title: Identification of the minimal promoter for specific expression of the GABAρ1 receptor in retinal bipolar cells.
abstract: γ-aminobutyric acid (GABA)ρ receptors regulate rapid synaptic ion currents in the axon end of retinal ON bipolar neurons, acting as a point of control along the visual pathway. In the GABAρ1 subunit knock out mouse, inhibition mediated by this receptor is totally eliminated, showing its role in neural transmission in retina. GABAρ1 mRNA is expressed in mouse retina after post-natal day 7, but little is known about its transcriptional regulation. To identify the GABAρ1 promoter, in silico analyses were performed and indicated that a 0.290-kb fragment, flanking the 5'-end of the GABAρ1 gene, includes putative transcription factor-binding sites, two Inr elements, and lacks a TATA-box. A rapid amplification of cDNA ends (RACE) assay showed three transcription start sites (TSS) clustered in the first exon. Luciferase reporter assays indicated that a 0.232-kb fragment upstream from the ATG is the minimal promoter in transfected cell lines and in vitro electroporated retinae. The second Inr and AP1 site are important to activate transcription in secretin tumor cells (STC-1) and retina. Finally, the 0.232-kb fragment drives green fluorescent protein (GFP) expression to the inner nuclear layer, where bipolar cells are present. This first work paves the way for further studies of molecular elements that control GABAρ1 transcription and regulate its expression during retinal development.
authors.affiliation: Departamento de Neurobiología Celular y Molecular, Universidad Nacional Autónoma de México, Instituto de Neurobiología, Querétaro, Mexico.
authors.forename: Arturo Israel
authors.initials: AI
authors.lastname: Machuca-Parra
authors.forename: Ricardo
authors.initials: R
authors.lastname: Miledi
authors.forename: Ataúlfo
authors.initials: A
authors.lastname: Martínez-Torres
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D045744:Cell Line, Tumor; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009924:Organ Culture Techniques; D011401:Promoter Regions, Genetic / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics; D051381:Rats; D018080:Receptors, GABA-B / Q000235:genetics*; D051245:Retinal Bipolar Cells / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D020033:Protein Isoforms; D018080:Receptors, GABA-B