THE HUMAN GROWTH-HORMONE GENE IS REGULATED BY A MULTICOMPONENT LOCUS-CONTROL REGION

The five-member human growth hormone (hGH)/chorionic somatomammotropin (hCS) gene cluster encodes the pituitary-specific hGH-N gene and four highly related genes (hGH-V, hCS-A, hCS-B, and hCS-L) that are expres sed only in the placenta, When the AGH-N or hCS-A gene, together with all previously identified cis-acting regulatory sequences, was integra ted into the mouse genome, it was expressed only sporadically and at l ow levels in the transgenic target organs. DNase I mapping of chromati n from expressing and nonexpressing cell types was used to identify a pituitary-specific set of DNase I-hypersensitive sites (HS) and a set of HS common to both the pituitary and placenta, centered approximatel y 15 and 30 kb 5' of hCH-N, respectively. When contained on a cosmid i nsert in their native genomic configuration, these HS consistently dir ected high-level, pituitary-specific expression of hGH-N in transgenic mice and appeared to define a locus control region required for hGH-N expression, Individually, each set of HS was able to mediate position -independent hGH-N expression in the pituitary but demonstrated loss o f physiologic control and loss of tissue specificity. The gene-proxima l set of HS contained a potent enhancer activity in the pituitary, whi le the more distal set appeared to function primarily to establish sit e-of-integration independence. These data indicate that synergistic in teractions among multiple elements are required to restrict hGH-N tran scription to the pituitary and generate appropriate levels of expressi on. In addition, these results suggest a role for both shared and uniq ue regulatory sequences in locus control region mediated expression of the hGH/hCS gene cluster in the pituitary and possibly the placenta.