Histologic sections of <i>Pax2^+/+</i> and <i>Pax2^A220G/A220G</i> mouse kidneys (axial) and cerebellum (sagittal) at E17.5.

<p>Whereas wild-type mice have begun to develop renal glomeruli (arrow, A) and tubules (arrowhead, A), the mutant mice have only primordial kidneys with poor differentiation of these structures (arrow, B) In contrast, the differentiation of the cerebellum of both wild-type (C) and mutant (D) mice is comparable at this time, despite the midbrain-hindbrain boundary being a site of <i>Pax2</i> expression during embryogenesis. By E14.5, cranial structure was grossly normal in both wild-type (E) and homozygous mutant (F) embryos.