α-Fetoprotein expression in fetal kidney cells does not require enhancers

Expression of the α-fetoprotein (AFP) and albumin genes was examined in fetal mouse kidney by analysis of tissue mRNA pool sizes during development and transient expression assays in primary kidney tissue culture cells. AFP is expressed at a much lower level in kidney than in liver but transcription of the gene is activated early during development and repressed after birth with a time-course similar to liver. However, albumin mRNA was not detected in fetal or new born mouse kidney. Transient expression assays using AFP- and albumin-CAT (chloramphenicol acetyl transferase) vectors were employed to characterize cis-acting elements active in the regulation of AFP expression in kidney. Primary fetal liver and kidney cells in culture were used for these assays. The AFP promoter is active in kidney cells and the information necessary for tissue specific expression and developmental repression are contained within the first 1.0 kb of 5′ flanking sequences of the AFP gene. In addition, the AFP upstream enhancer elements are inactive in primary kidney cells. The mouse albumin promoter is shown to be inactive in kidney cells. The results obtained using transient expression assays are consistent with the observed low level of AFP expression, developmental repression of AFP, and the absence of expression of albumin in the mouse kidney.