A putative Wilms tumor-secreted growth factor activity required for primary culture of human nephroblasts

Establishment of cell culture systems for the study of organogenesis during human embryonic development could provide the basis for the study of molecular mechanisms that regulate cellular proliferation and organ morphogenesis. We have developed a cell culture system for undifferentiated mesenchymal cells isolated from the human fetal kidney, which retain the potential for conversion to differentiated epithelia in vitro. Microdissected marginal zone nephroblasts were treated with trypsin and plated on gelatin prior to unlimited serial passage in suspension. An absolute requirement for the indefinite proliferation of these undifferentiated progenitors was nephroblast growth factor (NB-GF), a growth factor activity secreted by a Wilms tumor cell line. The mitogenic effects of NB-GF were not reproduced by previously described growth factors known to be mitogenic for renal cells or by leukemia inhibitory factor. In addition, cultured nephroblasts were shown to retain their ability to differentiate into epithelia when exposed to 10% serum-containing medium in the absence of NB-GF. Immunocytochemical cytoskeletal protein marker analysis showed mutually exclusive staining of vimentin in nephroblasts and cytokeratin in epithelia. These findings suggest that NB-GF may play an important role in the regulation of nephroblast proliferation during renal development and in Wilms tumor biology.