Distribution of prothymosin alpha in rat and human adrenal cortex

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Abstract
Background: Prothymosin alpha (ProT) is a polypeptide widely distributed in the organism and expressed by cell types with a high proliferative capacity. The aim of the current work was to investigate if ProT was localized in the progenitor compartment of the adrenal cortex which, following the cell migration theory, corresponds to the zona glomerulosa. Methods: We studied by immunohistochemical and in situ hybridization methods the distribution of ProT in rat and human adrenal cortex. Immunohistochemical techniques for the study of the proliferating cell nuclear antigen (PCNA) and incorporation of 5‐bromo‐2′‐deoxyuridin during DNA synthesis were also done. Immunoelectron microscopic procedures were performed to determine the exact subcellular localization of ProT. Results: ProT was found in the zona glomerulosa cells, but not in the cells of the remaining cortical layers (zonae fasciculata and reticularis). Glomerulosa cells showed immunostaining for ProT only in the nuclei, excluding the nucleoli. Variability in immunostaining intensity was found between different glomerulosa cells. In situ hybridization of ProT mRNA confirmed that ProT synthesis in adrenal cortex occurs only in the zona glomerulosa. The results obtained for proliferating cell nuclear antigen and incorporation of 5‐bromo‐2′‐deoxyuridin confirmed that adrenocortical proliferation occurs in the zona glomerculosa. Ultrastructural immunocytochemistry showed labelling for ProT over the euchromatin, but not on the heterochromatin aggregations nor the nucleoli. Conclusions: The results presented here: (1) support the migration theory for the adrenocortical cell renewal, (2) demonstrate that ProT is present in the nuclei of proliferating cells (being associated with euchromatin), and (3) suggest that the study of ProT expression would be useful in distinguishing cycling from resting cells.