Expression of angiotensin-converting enzyme (ACE) in the developing chicken retina

Angiotensin-converting enzyme (ACE) performs two contrasting enzymatic effects: as part of the renin-angiotensin system it converts angiotensin I into physiologically active angiotensin II, and it inactivates a number of peptides, e.g. substance P. These peptides are well known neurotransmitters in the retina and recently angiotensin II was described in retinal neurons. We therefore investigated a possible involvement of ACE in retinal metabolism by determining the mRNA and protein expression of ACE in the developing and mature chicken retina. ACE-mRNA expression was investigated by RT-PCR in the iris/ciliary body, the choroid, the optic nerve head, pecten, and the retina. Levels of ACE-mRNA were quantified by competitive PCR with heterologous competitor fragments in the retina at different developmental stages. To localize protein expression of ACE in the mature chicken retina an antibody directed against ACE was used. ACE-mRNA was present in all ocular tissues examined. Quantification of ACE-mRNA in avascular retinas of developing chickens revealed small amounts (0.13 attomol microl(-1)) at embryonic day 7 and values of about 0.6 attomol microl(-1)during embryonic days 7-17. ACE-mRNA expression transiently increased ten-fold (7.3 attomol microl(-1)) on postnatal day 1, decreased again to about 1.4 attomol microl(-1)on postnatal day 6, and remained constant thereafter. ACE-immunohistochemistry revealed labeling of photoreceptors, bipolar cells, amacrine cells, and cells in the ganglion cell layer as well as of Müller glia. Our data show that ACE-mRNA is an intrinsic component of the retina and that ACE itself has a widespread but distinct cellular distribution. The transient high expression of ACE-mRNA directly after hatching indicate, that ACE may be involved in fine tuning the neuropeptidergic equipment of the retinal network during the initial phase of visual experience.