Imunohistochemical profile of the neuroblasts of the peripheral sympathetic nervous system and human neuroblastoma of childhood

ABSTRACT I focused on the analysis of a protein involved in the development of the peripheral nervous system: the Wilms tumor1 (WT1). My thesis is divided into two experimental phases: I) spatio-temporal distribution of WT1 during human embryonic development, II) expression and functional roles of WT1 during development of the peripheral sympathetic nervous system and gastrointestinal tract. The Wilms tumor (WT1) gene and its protein product are known to exhibit a dynamic expression profile during development and in the adult organism. Apart from a nuclear expression observed in the urogenital system, its precise localization in other developing human tissues is still largely unknown. Accordingly, the aim of this study was to investigate immunohistochemically the temporal and spatial distribution of WT1 in epithelial and mesenchymal developing human tissues from gestational weeks 7 24. For this purpose we used antibodies against the N-terminal of WT1. As might be expected, WT1 nuclear expression was observed in mesonephric/metanephric glomeruli, metanephric blastema, celomderived membranes (pleura, peritoneum, serosal surfaces) and sex cords. With regard to mesenchymal tissues, a similar nuclear staining was also obtained in the mesenchyme surrounding Müllerian and Wolffian ducts, as well as in the submesothelial mesenchymal cells of all celomatic-derived membranes. The most striking finding was the detection of strong WT1 cytoplasmic immunostaining in developing skeletal and cardiac muscle cells and endothelial cells. The tissue-specific expression of WT1, together with its different nuclear/cytoplasmic localization, both suggest that WT1 protein may have shuttling properties, acting as a protein with complex regulator activity in transcriptional/translation processes during human ontogenesis. The reported cytoplasmic expression of WT1 in human rhabdomyosarcomas and in many vascular tumors strongly suggests an oncofetal expression of this protein. Although not specific, WT1 cytoplasmic expression can be used as a marker of skeletal muscle and endothelial differentiation in an appropriate morphological context. Developmental expression of Wilms tumor gene (WT1) and protein is crucial for cell proliferation, apoptosis, differentiation and cytoskeletal architecture regulation. More recently, it has been suggested a potential role of WT1 in the development of neural tissue and in neurodegenerative disorders. We have investigated immunohistochemically the developmentally regulated expression and distribution of WT1 in human fetal (from the 8th to the 28th week gestational age) peripheral sympathetic nervous system (PSNS) and gastro-enteric nervous system (GENS). Interestingly WT1 expression was restricted to the cytoplasm of sympathetic neuroblasts, while it progressively disappeared with advancing morphologic differentiation of these cells along both ganglionic and chromaffin cell lineages. In adult tissues, both ganglion and chromaffin cells lacked any WT1 expression. These findings show that WT1 is a reliable marker of human sympathetic neuroblasts, which can be used routinely in formalin-fixed, paraffin-embedded tissues. The progressive loss of WT1 in both ganglion and chromaffin cells, suggests its potential repressor role of differentiation in a precise temporal window during human PSNS and GENS development.