Absence of significant H–2 and β₂-microglobulin mRNA expression by mouse embryonal carcinoma cells

Abstract

Class I histocompatibility antigens (H–2 antigens in the mouse) are 44,000-moIecular weight cell-surface glycoproteins, the proper insertion of which depends on their noncovalent association with β₂-microglobulin (β₂m) (reviewed in ref. 1). They are involved in a variety of immune phenomena, particularly in self/non-self recognition (reviewed in ref. 2). H–2 antigens and β₂m are expressed by nearly all adult somatic cells. The status of their expression on pre-implantation mouse embryos remains controversial^3,4 although they are generally agreed to be serologically detectable at post-implantation stages⁵. H–2 and β₂m genes are therefore developmentally regulated. H–2 antigens have not been found on murine embryonal carcinoma (EC) cells⁶, which are widely used as an alternative to studying normal early embryonic cells^7–9, but they become detectable during in vitro differentiation of EC cells^10–12. During studies aimed at understanding the genetic mechanisms involved in the expression of H–2 antigens and β₂m during differentiation, cDNAs reverse transcribed from mRNAs coding for H–2 or H–2-related heavy chains and β₂m have been characterized^13–16. H–2 and β₂m cDNAs were used as probes to screen total poly(A)⁺ RNAs from various cell types. We report here that trace amounts of poly(A)⁺ RNA from EC cells were found to hybridize with these probes, finding which contrasts with results obtained on poly(A)⁺ RNA prepared from differentiated cells. These results, taken together with the absence of major rearrangements in H–2 and β₂m genes during differentiation, suggest that H–2 and β₂m expression is likely to be controlled at the level of transcription.