CIS AND TRANS CONTROL OF MURINE ALPHA-FETOPROTEIN GENE EXPRESSION

The mouse albumin and $\alpha$-fetoprotein (AFP) genes are activated in concert in three different cell types during development; the visceral endoderm of the yolk sac, the fetal liver, and the fetal gastrointestinal tract. Once activated, the two genes demonstrate independent transcriptional modulation. The experiments described in this thesis are based on the paradigm that tissue specific gene expression is achieved to a large extent by the availability and specificity of the interactions between cis -acting DNA sequences and trans -acting factors. I investigated a B1 middle repetitive sequence located in the first intron of the AFP gene of inbred mice as a potential cis -acting regulatory DNA sequence. The contribution of the B1 element to the control of AFP gene expression was examined in three experimental series: transient introduction of modified AFP gene constructs into Hela cells and HepG2 human hepatoma cells; analysis of chromosomal AFP gene transcription and B1 transcription in mouse tissues and HepG2 cells; and identification and analysis of a mouse species, M. caroli, lacking a B1 element in its AFP gene first intron. The results obtained from these studies do not support an important role for the B1 sequence in control of AFP gene expression. In addition, transcription of the B1 element was characterized in vitro and following transient introduction into primate cells in culture. To assay for cis -acting sequences important for activation of the AFP gene in the visceral endoderm, modified AFP genes were introduced into F9 embryonal carcinoma (EC) cells. Multiple sequences were identified within the 7.6 kilobases 5$\sp\prime$ of the AFP gene that were required to activate the introduced AFP gene upon F9 EC cell differentiation to visceral endoderm. These results, in conjunction with studies of modified AFP genes introduced into HepG2 cells, suggest that cis -acting sequences may exhibit pleiotropic roles in gene activation and modulation during cell differentiation. A genetically identified trans -acting regulatory locus, designated raf, contributes to the control of AFP gene transcription in postnatal liver. By analysis of AFP gene expression in mouse chimeras, I demonstrated that the raf locus acts in a liver cell autonomous manner