Abstract Secreted signalling molecules are important for the regulation of developmental cell responses. In the developing kidney, signalling occurs between epithelial ureteric bud and metanephric mesenchyme and in between their derivatives.

Wnt6 gene activity was localized to the ureteric bud and newly formed branches of the ureteric tree during early stages of kidney development. In a classic organ culture system, Wnt6 signalling induced the activation of marker genes for early nephrogenesis. The metanephric mesenchymes isolated from the Wnt4 deficient embryos were also induced, and the Wnt4 gene became activated in the presence of a Wnt6 signalling source. We propose that Wnt-6 is involved as a metanephric inducer and controls nephrogenesis.

Wnt4 is essential for nephrogenesis in mouse and we indicate an additional role for Wnt4 in the control of periureteric stromal differentiation. A failure in vascular development was also found. Bmp4 expression in the medullar stroma of the Wnt4-deficient kidneys was absent concomitantly with a loss of expression of the smooth muscle marker, α-SMA. In vitro Wnt4 signalling induced Bmp4 expression and local α-SMA production. Hence, we conclude that lack of Wnt4 signalling leads to a loss of the periureteric smooth muscle cells, and Wnt4 may locally regulate this cell population in normal kidneys via regulation of Bmp4 signalling.

The pluripotent neural crest cells are proposed to play regulatory roles in the early metanephros. Here, the use of transgenic animals allowed visualisation of the lumbo-sacral neural crest (NC) cells in close proximity to the early metanephros. The NC cells, however, disappeared in most part of the kidney by E12.5. The Splotch embryos lack the NCs from the early urogenital region. A developmental defect in the kidneys of Splotch embryos was not observed in vivo or in vitro. The results suggest that the neural crest is not essential for early embryonic kidney development.

In sum, the work presented indicates an important role for Wnt6 in the induction of kidney tubules in vitro, for Wnt4 in the specification of kidney smooth muscle cells and for endothelial development in kidney. The neural crest cells apparently have no active morphogenetic role in early kidney development.