Autoradiographic studies of migrating neurons and astrocytes of human fetal cerebral cortex in vitro

Building brains in a dish: Prospects for growing cerebral organoids from stem cells

The recent development of organoid techniques, in which embryonic brain-like tissue can be grown from human or mouse stem cells in vitro offers the potential to transform the way in which brain development is studied. In this review, we summarize key aspects of the embryonic development of mammalian forebrains, focussing in particular on the cerebral cortex and highlight significant differences between mouse and primates, including human. We discuss recent work using cerebral organoids that has revealed key similarities and differences between their development and that of the brain in vivo. Finally, we outline the ways in which cerebral organoids can be used in combination with CRISPR/Cas9 genome editing to unravel genetic mechanisms that control embryonic development of the cerebral cortex, how this can help us understand the causes of neurodevelopmental disorders and some of the key challenges which will have to be resolved before organoids can become a mainstream tool to study brain development.

Mechanism of methylmercury cytotoxicity

Although a large number of epidemiological, clinical, and pathological studies on methylmercury intoxication have been published, these investigations have not been able to elucidate the detailed mechanisms by which the metal alkyl causes a wide variety of biological dysfunctions. Thus, the cultured cells which are free from the influence of whole body complexities, such as absorption, distribution, metabolism, etc., which complicate the interpretation of in vivo experimental results, attract the attention of many scientists who are interested in clarifying the mode of toxic action of methylmercury. The aim of this article is to review the recent studies on the toxicity of methylmercury at the cellular level and to outline the mechanisms which have been proposed to be responsible for cell injuries.

Changes in the molecular structure of mouse fetal astrocyte nucleosomes produced in vitro by methylmercuric chloride

The fluorescent probe N-(3-pyrene)maleimide, which specifically labels the cysteine residues of histone H3 within the nucleosome, was used to monitor changes in the nucleosomal structure of mouse fetal astrocytes exposed to varying concentrations of methylmercuric chloride. Methylmercuric chloride treatment (10 microM) for 6 hr produced a significant decrease in the degree of fluorescence of the probe. The decrease was much smaller following a 4-hr incubation period. These results correlate with recent observations showing that significant changes in the thymidine labeling index occur following 4-6 hr of exposure to methylmercury (MeHg). It is hypothesized that MeHg enters the cells during the growth phase and attaches to the protein moiety of the nucleosome in or near the cysteine groups of histone H3, thus diminishing the binding capacity of the fluorescent probe. Addition of a detergent (sodium dodecyl sulfate) resulted in only a small increase in the degree of fluorescence of the treated nucleosomes as compared to controls, showing that the interaction of MeHg with the nuclear proteins was not dissociated by detergent. In view of the strong interaction between DNA and the histone dimer H3-H4 and the potential importance of the latter in gene regulation, these results suggest an additional means by which MeHg may exert its toxic effects.

The comparative effects of methylmercuric chloride and mercuric chloride upon DNA synthesis in mouse fetal astrocytes in vitro

The relative effects of direct exposure to methylmercuric chloride (MMC) and mercuric chloride (MC) upon [3H]thymidine incorporation were determined using cultured mouse fetal astrocytes. The labeling indices of cells exposed to MMC were significantly lower than those of cells exposed to equimolar concentrations of MC. These results indicate that on a mole-for-mole basis, MMC is much more deleterious upon DNA synthesis of mouse fetal astrocytes than those of MC.

Studies of cultured human and simian fetal brain cells. I. Characterization of the cell types

Explant cultures of the cerebral subventricular zone and cerebellar external germinal layer were established from fetal human, rhesus and cynomolgus monkey brains. Using comparable gestational ages, the morphogenesis of the cultures from these three sources was almost indistinguishable. Four cell types were distinguished by electron microscopy. Germinal cells or neuroblasts were confined largely to the primary explant and extended into a transitional outgrowth region. Astrocytes, which stained for glial fibrillary acidic protein, grew out of the explants and these could be distinguished from the large, mesenchymal epithelioid cells. A fourth cell type, not identified in previous studies, had the ultrastructural characteristics of an oligodendrocyte, but did not produce myelin in these culture conditions.

Radial glia in the human fetal cerebrum: a combined Golgi, immunofluorescent and electron microscopic study

Golgi techniques, immunofluorescence for glial fibrillary acidic (GFA) protein, and electron microscopy (EM) were used to determine the nature of radial glia in the cerebrum of human fetuses ranging from 7 to 20 weeks of ovulation age. Successful Golgi impregnation of radial fibers was achieved in fetuses 12 weeks of age and older. These fibers spanned the entire thickness of the hemisphere. At the pial surface many of them branched and terminated in pyramidal end feet expansions. Indirect immunofluorescent preparations utilizing antiserum to GFA protein, a protein specific for astrocytes, demonstrated numerous radially oriented nearly parallel fluorescent fibres between the ventricular zone and pia mater. GFA protein-positive fibers were demonstrated in all fetal specimens examined with this technique (10 weeks of age and older). Along the outer border of the marginal zone they formed a horizontal GFA protein-containing subpial membrane. By EM there were numerous linear electron lucent astrocytic processes containing 8-9 nm filaments and occasional glycogen granules at all levels of the cerebrum. They were interspersed among smaller and darker neuronal processes containing 20-25 nm neurotubules, and were demonstrable at all fetal ages between 7 and 18 weeks. They formed pericapillary investments and subpial terminal expansions closely abutting basal lamina of pia mater in every specimen examined. On the basis of these combined analyses, we conclude that radial glial fibers in early human fetal cerebrum represent processes of immature astrocytes. Although subsequently undergoing further maturation, radial glia already possess fundamental immunocytochemical and morphological characteristics indicative of astrocytic differentiation. A significant implication of our findings is that the development of astrocytes in the human fetal brain occurs much earlier than formerly believed.