Reexpression of a T/t-complex Antigen (t12) in Thymocyte X Embryonal Carcinoma Cell Hybrids

Hybrids between PCC4 aza 1 teratocarcinoma cells and thymocytes from an adult +/t12 mouse are phenotypically embryonal carcinoma cells. They express the t 12 antigen and do not express detectable H-2 antigens. Normally t12 is only expressed early in development and on male germ cells. Thus, the thymocyte genome is reprogramed such that adult thymocyte H-2 antigen is turned off but the thymocyte genome participates in the embryonal cell phenotype by reexpressing an embryonic antigen long silent in the adult. The expression of the t12 embryonic antigen represents the first example of the activation of a gene in somatic cell hybrids that is expressed only temporally in development.