Expression of the POU domain protein Tst-1/Oct6 during development of glia and neurons is subject to a tight multifactorial control, Here we show that 17β-estradiol increases the level of endogenous Tst-1/Oct6 in glial cells. This effect was mediated at the level of gene expression by an enhancer present in the 5' flanking region of the mouse gene for Tst-1/Oct6, ~5 kb upstream of the transcriptional start site. The enhancer contained as the functional element a sequence motif that closely resembled a classical estrogen response element, It consisted of an imperfect palindrome with a spacing of 3 bp, and was bound in vitro by activated estrogen receptor. Furthermore, this element was able to confer estrogen responsiveness when introduced into a heterologous promoter. In the Tst-1/Oct6 gene enhancer, a TPA response element was found in close proximity to the estrogen receptor binding site. As a consequence, TPA and estrogen activated transcription of the Tst-1/Oct6 gene in a synergistic manner.