Preparing paraffin sections of human iPSC-derived kidney organoids

1.  On D7+18, cut out kidney organoids (KO) and put in 24w plate containing PBS. 1 organoid /well.

2. Aspirate pbs, and add 300ul formalin 4% / well.

3. Fix 20 min on ice

4. Collect cassettes (with small inserts!), plastic molds (molds that people also use to make agarcyto's), 2.25% agarose-PBS and small electroforesis-like piece of papers .

5. Heat the agarose (2.25% w/v dissolved in PBS) (with no lid) in microwave (~2-3min max) and transfer tube to beaker containing boiled water → place beaker in styrofoam box containing boiled water

6. Label cassettes and place paper (folded) in cassette insert.

7. Cut 1mL pipet tip → Add a droplet agar to mold → place KO’s in agar → add a few droplet agar on top of KO’s → incubate a few minutes in fridge until polymerized

8. Take out agar embedded KO’s with tool/ spoon and transfer them into the cassettes on paper(KO’s on bottom side)

9. Place cassettes in a (urine) container containing formaline and further processing into paraffine tissue.