Expression of opsin mRNA in normal and vitamin A deficient retinas of the sphingid moth Manduca sexta

Two distinct opsin-encoding cDNAs, designated MANOP1 and MANOP2, were isolated as 3' fragments from the sphingid moth Manduca sexta. They were obtained by reverse transcription of retinal RNA and amplification with the polymerase chain reaction (PCR) using a degenerate primer designed to an amino-acid sequence conserved in arthropod opsins. The cDNA fragments labelled bands at approximately 1.8 kb on Northern blots of retinal RNA extracts. Levels of opsin message were compared in retinas from normal moths, whose diets were fortified with carotenoid precursors of the Manduca rhodopsin chromophore, 3-hydroxyretinal, and those reared on carotenoid/retinoid (vitamin A) deficient diets. The chromophore-depleted retinas contained more opsin mRNA;this was particularly true for MANOP2. Thus, the chromophore is not required for opsin gene transcription in Manduca.