Brain-derived neurotrophic factor interacts with adult-born immature cells in the dentate gyrus during consolidation of overlapping memories.

Successful memory involves not only remembering information over time but also keeping memories distinct and less confusable. The computational process for making representations of similar input patterns more distinct from each other has been referred to as "pattern separation." Although adult-born immature neurons have been implicated in this memory feature, the precise role of these neurons and associated molecules in the processing of overlapping memories is unknown. Recently, we found that brain-derived neurotrophic factor (BDNF) in the dentate gyrus is required for the encoding/consolidation of overlapping memories. In this study, we provide evidence that consolidation of these "pattern-separated" memories requires the action of BDNF on immature neurons specifically.The Biotechnology and Biological Sciences Research Council . Grant Number: BB/G019002/1 The Innovative Medicine Initiative Joint Undertaking . Grant Number: 115008 The European Union's Seventh Framework Programme . Grant Number: FP7/2007-2013 The James S. McDonnell Foundation, Mather's Foundation, NIMH, Ellison Foundation, NINDS, NIMH, NIA, JPB FoundationThis is the final published version, which can also be viewed online at: http://onlinelibrary.wiley.com/doi/10.1002/hipo.22304/ful

A Novel Checkpoint and RPA Inhibitory Pathway Regulated by Rif1

Cells accumulate single-stranded DNA (ssDNA) when telomere capping, DNA replication, or DNA repair is impeded. This accumulation leads to cell cycle arrest through activating the DNA–damage checkpoints involved in cancer protection. Hence, ssDNA accumulation could be an anti-cancer mechanism. However, ssDNA has to accumulate above a certain threshold to activate checkpoints. What determines this checkpoint-activation threshold is an important, yet unanswered question. Here we identify Rif1 (Rap1-Interacting Factor 1) as a threshold-setter. Following telomere uncapping, we show that budding yeast Rif1 has unprecedented effects for a protein, inhibiting the recruitment of checkpoint proteins and RPA (Replication Protein A) to damaged chromosome regions, without significantly affecting the accumulation of ssDNA at those regions. Using chromatin immuno-precipitation, we provide evidence that Rif1 acts as a molecular “band-aid” for ssDNA lesions, associating with DNA damage independently of Rap1. In consequence, small or incipient lesions are protected from RPA and checkpoint proteins. When longer stretches of ssDNA are generated, they extend beyond the junction-proximal Rif1-protected regions. In consequence, the damage is detected and checkpoint signals are fired, resulting in cell cycle arrest. However, increased Rif1 expression raises the checkpoint-activation threshold to the point it simulates a checkpoint knockout and can also terminate a checkpoint arrest, despite persistent telomere deficiency. Our work has important implications for understanding the checkpoint and RPA–dependent DNA–damage responses in eukaryotic cells

Long-term labeling of hippocampal neural stem cells by a lentiviral vector

Using a lentivirus-mediated labeling method, we investigated whether the adult hippocampus retains long-lasting, self-renewing neural stem cells (NSCs). We first showed that a single injection of a lentiviral vector expressing a green fluorescent protein (LV PGK-GFP) into the subgranular zone (SGZ) of the adult hippocampus enabled an efficient, robust, and long-term marking of self-renewing NSCs and their progeny. Interestingly, a subset of labeled cells showed the ability to proliferate multiple times and give rise to Sox2+ cells, clearly suggesting the ability of NSCs to self-renew for an extensive period of time (up to 6 months). In addition, using GFP+ cells isolated from the SGZ of mice that received a LV PGK-GFP injection 3 months earlier, we demonstrated that some GFP+ cells displayed the essential properties of NSCs, such as self-renewal and multipotency. Furthermore, we investigated the plasticity of NSCs in a perforant path transection, which has been shown to induce astrocyte formation in the molecular layer of the hippocampus. Our lentivirus (LV)-mediated labeling study revealed that hippocampal NSCs are not responsible for the burst of astrocyte formation, suggesting that signals released from the injured perforant path did not influence NSC fate determination. Therefore, our studies showed that a gene delivery system using LVs is a unique method to be used for understanding the complex nature of NSCs and may have translational impact in gene therapy by efficiently targeting NSCs