A 3-year-old child has become less active over the past 2 months. On physical examination an abdominal mass is palpable on the left. A urinalysis shows hematuria. Radiographic studies show an 8-cm mass in the left retroperitoneal space. The mass is excised and on microscopic examination shows a triphasic combination of blastemal, stromal, and epithelial cell types. The child is doing well 10 years later. Which of the following most likely related to the pathogenesis of this child's neoplasm?