Expression of c-mos proto-oncogene transcripts in mouse tissues

Abstract

Valuable information about proto-oncogenes and their physiological function has been obtained by studying their expression in normal cells. However, expression of the c-mos gene, the cellular homologue of the transforming gene of Moloney murine sarcoma virus1,2, has not been detected in normal mouse cells or tissues3–6. The conservation of the c-mos open reading frame7–9 strongly indicates that the gene must function during some portion of the animal life cycle, and other lines of evidence10–15 suggested to us that the c-mos proto-oncogene may be expressed at very low levels in normal tissues. We have used a sensitive S1 nuclease assay to screen RNA preparations from mouse tissues and describe here the detection of c-mos-related transcripts especially in mouse embryos, testes and ovaries. The transcripts found in testis RNA are estimated to be ∼1.7 kilobases (kb) long by Northern analysis. S1 analysis demonstrates that the entire mos open reading frame is present. In contrast, we detect ∼1.4-kb transcripts in ovary RNA and at least two major transcripts, ∼2.3 and ∼1.3 kb, in embryo RNA. The latter transcripts have in common sequences of at least 1 kb, representing most of the c-mos open reading frame. The variation in size of the mos transcript in different tissues suggests a novel regulatory mechanism for the expression of this proto-oncogene.