Pituitary-Interrenal Interaction in Zebrafish Interrenal Organ Development

Abstract

To further elucidate pituitary adrenal interactions during development, we studied the organogenesis of the interrenal organ, the teleost homolog of the mammalian adrenal gland, in zebrafish. To this end we compared wild-type zebrafish interrenal development with that of mutants lacking pituitary cell types including corticotrophs. In addition, we studied the effects of ACTH receptor (Mc2r) knockdown and dexamethasone (dex) on interrenal development and pituitary feedback. Until 2 d post fertilization (2 dpf) interrenal development assessed by transcripts of key steroidogenic genes (cyp11a1, mc2r, star) is independent of proopiomelanocortin (Pomc) as demonstrated in aal/eya1and lia/fgf3 mutants. However, at 5 dpf lack of pituitary cells leads to reduced expression of steroidogenic genes at both the transcriptional and the protein level. Pituitary control of interrenal development resides in corticotrophs, because pit1 mutants lacking pituitary cells except corticotrophs have a phenotype similar to that of wild-type controls. Furthermore, development in mc2r knockdown morphants does not differ from aal/eya1 and lia/fgf3 mutants. Inhibition of steroidogenesis by mc2r knockdown induces up-regulation of pomc expression in the anterior domain of pituitary corticotrophs. Accordingly, dex suppresses pomc in the anterior domain only, leading to impaired expression of steroidogenic genes commencing at 3 dpf and interrenal hypoplasia via reduced interrenal proliferation. In contrast, negative feedback on pituitary corticotrophs by dex is evident at 2 dpf and precedes effects of Pomc on the interrenal primordium. These data demonstrate a gradual transition from early pituitary-independent interrenal organogenesis to developmental control by the anterior domain of pituitary corticotrophs acting via Mc2 receptors.

In vivo alternative assessment of the chemicals that interfere with anterior pituitary POMC expression and interrenal steroidogenesis in POMC: EGFP transgenic zebrafish

“…ACTH is released into the blood to stimulate the adrenal cortex to produce and secrete glucocorticoids, whereas glucocorticoids produce negative feedback inhibition at the level of both the pituitary and hypothalamus to reduce ACTH output ( Fig. 1; To et al, 2007;Raff and Jacobson, 2007). The expression of POMC is believed to be regulated by hypothalamic corticotrophin-releasing hormone and arginine vasopressin.…”

Interrenal Organogenesis in the Zebrafish Model

“…Both cyp11a1 and star are expressed at embryonic interrenal tissue, starting from approximately 24 hpf, shortly after the specification and central convergence of interrenal primordia. 39 However, the functional differentiation of interrenal tissue, marked by the chromogenic detection of 3-beta-Hydroxysteroid dehydrogenase (3b-Hsd) enzymatic activity, is not initiated until about 28 hpf. The expressions of steroidogenic genes are abolished upon the knockdown of Ff1b by antisense morpholino injection, implying their direct transcriptional regulation by Ff1b protein.…”

“…The gene expressions associated with pituitary control of interrenal steroidogenesis, including those of proopiomelanocortin (pomc) 40,41 and acth receptor (mc2r), 39,42 also commence early at 18 and 32 hpf respectively. In mammals, ACTH is the major pituitary regulator derived from POMC to regulate adrenal glucocorticoid synthesis and secretion.…”

“…However, in contrast to the early onset of pomc and mc2r gene expressions, the hormonal control of interrenal steroidogenesis does not occur until larval stage. 39 In either mc2r morphant or mutants lacking pituitary corticotrophs, no perturbation of interrenal size or steroidogenesis is evident until 5 dpf, when the developing fish reaches larval stage. This indicates a developmental transition, from autonomous pituitary-independent phase, to pituitary-dependant phase of steroidogenesis and interrenal growth.…”

“…2). 16,39 Similar to the mammalian adrenal medulla, the chromaffin component of the interrenal organ is originated from the neural crest through sequential steps of differentiation. 45 In the zebrafish embryo, the trunk neural crest gives rise to dorsal root ganglion sensory neurons and autonomic sympathetic neurons.…”