EMBRYONIC KIDNEY RUDIMENTS GROWN IN ADULT MICE FAIL TO MIMIC THE WILMS PHENOTYPE, BUT SHOW STRAIN-SPECIFIC MORPHOGENESIS

12.5- to 14.5-day mouse embryonic kidney fragments were grown syngenei cally under kidney or testis capsules in 3 mouse strains for 5-26 week s to reproduce the Wilms' tumour (WT) phenotype previously reported. A bout 65% of the transplants grew, but none showed true WT morphology, invaded local tissue or developed metastases. In Swiss mice, most grow ths contained disorganized stromal and blast cells, but also had more mature structures. CBA growths had cysts, differentiated nephrons and glomeruli, while 129/SV growths gave both types of morphology. In situ mRNA hybridization using the Wilms' tumour predisposition gene (WT1) showed that, unlike the initial rudiments and WT, expression was limit ed to the glomeruli. The unexpected absence of expression by the appar ent blast cells in the growths implies that the system is not a model for WT.