The microRNAs let-7 and miR-9 down-regulate the axon-guidance genes Ntn1 and Dcc during peripheral nerve regeneration.

Axon guidance helps growing neural axons to follow precise paths to reach their target locations. It is a critical step for both the formation and regeneration of neuronal circuitry. Netrin-1 (Ntn1) and its receptor, deleted in colorectal carcinoma (Dcc) are essential factors for axon guidance, but their regulation in this process is incompletely understood. In this study, using quantitative real-time RT-PCR (qRT-PCR) and biochemical and reporter gene assays, we found that the Ntn1 and Dcc genes are both robustly up-regulated in the sciatic nerve stump after peripheral nerve injury. Moreover, we found that the microRNA (miR) let-7 directly targets the Ntn1 transcript by binding to its 3'-untranslated region (3'-UTR), represses Ntn1 expression, and reduces the secretion of Ntn1 protein in Schwann cells. We also identified miR-9 as the regulatory miRNA that directly targets Dcc and found that miR-9 down-regulates Dcc expression and suppresses the migration ability of Schwann cells by regulating Dcc abundance. Functional examination in dorsal root ganglion neurons disclosed that let-7 and miR-9 decrease the protein levels of Ntn1 and Dcc in these neurons, respectively, and reduce axon outgrowth. Moreover, we identified a potential regulatory network comprising let-7, miR-9, Ntn1, Dcc, and related molecules, including the RNA-binding protein Lin-28 homolog A (Lin28), SRC proto-oncogene nonreceptor tyrosine kinase (Src), and the transcription factor NF-κB. In summary, our findings reveal that the miRs let-7 and miR-9 are involved in regulating neuron pathfinding and extend our understanding of the regulatory pathways active during peripheral nerve regeneration.

Decoding cell death signals in liver inflammation.

Inflammation can be either beneficial or detrimental to the liver, depending on multiple factors. Mild (i.e., limited in intensity and destined to resolve) inflammatory responses have indeed been shown to exert consistent hepatoprotective effects, contributing to tissue repair and promoting the re-establishment of homeostasis. Conversely, excessive (i.e., disproportionate in intensity and permanent) inflammation may induce a massive loss of hepatocytes and hence exacerbate the severity of various hepatic conditions, including ischemia-reperfusion injury, systemic metabolic alterations (e.g., obesity, diabetes, non-alcoholic fatty liver disorders), alcoholic hepatitis, intoxication by xenobiotics and infection, de facto being associated with irreversible liver damage, fibrosis, and carcinogenesis. Both liver-resident cells (e.g., Kupffer cells, hepatic stellate cells, sinusoidal endothelial cells) and cells that are recruited in response to injury (e.g., monocytes, macrophages, dendritic cells, natural killer cells) emit pro-inflammatory signals including - but not limited to - cytokines, chemokines, lipid messengers, and reactive oxygen species that contribute to the apoptotic or necrotic demise of hepatocytes. In turn, dying hepatocytes release damage-associated molecular patterns that-upon binding to evolutionary conserved pattern recognition receptors-activate cells of the innate immune system to further stimulate inflammatory responses, hence establishing a highly hepatotoxic feedforward cycle of inflammation and cell death. In this review, we discuss the cellular and molecular mechanisms that account for the most deleterious effect of hepatic inflammation at the cellular level, that is, the initiation of a massive cell death response among hepatocytes.

Prefrontal cortex-specific Dcc deletion induces schizophrenia-related behavioral phenotypes and fail to be rescued by olanzapine treatment.

Multiple genome studies have discovered that variation in deleted in colorectal carcinoma (Dcc) at transcription and translation level were associated with the occurrences of psychiatric disorders. Yet, little is known about the function of Dcc in schizophrenia (SCZ)-related behavioral abnormalities and the efficacy of antipsychotic drugs in vivo. Here, we used an animal model of prefrontal cortex-specific knockdown (KD) of Dcc in adult C57BL/6 mice to study the attention deficits and impaired locomotor activity. Our results supported a critical role of Dcc deletion in SCZ-related behaviors. Notably, olanzapine rescued the SCZ-related behaviors in the MK801-treated mice but not in the cortex-specific Dcc KD mice, indicating that Dcc play a critical in the mechanism of antipsychotic effects of olanzapine. Knockdown of Dcc in prefrontal cortex results in glutamatergic dysfunction, including defects in glutamine synthetase and postsynaptic maturation. As one of the major risk factors of the degree of antipsychotic response, Dcc deletion-induced glutamatergic dysfunction may be involved in the underlying mechanism of treatment resistance of olanzapine. Our findings identified Dcc deletion-mediated SCZ-related behavioral defects, which serve as a valuable animal model for study of SCZ and amenable to targeted investigations in mechanistic hypotheses of the mechanism underlying glutamatergic dysfunction-induced antipsychotic treatment resistance.

Association Between DCC Polymorphisms and Susceptibility to Autism Spectrum Disorder.

Autism spectrum disorder (ASD) represents a group of childhood-onset lifelong neuro-developmental disorders. However, the association between single nucleotide polymorphisms (SNPs) in the deleted in colorectal carcinoma (DCC) gene and ASD susceptibility remains unclear. We investigated the association between ASD susceptibility and seven SNPs in DCC on the basis of a case-control study (231 ASD cases and 242 controls) in Chinese Han. We found that there was no association between ASD susceptibility and the seven SNPs in DCC; however, T-A haplotype (rs2229082-rs2270954), T-A-T-C haplotype (rs2229082-rs2270954-rs2292043-rs2292044), C-G-T-C-T haplotype (rs934345-rs17753970-rs2229082-rs2270954-rs2292043), C-G-T-C-T-G haplotype (rs934345-rs17753970-rs2229082-rs2270954-rs2292043-rs2292044), and G-G-T-C-C-C-C haplotype (rs934345-rs17753970-rs2229082-rs2270954-rs2292043-rs2292044-rs16956878) were associated with ASD susceptibility. Our results indicate that the haplotypes formed on the basis of the seven SNPs in DCC may be implicated in ASD.

An Association Study Between Genetic Polymorphisms in Functional Regions of Five Genes and the Risk of Schizophrenia.

Schizophrenia is a severe mental disorder that is likely to be strongly determined by genetic factors. To identify markers of disks, large homolog 2 (DLG2), FAT atypical cadherin 3 (FAT3), kinectin1 (KTN1), deleted in colorectal carcinoma (DCC), and glycogen synthase kinase-3ß (GSK3ß) that contribute to the genetic susceptibility to schizophrenia, we systematically screened for polymorphisms in the functional regions of these genes. A total of 22 functional single-nucleotide polymorphisms (SNPs) in 940 Chinese subjects were genotyped using SNaPshot. The results first suggested that the allelic and genotypic frequencies of the DCC polymorphism rs2229080 were nominally associated with schizophrenia. The patients were significantly less likely to be CC homozygous (P = 0.005, odds ratio [OR] = 0.635, 95 % confidence interval [95 % CI] = 0.462-0.873), and the schizophrenia subjects exhibited lower frequency of the C allele (P = 0.024, OR = 0.811, 95 % CI = 0.676-0.972). Regarding GSK3ß, there was a significant difference in genotype distribution of rs3755557 between schizophrenia and healthy control subjects (P = 0.009). The patients exhibited a significantly lower frequency of the T allele of rs3755557 (P = 0.002, OR = 0.654, 95 % CI = 0.498-0.860). Our results point to the polymorphisms of DCC and GSK3ß as contributors to the genetic basis of individual differences in the susceptibility to schizophrenia.

Genome-Wide Association Analysis Identifies Dcc as an Essential Factor in the Innervation of the Peripheral Vestibular System in Inbred Mice.

This study aimed to investigate the genetic causes of vestibular dysfunction. We used vestibular sensory-evoked potentials (VsEPs) to characterize the vestibular function of 35 inbred mouse strains selected from the Hybrid Mouse Diversity Panel and demonstrated strain-dependent phenotypic variation in vestibular function. Using these phenotypic data, we performed the first genome-wide association study controlling for population structure that has revealed two highly suggestive loci, one of which lies within a haplotype block containing five genes (Stard6, 4930503L19Rik, Poli, Mbd2, Dcc) on Chr. 18 (peak SNP rs29632020), one gene, deleted in colorectal carcinoma (Dcc) has a well-established role in nervous system development. An in-depth analysis of Dcc-deficient mice demonstrated elevation in mean VsEP threshold for Dcc (+/-) mice (-11.86 dB) compared to wild-type (-9.68 dB) littermates. Synaptic ribbon studies revealed Dcc (-/-) (P0) and Dcc (+/-) (6-week-old) mice showed lower density of the presynaptic marker (CtBP2) as compared to wild-type controls. Vestibular ganglion cell counts of Dcc (-/-) (P0) was lower than controls. Whole-mount preparations showed abnormal innervation of the utricle, saccule, and crista ampullaris at E14.5, E16.5, and E18.5. Postnatal studies were limited by the perinatal lethality in Dcc (-/-) mice. Expression analyses using in situ hybridization and immunohistochemistry showed Dcc expression in the mouse vestibular ganglion (E15.5), and utricle and crista ampullaris (6-week-old), respectively. In summary, we report the first GWAS for vestibular functional variation in inbred mice and provide evidence for the role of Dcc in the normal innervation of the peripheral vestibular system.

In and out from the cortex: development of major forebrain connections.

In this review we discuss recent advances in the understanding of the development of forebrain projections attending to their origin, fate determination, and axon guidance. Major forebrain connections include callosal, corticospinal, corticothalamic and thalamocortical projections. Although distinct transcriptional programs specify these subpopulations of projecting neurons, the mechanisms involved in their axonal development are similar. Guidance by short- and long-range molecular cues, interaction with intermediate target populations and activity-dependent mechanisms contribute to their development. Moreover, some of these connections interact with each other showing that the development of these axonal tracts is a well-orchestrated event. Finally, we will recapitulate recent discoveries that challenge the field of neural wiring that show that these forebrain connections can be changed once formed. The field of reprogramming has arrived to postmitotic cortical neurons and has showed us that forebrain connectivity is not immutable and might be changed by manipulations in the transcriptional program of matured cells.