In utero alcohol exposure impairs vessel-associated positioning and differentiation of oligodendrocytes in the developing neocortex

Prenatal alcohol exposure (PAE) is a major cause of nongenetic mental retardation and can lead to fetal alcohol syndrome (FAS), the most severe manifestation of fetal alcohol spectrum disorder (FASD). FASD infants present behavioral disabilities resulting from neurodevelopmental defects. Both grey and white matter lesions have been characterized and are associated with apoptotic death and/or ectopic migration profiles. In the last decade, it was shown that PAE impairs brain angiogenesis, and the radial organization of cortical microvessels is lost. Concurrently, several studies have reported that tangential migration of oligodendrocyte precursors (OPCs) originating from ganglionic eminences is vascular associated. Because numerous migrating oligodendrocytes enter the developing neocortex, the present study aimed to determine whether migrating OPCs interacted with radial cortical microvessels and whether alcohol-induced vascular impairments were associated with altered positioning and differentiation of cortical oligodendrocytes. Using a 3D morphometric analysis, the results revealed that in both human and mouse cortices, 15 to 40% of Olig2-positive cells were in close association with radial cortical microvessels, respectively. Despite perinatal vascular disorganization, PAE did not modify the vessel association of Olig2-positive cells but impaired their positioning between deep and superficial cortical layers. At the molecular level, PAE markedly but transiently reduced the expression of CNPase and MBP, two differentiation markers of immature and mature oligodendrocytes. In particular, PAE inverted their distribution profiles in cortical layers V and VI and reduced the thickness of the myelin sheath of efferent axons. These perinatal oligo-vascular defects were associated with motor disabilities that persisted in adults. Altogether, the present study provides the first evidence that Olig2-positive cells entering the neocortex are associated with radial microvessels. PAE disorganized the cortical microvasculature and delayed the positioning and differentiation of oligodendrocytes. Although most of these oligovascular defects occurred in perinatal life, the offspring developed long-term motor troubles. Altogether, these data suggest that alcohol-induced oligo-vascular impairments contribute to the neurodevelopmental issues described in FASD.

Chromatin remodeling in oligodendrogenesis

Oligodendrocytes are one type of glial cells responsible for myelination and providing trophic support for axons in the central nervous system of vertebrates. Thanks to myelin, the speed of electrical-signal conduction increases several hundred-fold because myelin serves as a kind of electrical insulator of nerve f ibers and allows for quick saltatory conduction of action potentials through Ranvier nodes, which are devoid of myelin. Given that different parts of the central nervous system are myelinated at different stages of development and most regions contain both myelinated and unmyelinated axons, it is obvious that very precise mechanisms must exist to control the myelination of individual axons. As they go through the stages of specif ication and differentiation – from multipotent neuronal cells in the ventricular zone of the neural tube to mature myelinating oligodendrocytes as well as during migration along blood vessels to their destination – cells undergo dramatic changes in the pattern of gene expression. These changes require precisely spatially and temporally coordinated interactions of various transcription factors and epigenetic events that determine the regulatory landscape of chromatin. Chromatin remodeling substantially affects transcriptional activity of genes. The main component of chromatin is the nucleosome, which, in addition to the structural function, performs a regulatory one and serves as a general repressor of genes. Changes in the type, position, and local density of nucleosomes require the action of specialized ATPdependent chromatin-remodeling complexes, which use the energy of ATP hydrolysis for their activity. Mutations in the genes encoding proteins of the remodeling complexes are often accompanied by serious disorders at early stages of embryogenesis and are frequently identif ied in various cancers. According to the domain arrangement of the ATP-hydrolyzing subunit, most of the identif ied ATP-dependent chromatin-remodeling complexes are classif ied into four subfamilies: SWI/SNF, CHD, INO80/SWR, and ISWI. In this review, we discuss the roles of these subunits of the different subfamilies at different stages of oligodendrogenesis

Haloxyfop-P-methyl induces developmental defects in zebrafish embryos through oxidative stress and anti-vasculogenesis

Haloxyfop-P-methyl, an aryloxyphenoxypropionate herbicide, is widely used to eliminate unwanted plants by inhibiting lipid synthesis and inducing oxidative stress. Since haloxyfop-P-methyl targets are limited within plants, few negative side effects on non-target crops have been reported. However, dissolved haloxyfop-P-methyl in rain or groundwater contaminates aquatic environments and affects marine ecosystems. In the present study, treatment with haloxyfop-P-methyl for 48 h induced developmental deficiencies in the eyes and bodies of the zebrafish embryos as a whole and was also linked to increases in the incidence of pericardial edema. Additionally, haloxyfop-P-methyl treatment decreased hatching ratio, embryo viability, and heart rate, while simultaneously increasing the expression levels of apoptotic and inflammatory genes. Moreover, haloxyfop-P-methyl hampered vasculogenesis in the embryos through down-regulation of functional genes, and disruption of vessel formation caused neurodegeneration in the olig2-positive notochord. Collectively, this study newly discovered the oxidative stress-related toxic mechanism of haloxyfop-P-methyl during embryonic development through anti-vasculogenesis, which suppresses neurogenesis of the notochord. This toxicity assessment of haloxyfop-P-methyl on embryogenesis may contribute to establishment of safety profiling of herbicide and to support hazard control in aquatic environment.