1. In vitro branching tubulogenesis: Implications for developmental and cystic disorders, nephron number, renal repair, and nephron engineering 
Hiroyuki Sakurai, Sanjay K. Nigam 
Kidney International 
Volume 54, Issue 1, Pages (July 1998)
DOI: /j x
Copyright © 1998 International Society of Nephrology Terms and Conditions

2. Figure 1
Serum-free culture of mouse embryonic kidney. Embryonic day 11.5 mouse kidney was dissected and placed on the filter. The picture was taken on third day of culture. Abbreviations are: UB, ureteric bud; MM, metanephric mesenchyme. Bar = 50 μm.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

3. Figure 2
Three-dimensional culture of murine inner medullary collecting duct (mIMCD)3 cells (A, B) and ureteric bud (UB) cells (C, D). The mIMCD3 cells were grown for 48hours in Matrigel (A) or Type 1 collagen gel (B) in the presence of 3T3 cell conditioned medium (contains HGF). UB cells were grown for five days in Matrigel (C) or in Type 1 collagen/Matrigel (80:20) mixture (D) in the presence of BSN cell conditioned medium and 0.5% serum. Bars = 25 μm.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

4. Figure 3
Schematic representation of three-dimensional cell culture system. Kidney derived epithelial cells suspended in extracellular matrix gel (either Type 1 collagen or mixture of Type 1 collagen and Matrigel) form branching tubular structures when cultured with embryonic day 13 to 14 kidneys or the isolated metanephric mesenchyme. The soluble factors secreted from embryonic kidneys induce branching tubulogenesis. Purified single growth factors induce similar morphogenetic changes in kidney epithelial cells grown in three-dimensional culture, though addition of serum is often required, especially for prolonged culture. There is substantial difference in growth factor responsiveness among MDCK, mIMCD3 and UB cells (see text).
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

5. Figure 4
Schematic model of hepatocyte growth factor (HGF) intracellular signaling pathways involved in tubulogenesis. HGF receptor (c-Met) is associated with docking protein Gab1 following ligand activation. Gab1 transmits the signal to other intracellular molecules yet to be defined completely. Finally, the signals are transmitted to “bridging proteins” between membrane and cytoskeleton such as β catenin and ezrin.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

6. Figure 5
Cellular model of tubulogenesis. As discussed in the text, interplay of growth factors, extracellular matrix proteins, integrins and extracellular proteases/protease inhibitors regulates morphogenetic processes.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

7. Figure 6 Potential applications of tubulogenesis research.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

8. Figure 7
Hypothetical model of growth factor regulation in branching morphogenesis. Balance of branch-promoting growth factors (such as, HGF, EGF receptor ligands) and branch-inhibiting factors (such as, TGF-β) regulates branching morphogenesis. At branching front (A), the ratio of branch-promoting growth factors/branch-inhibiting growth factors is high in favor of branching tubulogenesis, while near the root (B) the opposite occurs favoring non-branching tubulogenesis. These gradients may be global and/or local. Not shown is the critical contribution of cell-cell contact mediated by interactions between surface proteins of metanephric mesenchyme and ureteric bud cells.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions

9. Figure 8
Hypothetical model of matrix/proteolytic activity in branching tubulogenesis. These molecules are likely to be effectors of tubulogenesis regulated by growth factors. There are specific sets of molecules in specific locations (tip, branch point). At tips the proteolytic balance is in favor of proteolysis, while at branch points it is in favor of inhibition of proteolytic activities. The differential expression of these molecules is expected to regulate branching morphogenesis.
Kidney International  , 14-26DOI: ( /j x)
Copyright © 1998 International Society of Nephrology Terms and Conditions