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

Angiotensin-converting enzyme (ACE) performs two contrasting enzymatic effe cts: as part of the renin-angiotensin system it converts angiotensin I into physiologically active angiotensin II, and it inactivates a number of pept ides, 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 an d 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 r etina. Levels of ACE-mRNA were quantified by competitive PCR with heterolog ous competitor fragments in the retina at different developmental stages. T o localize protein expression of ACE in the mature chicken retina an antibo dy directed against ACE was used. ACE- mRNA was present in all ocular tissu es examined. Quantification of ACE-mRNA in avascular retinas of developing chickens revealed small amounts (0.13 attomol mul(-1)) at embryonic day 7 a nd values of about 0.6 attomol mul(-1) during embryonic days 7-17. ACE-mRNA expression transiently increased ten-fold (7.3 attomol mul(-1)) on postnat al day 1, decreased again to about 1.4 attomol mul(-1) on postnatal day 6, and remained constant thereafter. ACE-immunohistochemistry revealed labelin g of photoreceptors, bipolar cells, amacrine cells, and cells in the gangli on cell layer as well as of Muller 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 d irectly after hatching indicate, that ACE may be involved in fine tuning th e neuropeptidergic equipment of the retinal network during the initial phas e of visual experience. (C) 2001 Academic Press.