TGF-β superfamily members modulate growth, branching, shaping, and patterning of the ureteric bud

Abstract

Protein-rich fractions inhibitory for isolated ureteric bud (UB) growth were separated from a conditioned medium secreted by cells derived from the metanephric mesenchyme (MM). Elution profiles and immunoblotting indicated the presence of members of the transforming growth factor-beta (TGF-beta) superfamily. Treatment of cultured whole embryonic kidney with BMP2, BMP4, activin, or TGF-beta1 leads to statistically significant differences in the overall size of the kidney, the number of UB branches, the length and angle of the branches, as well as in the thickness of the UB stalks. Thus, the pattern of the ureteric tree is altered. LIF, however, appeared to have only minimal effect on growth and development of the whole embryonic kidney in organ culture. The factors all directly inhibited, in a concentration-dependent fashion, the growth and branching of the isolated UB, albeit to different extents. Antagonists of some of these factors reduced their inhibitory effect. Detailed examination of TGF-beta1-treated UBs revealed only a slight increase in the amount of apoptosis in tips by TUNEL staining, but diminished proliferation throughout by Ki67 staining. These data suggest an important direct modulatory role for BMP2, BMP4, LIF, TGF-beta1, and activin (as well as their antagonists) on growth and branching of the UB, possibly in shaping the growing UB by playing a role in determining the number of branches, as well as where and how the branches occur. In support of this notion, UBs cultured in the presence of fibroblast growth factor 7 (FGF7), which induces the formation of globular structures with little distinction between the stalk and ampullae [Mech. Dev. 109 (2001) 123], and TGF-beta superfamily members lead to the formation of UBs with clear stalks and ampullae. This indicates that positive (i.e., growth and branch promoting) and negative (i.e., growth and branch inhibiting) modulators of UB morphogenesis can cooperate in the formation of slender arborized UB structures similar to those observed in the intact developing kidney or in whole embryonic kidney organ culture. Finally, purification data also indicate the presence of an as yet unidentified soluble non-heparin-binding activity modulating UB growth and branching. The data suggest how contributions of positive and negative growth factors can together (perhaps as local bipolar morphogenetic gradients existing within the mesenchyme) modulate the vectoral arborization pattern of the UB and shape branches as they develop, thereby regulating both nephron number and tubule/duct caliber. We suggest that TGF-beta-like molecules and other non-heparin-binding inhibitory factors can, in the appropriate matrix context, facilitate "braking" of the branching program as the UB shifts from a rapid branching stage (governed by a feed-forward mechanism) to a stage where branching slows down (negative feedback) and eventually stops.

Expression of matrix metalloproteinases MMP-2 and MMP-9 is altered during nephrogenesis in fetuses from diabetic rats

“…21,23,24 In fetal kidney, TGF-b1 mRNA has been localized in the UB and in the differentiating mesenchyme and is crucial for the branching of the UB. 40,[43][44][45][46][47] In the present study, we clearly demonstrate for the first time that hyperglycemia increases both in vivo and in vitro the expression of TGF-b1 and of CTGF in renal tissue obtained from diabetic fetuses and from metanephroi cultivated with high glucose concentration. In addition, we show that conditioned medium taken from metanephroi cultured in high glucose concentration increases TGF-b responsive promoter activity in cells transfected with reporter construct (CAGA)9-MLP-Luc.…”

Staged in vitro reconstitution and implantation of engineered rat kidney tissue

“…Taken together with our previous studies (29,(33)(34)(35)(36), a minimal set of conditions can be defined for UB growth/ branching as pleiotrophin (PTN) plus GDNF (35) in a type IV collagen matrix. The most robust system for both tip and stalk formation, as well as growth, of the in vivo-isolated bud, however, appears to be BSN-CM supplemented with GDNF and FGF1 (36, 37) in a 50% Matrigel solution, which were the culture conditions used for the in vitro-formed UB described below.…”

FGF signaling segregates biliary cell‐lineage from chick hepatoblasts cooperatively with BMP4 and ECM components in vitro

“…BMP suppresses branching morphogenesis induced by FGF during organogenesis of the lung, kidney, and salivary gland (Weaver et al, 2000;Hoffman et al, 2002;Bush et al, 2004). Thus, we investigated whether BMP would also suppress the morphogenesis of the hepatic epithelium induced by FGF.…”