Figure 1.

Schematic of podocyte differentiation protocol. (A) Before differentiation, singularized IMR90-4 iPSCs are seeded on 12-well plates coated with Matrigel, vitronectin or Synthemax at 2 × 10⁴ cells/cm² and expanded for 3 days in mTeSR1. Differentiation to primitive streak-like cells is initiated by 48 hr treatment with 6 µM CHIR99021 in podocyte medium 1 (PM1). Cells progress to nephron progenitors at day 6 and eventually differentiate to podocytes in podocyte medium 2 (PM2) at day 16. The pluripotent state of expanded IMR90-4 iPSCs was verified prior to differentiation by immunofluorescence for (B) OCT4, (C) NANOG and (D) TRA1-60. Expression of brachyury during differentiation was assessed by (E) immunofluorescence and (F) flow cytometry 24 hr after CHIR99021 treatment, and (G) Western blot from day 0 to day 16. Expression of primitive streak marker MIXL1 during differentiation was assessed by (H) immunofluorescence and (I) flow cytometry. Expression levels of primitive streak gene MIXL1 (J) and the pluripotency gene POU5F1 (L) relative to the housekeeping gene GAPDH were assessed by qRT-PCR from day 0 to day 16. Expression levels were normalized to undifferentiated IMR90-4 iPSCs at day 0. (K) At day 4, expression of the intermediate mesoderm marker PAX2 was assessed by immunofluorescence and flow cytometry. In flow cytometry plots, red dots represent isotype control treated cells used to identify the gated regions and blue dots represent cells stained for the indicated marker. Numbers indicate the fraction of stained cells (blue) in the gated regions. Data were collected from three independent replicates and are plotted as mean ± SEM. Scale bars, 100 µm. Immunofluorescence labelling and flow cytometry were performed ten times from different differentiations on different days. Three technical replicates were used each time for flow cytometry. qPCR was performed three replicates each time and three times were performed from three different differentiations.