Patterns of histone acetylation suggest dual pathways for gene activation by a bifunctional locus control region

The five genes of the human growth hormone (hGH) cluster are expressed in e ither the pituitary or placenta. Activation of the cluster is dependent on a locus control region (LCR) comprising pituitary-specific (HSI,II, -15 kb) , placenta-specific (HSIV, -30 kb) and shared (HSIII, -28 kb; HSV, -32 kb) DNase I hypersensitive sites. Gene activation in the pituitary is parallele d by acetylation of a 32 kb chromatin domain 5' to the cluster centered at HSI,II, In the present study we observed that acetylation of this region in placental chromatin was discretely limited to shared HSIII and HSV. Transg enic studies revealed placenta-specific activation of linked genes by a det erminant (P-element) located 2 kb 5' to each of the four placentally expres sed genes. A localized peak of histone acetylation was observed at these P- elements in placenta but not pituitary. These data support a model for bifu nctional action of the hGH LCR in which separate positive determinants, HSI ,IZ and the P-elements, activate their respective target genes by tissue-sp ecific recruitment of distinctly regulated histone acetyl transferase activ ities.