The nucleoredoxin-like gene Nxnl1 (Txnl6) and
its paralogue Nxnl2 encode the rod-derived cone viability
factors (RdCVF and RdCVF2), which increase the resistance to photooxidative
damage and have therapeutic potential for the survival of cones in retinitis
pigmentosa. In this study, the transcription of Nxnl genes was
investigated as a function of the day/night cycle in rats. The transcript levels
of Nxnl1 and Nxnl2 were seen to display daily
rhythms with steadily increasing values during the light phase and peak
expression around dark onset in preparations of whole retina, photoreceptor
cells and—but only in regard to Nxnl1—in
photoreceptor-related pinealocytes. The cycling of Nxnl1 but
not that of Nxnl2 persisted in constant darkness in the retina.
This suggests that daily regulation of Nxnl1 is driven by a
circadian clock, whereas that of Nxnl2 is promoted by
environmental light. The present data indicate clock- and light-dependent
regulations of nucleoredoxin-like genes that may be part of a protective shield
against photooxidative damage.