A putative Xenopus Rho-GTPase activating protein (XrGAP) gene is expressed in the notochord and brain during the early embryogenesis

Brain transcriptomic signatures for mood disorders and suicide phenotypes: an anterior insula and subgenual ACC network postmortem study

Mood disorders affect over ten percent of humans, but studies dissecting the brain anatomical and molecular neurobiological mechanisms underlying mood (dys)functions have not consistently identified the patterns of pathological changes in relevant brain regions. Recent studies have identified pathological changes in the anterior insula (Ant-Ins) and subgenual anterior cingulate (sgACC) brain network in mood disorders, in line with this network's role in regulating mood/affective feeling states. Here, we applied whole-tissue RNA-sequencing measures of differentially expressed genes (DEGs) in mood disorders versus (vs.) psychiatrically unaffected controls (controls) to identify postmortem molecular pathological markers for mood disorder phenotypes. Using data-driven factor analysis of the postmortem phenotypic variables to determine relevant sources of population variances, we identified DEGs associated with mood disorder-related diagnostic phenotypes by combining gene co-expression, differential gene expression, and pathway-enrichment analyses. We found downregulation/under expression of inflammatory, and protein synthesis-related genes associated with psychiatric morbidity (i.e., all co-occurring mental disorders and suicide outcomes/death by suicide) in Ant-Ins, in contrasts to upregulation of synaptic membrane and ion channel-related genes with increased psychiatric morbidity in sgACC. Our results identified a preponderance of downregulated metabolic, protein synthesis, inflammatory, and synaptic membrane DEGs associated with suicide outcomes in relation to a factor representing longevity in the Ant-Ins and sgACC (AIAC) network. Our study revealed a critical brain network molecular repertoire for mood disorder phenotypes, including suicide outcomes and longevity, and provides a framework for defining dosage-sensitive (i.e., downregulated vs. upregulated) molecular signatures for mood disorder phenotypic complexity and pathological outcomes.

Mice carrying a schizophrenia-associated mutation of the Arhgap10 gene are vulnerable to the effects of methamphetamine treatment on cognitive function: association with morphological abnormalities in striatal neurons

We recently found a significant association between exonic copy-number variations in the Rho GTPase activating protein 10 (Arhgap10) gene and schizophrenia in Japanese patients. Special attention was paid to one patient carrying a missense variant (p.S490P) in exon 17, which overlapped with an exonic deletion in the other allele. Accordingly, we generated a mouse model (Arhgap10 S490P/NHEJ mice) carrying a missense variant and a coexisting frameshift mutation. We examined the spatiotemporal expression of Arhgap10 mRNA in the brain and found the highest expression levels in the cerebellum, striatum, and nucleus accumbens (NAc), followed by the frontal cortex in adolescent mice. The expression levels of phosphorylated myosin phosphatase-targeting subunit 1 and phosphorylated p21-activated kinases in the striatum and NAc were significantly increased in Arhgap10 S490P/NHEJ mice compared with wild-type littermates. Arhgap10 S490P/NHEJ mice exhibited a significant increase in neuronal complexity and spine density in the striatum and NAc. There was no difference in touchscreen-based visual discrimination learning between Arhgap10 S490P/NHEJ and wild-type mice, but a significant impairment of visual discrimination was evident in Arhgap10 S490P/NHEJ mice but not wild-type mice when they were treated with methamphetamine. The number of c-Fos-positive cells was significantly increased after methamphetamine treatment in the dorsomedial striatum and NAc core of Arhgap10 S490P/NHEJ mice. Taken together, these results suggested that schizophrenia-associated Arhgap10 gene mutations result in morphological abnormality of neurons in the striatum and NAc, which may be associated with vulnerability of cognition to methamphetamine treatment.

In silico tissue-distribution of human Rho family GTPase activating proteins

Rho family small GTPases are involved in the spatio-temporal regulation of several physiological processes. They operate as molecular switches based on their GTP- or GDP-bound state. Their GTPase activator proteins (Rho/Rac GAPs) are able to increase the GTP hydrolysis of small GTPases, which turns them to an inactive state. This regulatory step is a key element of signal termination. According to the human genome project the potential number of Rho family GAPs is approximately 70. Despite their significant role in cellular signaling our knowledge on their expression pattern is quite incomplete. In this study we tried to reveal the tissue-distribution of Rho/Rac GAPs based on expressed sequence tag (EST) database from healthy and tumor tissues and microarray experiments. Our accumulated data sets can provide important starting information for future research. However, the nomenclature of Rho family GAPs is quite heterogeneous. Therefore we collected the available names, abbreviations and aliases of human Rho/Rac GAPs in a useful nomenclature table. A phylogenetic tree and domain structure of 65 human RhoGAPs are also presented.

xGit2 and xRhoGAP 11A regulate convergent extension and tissue separation in Xenopus gastrulation

In a microarray-based screen for genes that are involved in tissue separation downstream of Paraxial Protocadherin (PAPC) and Frizzled-7 (Fz7)-mediated signaling we identified xGit2 and xRhoGAP 11A, two GTPase-activating proteins (GAP) for small GTPases. xGit2 and xRhoGAP 11A are expressed in the dorsal ectoderm, and their transcription is downregulated in the involuting dorsal mesoderm by PAPC and Fz7. Overexpression of xGit2 and xRhoGAP 11A inhibits Rho activity and impairs convergent extension movements as well as tissue separation behaviour. We propose that Rho activity in the involuting mesoderm is enhanced through inhibition of xGit2 and xRhoGAP 11A transcription by PAPC and Fz7. By this mechanism xRhoGAP 11A and xGit2 are restricted to the dorsal ectoderm, while Rho signaling is inhibited.

Current knowledge of the large RhoGAP family of proteins

The Rho GTPases are implicated in almost every fundamental cellular process. They act as molecular switches that cycle between an active GTP-bound and an inactive GDP-bound state. Their slow intrinsic GTPase activity is greatly enhanced by RhoGAPs (Rho GTPase-activating proteins), thus causing their inactivation. To date, more than 70 RhoGAPs have been identified in eukaryotes, ranging from yeast to human, and based on sequence homology of their RhoGAP domain, we have grouped them into subfamilies. In the present Review, we discuss their regulation, biological functions and implication in human diseases.