Developmental up-regulation and agonist-dependent down-regulation of GABAA receptor subunit mRNAs in chick cortical neurons.
We have used quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to analyze the expression of GABAA receptor subunit genes in cultured neurons from the chick embryo cerebral cortex. During maturation of the neurons between day 2 and day 8 in culture, levels of the alpha 1 subunit transcript (per ng total RNA) increased 3.8 +/- 0.3 fold, while those for the beta 2S and beta 4S subunits increased 2.4 +/- 0.4 and 1.8 +/- 0.2 fold, respectively. The accumulation of the beta 4 S subunit mRNA was more rapid than those encoding either the alpha 1 or beta 2S polypeptides. After 4 days in culture the beta 4S subunit transcript level reached 105 +/- 7.7% of that found after 8 days, while the corresponding amounts for the alpha 1 and beta 2S subunit mRNAs were 50 +/- 7.1% and 44 +/- 10.7%, respectively. On the other hand, no significant differences were observed in the level of either the gamma 1 or the gamma 2S subunit mRNA during development in vitro. Likewise, the ratios of the large/small splice variants (beta 2 = 0.16 +/- 0.02; beta 4 = 0.57 +/- 0.02; gamma 2 = 0.30 +/- 0.06) did not show detectable changes during this period. To study the down-regulation of the mRNAs, a single dose of 100 microM GABA was added to the culture medium. After 7 days of exposure to GABA, the levels of transcripts for the alpha 1, beta 2, beta 4, gamma 1, and gamma 2 subunits and their splice variants (where present) were all reduced by 47-65% compared to untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Baumgartner
B J
BJ
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030.
Harvey
R J
RJ
Darlison
M G
MG
Barnes
E M
EM
D000199:Actins / Q000096:biosynthesis; D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D002478:Cells, Cultured; D016922:Cellular Senescence; D002540:Cerebral Cortex / Q000378:metabolism*; D002642:Chick Embryo; D017931:DNA Primers; D015536:Down-Regulation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D011963:Receptors, GABA-A / Q000096:biosynthesis*; D014158:Transcription, Genetic; D015854:Up-Regulation; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D000199:Actins; D017931:DNA Primers; D046911:Macromolecular Substances; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid