Our behavioral work showed that the aPKC CBP pathway

Our behavioral work showed that the aPKC-CBP pathway is required for hippocampal-dependent fear memory formation in mature adult mice (6 months old) but not young adult mice (3 months old). This observation correlates well with the age-dependent functions of the aPKC-CBP pathway in maintaining hippocampal neuronal differentiation and maturation and CREB binding ability, suggesting that the aPKC-CBP/CREB signaling is key in the formation of hippocampal-dependent fear memory. This idea was also supported by a previous study showing that Cbpkix mutant mice that lack the interaction with CREB have reduced hippocampal-dependent fear memory associated with decreased CREB-mediated gene transcription (Wood et al., 2006). In addition, our comprehensive analysis of the MWM task indicated that the aPKC-CBP pathway is required for spatial learning and long-term spatial memory in mature adult mice. The mice lacking the aPKC-CBP pathway exhibit a delayed acquisition of spatial search strategies, showing impaired spatial learning, as well as the disruption of long-term spatial memory. These results are very intriguing, as previous findings from other Cbp mutants generated by modifying endogenous Cbp gene antifungal (Alarcón et al., 2004; Oike et al., 1999) show normal spatial memory measured by the MWM task. This strongly argues that CBP phosphorylation at Ser436 is a signaling cascade that specifically fine-tunes spatial memory by modulating adult hippocampal neurogenesis in an age-dependent manner.
Experimental Procedures
Author Contributions A.G. and K.H. equally performed experiments, analyzed data, and contributed to paper writing; Y.N. performed fear memory experiments; Y.N. and P.F. contributed to fear memory experimental design, data analysis, and interpretation; M.S. and G.I.C. performed experiments; S.B. contributed to search strategies analysis; D.L. contributed to MWM experimental design, data analysis, and interpretation; L.H. and F.W. generated CbpS436A knockin mouse strain; J.W. designed and performed experiments, analyzed and interpreted data, and wrote the paper.
Acknowledgments We are indebted to Dr. Freda Miller who provided very strong support for the work presented herein. This work was supported by the J.P. Bickell Foundation, Ottawa Hospital Foundation, and NSERC Discovery Grant (RGPIN-2016-05656) to J.W., and CIHR (FDN143227) to P.F. P.F. is a Canada Research Chair. We thank Dennis Aquino for mouse colony assistance, and Mirela Hasu and Christine Luckhart of the behavioral core for technical assistance.
Introduction Neural stem cells (NSCs) are found in the ventricular-subventricular zone (V-SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the hippocampus, the two main neurogenic niches in the adult mammalian brain (Fuentealba et al., 2012; Aimone et al., 2014). Adult NSCs in the V-SVZ mainly give rise to neurons that populate the olfactory bulbs (OBs) and oligodendrocytes in the corpus callosum. Pioneering work and more recent experiments have demonstrated that NSC divisions generate actively dividing transit amplifying cells (TACs) that form a pool of intermediate progenitors (Doetsch et al., 1999). These cells further differentiate into proliferating immature neuroblasts (Im. Nbs) that become migrating neuroblasts (Mig. Nbs), which integrate within the OBs to produce functional neurons critical for olfactory memory (Lepousez et al., 2013). Quiescent and activated NSCs coexist in adult stem cell niches (Albizu et al., 2010). Quiescent NSCs (qNSCs) are slowly dividing cells that can survive antimitotic drugs or irradiation; they can regenerate the V-SVZ, giving rise to new neurons (Doetsch et al., 1999; Daynac et al., 2013). In contrast, activated NSCs (aNSCs) are actively dividing and can be eliminated by antimitotic drugs or irradiation (Pastrana et al., 2009; Daynac et al., 2013). Both qNSCs and aNSCs have astrocyte-like phenotypes and express glial fibrillary acidic protein (GFAP) and the astrocyte-specific glutamate transporter, GLAST (Doetsch et al., 1999; Browd et al., 2006). However, the combination of markers allowing the isolation of the different prospective subpopulations of V-SVZ cells, including qNSCs, were identified only recently (Pastrana et al., 2009; Beckervordersandforth et al., 2010; Daynac et al., 2013; Codega et al., 2014; Mich et al., 2014). Furthermore, only limited knowledge exists on the gene-regulatory networks of quiescent and activated NSCs. Such information is of primary importance in understanding the mechanisms controlling V-SVZ maintenance and regeneration, and its role in diseases.