Figure 3.

A working model of current common intermediate differentiation steps used to guide pluripotent stem cells to adopt a renal lineage in vitro for creation of kidney organoids. The schematic outlines the approximate time interval for each progressive culture condition and the resulting lineage specification of the cells that is associated with the sequence of provided factors, where the lineage state is surmised based on the accrual of particular combinations of molecular hallmarks. Beginning with OCT4⁺SOX2⁺ iPS cells, modulation of Wnt signaling for four days induces the cells to adopt a primitive streak identity based on expression of T and TBX6. Upon subsequent FGF2 and RA treatment for three days, intermediate mesoderm (IM) cells result, which express WT1, OSR1, HOXD11, PAX2, and LHX1. After this, two days of treatment with FGF9 and Activin A leads IM to metanephric mesenchyme (MM) that is distinguished based on expression of SIX2, SALL1, WT1, and PAX2. Following the removal of Activin A but continued exposure to FGF9 for 2 additional days, the MM is observed to form pre-tubular aggregates that express PAX8 and LHX1. This model is largely based on schemes reported by references [3,36–38].