The adrenal capsule is postulated to harbor stem/progenitor cells, the progenies of which contribute to the growth of adrenocortex. We discovered that cells in the adrenal capsule are positive for Ptch1 and Gli1, genes indicative of responsiveness to the stimulation of Hedgehog (Hh) ligands. On the other hand, Sonic hedgehog (Shh), one of the mammalian Hh ligands, is expressed in the adrenocortex underneath the adrenal capsule, possibly acting upon the Hh-Responsive capsule. To investigate the functional significance of Shh in adrenal growth, we ablated Shh in an adrenocortex-specific manner using the Steroidogenic factor 1-Cre mouse. Loss of Shh in the adrenocortex led to reduced proliferation of capsular cells and a 50–75% reduction in adrenocortex thickness and adrenal size. The remaining adrenocortex underwent proper zonation and was able to synthesize steroids, indicating that Shh is dispensable for differentiation of adrenocortex. When these animals reached adulthood, their adrenocortex did not undergo compensatory growth in response to a high level of plasma ACTH, and the size of the adrenal remained significantly smaller than the control adrenal. Using a genetic lineage-tracing model, we further demonstrated that the Hh-responding cells in the adrenal capsule migrated centripetally into the adrenocortex. Our results not only provide the genetic evidence to support that the adrenal capsule contributes to the growth of adrenocortex in both fetal and adult life but also identify a novel role of Shh in this process.

The X-zone is a transient cortical region enriched in eosinophilic cells located in the cortical–medullary boundary of the mouse adrenal gland. Similar to the X-zone, the fetal zone in human adrenals is also a transient cortical compartment, comprising the majority of the human fetal adrenal gland. During adrenal development, fetal cortical cells are gradually replaced by newly formed adult cortical cells that develop into outer definitive zones. In mice, the regression of this fetal cell population is sexually dimorphic. Many mouse models with mutations associated with endocrine factors have been reported with X-zone phenotypes. Increasing findings indicate that the cell fate of this aged cell population of the adrenal cortex can be manipulated by many hormonal and nonhormonal factors. This review summarizes the current knowledge of this transient adrenocortical zone with an emphasis on genes and signaling pathways that affect X-zone cells.

Histone deacetylase (HDAC) inhibitors such as trichostatin A and valproic acid modulate transcription of many genes by inhibiting the activities of HDACs, resulting in the remodeling of chromatin. Yet this effect is not universal for all genes. Here we show that HDAC inhibitors suppressed the expression of steroidogenic gene CYP11A1 and decreased steroid secretion by increasing the ubiquitination and degradation of SF-1, a factor important for the transcription of all steroidogenic genes. This was accompanied by increased expression of Ube2D1 and SKP1A, an E2 ubiquitin conjugase and a subunit of the E3 ubiquitin ligase in the Skp1/Cul1/F-box protein (SCF) family, respectively. Reducing SKP1A expression with small interfering RNA resulted in recovery of SF-1 levels, demonstrating that the activity of SCF E3 ubiquitin ligase is required for the SF-1 degradation induced by HDAC inhibitors. Overexpression of exogenous SF-1 restored steroidogenic activities even in the presence of HDAC inhibitors. Thus, increased SF-1 degradation is the cause of the reduction in steroidogenesis caused by HDAC inhibitors. The increased SKP1A expression and SCF-mediated protein degradation could be the mechanism underlying the mode of action of HDAC inhibitors.

Background: The synthesis of microRNA (miRNA) is a multi-step process that requires the action of the ribonuclease Dicer1. Dicer1 is responsible for the final processing of miRNA and has been implicated in cellular processes such as proliferation, apoptosis, and differentiation. Mouse embryos lacking Dicer1 die in early embryogenesis. In this study, we investigated whether Dicer1 is required for development of adrenal, testis, and ovary in mouse embryos. Results: To target Dicer1 deletion specifically in developing adrenals and gonads, we used Steroidogenic factor 1-cre (Sf1/Cre) line in which Cre recombinase is active in the progenitor cells of adrenals and gonads. Lack of Dicer1 in the SF1-positive cells did not affect formation and early differentiation of the adrenals and gonads. However, increasing numbers of apoptotic cells were first detected in the Dicer1 knockout adrenal cortex at 18.5 days post coitum (dpc), followed by apoptosis of somatic cells and germ cells in the testis at postnatal day 0. Affected adrenal and testes underwent complete degeneration 48 hrs after the onset of apoptosis. However, ovaries were not affected at least until postnatal day 5, when the animals died due to adrenal insufficiency. Conclusions: Dicer1 is dispensable for formation and differentiation of fetal tissues derived from the SF1-positive adrenogonadal primordium. Dicer1 is essential for maintaining cell survival in adrenal and testis; however, development of the ovary from fetal stages to postnatal day 5 does not require the presence of Dicer1. Our results reveal a tissue-specific requirement of Dicer1 and microRNAs. Future research is needed to understand how the tissue-specific role of Dicer1 is established.

During pregnancy, fetal glucocorticoid is derived from both maternal supply and fetal secretion. We have created mice with a disruption of the Cyp11a1 gene resulting in loss of fetal steroid secretion but preserving the maternal supply. Cyp11a1null embryos have appreciable although lower amounts of circulating corticosterone, the major mouse glucocorticoid, suggesting that transplacental corticosterone is a major source of corticosterone in fetal circulation. These embryos thus provide a means to examine the effect of fetal glucocorticoids. The adrenal in Cyp11a1 null embryos was disorganized with abnormal mitochondria and oil accumulation. The adrenal medullary cells did not express phenylethanolamine N-methyltransferase and synthesized no epinephrine. Cyp11a1 null embryos had decreased diencephalon Hsd11b1, increased diencephalon Crh, and increased pituitary Pomc expression, leading to higher adrenocorticotropin level in the plasma. These data indicate blunted feedback suppression despite reasonable amounts of circulating corticosterone. Thus, the corticosterone synthesized in situ by the fetus is required for negative feedback suppression of the hypothalamus-pituitary-adrenal axis and for catecholamine synthesis in adrenal medulla.

Adrenal, testis, and ovary are steroidogenic organs derived from a common primordium that consists of steroidogenic factor 1 (SF1)‐positive precursor cells. SF1 not only defines the steroidogenic lineages in these organs but also controls their differentiation. Recent evidence implicates the Hedgehog (Hh) signaling pathway as a downstream regulator of SF1 in the appearance of steroidogenic cells in these organs. The Hh signaling pathway serves as a common crosstalk component, yet has evolved diverse functions in the expansion and differentiation of the steroidogenic cells in a tissue‐specific manner. The purpose of this review is to compare and contrast the different roles of Hh signaling in these three organs during development. Mol. Reprod. Dev. 77: 489–496, 2010.