The role of the hGH locus control region in somatotrope restriction of hGH-N gene expression.

Expression of mammalian GH is normally restricted to somatotropes and somatolactotropes (somatotrope lineages) in the anterior pituitary. The basis for this restriction remains incompletely understood. Recent studies indicate that deoxyribonuclease I hypersensitive site I (HSI) of the hGH locus control region, located at -14.5 kb relative to the hGH-N promoter, acts as a potent long-range enhancer of hGH-N transcription. Here we report that HSI is also critical to somatotrope-restriction of hGH-N expression. Loss of HSI activity, either by direct inactivation of HSI or by interference with HSI-dependent downstream events, results in a relaxation of hGH-N cell-type specification with expansion of hGH-N expression to the full spectrum of Pit-1 positive pituitary cell types. These findings expand the defined roles for HSI of the hGH locus control region to include somatotrope lineage restriction as well as transcriptional enhancement of hGH-N gene expression.