Overactivity or blockade of transforming growth factor-β each generate a specific ureter malformation

Transforming growth factor-beta (TGF beta) has been reported to be dysregulated in malformed ureters. There exists, however, little information on whether altered TGF beta levels actually perturb ureter development. We therefore hypothesised that TGF beta has functional effects on ureter morphogenesis. Tgfb1, Tgfb2 and Tgfb3 transcripts coding for TGF beta ligands, as well as Tgfbr1 and Tgfbr2 coding for TGF beta receptors, were detected by quantitative polymerase chain reaction in embryonic mouse ureters collected over a wide range of stages. As assessed by in situ hybridisation and immunohistochemistry, the two receptors were detected in embryonic urothelia. Next, TGF beta 1 was added to serum-free cultures of embryonic day 15 mouse ureters. These organs contain immature smooth muscle and urothelial layers and their in vivo potential to grow and acquire peristaltic function can be replicated in serum-free organ culture. Such organs therefore constitute a suitable developmental stage with which to define roles of factors that affect ureter growth and functional differentiation. Exogenous TGF beta 1 inhibited growth of the ureter tube and generated cocoon-like dysmorphogenesis. RNA sequencing suggested that altered levels of transcripts encoding certain fibroblast growth factors (FGFs) followed exposure to TGF beta. In serum-free organ culture exogenous FGF10 but not FGF18 abrogated certain dysmorphic effects mediated by exogenous TGF beta 1. To assess whether an endogenous TGF beta axis functions in developing ureters, embryonic day 15 explants were exposed to TGF beta receptor chemical blockade; growth of the ureter was enhanced, and aberrant bud-like structures arose from the urothelial tube. The muscle layer was attenuated around these buds, and peristalsis was compromised. To determine whether TGF beta effects were limited to one stage, explants of mouse embryonic day 13 ureters, more primitive organs, were exposed to exogenous TGF beta 1, again generating cocoon-like structures, and to TGF beta receptor blockade, again generating ectopic buds. As for the mouse studies, immunostaining of normal embryonic human ureters detected TGF beta RI and TGF beta RII in urothelia. Collectively, these observations reveal unsuspected regulatory roles for endogenous TGF beta in embryonic ureters, fine-tuning morphogenesis and functional differentiation. Our results also support the hypothesis that the TGF beta up-regulation reported in ureter malformations impacts on pathobiology. Further experiments are needed to unravel the intracellular signalling mechanisms involved in these dysmorphic responses. (c) 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.