HCN1−/− mice have delayed glomerular formation. A, B, At E17 protoglomeruli normally seen in WT mice (A) have yet to form in HCN1−/− mice (B). C–F, At P4 glomeruli can be seen in WT and HCN1−/− mice. However, in the HCN1−/− mice glomeruli are poorly formed and lack discrete boundaries (D, F). Scale bar (in F), 100 μm in A–D; 200 μm in E and F.