Ureteric buds and their cells eschew sources of BMP7. Placing control, BSA-soaked Affigel beads near ureteric buds (a) shows no obvious repulsive effect and branches will run into beads that happen to be in their way. In contrast, branches do not make contact with BMP7-soaked Affigel beads (b), nor do they approach them very closely: these data are shown quantitatively in (c), which shows the distance between the branch and bead that are closest in each culture. (d) In a completely different assay, ureteric bud-derived cells were cultured on filters, with medium supplemented with different concentrations of BMP7 under the filter. The graph shows the frequency of cells crossing the filter: filter crossing is inhibited by BMP7.