Cytoskeletal changes of glioblasts after morphological differentiation induced by glia maturation factor

Gene expression in astrocytes is affected by subculture

We have investigated the effects of cell passaging and time in culture on astrocyte morphology, transferrin expression and the expression of two main astrocyte markers, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS: EC 6.3.1.2). When primary astrocytes were subcultured, giving rise to secondary and tertiary cultures, their morphology changed, regardless of the split ratio used to passage the cells. Correlating with this morphological change, a dramatic increase in the accumulation of GFAP and GS mRNAs was observed after cells had been passaged. This effect was in marked contrast to the moderate increase in the levels of GFAP and GS mRNAs observed over several weeks in primary culture. Hydrocortisone induction of GS gene expression was not affected by cell passage. Transferrin mRNA, which is not normally found in astrocytes in vivo, was expressed at a high level in primary cultures of astrocytes. However, transferring mRNA almost completely disappeared after the second passage. Astrocyte-conditioned media, or co-cultures with oligodendrocytes, modified transferrin gene expression. Taken together, these results show that subculturing of primary rat astrocytes leads to a dramatic change in the genetic expression of several proteins and provides a new approach to modify astrocyte differentiation in vitro.

Effect of thyroid deficiency on glial fibrillary acidic protein (GFAP) and GFAP-mRNA in the cerebellum and hippocampal formation of the developing rat

The concentrations of glial fibrillary acidic protein (GFAP) and its encoding mRNA in the cerebellum and hippocampal formation were assayed during the development of normal and hypothyroid rats. Neonatal hypothyroidism induced a significant reduction in the GFAP concentration in both regions from day 14. The reduction was especially marked on day 35 in the cerebellum (-43%) and the hippocampal formation (-55%). The immunocytochemical study of vimentin showed that the developmental disappearance of this protein from the Bergmann and internal astrocytes is greatly delayed in the cerebellum of the hypothyroid rats. The reduction in GFAP concentration together with the delayed vimentin-GFAP transition could explain how astrocyte morphogenesis is impaired by neonatal thyroid deficiency. The GFAP-mRNA concentration in the hippocampal formation was reduced throughout the development of thyroid-deficient rats, while the GFAP-mRNA concentration in the cerebellum first increased between birth and day 14 to reach a peak well above the normal value (+78%) and decreased thereafter to reach 53% of the normal value by day 35. This transient increase in the cerebellar GFAP-mRNA concentration may be related to the astroglial hyperplasia that occurs in these animals. The difference between the developmental profile of GFAP and its encoding mRNA, especially under pathological conditions, indicates that two distinct mechanisms control the synthesis or stability of the protein and its messenger RNA, as was previously found in the forebrain of the developing normal rat.

GFAP turnover during astroglial proliferation and differentiation

The expression and turnover of the glial fibrillary acidic protein (GFAP) were studied in astroglial primary cultures during postnatal proliferation and maturation. 1. Immunocytochemical studies demonstrated that in immature proliferating astrocytes. GFAP was expressed as a filamentous organized crown around the nucleus whereas in the maturating cells, a GFAP labelled network began to radiate throughout the cytoplasm and GFAP was highly expressed in the astroglial processes. 2. GFAP turnover was studied at 3 periods of culture. The decay of radioactivity from prelabelled GFAP was followed from day 4-12 (immature stage), 11-19 (maturing stage) and 21-29 (morphologically differentiated stage). GFAP displayed a biphasic decay kinetic at each considered period. Two pools of GFAP distinctly appeared. The first one was a fast decaying pool with a half life of 16-18 h and of 5-6 days for the stable one. The unstable pool decreased from 70% to 30% of the total incorporated radioactivity from the proliferating stage to the most mature stage, whereas the stable pool increased proportionally.

Neuron-glia interactions: effect of serotonin on the astroglial expression of GFAP and of its encoding message

The trophic effect of serotonin on the glial fibrillary acidic protein (GFAP) expression was investigated in rat brainstem astrocytes in primary culture. GFAP immunolabelling decreased and gliofilaments appeared localized in the cytoplasm periphery. GFAP protein level decreased in parallel with a decrease in its encoding message. Serotonin may act as an inhibitor of GFAP expression either on the transcription or on the stability of the GFAP-mRNA.

Effect of thyroid deficiency on actin mRNA content in the developing rat cerebellum

The actin mRNA content of the cerebellum was determined in normal and hypothyroid developing rats using RNA dot hybridization with a beta-actin cDNA probe. The decline in actin mRNA content occurring during the second postnatal week in normal development was delayed by about 1 week in hypothyroid rats. Since this effect coincides exactly with the delay in actin filament formation recently reported in thyroid-deficient rats, it strengthens the hypothesis of an inverse relationship in the developing brain between the polymerization state of actin and the production of actin mRNA.

Glial filaments in the subcutaneous tumors of mouse glioma clones differently expressing glial fibrillary acidic protein. An immunohistochemical and ultrastructural study

Glial filaments contain vimentin and glial fibrillary acidic protein (GFAP). The question of how glial filaments change morphologically according to the expression of vimentin and/or GFAP has remained unclear. In this study, immunohistochemical and ultrastructural examinations were performed on the subcutaneously transplanted tumors of two clones (F6B3 and G10A10) derived from a mouse glioma. F6B3 tumor expressed GFAP and vimentin in large quantities. G10A10 tumor expressed plenty of vimentin but only a little of GFAP. Ultrastructurally, F6B3 tumor contained abundant cytoprocesses in most of which numerous intermediate filaments (IFs) were arranged in a parallel array. On the other hand, only a small number of the processes were seen in G10A10 tumor, which showed a few IFs arranged either randomly or sparsely in the processes. Both tumors commonly had the IFs accompanied by visible sidearms, but there was a difference in that the smooth and firm IFs were confined to part of F6B3 tumor. Thus, the comparison made between the two models presented differences in the content, arrangement and morphology of IFs, as well as in the manner of GFAP expression, suggesting correlation between these differences.