The adult Drosophila malpighian tubules are maintained by multipotent stem cells

Abstract

All animals must excrete the waste products of metabolism. Excretion is performed by the kidney in vertebrates and by the Malpighian tubules in Drosophila. The mammalian kidney has an inherent ability for recovery and regeneration after ischemic injury. Stem cells and progenitor cells have been proposed to be responsible for repair and regeneration of injured renal tissue. In Drosophila, the Malpighian tubules are thought to be very stable and no stem cells have been identified. We have identified multipotent stem cells in the region of lower tubules and ureters of the Malpighian tubules. Using lineage tracing and molecular marker labeling, we demonstrated that several differentiated cells in the Malpighian tubules arise from the stem cells and an autocrine JAK-STAT signaling regulates the stem cells' self-renewal. Identifying adult kidney stem cells in Drosophila may provide important clues for understanding mammalian kidney repair and regeneration during injury.

Figure 1

The Drosophila MTs and Their Cells (A) A drawing (adapted from Wessing and Eichelberg, 1978) of the Drosophila MTs. Drosophila has four tubules; the anterior pair is longer than the posterior pair (one tubule of each pair is depicted). Each tubule has four distinct morphologic regions: initial, transitional, and main segments and lower tubule. The two tubules in each pair merge together at ureters and connect to the gut at the midgut-hindgut boundary. (B and F) The MTs from a tsh-lacZ fly stained with DAPI (blue), anti-β-galatosidase (green), and anti-Cut (red). Red arrows point to the Cut-positive cells in ureter, lower tubule, and main segment. Green arrows point to β-galactosidase-positive type II cell in the main segment. White arrowheads point to tiny cells in the region of lower tubules and ureters. Yellow arrow points to posterior midgut that is negative for both Cut and β-galactosidase. β-galactosidase-positive type II cells interspersed with Cut-positive type I cells in the upper tubules (main, transitional, and initial segments). Scale bars: in (B), (C), and (F) represent 10 μm; in (D) and (E), 5 μm.

Figure 2

The Small Nuclear Cells are Proliferating and Express Unique Molecular Markers in the Region of Lower Tubules and Ureters of Adult Drosophila MTs (A and B) Cells with three different-sized nuclei occupy distinct positions in the region of lower tubules and ureters (phalloidin, red; DAPI, blue). White arrow, green arrowhead, and white arrowhead in (A) point to the large, intermediate, and small nuclear cells, respectively. The cells with small nuclei lie primarily in close proximity to the tubular walls, while the cells with large and oval nuclei are distant from the tubular walls (B). (C) BrdU labels the small (white arrows), intermediate (yellow arrow), and large (green arrow) nuclear cells (anti-BrdU, red; DAPI, blue). (D and E) The phospho-histone-H3 labels only a small nuclear cell (yellow arrows; anti-phospho-histone H3, red; anti-Arm, green; DAPI, blue). (F) Anti-Arm staining outlines the small nuclear cells (white arrows; anti-Arm, red; DAPI, blue). (G) esg-Gal4/UAS-GFP is specifically expressed in the small nuclear cells (white arrows in G and I) and (white arrows; anti-GFP, green; anti-Arm, red; DAPI, blue) (H) kr-Gal4/UAS-GFP is specifically expressed in the small nuclear cells (white arrows anti-GFP, green; anti-Arm, red; DAPI, blue). (I and J) Both esg (I) and kr (J) sometimes label a pair of phospho-histone-H3 positive dividing cells (white arrows in I and J; anti-GFP, green; anti-phospho-histone H3, red; DAPI, blue). Scale bars: in (G) and (H) represent 10 μm; in (A), (C–F), and (I–J), 5 μm; in (B), 2 μm.

Figure 3

The Tiny Cells in the Regions of Lower Tubules and Ureters are Pluripotent Stem Cells. GFP (green) label cells derived from PMML clones. (A) GFP marks primarily the small nuclear cells (white arrow) in the region of lower tubules and ureters but not the TSH-positive (red, green arrow) type II cells in the upper tubules of the MTs (two days ACI). One transient large nuclear cell GFP clone (white arrowhead) was also detected in the MTs. DAPI staining in blue. (B) An enlarged view of GFP-marked clones (two days ACI) showing that the GFP marks primarily the small nuclear cells (anti-Arm, red; anti-GFP, green; DAPI, blue). (C-F) 4 days ACI. The GFP marks clones of cluster cells with small, intermediate, and large nuclei. Two examples of clones show the basal RNSC (arrowheads), RB (arrows) and apical direction of growth (dashed arrows; anti-GFP, green; DAPI, blue). (G and H) 6 days ACI. The GFP marks cluster cells with small, intermediate, and large nuclei in the region of the lower tubules and ureters (anti-Arm, red; anti-GFP, green; DAPI, blue). (I) 4 days ACI. Some of the GFP-marked small nuclear cells (arrows) migrated to the main segment (anti-Arm, red; anti-GFP, green; DAPI, blue). (J-N) 10 days ACI. In the region of the lower tubules and ureters, the GFP marks cell clusters (one cluster of cells is highlighted in [K]). In the upper tubule, the GFP labels both Cut-positive (red in [M] and [N]) type I cells (yellow arrowheads) and TSH-positive (red in [L]) type II cells (yellow arrows in [L–N]). White dashed arrows in (A) point from the ureter to upper tubules. Scale bars: in (A) represents 20 μm; in (G) and (J), 10 μm; in (B–F), (H–I), and (K–N), 5 μm.

Figure 4

The JAK-STAT Signaling is Operating in RNSCs. (A) dome-Gal4/UAS-GFP is expressed in the whole MT (anti-GFP, green; DAPI, blue). (B) In the region of lower tubules and ureters, dome-Gal4/UAS-GFP is expressed in both the small nuclear cells (arrows) and the large nuclear cells (arrowheads; anti-Arm, red; anti-GFP, green; DAPI, blue). (C) upd-Gal4/UAS-GFP is only expressed in the region of lower tubules and ureters (arrows), but not in the upper tubules (anti-GFP, green; DAPI, blue). (D) In the region of lower tubules and ureters, upd-Gal4/UAS-GFP is expressed only in the small nuclear cells (arrows; anti-Arm, red; anti-GFP, green; DAPI, blue) and one upd-expressed cell is also phospho-histone-H3 positive (arrow in [E]; anti- phospho-histone-H3, red; anti-GFP, green; DAPI, blue). (F) Stat92E protein is expressed only in the small nuclear cells (arrow) in the region of lower tubules and ureters (anti-Stat92E, green; anti-Arm, red; DAPI, blue). White dashed arrows in (A–D) point from the ureter to upper tubules. Scale bars: in (A) represent 40 μm; in (C), 20 μm; in (B) and (D), 10 μm; in (E) and (F), 5 μm.

Figure 5

The JAK-STAT signaling regulates MT proliferation. (A) MTs with PMML wild-type clones. (B) MTs with PMML clones that overexpress upd (PMML-UAS-upd). In the PMML-UAS-upd flies, the MT size was enlarged dramatically (compare [B] with [A]), and the number of GFP-marked clones increased greatly ([C]: anti-GFP, green; DAPI, blue). (D) MTs with PMML clones that overexpress socs36E (PMML-UAS-socs36E). In the PMML-UAS-socs36E flies, only a few of the GFP-marked large nuclear cells were detected in the MTs (anti-Arm, red; anti-GFP, green; DAPI, blue). (E) In the PMML-UAS-upd flies, the number of Stat92E-positive (red) small nuclear cells is dramatically increased (anti-Stat92E, red; anti-GFP, green; DAPI, blue). However, most Stat92E-positive cells are GFP-negative, indicating that the secreted-Upd from the GFP-positive clones stimulate cells proliferation in the neighbor cells. (F–J) 2 days ACI in the PMML-UAS-upd flies, most GFPs mark cluster cells. Two examples of clones are shown in (G-J) (outlined by dashed lines). Each cluster has one RNSC (arrowhead), one RB (arrow), and one RC. Dashed arrows in (A–D) point from the ureter to upper tubules. Scale bars: in (A) and (B) represent 20 μm; in (C–E), 10 μm; in (F–J), 5 μm.

Figure 6

The JAK-STAT Signaling Autonomously Regulates RNSC Self-renewal. MTs with GFP-marked wild-type (A), Stat92E⁰⁶³⁴⁶ (B), Stat92E^j6C8 (C), and Stat92E^j6C8 UAS-Stat92E (D) MARCM clones. Notice that the Arm-positive small nuclear RNSCs (white arrows) were lost in MTs with Stat92E mutant MARCM clones (B and C) and recovered in MTs with UAS-Stat92E rescue (D). Red arrows in A–D point to the large RCs. MTs with GFP-marked clones homozygous for wild type control (E), Stat92E⁰⁶³⁴⁶ (F), Stat92E^j6C8 (G), and Stat92E^j6C8 UAS-Stat92E (H) were stained with anti-GFP and Apoptag kit to detect dead cells. Dashed arrows in (A–H) point from ureter to upper tubules. Scale bars in (A-H) represent 10 μm.

Figure 7

The Relative Strength of the JAK-STAT Signaling may Regulate RNSCs Either Self-renewal or Differentiation. (A and B) Stat92E reporter-GFP is expressed only in small nuclear cells in the region of the lower tubules and ureters (anti-Arm, red; anti-GFP, green; DAPI, blue). From the ureter upward, the GFP signal is gradually reduced and completely diminished in the lower part of main segment. We may call the Stat92E reporter-GFP-positive segment (from the ureter to lower part of main segment) the JAK-STAT signaling domain. Even in the JAK-STAT signaling domain, some small nuclear cells express strong GFP (white arrows), while the other small nuclear cells express weak GFP (red arrows). The strong GFP cells may identify RNSCs, and the weak GFP cells may identify RBs. (C) Proposed model of the RNSC lineage (discussed in text). Dashed arrows in (A) and (B) point from the ureter to upper tubules. Scale bars in (A and B) represent 10 μm.