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Figure 8


Fig. 8. Reduction of BMP4 activity by gremlin 1 in the mesenchyme around the ureteric bud is essential to enable ureteric epithelial outgrowth, GDNF-RET and WNT11-mediated e-m feedback signalling and branching morphogenesis. (A) In mouse, the ureteric bud forms in the caudal-most part of the Wolffian duct under the influence of GDNF-RET signalling. During this inductive period, Bmp4 is expressed by the mesenchyme enveloping the Wolffian duct. High levels of mesenchymal BMP4 activity inhibit the formation of ectopic epithelial buds and epithelial branching at this stage (prior to E11.0). At this early stage only low levels of Grem1 transcripts are detected (not shown). (B) Expression of the BMP antagonist Grem1 is upregulated in the mesenchyme around the nascent ureteric bud thereby locally reducing BMP4 signal transduction (around E11.75-11.0). This reduction of BMP4 activity by GREM1 enables initiation of ureteric bud outgrowth and its invasion into the metanephric mesenchyme. (C) GREM1 is required to maintain and propagate expression of Wnt11 in the ureteric epithelial tip(s) and Gdnf in the mesenchyme via e-m feedback signalling. For details see Discussion.





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