Endocrine Abstracts

The mouse steroid 21-hydroxylase-A gene promoter (21-OH) directs adrenal cortex-specific expression of the β-galactosidase reporter in 21-OHase/LacZ transgenic mice. Multiple independent 21-OHase/LacZ transgenic lines show a similar mosaic pattern of reporter expression probably reflecting stochastic transgene silencing. In the adult, the mosaic reporter expression occurs as radial stripes spanning the adrenal cortex. A similar radial striped pattern occurs in mouse chimeras and X-inactivation mosaics which may represent clonal lineages arising from stem cells during maintenance of the adult cortex. During adrenal organogenesis the intermingled cortical and medullary cells separate to form the medulla and cortex. The fetal adrenal cortex shows mosaic patches of reporter expression but not the radial stripes seen in the adult. The mosaic reporter pattern was compared in adrenal cortices of 21-OHase/LacZ transgenics from fetal (E14.5) to weaning age (P21) to characterise the emergence of radial striped pattern during organogenesis and perinatal growth of the adrenal cortex. Initially the β-galactosidase staining pattern appeared as clusters of spots. At fetal stages these clusters appeared more or less randomly orientated and radial arrays appeared gradually around birth (P0–P5). Continuous radial stripes emerged later (P7–P10), and by P14 stripes formed the dominant pattern, while by P21 the pattern was identical to the adult. The emergence of continuous stripes occurred during a period of adrenal growth (after P5) but the initial formation of radial arrays (P0–P5) was not accompanied by any net adrenal growth. Further investigations are required to determine whether formation of radial arrays is accompanied by localised cell proliferation (balanced by cell death), cell shape/histological changes or cell movement.