IF3, a novel cell-differentiation factor, highly expressed in murine liver and ovary.

The IF3 gene was isolated by expression cloning from a cDNA library of mouse oocytes. This gene was revealed to have no homology to any known gene and its cDNA encodes a 202-amino acid protein that contains a signal-peptide sequence. Moreover, an IF3 isoform, IF3(2), was expressed in both liver and ovary. Its cDNA encoded a 92-amino acid protein contains a signal-peptide sequence, which may be an alternative splice and frameshift form of IF3. The mRNA of IF3s was expressed in oocytes, ovary, and liver. Moreover, the gene expression of IF3s was regulated in a development-dependent manner in preimplantation-embryo and liver. Both IF3(1) and IF3(2) isoforms induced the differentiation of 2T3 and ATDC5 cells to the osteogenic and chondrogenic phenotype, respectively, suggesting that IF3s may modulate the differentiation status. Our findings suggest that IF3 may be one of the secreted factors that regulate oogenesis and certain liver functions.