Alpha‐fetoprotein regulator‐1 posttranscriptionally represses alpha‐fetoprotein expression

The alpha‐fetoprotein (AFP) and H19 genes are transcribed at high levels in the mammalian fetal liver but are rapidly repressed postnatally. This repression in the liver is controlled, at least in part, by alpha‐fetoprotein regulator‐1(Afr1). Afr1 was defined when BALB/cJ mice were found to have 5–20 fold higher adult serum AFP levels compared with all other mouse strains; subsequent studies showed that this elevation was due to increased liver AFP mRNA levels. H19 was later identified as another Afr1 target in a molecular genetic screen. We have hypothesized that Afr1 acts as a repressor of AFP and H19 expression in the adult liver. To test this, we performed high resolution mapping and positional cloning to identify Afr1 as the product of the zinc fingers and homeoboxes protein 2 (Zhx2) gene (PNAS 102(2):396–401, 2005). This was confirmed by transgene complementation in BALB/cJ mice. Northern blot analysis revealed ubiquitous Afr1 expression with surprisingly low expression level in the adult liver. Current studies have focused on the mechanism by which Afr1 controls AFP and H19 expression and suggest that this is mainly at the post‐transcriptional level. We have generated transgenic mice in which an Afr1‐HA transgene is ubiquitously expressed for use in mechanistic studies. Chromatin immunoprecipitation (ChIP) assays are being used to monitor interactions between Afr1 and its target genes and co‐IP experiments will determine if Afr1 interacts with chromatin modification proteins. Because the BALB/cJ Afr1 allele is a hypomorph, to better understand the biological function of Afr1, we are generating conditional Afr1 knock‐out mice.