than 10% of patients have a family history of the disease. Most patients have normal numbers of B cells but lack plasma cells. METHODS We used whole-exome sequencing and array-based comparative genomic hybridization to evaluate a subset of patients with CVID and low B-cell numbers. Mutant proteins were analyzed for DNA binding with the use of an electrophoretic mobility-shift assay (EMSA) and confocal microscopy. Flow cytometry was used to analyze peripheral-blood lymphocytes and bone marrow aspirates. RESULTS Six different heterozygous mutations in IKZF1, the gene encoding the transcription factor IKAROS, were identified in 29 persons from six families. In two families, the mutation was a de novo event in the proband. All the mutations, four amino acid substitutions, an intragenic deletion, and a 4.7-Mb multigene deletion involved the DNA-binding domain of IKAROS. The proteins bearing missense mutations failed to bind target DNA sequences on EMSA and confocal microscopy; however, they did not inhibit the binding of wild-type IKAROS. Studies in family members showed progressive loss of B cells and serum immunoglobulins. Bone marrow aspirates in two patients had markedly decreased early B-cell precursors, but plasma cells were present. Acute lymphoblastic leukemia developed in 2 of the 29 patients. CONCLUSIONS Heterozygous mutations in the transcription factor IKAROS caused an autosomal dominant form of CVID that is associated with a striking decrease in B-cell numbers. (Funded by the National Institutes of Health and others.)

Fö rster resonance energy transfer (FRET) microscopy is a powerful technique that enables the visualization of signaling intermediates, protein interactions, and protein conformational and biochemical status. With the availability of an ever-increasing collection of fluorescent proteins, pairs of spectrally different variants have been used for the study of FRET in living cells. However, suitable spectral overlap, necessary for efficient FRET, is limited by the requirement for proper emission separation. Currently used FRET pairs represent compromises between these opposing spectral demands that reduce the maximally attainable FRET sensitivity. We present a previously undescribed FRET acceptor, a nonfluorescent yellow fluorescent protein (YFP) mutant called REACh (for Resonance Energy-Accepting Chromoprotein). REACh allows the use of the photophysically superior FRET donor EGFP, with which it exhibits optimal spectral overlap, which obviates the need for narrow spectral filtering and allows additional fluorescent labels to be used within the same cell. The latter allows the generation of sophisticated bioassays for complex biological questions. We show that this dark acceptor is ideally suited for donor fluorescence lifetime imaging microscopy (FLIM) and confirm these measurements with an independent intensity-based donor fluorescence quenching resonance energy transfer (FqRET) assay. REACh also can be used in donor photobleaching kinetics-based FRET studies. By detecting FRET between a GFP-tagged ubiquitination substrate and REACh-labeled ubiquitin, we imaged the active ubiquitination machinery inside cells. This assay therefore can be used to study proteins whose function is regulated by ubiquitination.biosensor ͉ fluorescence lifetime imaging microscopy ͉ ubiquitin ͉ proteasome F luorescent protein-based Förster resonance energy transfer (FRET) (1) assays allow the detection and quantification of a variety of cellular biochemical events, e.g., GTPase activity status, protein phosphorylation, degradation, conformational changes, and interactions (2, 3). Spectral contamination, i.e., donor emission bleed-through and direct acceptor excitation, complicates the measurement of FRET between fluorescent protein conjugates and reduces the dynamic range and sensitivity even when both fluorophores are included in the same reporter construct. The ideal FRET couple should possess a large spectral overlap between donor emission and acceptor absorption but separated emission spectra to allow their selective imaging. Because of the relatively broad emission spectra and small Stokes shift, fluorescent proteins generally fail to fulfill these criteria.The most used FRET pair is a cyan fluorescent protein (CFP) donor and a yellow fluorescent protein (YFP) acceptor (3, 4). CFP furthermore suffers from a reduced fluorescence yield when compared with most members of the fluorescent protein family (5). Moreover, its excitation at low wavelengths causes substantial autofluorescence in cells and is not compatible with commonly used ...

The glucocorticoid receptor's oligomerization state is revealed to not correlate with its activity; this challenges the current prevailing view that this state defines its transcriptional activity.