Apolipoprotein B messenger RNA editing is developmentally regulated and widely expressed in human tissues

Apolipoprotein B (apoB) messenger RNA (mRNA) undergoes posttranscriptional (C to U) editing, producing tissue-specific forms of apoB from the unedited (apoB₁₀₀) and edited (apoB₄₈) transcripts. ApoB mRNA editing is developmentally regulated in human fetal small intestine, producing parallel changes in the synthesis and secretion of apoB₁₀₀ and apoB₄₈. Neither fetal nor adult liver contained detectable levels (<1%) of edited apoB mRNA. By contrast, apoB mRNA is incrementally edited during development in several extraintestinal fetal tissues. These tissues demonstrated significant differences, however, in both the extent and developmental profile of apoB mRNA editing. Additionally, while apoB₁₀₀ synthesis and secretion was demonstrated in these tissues, apoB₄₈ synthesis was confined to the small intestine. Thus, although the molecular mechanism underlying this process remains unclear, the capacity to edit apoB mRNA is widely distributed among both fetal and adult tissues. We speculate that the asynchronous and developmentally modulated induction of apoB mRNA editing may provide a novel mechanism for regulating lipoprotein biogenesis in both the developing fetus and adult human.