Identification of a multipotent self-renewing stromal progenitor population during mammalian kidney organogenesis

Abstract

The mammalian kidney is a complex organ consisting of multiple cell types. We previously showed that the Six2-expressing cap mesenchyme is a multipotent self-renewing progenitor population for the main body of the nephron, the basic functional unit of the kidney. However, the cellular mechanisms establishing stromal tissues are less clear. We demonstrate that the Foxd1-expressing cortical stroma represents a distinct multipotent self-renewing progenitor population that gives rise to stromal tissues of the interstitium, mesangium, and pericytes throughout kidney organogenesis. Fate map analysis of Foxd1-expressing cells demonstrates that a small subset of these cells contributes to Six2-expressing cells at the early stage of kidney outgrowth. Thereafter, there appears to be a strict nephron and stromal lineage boundary derived from Six2-expressing and Foxd1-expressing cell types, respectively. Taken together, our observations suggest that distinct multipotent self-renewing progenitor populations coordinate cellular differentiation of the nephron epithelium and renal stroma during mammalian kidney organogenesis.

Graphical abstract

Figure 1

The Six2+ Cap Mesenchyme and Foxd1+ Cortical Stroma Give Rise to Distinct Cellular Lineages of the Kidney β-gal-stained (blue) kidneys from Six2^TGC/+; R26R^lacZ/+ (A, C, and E), and Foxd1^GC/+; R26R^lacZ/+ (B, D, and F) embryos at 14.5 dpc counterstained with eosin (pink). (A and B) Whole kidney. (C–F) Higher magnification of the nephrogenic zone (C and D) and renal cortex with glomeruli (E and F). a, adrenal gland; cd, collecting duct; ci, renal cortical interstitium; cm, cap mesenchyme; cs, cortical stroma; k, kidney; mi, renal medullary interstitium; ms, mesangium; nt, nephron tubule; pe, parietal epithelium; rv, renal vesicle; sb, S-shaped body; ue, ureter epithelium; um, ureter mesenchyme; ut, ureteric tip; ve, visceral epithelium (podocyte). Scale bars, 200 μm (A and B) and 50 μm (C–F).

Figure 2

The Foxd1+ Cortical Stroma Is a Progenitor Population for Stromal Tissues in the Kidney Confocal immunofluorescence images of Foxd1^GC/+; R26R^lacZ/+ kidneys at 15.5 dpc with anti-β-gal staining (green). (A–D) Nephrogenic zone. (A) FOXD1 (red). (B) SIX2 (red). Black arrows indicate β-gal+ SIX2+ cap mesenchyme cells. (C) KRT (red). (D) LIV2 (red). White and black arrows indicate inner LIV2+ β-gal+ cells in the renal capsule and outer LIV2+ β-gal− cells in the connective tissue, respectively. (E and F) Renal cortex with glomeruli. (E) PDGFRB (red) and WT1 (blue). Yellow and white arrows indicate PDGFRB+ β-gal+ pericytes and mesangial cells, respectively. (F) FLK1 (red) and WT1 (blue). Yellow and white arrowheads indicate FLK1+ β-gal− vascular cells in the renal cortex outside of the glomerulus and within the glomerular tuft, respectively. Black arrowheads in (E) and (F) indicate WT1+ β-gal+ podocytes. (G and H) Renal medulla. (G) CDKN1C (P57KIP2, red) and KRT (white). (H) F4/80 (red). (I) Ureter with SMA (red). Scale bars, 50 μm.

Figure 3

The Foxd1+ Cortical Stroma Contributes to Stromal Tissues throughout Kidney Organogenesis β-gal-stained (blue) kidneys from Foxd1^GCE/+; R26R^lacZ/+ embryos at 19.5 dpc after three successive injections of oil vehicle only at 10.5, 12.5, and 14.5 dpc (A, E, I, M, and Q) or after a single injection of 2 mg tamoxifen at 10.5 dpc (B, F, J, N, and R), 12.5 dpc (C, G, K, O, and S), or 14.5 dpc (D, H, L, P, and T). (A–D) Whole-mount view. (E–T) Sections counterstained with eosin (pink). (E–H) Whole kidney. (I–L) Nephrogenic zone and renal cortex. (M–P) Outer renal medulla. (Q–T) Inner renal medulla (papilla). Arrows in (R) indicate β-gal+ interstitial cells in the inner medulla adjacent to the pelvic urothelial lining. a, adrenal gland; k, kidney. Scale bars, 500 μm (A–H) and 100 μm (I–T).

Figure 4

Six2+ Cap Mesenchymal Cells and Foxd1+ Cortical Stromal Cells Differentiate in a Coordinated Manner Kidneys at 19.5 dpc from Six2^GCE/+; Foxd1^GCE/+; R26R^lacZ/+ mice with oil-only injection at 14.5 dpc (A, E, I, M, Q, and U), Six2^GCE/+; R26R^lacZ/+ with 6 mg tamoxifen at 14.5 dpc (B, F, J, N, R, and V), Foxd1^GCE/+; R26R^lacZ/+ with 6 mg tamoxifen at 14.5 dpc (C, G, K, O, S, and W), and Six2^GCE/+; Foxd1^GCE/+; R26R^lacZ/+ with 6 mg tamoxifen at 14.5 dpc (D, H, L, P, T, and X). (A–D) β-gal-stained (blue) whole-mount kidney. (E–P) β-gal-stained (blue) sections counterstained with eosin (pink). (E–H) Nephrogenic zone and renal cortex. Black arrows and white arrows indicate capillary loop-stage and maturing-stage glomeruli, respectively. (I–L) Capillary loop-stage glomerulus. (M–P) Maturing-stage glomerulus. (Q–X) Confocal immunofluorescence images with anti-β-gal (red), a podocyte marker anti-NPHS1 (nephrin, green), and a mesangium marker anti-PDGFRB (white). (Q–T) Capillary loop-stage glomerulus. Yellow arrowheads and yellow arrows in (R)–(T) indicate the β-gal+ NPHS1+ podocytes and β-gal+ PDGFRB+ mesangial cells, respectively. (U–X) Maturing-stage glomerulus. a, adrenal gland; ci, renal cortical interstitium; k, kidney; ms, mesangium; nt, nephron tubule; pe, parietal epithelium; pr, pericyte; ve, visceral epithelium (podocyte). Scale bars, 500 μm (A–D), 100 μm (E–H), and 25 μm (I–X).

Figure 5

Foxd1+ Cortical Stromal Cells Self-Renew (A and B) Models for maintenance of cortical stromal cells. (A) A pulse-labeled β-gal+ (blue) Foxd1+ cortical stromal (cs) cell produces another β-gal+ Foxd1+ cortical stromal cell, which results in retention of β-gal+ cells in the Foxd1+ cortical stroma. Differentiated stromal cells (st) are β-gal+ cells along the cortico-medullary axis throughout kidney organogenesis. (B) A Foxd1− stromal precursor population (sp) that generates Foxd1+ cortical stromal cells (cs) resides outside of the Foxd1+ population. Contribution of β-gal− cells from the Foxd1− stromal precursor population (sp) dilutes the pulse-labeled β-gal+ (blue) cells in the Foxd1+ cortical stroma (cs; light green). Only differentiated stromal cells (st) at early stages will be β-gal+ (blue) cells that will be seen in the inner medulla (papilla), but stromal cells in the renal cortex (st; dark green), which differentiate at later stages, will be β-gal−. (C–Q) Foxd1^GCE/+; R26R^lacZ/+ kidneys at 19.5 dpc after injection of 2 mg tamoxifen at 9.5 dpc (C, F, I, L, and O) and 10.5 dpc (E, H, K, N, and Q), and oil only at 10.5 dpc (D, G, J, M, and P). (C–E) Whole-mount β-gal-stained (blue) kidneys. (F–H) Sections of β-gal-stained (blue) kidneys counterstained with eosin (pink). (I–K) Higher magnification of the cortical region in (F)–(H), respectively. White arrows in (K) indicate multiple β-gal+ cells in the cortical stroma. (L–Q) Confocal immunofluorescence images with anti-GFP (green), anti-β-gal (red), with (L–N) or without (O–Q) Hoechst (blue) staining. White arrows in (N) and (Q) indicate β-gal+ GFP+ cortical stromal cells. a, adrenal gland; ci, renal cortical interstitium; cm, cap mesenchyme; k, kidney; ms, mesangium; nt, nephron tubule; pe, parietal epithelium; pr, pericyte; rv, renal vesicle; ve, visceral epithelium (podocyte). Scale bars, 500 μm (C–H) and 50 μm (I–Q).

Figure 6

Foxd1+ Cortical Stromal Cells Can Be Multipotent Stromal Progenitors (A and B) Models for developmental potential of Foxd1+ cells. (A) A Foxd1+ cortical stromal cell retains multipotency to differentiate into different stromal tissues. (B) Developmental potential of a Foxd1+ cell is restricted to limited stromal cell types within the Foxd1+ cortical stroma. (C–G′) β-gal-stained (blue) kidneys from Foxd1^GCE/+; R26R^lacZ/+ embryos at 19.5 dpc after injection of oil only (C and E), and 0.1 mg tamoxifen (D, F, G, and G′) at 12.5 dpc. (C and D) Whole-mount view. The inset in (D) shows a higher magnification of a clone in the dashed region. The arrow in (D) indicates a β-gal+ clone. (E and F) Sections counterstained with eosin (pink). (G and G′) Adjacent sections 96 μm apart showing the same clone. (G) is a higher magnification of the dashed region in (F). White arrows in (G) indicate multiple β-gal+ cells in the cortical stroma. a, adrenal gland; ci, renal cortical interstitium; cm, cap mesenchyme; cs, cortical stroma; k, kidney; mi, renal medullary interstitium; ms, mesangium; np, nephron precursor; nt, nephron tubule; ut, ureteric tip. Scale bars, 500 μm (C and D), 200 μm (E and F), and 50 μm in (G and G′).

Figure 7

Foxd1 Activity Is Dispensable for Cell-type Specification of Stromal Tissues Kidneys from Foxd1^GC/+; R26R^lacZ/+ (A, C, E, G, and I) and Foxd1^GC/CE; R26R^lacZ/+ (B, D, F, H, and J) embryos at 15.5 dpc. (A and B) β-gal-stained (blue) sections counterstained with eosin (pink). (C–J) Confocal immunofluorescence imaging with anti-β-gal (green) and anti-KRT (white) staining in (E)-(J). KRT is expressed in the ureteric tip and collecting duct. (C and D) PDFGRB (red) and WT1 (blue). Yellow arrowheads indicate β-gal+ WT1+ podocytes. (E and F) P57KIP2 (CDKN1C, red). (G and H) LIV2 (red). (I and J) SIX2 (red). cd, collecting duct; ci, renal cortical interstitium; cm, cap mesenchyme; cp, capsule; mi, renal medullary interstitium; ms, mesangium; pr, pericyte; ut, ureteric tip; ve, visceral epithelium (podocyte). (K) A model for cellular differentiation from mesenchymal progenitor populations during mammalian kidney development. The Six2+ cap mesenchyme and Foxd1+ cortical stroma are a multipotent self-renewing progenitor population for nephron epithelial and renal stromal cell types. Although Six2+ cells differentiate into all cell types of the main body of the nephron, Foxd1+ cortical stromal cells contribute to all stromal cells in the kidney, including cortical and medullary interstitial cells, mesangial cells, and pericytes. Only around the onset of kidney development, a small fraction of Foxd1+ cells becomes Six2+ cells (gray dashed arrow). Thereafter, the Six2+ cell-derived nephron lineage and Foxd1+ cell-derived stromal lineage form compartments with a lineage boundary throughout kidney development. Although the Osr1+ nephrogenic mesenchyme can contribute to both Six2+ cap mesenchyme and Foxd1+ cortical stroma, currently, it is unclear whether a single Osr1+ cell can differentiate into both Six2+ and Foxd1+ mesenchymal progenitor cells. Scale bars, 200 μm (A and B) and 50 μm (C–J).