As a potent inhibitor, CT99021(CHIR-99021) can inhibit GSK3alpha and GSK3beta with IC50 of 10 nM and 6.7 nM. Inhibition of GSK3 with CT99021 (3 microM) resulted in a significant increase in the percentage and quality of blastocysts. CT99021 can reduced the phosphorylation of beta-catenin on Ser45 in two-cell embryos.