Expression of genes for intracisternal A particle antigen in somatic cell hybrids

An antigen specific for mouse intracisternal A particles was assayed by complement fixation in homogenates of cells cultured in vitro. Mouse neuroblastoma, fibroblast, and rat glioblastoma cell lines were characterized by clonal differences in the amount of antigen per mg cell protein. The antigen levels varied little as cells passed from the logarithmic to the stationary phase of growth. When parental mouse cell lines with high levels of antigen were fused to cells with low or undetectable levels, the resulting hybrid clones exhibited antigen levels similar to those of the high level parent. In control experiments, cocultivation of parental cells without induced fusion did not lead to inheritance of antigen in a previously negative line nor did fusion between 2 antigen negative cells itself generate antigen production. Antigen levels were usually sustained in parental and hybrid clones and subclones over at least 40 to 80 cell generations. However, some hybrid clones yielded segregating subclones with lower antigen content. A particle antigen was not detectable in 5 of 11 independent clones derived from fusion between antigen positive mouse fibroblasts and antigen negative rat glioblastoma cells; the basis of this variation is not known. With respect to mouse cells, the results revealed a dominant mode of inheritance for expression of A particle antigen. Further genetic analysis of A particle formation probably will be possible in vitro.