Fbx15, otherwise known as Fbxo15, is a protein expressed in undifferentiated embryonic stem cells.
It is expressed during coexpression of Oct3/4, c-Myc, Klf4, and SOX2, four genes identified to be important in embryonic stem cell self-renewal and differentiation repression.
In mice having a beta-galactosidase gene knocked into the Fbx15 locus, stain was detected in ES cells, early embryos (from two-cell to blastocyst stages), and testis tissue. There is an enhancer site upstream of the Fbx15-encoding transcription gene that contains an octamer-like binding motif and a Sox-like binding motif. Reporter gene analyses demonstrated that the ES cell-specific expression required this 18-bp enhancer element located approximately 500 nucleotides upstream from the transcription initiation site. Deletion or point mutation of either motif abolished the enhancer activity. It became active in NIH 3T3 cells when Oct3/4 and Sox2 were coexpressed and cooperatively bind to the enhancer sequence.
Lacking of Fbx15 leads to normal embryonic development, but it is often used as a downstream identifier to check for stem cell pluripotency and also Oct3/4 activation, as Oct3/4 deactivation leads to a complete lack of Fbx15 expression.
After the process of iPS Cells the right cells have to be chosen, so this gene Fbx15 can be used. This gene is a selection device to see which cells are pluripotent.