We previously isolated and characterized a coding region determinant-binding 
protein (CRD-BP) that might regulate c-myc mRNA post-transcriptionally. CRD-BP 
binds specifically to the coding region of c-myc mRNA and might stabilize c-myc 
mRNA in vitro by protecting it from endonucleolytic cleavage. Since c-myc 
abundance is regulated during embryonic development and cell replication, we 
investigated whether CRD-BP is also regulated in animal tissues. We focused on 
CRD-BP expression during rat liver development and liver regeneration, because 
c-myc mRNA is regulated post-transcriptionally in both cases. CRD-BP expression 
parallels c-myc expression during liver development; the protein is present in 
fetal and neonatal liver but is absent or in low abundance in adult liver. In 
contrast, the up-regulation of c-myc mRNA following partial hepatectomy is not 
accompanied by up-regulation of CRD-BP. To our knowledge, CRD-BP is the first 
example of a putative mammalian mRNA-binding protein that is abundant in a fetal 
tissue but either absent from or scarce in adult tissues. Its expression in 
fetal liver and in transformed cell lines suggests CRD-BP is an oncofetal 
protein.