Expression and role of phosphodiesterase 6 in the chicken pineal gland

Abstract

The chicken pineal gland is directly photosensitive, with light causing an inhibition of melatonin synthesis. A possible role of phosphodiesterase 6 (PDE6, the primary effector of retinal phototransduction) in mediating this response was investigated. RT-PCR, DNA sequencing and northern blots revealed the presence of RNA encoding both catalytic and regulatory subunits of PDE6 in the chicken pineal gland. Both rod and cone forms of PDE6 subunits mRNA were detected. The concentration of the transcripts encoding PDE6 catalytic subunits peaked at night. Western blot analysis of chicken pineal proteins with an antibody directed against the catalytic subunits of bovine rod PDE6 identi®ed a single immunoreactive protein of 97 kDa. Anion exchange chromatography of chicken pineal soluble proteins revealed a peak of PDE6 activity that accounted for about 30% of cyclic GMPhydrolysis. In cultured chick pineal glands, arylalkylamine N-acetyltransferase (AA-NAT), the rate-limiting enzyme of melatonin synthesis, was protected from inhibition by light when selective PDE5/6 inhibitors (zaprinast, DMPPO) were added to the culture medium. PDE5/6 inhibitors did not affect AA-NAT activity in the dark. In contrast, a general PDE inhibitor (IBMX) increased AA-NAT in a light-independent manner. Together, the data indicate that rod and cone forms of PDE6 are expressed in chick pineal cells and that this enzyme plays a role in the inhibition of melatonin synthesis by light.

Increased Plasma cGMP in a Family With Autosomal Recessive Retinitis Pigmentosa Due to Homozygous Mutations in the PDE6A Gene

“…The latter may occur because of a cGMP connection to other clinical or nonclinical situations, as mentioned above, and in this context there are reports suggesting PDE6 expression also in nonphotoreceptor tissues and in different developmental stages, 69 at least in other animals, which may have a bearing on the plasma cGMP levels. Still, the measurement of plasma cGMP is relatively simple and could readily act as a complement to other ophthalmic investigations in order to improve the RP diagnosis, which is not always straightforward.…”

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

“…In contrast to the subunit structure of the rod PDE6 enzymes from most species studied to date, in birds there is as yet no evidence for a PDE6 ␣ subunit from studies on both the pineal gland (Morin et al, 2001) and the chicken retina (Huang et al, 2004). In both cases only a PDE6 ␤ subunit has been found.…”

Molecular Determinants of cGMP Binding to Chicken Cone Photoreceptor Phosphodiesterase

“…However, our mass spectrometry analysis of the enzyme of the second DE52 peak from chicken retina only detected the ␤-subunit of rod PDE6 (PDE6B). Initially we thought that this was due to the fact that only the ␣Ј-subunit of chicken cone (PDE6C) and ␤-subunit of chicken rod (PDE6B) were in the data base (10,11). However, when all of the acquired MS/MS spectra were searched against all the available PDE6A sequences from all species in the National Center for Biotechnology Information data base, no unique PDE6A peptide matches were found.…”

“…Nevertheless a cDNA predicted from homology arguments to encode the chicken cone PDE6 ␣Ј-subunit has been isolated and characterized (10). Similarly a cDNA most homologous to the bovine PDE6 ␤-subunit cDNA also has been reported from chicken pineal gland (11).…”