The purpose of this work was to elucidate the characteristics and the expression profiles of porcine Opn4 during developmental stages and different times of the day. The coding sequence of Opn4 gene was cloned. The mRNA expression levels of Opn4 gene in the retina of the swines during developmental stages and different times of the day were examined. The results showed that the swine ORF of Opn4 gene was 1 437 bp in length which encodes 478 amino acids residues with the molecular formula of C

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... 98 H 3705 N 623 O 651 S 23 . The expression level of Opn4 in the day was significantly higher than that in the night (P<0.01). During the growing periods, Opn4 started expressing as early as 34 d in the embryonic phase with the lowest level (P<0.01), reached to a peak 1 day after birth (P<0.01), and then stayed at a moderate standard. The difference of Opn4 expressions among the swines at 1 th month, 4 th month, and 84 th month was not significantly different (P>0.05). In total, results showed that the Opn4 gene can regulate the biological rhythm of the swines. Furthermore, it play an important role in mediate the responsibility to the light in the postnatal swines.