The Role Of FGF10/FGFR2b Signaling In Mouse Kidney Development

The kidney is an important organ for the production of urine in the human body,and the normal development of the kidney is essential to ensure the homeostasis of the body.Mouse kidney development starts from day 10.5(E10.5d)of during embryonic development,and the ureteric bud(UB)receives signals and branches continuously,eventually forming collecting duct and ureter.At the same time,the cap mesenchyme(CM)continues to differentiate.At E14.5d,glomeruli begin to develop,and then fully functional nephron was formed at E18.5d.Fibroblast growth factor 10(FGF10)can promote the differentiation and proliferation of embryonic cells during the development of embryonic kidney.The loss of FGF10/FGFR2b signal can lead to renal dysplasia and a significant decrease in the number of collecting ducts and nephron.How FGF10/FGFR2b signal regulates renal development and its temporal regulation is still not clearly addressed.In the current research,we employed FGF10 germline knockout(fgf10^-/-)mice to investigate the role and potential mechanism of FGF10 signaling in kidney development.A transgenic mouse for doxycycline induced soluble FGFR2b(s-FGFR2b)model was also used to validate the temporal regulation mechanism of FGF10/FGFR2b signal on renal development.The embryonic kidneys of E14.5d and E18.5d fgf10^-/-mice(these mice die after birth)were obtained by mating between fgf10^+/-male and fgf10^+/-female mice.The genetic,morphological and pathological phenotypes were compared with those of wild-type mice with the littermate.For the generation of s-FGFR2b mice,the male Rosa26rt TATet(O)s FGFR2b mated with the female Rosa 26rt TATet(O)FGFR2b WT mice.After the pregnancy was confirmed by thrombus examination,Doxycycline(Dox,15mg/kg)was injected intraperitoneally daily during E10.5d-E13.5d,and the embryonic kidney was harvested on E14.5d.Upon genotyping confirmation,Rosa 26rt TA Tet(O)s FGFR2b was compared with Rosa 26rt TA Tet(O)FGFR2b WT mice in the same littermate.The development of kidney;the downstream FGF signaling pathway(MAPK)and the expression of Wnt/SOX9 pathway after fgf10^-/-or temporary blocking of FGFR2b signal were studied by H&E,immunohistochemical and immunofluorescence.In this study,no significant difference was found between fgf10^+/-and wild-type embryonic kidney,but,compared with wild-type embryonic kidney,the kidney size of Fgf10 homozygous deletion(fgf10^-/-)embryonic was significantly smaller.The number of epithelial cells,mesenchymal cells,as well as the stromal cells were significantly reduced,which is characterized by decreased proliferation and concomitant increase in apoptosis.The analysis of downstream pathway showed that there was no significant change in the activation of MAPK/p38 and MAPK/Erk pathways in the kidney of fgf10^-/-,but AKT pathway was significantly hyperactivated on E14.5d and significantly inhibited on E18.5d.The number of Sox9+positive progenitor cells was significantly decreased and Wnt pathway was inhibited.Embryonic kidney of mice with induced s-FGFR2b was also found significantly smaller in size.The number of epithelial cells and collecting ducts,as well as the number of Sox9+positive progenitor cells were significantly decreased and the Wnt pathway was inhibited compared with the wild-type,which is consistent with and largely resembled the phenotype FGF10 deficient embryonic kidneys,except no significant increase in apoptosis was observed.Collectively,our results suggest that FGF10/FGFR2b mainly affects the Wnt and AKT pathways by activating Sox9+progenitor cells,and then promotes the differentiation and proliferation of mesenchymal and epithelial cells to maintain the normal development of kidney;the E10.5d-E13.5d FGF10/FGFR2b signaling through regulating Sox9/Wnt plays a crucial role in renal development.