Identification of rat brain polysomes synthesizing the brain specific enolase (14.3.2 protein), S100 protein and alpha and beta tubulin subunits

Regulation of neuron-specific enolase isozyme levels during differentiation of murine neuroblastoma cell cultures

A specific event which accompanies the terminal differentiation of most neurons is the isozymic enolase transition from the ?? form to the ?? and ?? adult neuronal forms. It is partly expressed during maturation of a mouse neuroblastoma clonal cell line (NIE-115). We demonstrate, in these cell cultures, that the significant increase in the concentration of ? gene product, expressed as ?? enolase during differentiation, is due to a parallel and similar increase in its synthesis. The capacities of poly (A)(+) RNA from undifferentiated and differentiated cultures to direct the synthesis of ? gene product were compared in a reticulocyte cell-free protein-synthesizing system. This translating capacity is stimulated in the same proportion as the rate of synthesis of ? antigen in differentiating cell cultures. Therefore the increase in the level of ? protein (expressed mostly as ?? enolase) during differentiation results from the increased translating activity or relative amount of ?mRNA.

Thyroid hormone action on astroglial cells from distinct brain regions during development

Astrocytes are target to triiodothyronine (T3) hormone action during rat brain development. In this work, we show that astrocytes from distinct developing brain regions are differently responsive to thyroid hormone. Distinctly from embryonic or newborn cerebral hemisphere and mesencephalic astrocytes, newborn cerebellar and embryonic hippocampal astrocytes do not change their morphology in response of hormone treatment. We also analysed protein synthesis and secretion from these T3-treated astrocytes. The results showed a significant increase in protein synthesis in astrocytes from older brain regions. Maximum effect, however, was observed in cerebral hemisphere astrocytes from newborn rats. The protein secretion effect was also more evident in the cerebral hemisphere as well as in cerebellar astrocytes from newborn rats. In addition, we examined T3 effects on GFAP/vimentin expression by culturing 6-day old cerebellar astrocytes. In this case T3 seems to induce GFAP expression which might be occurring as a first step to astrocyte differentiation.

Purification of gamma-enolase messenger ribonucleic acid from rat brain by an immunoadsorption method

Messenger ribonucleic acid (mRNA) coding for the brain-specific protein gamma-enolase was isolated by an immunopurification procedure. Rat brain polysomes including nascent polypeptide chains were reacted with specific gamma-enolase antibody. The polysome-antibody complexes were subsequently adsorbed to protein A-Sepharose. After extensive washing, RNA was eluted and applied to an oligo(dT)-cellulose column. Purified mRNA was translated in vitro in a mRNA-dependent rabbit reticulocyte lysate system. The synthesized product was identical to gamma-enolase synthesized by free polysomes from rat brain. Immunoisolated gamma-enolase mRNA was enriched 380-fold compared to total mRNA extracted from free polysomes. This result indicates that low-abundance mRNAs may conveniently be isolated from brain tissue by immunoadsorption of polysomes.

Developmental changes in the translatable mRNA for beta subunit of S-100 protein in rat brain

The presence of mRNA coding for beta subunit of S-100 protein was demonstrated in polyadenylated RNA from the rat brain in vitro translation in a reticulocyte lysate cell-free system. The products were identified with S-100 protein beta subunit using the immunoprecipitation of the reaction products with the specific antisera, comigration of the isolated, labelled peptide with the purified S-100 protein in SDS-polyacrylamide gel electrophoresis and fluorography and the same retention time of the labelled S-100 protein beta subunit with authentic S-100 beta subunit by high performance liquid chromatography. The size determination of mRNA for S-100 protein on sucrose density gradient centrifugation gave 6-8 S. The assay gave a linear response with increasing amounts of polyadenylated RNA, allowing quantitation of mRNA level for S-100 protein in polyadenylated RNA. During the prenatal period and 10 postnatal days, only minute amounts of mRNA for beta subunit of S-100 protein could be found, however a dramatic increase of mRNA for beta subunit of S-100 was observed within the period of 10 to about 30 days and the mRNA level maintained a plateau from 40 days to adult age. These date indicate that the development changes in the amount of S-100 protein in the rat brain found by other authors is strongly correlated with the changes in the level of its translatable mRNA.

Synthesis of S100 protein on free and membrane-bound polysomes of the rabbit brain

Free and membrane-bound polysomes were isolated from the cerebral hemispheres and cerebellum of the young adult rabbit. The two polysomal populations were translated in an mRNA-dependent cell-free system derived from rabbit reticulocytes. Analysis of the [35S]methionine-labeled translation products on two-dimensional polyacrylamide gels indicated an efficient separation of the two classes of brain polysomes. The relative synthesis of S100 protein by free and membrane-bound polysomes was determined by direct immuno-precipitation of the cell-free translation products in the presence of detergents to reduce nonspecific trapping. Synthesis of S100 protein was found to be twofold greater on membrane-bound polysomes compared with free polysomes isolated from either the cerebral hemispheres or the cerebellum. In addition, the proportion of poly-(A+)mRNA coding for S100 protein was also twofold greater in membrane-bound polysomes compared with free polysomes isolated from the cerebral hemispheres. These results indicate that the cytoplasmic S100 protein is synthesized predominantly on membrane-bound polysomes in the rabbit brain. We suggest that the nascent S100 polypeptide chain translation complex is attached to the rough endoplasmic reticulum by an ionic interaction involving a sequence of 13 basic amino acids in S100 protein.