is expressed in pluripotent murine embryonic stem cells and is a functional target of STAT3 and POU5F1, although it is in itself dispensible for maintenance of stem cell pluripotency and self-renewal. Both transcripts encode a highly basic 421-amino acid protein containing 5 C2H2-type zinc finger motifs, followed by a putative nuclear localization signal and an acidic region at the C terminus. Northern blot analysis detected 2 transcripts in undifferentiated F9 mouse teratocarcinoma cells, but only 1 transcript was present in testis. No expression was detected in other adult mouse tissues. During mouse development, Zfp57 expression increased at embryonic day 11 and peaked at day 13. Immunohistochemical analysis revealed Zfp57 in the nucleus of F9 cells.