Variant embryonal carcinoma cells lacking SSEA-1 and Forsmann antigens remain developmentally pluripotent

Six embryonal carcinoma (EC) cell lines that are resistant to the cytotoxic, galactose-specific lectin abrin were isolated from mutagenized populations of either PSA-1 or F9 cells. The LD10 for each of the variant lines was at least 150-fold greater than that for parental cells. Indirect cytotoxicity tests demonstrated that all of the variant cell lines lacked both Stage Specific Embryonic Antigen-1 (SSEA-1, less than 1% of wild-type levels) and Forsmann antigen (less than 5% of wild-type levels). When abrin-resistant cells were fused to previously isolated SSEA-1-negative cells (M. J. Rosenstraus (1983), Dev. Biol. 99, 318-323) that express Forsmann antigen, the resulting hybrids expressed SSEA-1. This implies the mutation conferring abrin resistance is in a different gene than that defined by the previously isolated mutation. Thus, we have identified two genes that are required for SSEA-1 expression, one of which also appears to be required for Forsmann antigen expression. The F9-derived variants differentiated into visceral-like or parietal-like endoderm when treated with retinoic acid in the absence or presence of 8-bromo-cAMP, respectively. PSA-1-derived variants formed differentiated teratocarcinomas containing derivatives of all three germ layers. Thus the SSEA-1 and Forsmann haptenic determinants are not required for EC cells to differentiate into a broad spectrum of cell types; nor do they appear to be involved in the cell-cell interactions that are postulated to regulate visceral versus parietal endoderm differentiation.