Oxygen-dependent acetylation and dimerization of the corepressor CtBP2 in neural stem cells

The corepressor CtBP2 is required for proper development of the mouse cerebral cortex

The development of the cerebral cortex depends on numerous parameters, including extracellular cues and microenvironmental factors that also affect gene expression. C-Terminal Binding Proteins (CtBPs) 1 and 2 are transcriptional co-repressors which have been shown to be critically involved in embryonic development. CtBPs are oxygen sensing molecules, and we have previously demonstrated an important role for CtBP1 in integrating oxygen levels and BMP-signaling to influence neural progenitor fate choice. In turn, CtBP2 has been associated with neurodevelopment and neurological disease, and we have shown that CtBP2 acetylation and dimerization, required for proper transcriptional activity, are regulated by microenvironmental oxygen levels. Yet, the putative function of CtBP2 in mammalian cortical development and neurogenesis in vivo is still largely unknown. Here we show that CtBP2 was widely expressed by neural stem and progenitor cells (NSPCs) as well as neurons during cortical development in mice. By using in utero electroporation of siRNA to reduce the levels of CtBP2 mRNA and protein in the developing mouse brain, we found that the NSPC proliferation and migration were largely perturbed, while glial differentiation under these conditions remained unchanged. Our study provides evidence that CtBP2 is required for the maintenance and migration of the NSPCs during mouse cortical development.

Sensory Processing at Ribbon Synapses in the Retina and the Cochlea

In recent years, sensory neuroscientists have made major efforts to dissect the structure and function of ribbon synapses which process sensory information in the eye and ear. This review aims to summarize our current understanding of two key aspects of ribbon synapses: 1) their mechanisms of exocytosis and endocytosis and 2) their molecular anatomy and physiology. Our comparison of ribbon synapses in the cochlea and the retina reveals convergent signaling mechanisms, as well as divergent strategies in different sensory systems.

Dimerization of MORC2 through its C-terminal coiled-coil domain enhances chromatin dynamics and promotes DNA repair

Decondesation of the highly compacted chromatin architecture is essential for efficient DNA repair, but how this is achieved remains largely unknown. Here, we report that microrchidia family CW-type zinc finger protein 2 (MORC2), a newly identified ATPase-dependent chromatin remodeling enzyme, is required for nucleosome destabilization after DNA damage through loosening the histone-DNA interaction. Depletion of MORC2 attenuates phosphorylated histone H2AX (γH2AX) focal formation, compromises the recruitment of DNA repair proteins, BRCA1, 53BP1, and Rad51, to sites of DNA damage, and consequently reduces cell survival following treatment with DNA-damaging chemotherapeutic drug camptothecin (CPT). Furthermore, we demonstrate that MORC2 can form a homodimer through its C-terminal coiled-coil (CC) domain, a process that is enhanced in response to CPT-induced DNA damage. Deletion of the C-terminal CC domain in MORC2 disrupts its homodimer formation and impairs its ability to destabilize histone-DNA interaction after DNA damage. Consistently, expression of dimerization-defective MORC2 mutant results in impaired the recruitment of DNA repair proteins to damaged chromatin and decreased cell survival after CPT treatment. Together, these findings uncover a new mechanism for MORC2 in modulating chromatin dynamics and DDR signaling through its c-terminal dimerization.

CtBP2 ameliorates palmitate-induced insulin resistance in HepG2 cells through ROS mediated JNK pathway

Oxidative stress plays a significant role in the development of hepatic insulin resistance, but the underlying molecular mechanisms remain poorly understood. In this study, we discovered that C-terminal-binding protein 2 (CtBP2) level was decreased in insulin resistance. Taking into account the relationship between CtBP family protein (ANGUSTIFOLIA) and reactive oxygen species (ROS) accumulation, we conjectured CtBP2 was involved in insulin resistance through ROS induced stress. In order to verify this hypothesis, we over-expressed CtBP2 in palmitate (PA) treated HepG2 cells. Here, we found that over-expression of CtBP2 ameliorated insulin sensitivity by increasing phosphorylation of glycogen synthase kinase 3β (GSK3β) and protein kinase B (AKT). These data suggest that CtBP2 plays a critical role in the development of insulin resistance. Moreover, CtBP2 reversed the effects of PA on ROS level, lipid accumulation, hepatic glucose uptake and gluconeogenesis. We also found that over-expression of CtBP2 could suppress PA induced c-jun NH2 terminal kinase (JNK) activation. Furthermore, JNK inhibitor SP600125 was shown to promote the effect of CtBP2 on insulin signaling. Thus, we demonstrated that CtBP2 ameliorated PA-induced insulin resistance via ROS-dependent JNK pathway.

RIBEYE(B)-domain binds to lipid components of synaptic vesicles in an NAD(H)-dependent, redox-sensitive manner

Synaptic ribbons are needed for fast and continuous exocytosis in ribbon synapses. RIBEYE is a main protein component of synaptic ribbons and is necessary to build the synaptic ribbon. RIBEYE consists of a unique A-domain and a carboxyterminal B-domain, which binds NAD(H). Within the presynaptic terminal, the synaptic ribbons are in physical contact with large numbers of synaptic vesicle (SV)s. How this physical contact between ribbons and synaptic vesicles is established at a molecular level is not well understood. In the present study, we demonstrate that the RIBEYE(B)-domain can directly interact with lipid components of SVs using two different sedimentation assays with liposomes of defined chemical composition. Similar binding results were obtained with a SV-containing membrane fraction. The binding of liposomes to RIBEYE(B) depends upon the presence of a small amount of lysophospholipids present in the liposomes. Interestingly, binding of liposomes to RIBEYE(B) depends on NAD(H) in a redox-sensitive manner. The binding is enhanced by NADH, the reduced form, and is inhibited by NAD⁺, the oxidized form. Lipid-mediated attachment of vesicles is probably part of a multi-step process that also involves additional, protein-dependent processes.