Novelty-induced memory consolidation is accompanied by increased Agap3 transcription: a cross-species study

Novelty-induced memory consolidation is a well-established phenomenon that depends on the activation of a locus coeruleus-hippocampal circuit. It is associated with the expression of activity-dependent genes that may mediate initial or cellular memory consolidation. Several genes have been identified to date, however, to fully understand the mechanisms of memory consolidation, additional candidates must be identified. In this cross-species study, we used a contextual novelty-exploration paradigm to identify changes in gene expression in the dorsal hippocampus of both mice and rats. We found that changes in gene expression following contextual novelty varied between the two species, with 9 genes being upregulated in mice and 3 genes in rats. Comparison across species revealed that ArfGAP with a GTPase domain, an ankyrin repeat and PH domain 3 (Agap3) was the only gene being upregulated in both, suggesting a potentially conserved role for Agap3. AGAP3 is known to regulate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor trafficking in the synapse, which suggests that increased transcription of Agap3 may be involved in maintaining functional plasticity. While we identified several genes affected by contextual novelty exploration, we were unable to fully reverse these changes using SCH 23390, a dopamine D1/D5 receptor antagonist. Further research on the role of AGAP3 in novelty-induced memory consolidation could lead to better understanding of this process and guide future research.

Forebrain-specific deficiency of the GTPase CRAG/Centaurin-γ3 leads to immature dentate gyri and hyperactivity in mice

Mouse models of various neuropsychiatric disorders, such as schizophrenia, often display an immature dentate gyrus, characterized by increased numbers of immature neurons and neuronal progenitors and a dearth of mature neurons. We previously demonstrated that the CRMP5-associated GTPase (CRAG), a short splice variant of Centaurin-γ3/AGAP3, is highly expressed in the dentate gyrus. CRAG promotes cell survival and antioxidant defense by inducing the activation of serum response factors at promyelocytic leukemia protein bodies, which are nuclear stress-responsive domains, during neuronal development. However, the physiological role of CRAG in neuronal development remains unknown. Here, we analyzed the role of CRAG using dorsal forebrain-specific CRAG/Centaurin-γ3 knockout mice. The mice revealed maturational abnormality of the hippocampal granule cells, including increased doublecortin-positive immature neurons and decreased calbindin-positive mature neurons, a typical phenotype of immature dentate gyri. Furthermore, the mice displayed hyperactivity in the open-field test, a common measure of exploratory behavior, suggesting that these mice may serve as a novel model for neuropsychiatric disorder associated with hyperactivity. Thus, we conclude that CRAG is required for the maturation of neurons in the dentate gyrus, raising the possibility that its deficiency might promote the development of psychiatric disorders in humans.

CRMP5-associated GTPase (CRAG) Is a Candidate Driver Gene for Colorectal Cancer Carcinogenesis

BACKGROUND/AIM

Certain chromosomal arms are clonally amplified in colorectal cancer (CRC) and may contain novel driver genes. The aim of this study was to identify a novel driver gene for colorectal cancer carcinogenesis on long arm of chromosome 7 and the clarify its biological function.

MATERIALS AND METHODS

We identified ArfGAP with GTPase domain, ankyrin repeat and PH domain 3 (AGAP3) as a putative driver gene using the CRC dataset in The Cancer Genome Atlas (TCGA). Biological functions of AGAP3 and CRMP5-associated GTPase (CRAG), a splicing variant of AGAP3, were explored by overexpression. AGAP3/CRAG expression in our cohort was examined by quantitative reverse transcription polymerase chain reaction. Clinical significance of AGAP3/CRAG expression in TCGA dataset, Gene Expression Omnibus datasets and our clinical cohort was evaluated.

RESULTS

AGAP3 expression was significantly increased in CRC and colorectal adenoma compared to normal tissue. CRAG overexpression up-regulated c-Jun expression, and significantly increased cell proliferation and colony formation capability. AGAP3 expression did not have a concordant association with patient prognosis among datasets.

CONCLUSION

CRAG may contribute to development of CRC via activator protein 1 activation.