Halder S K, Takemori H, Hatano O, Nonaka Y, Wada A, Okamoto M
Department of Molecular Physiological Chemistry, Osaka University Medical School, Suita, Japan.
Endocrinology. 1998 Jul;139(7):3316-28. doi: 10.1210/endo.139.7.6081.
The three zones of adrenal cortex are thought to arise from a single multipotential stem cell, but the mechanisms underlying the zonal differentiation during embryonic development of adrenal cortex are poorly understood. Employing subtraction cloning strategy, we isolated three distinct clones that were specifically expressed in the rat glomerulosa zone. One clone, named zona glomerulosa specific clone, encoded a membrane-spanning protein with a signal peptide at the N-terminus, six epidermal growth factor-like repeat motifs, and a transmembrane domain near the C-terminus. It was identified as a rat homolog of preadipocyte factor-1 (Pref-1), a factor involved in maintaining the undifferentiated status of preadipocyte. Immunohistochemical studies confirmed the presence of Pref-1 protein in the glomerulosa zone. Detailed examination revealed that the zone is divided into two layers; the first is a few-cells-thick layer present underneath the capsule (expressing both Pref-1 protein and aldosterone synthase cytochrome P450), and the second layer is beneath the first (containing Pref-1 protein but not aldosterone synthase). Moreover, another cell layer was found beneath the second layer and above the fasciculata zone, whose cells contained no Pref-1 protein, aldosterone synthase, or 11beta-hydroxylase. These findings suggest that a recently reported aldosterone synthase- and 11beta-hydroxylase-less cell layer between the two zones is composed of two kinds of cell: Pref-1 protein-positive and -negative cells. The level of Pref-1 message in the adrenal glands of animals having various pituitary-adrenal axis activities, as well as various plasma salt concentrations, correlated with the total number of glomerulosa cells. However, the specific content of Pref-1 message in a cell was fairly constant. When the adrenal gland was surgically enucleated and the remaining capsule regenerated, the level of Pref-1 transcript was significantly suppressed at the early phase. At this phase, only a minor population of the cortical cells expressed Pref-1 protein, most of these cells already expressing a fasciculata/reticularis-specific marker, inner zone antigen. These findings suggest that the capsular cells, mostly composed of the glomerulosa cells, may have potential for differentiating into other zones' cells, and the down-regulation of Pref-1 expression may be an important step in the adrenal zonal differentiation.
肾上腺皮质的三个带被认为起源于单个多能干细胞，但肾上腺皮质胚胎发育过程中区域分化的潜在机制仍知之甚少。利用消减克隆策略，我们分离出三个在大鼠球状带特异性表达的不同克隆。其中一个克隆，命名为球状带特异性克隆，编码一种跨膜蛋白，其N端有一个信号肽，六个表皮生长因子样重复基序，C端附近有一个跨膜结构域。它被鉴定为前脂肪细胞因子-1（Pref-1）的大鼠同源物，Pref-1是一种参与维持前脂肪细胞未分化状态的因子。免疫组织化学研究证实了球状带中存在Pref-1蛋白。详细检查发现该带分为两层；第一层是位于被膜下方的几层细胞厚的层（同时表达Pref-1蛋白和醛固酮合成酶细胞色素P450），第二层在第一层下方（含有Pref-1蛋白但不含有醛固酮合成酶）。此外，在第二层下方和束状带上方发现了另一细胞层，其细胞不含Pref-1蛋白、醛固酮合成酶或11β-羟化酶。这些发现表明，最近报道的两个带之间的无醛固酮合成酶和11β-羟化酶的细胞层由两种细胞组成：Pref-1蛋白阳性和阴性细胞。在具有不同垂体-肾上腺轴活性以及不同血浆盐浓度的动物的肾上腺中，Pref-1信息的水平与球状带细胞的总数相关。然而，细胞中Pref-1信息的具体含量相当恒定。当肾上腺被手术摘除且剩余的被膜再生时，Pref-1转录本的水平在早期显著受到抑制。在此阶段，只有一小部分皮质细胞表达Pref-1蛋白，这些细胞中的大多数已经表达束状带/网状带特异性标志物，即内区抗原。这些发现表明，主要由球状带细胞组成的被膜细胞可能具有分化为其他带细胞的潜力，而Pref-1表达的下调可能是肾上腺区域分化中的一个重要步骤。
