 The expression of Sry and Sox9 genes in gonads of XY Cbx2-knockout mice is reduced, suggesting that Cbx2 is required for the expression of Sry in gonadal development.Moreover, the deficient of M33 also possessed abnormally few nucleated cells in the thymus and spleen, due to the aberrant T-cell expansion.In transiently transfected cells, M33 acts as a transcriptional repressor .