First check to see if your Cre enzyme is expressed. We use 0.5-1 uM of 4-OH-Tam and excision usually happens within 24 hours. Tam is prepared in 100% DMSO at a concentration of 10 mM and stored at -20. Should be stable in DMSO for a while. Also, have you tested your primer pairs to see that they can distinguish the deleted, floxed out, allele?

Gregory Dressler thanks for the reply. Is this a concentration you have use in mouse ALI culture? Yes we have tested to see if we can distinguish the floxed allele. They are Krt5-CreERT2 driven mice

We have done organ rudiments from mouse embryos cultured in transwells, air liquid interface, and have gotten good excision.