1) In the Freedom CHO-S kit user guide it was mentioned that CHO-S cells contain basal expression of DHFR, upon transfection how to distinguish b/n untransfected and transfected cells which take up plasmid (DHFR + GOI) as both type of cells contain DHFR so both will survive in Media.
2) How the initial added MTX will kill only the untransfected cell (which contain basal level of endogenous DHFR) but not transfected cell (which contain DHFR from plasmid along with endogenous basal DHFR), as MTX will inhibit DHFR irrespective of endogenous/plasmid derived.
3) Here in CHO-S does the salvage pathway is operating/mutated ?
4) What is the differance between protein production in CHO-DG44 (DHFR negative) and CHO-S (Basal DHFR activity) ?
5) As Untransfected CHO-DG44 (DHFR negative) grows in media supplemented with Hypoxanthine and thymidine, Upon transfection in media lacking the suplementation of Hypoxanthine and thymidine with plasmid containing DHFR + GOI it is easy to select between Transformed cells vs Untransformed cells. But my doubt is why there is need to create CHO-S which has Basal DHFR activity, What is the advantage of this CHO-S over DG44 ?
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