Embryonic stem (ES) cell-specific transcription factor required to regulate ES cell pluripotency. Binds telomeres and plays a key role in genomic stability in ES cells by regulating telomere elongation. Acts as an activator of spontaneous telomere sister chromatid exchange (T-SCE) and telomere elongation in undifferentiated ES cells. Embryonic stem (ES) cell-specific. Expressed in only 5% of ES cells at a given time, but nearly all ES cells express it at least once during 9 passages. Transcriptionally regulated by ZSCAN10.