Comparative immunohistochemical analysis of the expression of cytokeratins, vimentin and alpha-smooth muscle actin in human foetal mesonephros and metanephros

The human mesonephros is currently regarded as a simplified version of the foetal metanephros, primarily due to the close morphological resemblance be tween these two structures. The aim of the present study was to define whet her human mesonephric and foetal metanephric nephrons share immunophenotypi cal traits in their corresponding structures (glomeruli, proximal and dista l tubules). For this purpose we first investigated immunohistochemically th e overall expression and topographical distribution of cytokeratins 7, 8, 1 8, 19, and 20, vimentin and alpha -smooth muscle actin in mature mesonephri c nephrons and compared the results with those obtained in maturing-stage f oetal metanephric nephrons. No expression of cytokeratins 7 and 20 was foun d. Cytokeratins 8, 18, and 19 and vimentin showed a restricted and basicall y coincident expression along the different components of both mesonephric and metanephric nephrons. These findings indicate that the intermediate fil ament protein profile of human mature mesonephric nephrons closely recapitu lates that observed in developing metanephros and thereby strengthens the c oncept that human mesonephros, a transient ontogenic structure, is largely similar to the foetal metanephros. The sole difference between human mesonephros and foetal metanephros was th e divergent expression of alpha -smooth muscle actin. This protein exhibite d an increasingly accentuated mesangial expression paralleling the morpholo gical maturation of metanephric glomerulus, whereas it was absent from the mesonephric one. This would suggest that the mesangial cells in these two r enal structures have a different function during the foetal life.