Quantitative estimation of RNA transcripts suggests persistence of Pax-6 expression in the postembryonic chick retina

Pax-6 is expressed during early embryonic development of the eye. Very litt le is known about its expression in the functionally mature retina. We have detected Pax-6 transcripts in the ganglion cell- and amacrine cell layers at days 3, 10, 17 and 31 posthatching and in 2- to 3-month-old chick retina by in situ hybridization. These observations were confirmed by a quantitat ive analysis. Competitive RT-PCR with a homologous internal control reveale d a significant reduction (p < 0.001) in the number of Pax-6 transcripts in day 17 retina [(0.39 +/- 0.13) x 10(10)/mg tissue] compared to day 3 retin a [(1.65 +/- 0.48) x 10(10)/mg tissue]. Although significantly lower than a t day 3, the day 31 retina [(0.7 +/- 0.16) x 10(10)/mg tissue] and retina f rom 2- to 3-month-old chicks [(0.9 +/- 0.28) x 10(10)/mg tissue] contained an increased number of Pax-6 transcripts in comparison to day 17. On the ba sis of the amount of RNA, the number of Pax-6 transcripts in the day 3 reti na [(0.45 +/- 0.14) x 10(10)/mu g RNA] relative to day 17 retina [(0.4 +/- 0.08) x 10(10)/mu g RNA] did not change significantly (p = 0.29). However, at day 31 and at 2-3 months of age an increased number of Pax-6 transcripts [(0.65 +/- 0.14) x 10(10)/mu g RNA and (0.65 +/- 0.2) x 10(10)/mu g RNA, r espectively)] were found. In view of the known association of Pax-6 express ion with proliferation and emergence of different cell types, these data su ggest that cell types in ganglion and inner nuclear cell layers may retain proliferative potential for an extended period in the young adult retina.