Homeobox expressed in ES cells 1 is a protein in humans that is encoded by HESX1 gene. Required for the normal development of the forebrain, eyes and other anterior structures such as the olfactory placodes and pituitary gland. Possible transcriptional repressor. Binds to the palindromic PIII sequence, 5'-AGCTTGAGTCTAATTGAATTAACTGTAC-3'. HESX1 and PROP1 bind as heterodimers on this palindromic site, and, in vitro, HESX1 can antagonize PROP1 activation.