Hippocampal CARP over-expression solidifies consolidation of contextual fear memories

Spatial and temporal diversity of DCLK1 isoforms in developing mouse brain

Doublecortin-like kinase 1 (DCLK1) is a Doublecortin family kinase involved in a range of brain development processes including cell migration, axon/dendrite growth, and synapse development. The Dclk1 gene potentially generates multiple splicing isoforms, but the detailed expression patterns in the brain as well as in vivo functions of each isoform are still incompletely understood. Here we assessed expression patterns of DCLK1 isoforms using multiple platforms including in silico, in situ, and in vitro datasets in the developing mouse brain, and show quantitative evidence that among the four DCLK1 isoforms, DCLK1-L and DCL are mainly expressed in the embryonic cortex whereas DCLK1-L and CPG16 become dominant compared to DCL and CARP in the postnatal cortex. We also provide compelling evidence that DCLK1 isoforms are distributed in the partially distinct brain regions in the embryonic and the postnatal stages. We further show that overexpression of DCLK1-L, but not the other isoforms, in neural progenitors causes severe migration defects in the cortex, and that the migration defects are dependent on the kinase activity of DCLK1-L. Our data thus uncover partially segregated localization of DCLK1 isoforms in the developing mouse brain and suggest different roles for distinct DCLK1 isoforms in the brain development and function.

Kainate-induced epileptogenesis alters circular hole board learning strategy but not the performance of C57BL/6J mice

Patients with mesial temporal lobe epilepsy (mTLE) frequently show cognitive deficits. However, the relation between mTLE and cognitive impairment is poorly understood. To gain more insight into epilepsy-associated alterations in cognitive performance, we studied the spatial learning of C57BL/6J mice five weeks after kainate-induced status epilepticus (SE). Typically, structural hippocampal rearrangements take place within five weeks after SE. Mice were monitored by exposing them to four tasks with a focus on spatial memory and anxiety: the circular hole board, modified hole board, novel object-placement task, and elevated plus maze. On the circular hole board, animals showed a higher preference for hippocampus-independent strategies after SE. In contrast, no change in strategy was seen on the modified hole board, but animals with SE were able to finish the task more often. Animals did not have an increased preference for a relocated object in the novel object-placement task but showed an increased locomotion after SE. No indications for altered anxiety were found when tested on the elevated plus maze following SE. These data suggest that the circular hole board is a well-suited paradigm to detect subtle SE-induced hippocampal deficits.

Use of RNA interference by in utero electroporation to study cortical development: the example of the doublecortin superfamily

The way we study cortical development has undergone a revolution in the last few years following the ability to use shRNA in the developing brain of the rodent embryo. The first gene to be knocked-down in the developing brain was doublecortin (Dcx). Here we will review knockdown experiments in the developing brain and compare them with knockout experiments, thus highlighting the advantages and disadvantages using the different systems. Our review will focus on experiments relating to the doublecortin superfamily of proteins.

DCLK1 variants are associated across schizophrenia and attention deficit/hyperactivity disorder

Doublecortin and calmodulin like kinase 1 (DCLK1) is implicated in synaptic plasticity and neurodevelopment. Genetic variants in DCLK1 are associated with cognitive traits, specifically verbal memory and general cognition. We investigated the role of DCLK1 variants in three psychiatric disorders that have neuro-cognitive dysfunctions: schizophrenia (SCZ), bipolar affective disorder (BP) and attention deficit/hyperactivity disorder (ADHD). We mined six genome wide association studies (GWASs) that were available publically or through collaboration; three for BP, two for SCZ and one for ADHD. We also genotyped the DCLK1 region in additional samples of cases with SCZ, BP or ADHD and controls that had not been whole-genome typed. In total, 9895 subjects were analysed, including 5308 normal controls and 4,587 patients (1,125 with SCZ, 2,496 with BP and 966 with ADHD). Several DCLK1 variants were associated with disease phenotypes in the different samples. The main effect was observed for rs7989807 in intron 3, which was strongly associated with SCZ alone and even more so when cases with SCZ and ADHD were combined (P-value = 4×10⁻⁵ and 4×10⁻⁶, respectively). Associations were also observed with additional markers in intron 3 (combination of SCZ, ADHD and BP), intron 19 (SCZ+BP) and the 3′UTR (SCZ+BP). Our results suggest that genetic variants in DCLK1 are associated with SCZ and, to a lesser extent, with ADHD and BP. Interestingly the association is strongest when SCZ and ADHD are considered together, suggesting common genetic susceptibility. Given that DCLK1 variants were previously found to be associated with cognitive traits, these results are consistent with the role of DCLK1 in neurodevelopment and synaptic plasticity.

Latent process genes for cell differentiation are common decoders of neurite extension length

A latent process involving signal transduction and gene expression is needed as a preparation step for cellular function. We previously found that nerve growth factor (NGF)-induced cell differentiation has a latent process, which is dependent on ERK activity and gene expression and required for subsequent neurite extension. A latent process can be considered a preparation step that decodes extracellular stimulus information into cellular functions; however, molecular mechanisms of this process remain unknown. We identified Metrnl, Dclk1, and Serpinb1a as latent process (LP) genes that are induced during the latent process with distinct temporal expression profiles and are required for subsequent neurite extension in PC12 cells. The LP genes showed distinct dependency on the duration of ERK activity, and they were also induced during the latent process of PACAP- and forskolin-induced cell differentiation. Regardless of neurotrophic factors, expression levels of the LP genes during the latent process (0–12 h), but not phosphorylation levels of ERK, always correlated with subsequent neurite extension length (12–24 h). Overexpression of all LP genes together, but not of each gene separately, enhanced NGF-induced neurite extension. The LP gene products showed distinct spatial localization. Thus, the LP genes appeared to be the common decoders for neurite extension length regardless of neurotrophic factors, and they may function in distinct temporal and spatial manners during the latent process. Our findings provide molecular insight into the physiological meaning of the latent process as the preparation step for decoding information for future phenotypic change.

Fear conditioning and extinction: emotional states encoded by distinct signaling pathways

Conditioning and extinction of fear have traditionally been viewed as two independent learning processes for encoding representations of contexts or cues (conditioned stimuli, CS), aversive events (unconditioned stimuli, US), and their relationship. Based on the analysis of protein kinase signaling patterns in neurons of the fear circuit, we propose that fear and extinction are best conceptualized as emotional states triggered by a single CS representation with two opposing values: aversive and non-aversive. These values are conferred by the presence or absence of the US and encoded by distinct sets of kinase signaling pathways and their downstream targets. Modulating specific protein kinases thus has the potential to modify emotional states, and hence, may emerge as a promising treatment for anxiety disorders.