Regulatory mechanisms for differentiation of adrenocortical cells

哺乳动物的肾上腺皮质包含三个同心圆区，即球状肾上腺（zG）、束状肾上腺（zF）和网状肾上腺（zR）。我们以前曾报道，一个功能未分化的细胞带之间存在zG和zF在大鼠。皮质中的大多数复制细胞在细胞带中以及在带内外的相邻区域中可观察到，这表明细胞带含有能够产生能够分化成zG或zF/zR细胞的细胞的干细胞。为了开发用于分析分化过程的体外模型系统，我们试图获得与zG和zF之间发现的细胞相似的未分化阶段的肾上腺皮质细胞系。具有这些特性的细胞系是从来自携带SV 40大T抗原基因的温度敏感突变体的转基因小鼠的肾上腺细胞的原代培养物中建立的。然后，我们试图通过差异杂交筛选来克隆编码在未分化细胞中表达的蛋白质的cDNA。分离了几个cDNA克隆。发现其中一个cDNA克隆可能编码一种新的细胞外基质蛋白。另一个cDNA编码一种新的蛋白质，其氨基酸序列没有任何已知的同源序列。它们的mRNA分别在ZG至未分化细胞带和未分化细胞带至ZF的区域被检测到。它们的表达部位对应于肾上腺皮质细胞增殖和分化最活跃的区域，这些结果表明，这些蛋白质在肾上腺皮质细胞的生长和分化中起作用。

The adrenal cortex in mammals contains three concentric zones, the zona glomerulosa (zG), zona fasciculata (zF), and zona reticularis (zR). We have previously reported that a functionally undifferentiated cell zone is present between zG and zF in rats. Most of replicating cells in the cortex were observable in the cell zone as well as in the adjacent regions both outside and inside the zone, suggesting that the cell zone contains stem cells which produce cells capable to differentiate into the zG or zF/zR cells. To develop in vitro model systems for analyzing the differentiation processes, we attempted to obtain adrenocortical cell lines at undifferentiated stages similar to that of the cells found between zG and zF. Cell lines with such properties were established from a primary culture of the adrenal cells from transgenic mice harboring a temperature sensitive mutant of SV40 large T antigen gene. Then, we tried to clone cDNAs encoding proteins which were expressed in the undifferentiated cells by using differential hybridization screening. Several cDNA clones were isolated. One of cDNAs clones was found to presumably encode a new extracellular matrix protein. Another cDNA encoded a new protein whose amino acid sequence did not have any known homologous sequence. Their mRNAs were detected, respectively, in the region from ZG to the undifferentiated cell zone and that from the undifferentiated cell zone to ZF. The sites of their expression correspond to the regions where cell proliferation and differentiation of the adrenocortical cells take place most actively, These results suggest that the proteins have a role in growth and differentiation of adrenocortical cells.