Endocrine Abstracts

To clarify the role of the pituitary in zebrafish interrenal development we investigated wildtype (wt) zebrafish and 3 pituitary mutants: aal (with lactotrophes only), and pit1 (with corticotrophes only), fgf3-lia (lacking all adenohypophyseal cell types) and in MC2R knockdown embryos (MC2R morphants).

The interrenal primordium (IP) is detectable at 22hpf (hours post fertilization) as bilateral clusters of ff1b expressing cells which fuse to one domain at 24hpf. Only after this fusion, additional specific genes (e.g. P450scc, StAR, 3ß-HSD and MC2R) become detectable. The adrenomedullary primordia expressing dopamine ß-hydroxylase (dßh) migrate into the region of the IP at 2dpf and later develop into a bilobal organ. Interrenal and chromaffine cells are then highly intermingled. In the lia and aal mutants we observed normal development up to 2dpf compared to wt with unaltered expression of P450scc, MC2R, StAR, and the medullary gene dßh. However, at day 5 expression of interrenal genes was significantly reduced. In MC2R morphants we found changes similar to mutants lacking pituitary POMC with dramatic reduction of expression of interrenal markers demonstrating that ACTH plays a key role for the observed changes in mutants, whereas POMC expression was 4-fold increased in the anterior pituitary domain at day 5 indicating feedback regulation by impaired interrenal steroidogenesis. Significant reduction of dßh expression was also observed in lia and aal mutants, demonstrating the functional interaction between interrenal and medullary cells. In pit1 mutants normal interrenal development was observed indicating that only corticotroph cells are required for normal development.

Taken together, interrenal development and expression of interrenal key proteins initially take place in a pituitary independent manner. However, POMC influences further interrenal development by regulating the expression of P450scc, StAR, MC2R in later stages and feedback control is clearly established at day 5. Interrenal steroidogenesis is essential for normal development of chromaffine tissue.