Eph receptors and zonation in the rat adrenal cortex Caroline H. Brennan, Alexandra Chittka, Stewart Barker and Gavin P Vinson School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS. Abstract Although the zonation of the adrenal cortex has a clear functional role, the mechanisms that maintain it remain largely conjectural. The concept that an outer proliferative layer gives rise to cells that migrate inwards, adopting sequentially the zona glomerulosa, fasciculata and reticularis phenotypes, has yet to be explained mechanistically. In other tissues, Eph receptor/ephrin signalling provides a mechanism for cellular orientation and migration patterns. Real time -PCR and other methods were used to determine the possible role of Eph/ephrin systems in the rat adrenal. Messenger RNA coding for several members of the Eph receptor family was detected, but of these, EphA2 provided the closest parallel to zonal organisation. In situ hybridisation showed that EphA2 mRNA and EphA protein were predominantly located in the zona glomerulosa. Its transcription closely reflected expected changes in the glomerulosa phenotype, thus it was increased after a low sodium diet, but decreased by pretreatment with the angiotensin converting enzyme inhibitor, captopril. It was also decreased by ACTH treatment, but unaffected by betamethasone. Messenger RNA coding for ephrin A1, the major ligand for the Eph A receptors, was also detected in the rat adrenal, though changes evoked by the various pretreatments did not clearly reflect the expected changes in zonal function. Because the maintenance of cellular zonation requires clear positional signals within the adrenal cortex, these data support a role for Eph forward and reverse signalling in the maintenance of adrenocortical zonation. Introduction Aspects of adrenocortical zonation remain enigmatic. Functionally, the accepted view is that the glomerulosa is the source of aldosterone secretion and the fasciculata and reticularis are the source of glucocorticoids (Deane, 1962; Ogishima et al., 1992; Vinson et al., 1992; Ennen et al., 2005) and (depending on species) androgens as well (Deane, 1962; Parker et al., 1983; Vinson et al., 1992; Rehman and Carr, 2004). Within this system, alsosterone secretion is under the regulation of angiotensin (and other agents) and ACTH supports fasciculata and reticularis function. Though this simple model probably needs adjustment and reappraisal (Vinson, 2003, 2004), it nevertheless seems evident that the zonal arrangement is important in the maintenance of adrenocortical function, so it is important to determine how it arises. Page 1 of 20 Accepted Preprint first posted on 7 May 2008 as Manuscript JOE-08-0084