A distal super enhancer mediates estrogen-dependent mouse uterine–specific gene transcription of Insulin-like growth factor 1 (Igf1)

Insulin-like growth factor 1 (IGF1) is primarily synthesized in and secreted from the liver; however, estrogen (E2), through E2 receptor α (ERα), increases uterine Igf1 mRNA levels. Previous ChIP-Seq analyses of the murine uterus have revealed a potential enhancer region distal from the Igf1 transcription start site (TSS) with multiple E2-dependent ERα-binding regions. Here, we show E2-dependent super enhancer–associated characteristics and suggest contact between the distal enhancer and the Igf1 TSS. We hypothesized that this distal super-enhancer region controls E2-responsive induction of uterine Igf1 transcripts. We deleted 430 bp, encompassing one of the ERα-binding sites, thereby disrupting interactions of the enhancer with gene-regulatory factors. As a result, E2-mediated induction of mouse uterine Igf1 mRNA is completely eliminated, whereas hepatic Igf1 expression remains unaffected. This highlights the central role of a distal enhancer in the assembly of the factors necessary for E2-dependent interaction with the Igf1 TSS and induction of uterus-specific Igf1 transcription. Of note, loss of the enhancer did not affect fertility or uterine growth responses. Deletion of uterine Igf1 in a PgrCre;Igf1f/f model decreased female fertility, but did not impact the E2-induced uterine growth response. Moreover, E2-dependent activation of uterine IGF1 signaling was not impaired by disrupting the distal enhancer or by deleting the coding transcript. This indicated a role for systemic IGF1, suggested that other growth mediators drive uterine response to E2, and that uterine-derived IGF1 is essential for reproductive success. Our findings elucidate the role of a super enhancer in Igf1 regulation and uterine growth. ERa or Histone 3 modifications ChIP seq of pre-pubertal (21 days old) or ovariectomized adult uterine tissue treated for one hour with saline vehicle (V) or estradiol (E2); ERa ChIP seq of ovariectomized adult uterine tissue treated for 6, 8 or 12 hours with estradiol (E2); SMC1a ChIP seq or HiC of ovariectomized adult uterine tissue treated for one hour with saline vehicle (V) or estradiol (E2) or progesterone (P4); RNA seq of ovariectomized adult uterine tissue treated for two hours with saline vehicle (S) or for two, six or 24 hours with estradiol (E2)