The rockefeller university

Ventral tegmental area(VTA) dopamine neurons in the brain's reward circuit have a crucial role in mediating stress responses(1-4), including determining susceptibility versus resilience to social-stress-induced behavioural abnormalities(5). VTA dopamine neurons show two in vivo patterns of firing: low frequency tonic firing and high frequency phasic firing(6-8). Phasic firing of the neurons, which is well known to encode reward signals(6,7,9), is upregulated by repeated social-defeat stress, a highly validated mouse model of depression(5,8,10-13). Surprisingly, this pathophysiological effect is seen in susceptible mice only, with no apparent change in firing rate in resilient individuals(5,8). However, direct evidence-in real time-linking dopamine neuron phasic firing in promoting the susceptible (depression-like) phenotype is lacking. Here we took advantage of the temporal precision and cell-type and projection-pathway specificity of optogenetics to show that enhanced phasic firing of these neurons mediates susceptibility to social-defeat stress in freely behaving mice. We show that optogenetic induction of phasic, but not tonic, firing in VTA dopamine neurons of mice undergoing a subthreshold social-defeat paradigm rapidly induced a susceptible phenotype as measured by social avoidance and decreased sucrose preference. Optogenetic phasic stimulation of these neurons also quickly induced a susceptible phenotype in previously resilient mice that had been subjected to repeated social-defeat stress. Furthermore, we show differences in projection-pathway specificity in promoting stress susceptibility: phasic activation of VTA neurons projecting to the nucleus accumbens (NAc), but not to the medial prefrontal cortex (mPFC), induced susceptibility to social-defeat stress. Conversely, optogenetic inhibition of the VTA-NAc projection induced resilience, whereas inhibition of the VTA-mPFC projection promoted susceptibility. Overall, these studies reveal novel firing-pattern-and neural-circuit-specific mechanisms of depression.

Beyond its well-characterized functions in antibody diversification, the cytidine deaminase AID can catalyze off-target DNA damage and has been hypothesized to edit RNA and mediate DNA demethylation. To comprehensively examine the effects of AID on the transcriptome and the pattern of DNA methylation ('methylome'), we analyzed AID-deficient (Aicda(-/-)), wild-type and AID-overexpressing activated B cells by high-throughput RNA sequencing (RNA-Seq) and reduced-representation bisulfite sequencing (RRBS). These analyses confirmed the known role of AID in immunoglobulin isotype switching and also demonstrated few other effects of AID on gene expression. Additionally, we detected no evidence of AID-dependent editing of mRNA or microRNA. Finally, the RRBS data did not support the proposed role for AID in regulating DNA methylation. Thus, despite evidence of its additional activities in other systems, antibody diversification seems to be the sole physiological function of AID in activated B cells.

Vaccine candidates for HIV-1 so far have not been able to elicit broadly neutralizing antibodies (bNAbs) although they express the epitopes recognized by bNAbs to the HIV envelope glycoprotein (Env). To understand whether and how Env immunogens interact with the predicted germline versions of known bNAbs, we screened a large panel (N:56) of recombinant Envs (from clades A, B and C) for binding to the germline predecessors of the broadly neutralizing anti-CD4 binding site antibodies b12, NIH45-46 and 3BNC60. Although the mature antibodies reacted with diverse Envs, the corresponding germline antibodies did not display Env-reactivity. Experiments conducted with engineered chimeric antibodies combining the mature and germline heavy and light chains, respectively and vice-versa, revealed that both antibody chains are important for the known cross-reactivity of these antibodies. Our results also indicate that in order for b12 to display its broad cross-reactivity, multiple som!

Hepatitis C virus (HCV) is a major causative agent of severe liver disease including fibrosis, cirrhosis and liver cancer. Therapy has improved over the years, but continues to be associated with adverse side effects and variable success rates. Furthermore, a vaccine protecting against HCV infection remains elusive. Development of more effective intervention measures has been delayed by the lack of a suitable animal model. Naturally, HCV infects only humans and chimpanzees. The determinants of this limited host range are poorly understood in part due to difficulties of studying HCV in cell culture. Some progress has been made elucidating the barriers for the HCV lifecycle in non-permissive species which will help in the future to construct animal models for HCV infection, immunity and pathogenesis. (C) 2012 Elsevier Inc. All rights reserved.

Early life adversity, including adverse gestational and postpartum maternal environment, is a contributing factor in the development of autism, attention deficit hyperactivity disorder (ADHD), anxiety and depression but little is known about the underlying molecular mechanism. In a model of gestational maternal adversity that leads to innate anxiety, increased stress reactivity and impaired vocal communication in the offspring, we asked if a specific DNA methylation signature is associated with the emergence of the behavioral phenotype. Genome-wide DNA methylation analyses identified 2.3% of CpGs as differentially methylated (that is, differentially methylated sites, DMSs) by the adverse environment in ventral-hippocampal granule cells, neurons that can be linked to the anxiety phenotype. DMSs were typically clustered and these clusters were preferentially located at gene bodies. Although CpGs are typically either highly methylated or unmethylated, DMSs had an intermediat!

Mycobacterium tuberculosis persists in the tissues of mammalian hosts despite inducing a robust immune response dominated by the macrophage-activating cytokine gamma interferon (IFN-gamma). We identified the M. tuberculosis phosphate-specific transport (Pst) system component PstA1 as a factor required to resist IFN-gamma-dependent immunity. A Delta pstA1 mutant was fully virulent in IFN-gamma(-/-) mice but attenuated in wild-type (WT) mice and mice lacking specific IFN-gamma-inducible immune mechanisms: nitric oxide synthase (NOS2), phagosome-associated p47 GTPase (Irgm1), or phagocyte oxidase (phox). These phenotypes suggest that Delta pstA1 bacteria are sensitized to an IFN-gamma-dependent immune mechanism(s) other than NOS2, Irgm1, or phox. In other species, the Pst system has a secondary role as a negative regulator of phosphate starvation-responsive gene expression through an interaction with a two-component signal transduction system. In M. tuberculosis, we found th!

Grb2-associated binder 2 (Gab2) serves as a critical amplifier in the signaling network of Bcr-Abl, the driver of chronic myeloid leukemia (CML). Despite the success of tyrosine kinase inhibitors (TKIs) in CML treatment, TKI resistance, caused by mutations in Bcr-Abl or aberrant activity of its network partners, remains a clinical problem. Using inducible expression and knockdown systems, we analyzed the role of Gab2 in Bcr-Abl signaling in human CML cells, especially with respect to TKI sensitivity. We show for the first time that Gab2 signaling protects CML cells from various Bcr-Abl inhibitors (imatinib, nilotinib, dasatinib and GNF-2), whereas Gab2 knockdown or haploinsufficiency leads to increased TKI sensitivity. We dissected the underlying molecular mechanism using various Gab2 mutants and kinase inhibitors and identified the Shp2/Ras/ERK and the PI3K/AKT/mTOR axes as the two critical signaling pathways. Gab2-mediated TKI resistance was associated with persistent p!

In this Reflections, I review a few early and very lucky events that gave me a running start for the rest of a long and wonderfully enjoyable career. For the main part, a discussion is provided of what I recall as the main illuminating results that my many dozens of students and postdoctoral fellows (approximately 140 in all) provided to our biochemical/molecular biological world.