Specific frequencies of spontaneous Ca2+ transients upregulate GAD 67 transcripts in embryonic spinal neurons.
Spontaneous Ca2+ transients expressed prior to synaptogenesis regulate the developmental appearance of GABA in cultured Xenopus spinal neurons. We find that glutamic acid decarboxylase (GAD) immunoreactivity is also Ca(2+)-dependent and parallels the appearance of GABA. We show that xGAD 67 transcripts first appear in the embryonic spinal cord during the period in which these Ca2+ spikes are generated, in a pattern that is temporally and spatially appropriate to account for differentiation of GABAergic interneurons. RNase protection and competitive quantitative RT-PCR demonstrate that transcript levels are approximately threefold greater when neurons are cultured in the presence of extracellular Ca2+ that permits generation of transients than when cultured in its absence. The frequency of spontaneous Ca2+ spikes plays a crucial role in the regulation of transcripts, since reimposition of Ca2+ transients at the frequency generated in cultured neurons rescues normal expression. We conclude that naturally occurring low frequencies of these Ca2+ transients regulate levels of xGAD 67 mRNA in differentiating neurons.
Watt
S D
SD
Department of Biology, University of California at San Diego, La Jolla 92093-0357, USA.
Gu
X
X
Smith
R D
RD
Spitzer
N C
NC
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D005968:Glutamate Decarboxylase / Q000032:analysis / Q000235:genetics*; D007527:Isoenzymes / Q000032:analysis / Q000235:genetics*; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000201:enzymology*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012260:Ribonucleases; D013116:Spinal Cord / Q000166:cytology* / Q000196:embryology; D014158:Transcription, Genetic / Q000502:physiology*; D014981:Xenopus; D005680:gamma-Aminobutyric Acid / Q000235:genetics
D007527:Isoenzymes; D012333:RNA, Messenger; D005680:gamma-Aminobutyric Acid; D012260:Ribonucleases; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; D002118:Calcium