Commissural axon navigation in the spinal cord: A repertoire of repulsive forces is in command.

The navigation of commissural axons in the developing spinal cord has attracted multiple studies over the years. Many important concepts emerged from these studies which have enlighten the general mechanisms of axon guidance. The navigation of commissural axons is regulated by a series of cellular territories which provides the diverse guidance information necessary to ensure the successive steps of their pathfinding towards, across, and away from the ventral midline. In this review, we discuss how repulsive forces, by propelling, channelling, and confining commissural axon navigation, bring key contributions to the formation of this neuronal projection.

Axon pathfinding for locomotion.

Motor neurons of the spinal cord are responsible for the assembly of neuromuscular connections indispensable for basic locomotion and skilled movements. A precise spatial relationship exists between the position of motor neuron cell bodies in the spinal cord and the course of their axonal projections to peripheral muscle targets. Motor neuron innervation of the vertebrate limb is a prime example of this topographic organization and by virtue of its accessibility and predictability has provided access to fundamental principles of motor system development and neuronal guidance. The seemingly basic binary map established by genetically defined motor neuron subtypes that target muscles in the limb is directed by a surprisingly large number of directional cues. Rather than being simply redundant, these converging signaling pathways are hierarchically linked and cooperate to increase the fidelity of axon pathfinding decisions. A current priority is to determine how multiple guidance signals are integrated by individual growth cones and how they synergize to delineate class-specific axonal trajectories.

Restoration of early deficiency of axonal guidance signaling by guanxinning injection as a novel therapeutic option for acute ischemic stroke.

Despite of its high morbidity and mortality, there is still a lack of effective treatment for ischemic stroke in part due to our incomplete understanding of molecular mechanisms of its pathogenesis. In this study, we demonstrate that SHH-PTCH1-GLI1-mediated axonal guidance signaling and its related neurogenesis, a central pathway for neuronal development, also plays a critical role in early stage of an acute stroke model. Specifically, in vivo, we evaluated the effect of GXNI on ischemic stroke mice via using the middle cerebral artery embolization model, and found that GXNI significantly alleviated cerebral ischemic reperfusion (I/R) injury by reducing the volume of cerebral infarction, neurological deficit score and cerebral edema, reversing the BBB permeability and histopathological changes. A combined approach of RNA-seq and network pharmacology analysis was used to reveal the underlying mechanisms of GXNI followed by RT-PCR, immunohistochemistry and western blotting validation. It was pointed out that axon guidance signaling pathway played the most prominent role in GXNI action with Shh, Ptch1, and Gli1 genes as the critical contributors in brain protection. In addition, GXNI markedly prevented primary cortical neuron cells from oxygen-glucose deprivation/reoxygenation damage in vitro, and promoted axon growth and synaptogenesis of damaged neurons, which further confirmed the results of in vivo experiments. Moreover, due to the inhibition of the SHH-PTCH1-GLI1 signaling pathway by cyclopropylamine, the effect of GXNI was significantly weakened. Hence, our study provides a novel option for the clinical treatment of acute ischemic stroke by GXNI via SHH-PTCH1-GLI1-mediated axonal guidance signaling, a neuronal development pathway previously considered for after-stroke recovery.

Rare genetic variants suggest dysregulation of signaling pathways in low- and high-risk patients developing severe ovarian hyperstimulation syndrome.

PURPOSE: To investigate if rare gene variants in women with severe ovarian hyperstimulation syndrome (OHSS) provide clues to the mechanisms involved in the syndrome. METHODS: Among participants in a prospective randomized study (Toftager et al. 2016), six women with predicted low and six women with predicted high risk of OHSS developing severe OHSS (grades 4 and 5, Golan classification) were selected. In the same cohort, six plus six matched controls developing no signs of OHSS (Golan grade 0) were selected. Whole-exome sequencing was performed. Analysis using a predefined in silico OHSS gene panel, variant filtering, and pathway analyses was done. RESULTS: We found no convincing monogenetic association with the development of OHSS using the in silico gene panel. Pathway analysis of OHSS variant lists showed substantial overlap in highly enriched top pathways (p value range p < 0.0001 and p > 9.8E-17) between the low- and high-risk group developing severe OHSS, i.e., "the integrin-linked kinase (ILK) signaling pathway" and the "axonal guidance signaling pathway," both being connected to vasoactive endothelial growth factor (VEGF) and endothelial function. CONCLUSION: Rare variants in OHSS cases with two distinct risk profiles enrich the same signaling pathways linked to VEGF and endothelial function. Clarification of the mechanism as well as potentially defining genetic predisposition of the high vascular permeability is important for future targeted treatment and prevention of OHSS; the potential roles of ILK signaling and the axonal guidance signaling need to be validated by functional studies.

Developmental expression profiles of axon guidance signaling and the immune system in the marmoset cortex: potential molecular mechanisms of pruning of dendritic spines during primate synapse formation in late infancy and prepuberty (I).

The synapse number and the related dendritic spine number in the cerebral cortex of primates shows a rapid increase after birth. Depending on the brain region and species, the number of synapses reaches a peak before adulthood, and pruning takes place after this peak (overshoot-type synaptic formation). Human mental disorders, such as autism and schizophrenia, are hypothesized to be a result of either too weak or excessive pruning after the peak is reached. Thus, it is important to study the molecular mechanisms underlying overshoot-type synaptic formation, particularly the pruning phase. To examine the molecular mechanisms, we used common marmosets (Callithrix jacchus). Microarray analysis of the marmoset cortex was performed in the ventrolateral prefrontal, inferior temporal, and primary visual cortices, where changes in the number of dendritic spines have been observed. The spine number of all the brain regions above showed a peak at 3 months (3 M) after birth and gradually decreased (e.g., at 6 M and in adults). In this study, we focused on genes that showed differential expression between ages of 3 M and 6 M and on the differences whose fold change (FC) was greater than 1.2. The selected genes were subjected to canonical pathway analysis, and in this study, we describe axon guidance signaling, which had high plausibility. The results showed a large number of genes belonging to subsystems within the axon guidance signaling pathway, macrophages/immune system, glutamate system, and others. We divided the data and discussion of these results into 2 papers, and this is the first paper, which deals with the axon guidance signaling and macrophage/immune system. Other systems will be described in the next paper. Many components of subsystems within the axon guidance signaling underwent changes in gene expression from 3 M to 6 M so that the synapse/dendritic spine number would decrease at 6 M. Thus, axon guidance signaling probably contributes to the decrease in synapse/dendritic spine number at 6 M, the phenomenon that fits the overshoot-type synaptic formation in primates. Microglial activity (evaluated by quantifying AIF1 expression) and gene expression of molecules that modulate microglia, decreased at 6 M, just like the synapse/dendritic spine number. Thus, although microglial activity is believed to be related to phagocytosis of synapses/dendritic spines, microglial activity alone cannot explain how pruning was accelerated in the pruning phase. On the other hand, expression of molecules that tag synapses/dendritic spines as a target of phagocytosis by microglia (e.g., complement components) increased at 6 M, suggesting that these tagging proteins may be involved in the acceleration of pruning during the pruning phase.

Long-term effects of stress early in life on microRNA-30a and its network: Preventive effects of lurasidone and potential implications for depression vulnerability.

Exposure to early life stress can interfere with neurodevelopmental trajectories to increase the vulnerability for psychiatric disorders later in life. With this respect, epigenetic mechanisms play a key role for the long-lasting changes in brain functions that may elicit and sustain psychopathologic outcomes. Here, we investigated DNA methylation changes as possible epigenetic mechanism mediating the effect of prenatal stress (PNS), an experimental paradigm associated with behavioral and molecular alterations relevant for psychiatric disorders. We identified 138 genes as being differentially methylated in the prefrontal cortex (PFC) and in the hippocampus (HIP) of male and female adult rats exposed to PNS. Among these genes, miR-30a and Neurod1 emerged as potential players for the negative outcomes associated with PNS exposure. Indeed, in addition to showing consistent methylation differences in both brain regions and in both sexes, and interacting with each other, they are both involved in Axon guidance and Neurotrophin signaling, which are important to neurodevelopmental disorders. We also found a significant reduction in the expression of a panel of genes (CAMK2A, c-JUN, LIMK1, MAP2K1, MAP2K2, PIK3CA and PLCG1) that belong to these two biological pathways and are also validated targets of miR-30a, pointing to a down-regulation of these pathways as a consequence of PNS exposure. Interestingly, we also found that miR-30a levels were significantly upregulated in depressed patients exposed to childhood trauma, as compared to control individuals. Importantly, we also found that a sub-chronic treatment with the atypical antipsychotic drug, lurasidone, during adolescence was able to prevent the up-regulation of miR-30a and normalized the expression of its target genes in response to PNS exposure. Our results demonstrate that miR-30a undergoes epigenetic changes following early life stress exposure and suggest that this miRNA could play a key role in producing broad and long-lasting alterations in neuroplasticity-related pathways, contributing to the etiology of psychiatric disorders.

Sema3A - mediated modulation of NR1D1 expression may be involved in the regulation of axonal guidance signaling by the microbiota.

AIMS: The microbiota has a profound impact on host development and function. Axon guidance is essential for the formation of neural circuits and plays an important role in neurological diseases and behavioral disorders. However, the impact of the microbiota on axon guidance signaling is unclear. MAIN METHODS: Gnotobiotic models-germ free mice were applied to explore behavioral phenotypes and possible molecular mechanisms that were evaluated by Realtime-PCR and western blot analysis. Primary cultures of mouse cortical neurons were performed to demonstrate the role of Sema3A on NR1D1 expression. KEY FINDINGS: The results showed that the microbiota modulates host behavior, and that colonization is not sufficient to normalize behavioral alterations in germ-free (GF) mice. Five genes, Sema3A, Sema3E, EphB2, Slit3 and Robo1, were differentially expressed in GF and specific pathogen-free (SPF) mice. Furthermore, colonization did not completely reverse the differential expression, which was consistent with the behavioral phenotypes in colonization germ-free (CGF) mice. The transcript and protein levels of Sema3A, and of its membrane-bound co-receptor NRP1, were increased in GF mice. Interestingly, Sema3A inhibited the expression of NR1D1, which was blocked by a RhoA/ROCK pathway agonist in primary cortical neurons. The NR1D1 and ROCK2 expression levels were reduced in GF and CGF mice compared with SPF mice, consistent with the increased expression of Sema3A. SIGNIFICANCE: Our findings suggest that the microbiota regulates axon guidance signaling in the prefrontal cortex. Furthermore, this effect appears to involve the inhibition of NR1D1 expression by Sema3A through the RhoA/ROCK pathway.