Diane M. Robins

Transforming DNA integrates into the host chromosome

A series of rat liver cotransformed cell lines have been constructed containing from 5 to 100 copies of a variant human growth hormone gene. We have used hybridization in situ to demonstrate that most, if not all, cotransformed sequences reside in a chromosome of the host cell. In each of four cell lines examined, hybridization was restricted to a single chromosomal site with no extrachromosomal sites apparent. The site was invariant within each line; however, each line revealed a different site of integration for transforming sequences. In two of the four lines, transforming DNA resided at or near the site of gross chromosomal rearrangements, in one line near an rDNA site, and in one line in the middle of an apparently normal chromosome. Thus, insertion is not restricted to a unique chromosome or chromosomal region.

Trans-regulatory genes affect Slpa and Slpo expression and act in a tissue-specific manner

The plasma protein C4 and its androgen-dependent homologue Slp are encoded by genes located in the mouse major histocompatibility complex, H-2. The C4 and Slp protein levels and liver mRNA levels are influenced by non-H-2-linked regulatory genes. The allele-specific regulation of C4 expression and the androgen regulation of Slp expression are manifest only in some of the tissues where these genes are expressed. Therefore, we studied tissues in which the effects of the non-H-2 regulatory genes are apparent. We show that these genes only affect the Slp expression in tissues where it is androgen-dependent. This indicates that the non-H-2 regulatory genes most likely act through interaction with the androgen regulation of Slp expression. We also show that liver cells of mice with the Slpo allele, which do not produce Slp protein, do express Slp mRNA; this expression is also androgen-induced and regulated by non-H-2 genes. Thus, both the Slpa and Slpo alleles appear to be regulated in the same way.

EXPRESSION OF THE HUMAN GROWTH HORMONE GENE IS REGULATED IN MOUSE CELLS

Publisher Summary Steroid hormones regulate the expression of restricted sets of gene products in a tissue-specific manner. A model of hormone action compatible with available data assumes that the interaction of steroid–receptor complex with appropriate DNA sequences enhances transcription. The introduction of hormonally responsive genes into cells provides an experimental system to determine whether deducibility is a property inherent in discrete nucleotide sequences. In vertebrates, growth hormone synthesis is restricted to the pituitary gland. The human growth hormone (hGH) gene is a member of a small multi-gene family composed of at least two additional hormones, chorionic soimtomammotropin and prolactin. Several different recombinant phage containing hGH sequences have been isolated from a library of human DNA. The introduction of recombinant clones containing the human growth hormone gene into mouse fibroblasts results in the regulated expression of hGH mRNA.