Glial fibrillary acidic protein synthesized in vitro using messenger RNA from a human glioma cell line

Dehydration-induced proliferation of identified pituicytes in fully adult rats

The mitotic activity astrocytes in the adult central nervous system (CNS) is of interest due to their roles in gliosis and tumorigenesis, and their potential in aiding recovery of function following injury or disease. The posterior pituitary offers a potentially powerful model to study proliferation in vivo, since its resident astrocytes, called pituicytes, have been reported to divide concurrently with hormone release from the neurosecretory terminals there. our aim in this study was to confirm and characterize this proliferative response during dehydration and rehydration in fully adult animals using contemporary techniques. Adult male rats were given 2% saline in substitution for water for 0-9 days. Proliferation of pituicytes was quantified in tissue sections triple-labeled with the proliferation marker, 5-bromodeoxyuridine (BrdU), the astrocyte marker glial fibrillary acidic protein (GFAP), and the DNA marker 4,6,diamidino-2-phenylindole, HCL(DAPI). A robust proliferative response began within three days of dehydration and continued at a constant rate thereafter. In animals allowed to rehydrate, this response continued. After 9 days of dehydration, approximately 35% of pituicytes had participated in mitosis. While cell density remained constant across conditions, a reversible increase in posterior pituitary area was seen, suggesting that some cell death also occurs simultaneously. A significant proportion of non-pituicytes also underwent similar changes. These results indicate that pituicytes in the adult posterior pituitary retain characteristics necessary for reentering the cell cycle in response to local factors present during neurosecretory activity. We hypothesize that this proliferative response is directly related to the morphological changes previously reported for these cells under activating conditions.

Fetal calf spinal cords as enriched source of mRNA encoding glial fibrillary acidic protein

Total poly(A)+ RNA was isolated from fetal calf spinal cord, adult rat spinal cord, and young rat brain, and was translated using the rabbit reticulocyte lysate system. The amount of glial fibrillary acidic protein in the translation products was measured by immunoprecipitation with antiserum against glial fibrillary acidic protein. RNA from fetal calf spinal cord could direct glial fibrillary acidic protein synthesis such that this protein comprised approximately 1.4% of the total products. RNAs from adult rat spinal cord and brain could direct glial fibrillary acidic protein synthesis much less efficiently, with this protein comprising less than 0.3% of the total products. These results suggest that the gene for glial fibrillary acidic protein is strongly expressed in fetal calf spinal cord and that this tissue is an enriched source of mRNA encoding glial fibrillary acidic protein.

Proteolytic degradation of vimentin and glial fibrillary acidic protein in rat astrocytes in primary culture

Vimentin and glial fibrillary acidic (GFA) protein in rat astrocytes in primary culture were identified with their respective specific antisera on electroblots of one-dimensional and two-dimensional polyacrylamide gels. Each antiserum revealed respectively vimentin (58 kDa, pI 5.3), GFA protein (50 kDa, pI 6-5.8) and several more acidic, lower molecular mass vimentin-immunoreactive and GFA protein-immunoreactive polypeptides. These were more apparent when astrocyte proteins were extracted in the absence of EGTA and in the presence of Ca2+ ions suggesting that the lower immunoreactive polypeptides result from a Ca2+-sensitive proteolytic degradation of vimentin and GFA protein. The extent of proteolysis of GFA protein was higher when the differentiation of astrocytes was induced with 1,N6-dibutyryl-adenosine 3',5'-monophosphate (Bt2cAMP). In contrast, the proteolysis of vimentin was not affected by the state of differentiation of astrocytes. The results indicate the existence of at least two distinct degradative pathways for intermediate filament proteins in astrocytes in primary culture and suggest that in differentiated astrocytes the activity of proteinase(s) involved in the degradation of GFA protein increases.

Synthesis and turnover of cytoskeletal proteins in cultured astrocytes

We previously reported that the cytoskeleton of rat astrocytes in primary culture contains vimentin, glial fibrillary acidic protein (GFAP), and actin. These proteins were found in a fraction insoluble in Triton X-100 and thought to be assembled in filamentous structures. We now used primary astrocyte cultures to study the kinetics of synthesis and turnover of these cytoskeletal proteins. The intermediate filament proteins were among the most actively synthesized by astrocytes. High levels of synthesis were detectable by the third day of culture in the early log phase of growth, and the pattern of labeling at day 3 was similar to that at 14 days when the cultures had reached confluency. In short-term incorporation experiments vimentin, GFAP, and actin in the Triton-insoluble fraction were labeled within 5 min after exposure of the cultures to radioactive leucine. We did not detect any saturation of labeling for up to 6 h of incubation. The turnover of filament proteins studied by following the decay of radioactivity from prelabeled vimentin, GFAP, and cytoskeletal actin displayed biphasic decay kinetics for all three proteins. In the initial phase a fast-decaying pool with a half-life of 12-18 h contributed about 40% of the total activity in each protein. A major portion, about 60%, of each protein, however, decayed much more slowly, exhibiting a half-life of about 8 days.

Glial fibrillary acidic protein synthesized in vitro using messenger RNA from jimpy mouse spinal cord

Glial fibrillary acidic (GFA) protein was synthesized in vitro in a rabbit reticulocyte lysate system programmed with messenger RNA (mRNA) extracted from Jimpy mouse spinal cord. It was identical in molecular weight and charge to that synthesized from normal mouse mRNA and GFA protein extracted from normal mouse cord. These data suggest that the Jimpy mutation does not affect the primary phenotypic expression of GFA protein.