Cell Type Specific Expression of the Growth Hormone Gene and its Control by GHF-1

One of the major challenges in molecular genetics is to determine the mechanisms which control the utilization of genetic information in time -and space -dependent manners. Differential gene activation is the basis for the processes of cellular differentiation and specialization. Through genetic analysis, a great deal has been learned about the general mechanisms which control these processes in organisms such as D. melanogaster and C . elegans . Although mammals, on the other hand, are refractory to genetic analysis, significant progress has been made in understanding the mechanisms involved in determining tissue specific gene expression in these organisms. This can be mostly attributed to a biochemical approach employing in vitro transcription systems in which differential promoter utilization could be observed, resulting in identification of transcription factors mediating cell-type specific gene expression (Scheidereit et al. 1987;