Developmentally regulated expression of GABA receptor ρ1 and ρ2 subunits, L7 and cone-rod homeobox (CRX) genes in mouse retina

In this study, we compared the temporal expression pattern of four retinal genes; ρ1 and ρ2 that encode subunits of GABA_c receptors, L7 that encodes Purkinje cell protein and CRX that encodes the cone-rod homeobox transcription factor. A reverse-transcription-polymerase chain reaction (RT-PCR) strategy that generated a linear correlation between the amount of retinal RNA and the amount of amplified product was used to quantify transcripts from each gene. Results with this method showed that the ρ1 and L7 have similar developmental patterns. Both exhibit basal level expression before P7. From P7 to P20, the RNA levels for both genes were increased about 12-fold. After P20, the RNA levels remained unchanged. Compared to ρ1 and L7, expression of ρ2 began later, since the ρ2 RNA could not be detected until P10. At P10, the ρ2 RNA level was about 10% of its level at P35. Expression of ρ2 reached its peak at a later developmental stage compared to that of ρ1 and L7. The different temporal patterns were confirmed by co-amplification of ρ1, ρ2, and L7 in a single PCR tube. CRX RNA was detected at embryonic day 15 (E15) and increased progressively, in agreement with a prior study using in situ hybridization. These data, combined with evidence that the tissue distribution of ρ1 and L7 RNA in the CNS are similar, indicates that ρ1 and L7 may share common transcriptional regulatory elements. Furthermore, the difference in the timing of ρ subunit expression suggests that the subunit composition of GABA_c receptors vary during retinal development.