The expression of glial fibrillary acidic protein (GFAP)-mRNA during mouse brain development and in astroglial primary cultures has been investigated by using two approaches: Northern-blot evaluation using a specific cDNA probe, and cell-free translation associated with immunoprecipitation. During brain maturation (4-56 days postnatal), the GFAP-mRNA underwent a biphasic evolution. An increase was observed between birth and day 15 (i.e., during the period of astroglial proliferation), which was followed by a decrease until day 56 (i.e., during astroglial cell differentiation). At older stages (300 days), an increase was observed, which might reflect gliosis. During astroglial in vitro development (7-32 days in culture), the GFAP-mRNA showed similar variations. An increase, observed during the period of astroglial proliferation (7-18 days), was followed by a decrease which occurred in parallel to marked changes in cell shape, cell process outgrowth, and the organization and accumulation of gliofilaments. During the same culture period (7-32 days), alpha-tubulin mRNA, which was used as an internal standard, did not vary significantly. These results show that the increase of the GFAP protein and of gliofilaments observed both in vivo and in vitro during astroglial differentiation cannot be ascribed to an accumulation of the GFAP-mRNA. It might be that more than one mechanism regulates the levels of free and polymerized GFAP and of its encoding mRNA.

The time course changes in levels of mRNA encoding glutamic acid decarboxylase (GAD) and proenkephalin (PPE) was analyzed in the rat striatum following unilateral lesion of substantia nigra with 6-hydroxydopamine. The levels of both GAD and PPE mRNAs increased after the dopaminergic deafferentation, reaching concomitantly a maximal twofold increase on day 25. Thereafter, the mRNA levels declined; at 4 months, the amount of PPE mRNA remained slightly elevated whereas GAD mRNA had returned to the control value, suggesting the action of a compensatory mechanism. We also observed a rise of glial fibrillary acidic protein mRNA level which reflects a reactive astrocytosis. In contrast, alpha-tubulin mRNA level remained unchanged, indicating that no significant synaptogenesis occurs in this experimental situation. No obvious modification in mRNA levels was detected in the striatum contralateral to the lesion. These results highlight the role of the modulation of gene expression in adaptive processes to dopamine deficiency in striatal efferent pathways. Its relevance to the pathophysiology of Parkinson's disease is discussed.

Two clones encoding human glial fibrillary acidic protein (GFAP) were isolated from a human astrocytoma cDNA library. The clones pHGFAP1 and pHGFAP2 were selected by the combined use of differential colony hybridization and hybridization-selection technique with polyclonal anti GFAP antiserum. The longer one, pHGFAP1, encompasses 3.0 kb and includes the 1.8 kb long 3' untranslated region specific to the human mRNA. Sequence data disclosed an extensive homology within the coding region of human and mouse GFAP cDNAs even in the end domains. Blot hybridization analysis of RNAs from human, rat and mouse brain revealed a single GFAP mRNA species of 3.1, 2.8 and 2.7 kb respectively and Southern blot experiments indicated that this mRNA is most probably transcribed from a unique gene. In situ hybridization performed with biotinylated probes on cultured mouse brain cells suggests both the sorting and the transport of GFAP mRNA throughout the cytoplasm and processes of the astrocytes. As a model of reactive gliosis secondary to degenerative disorders, 6-hydroxydopamine (6-OHDA) lesion of the substantia nigra in the rat was performed. GFAP mRNA increased 1.4 fold in the ipsilateral striatum on day 10 after the lesion. It then declined to the control level 4 months later contrasting with the lower and more sustained increase in preproenkephalin (PPE) mRNA. The interspecies cross-reactivity of the HGFAP probes make them useful as a tool for the molecular analysis of reactive gliosis in various experimental models.