POST-TRANSCRIPTIONAL REGULATION OF AFP AND IgM GENES ABSTRACT OF DISSERTATION POST-TRANSCRIPTIONAL REGULATION OF AFP AND IgM GENES
Lilia Turcios, Lilia Turcios, Lilia Turcios, Lilia Turcios, Lilia Turcios, Martha Peterson
OF DISSERTATION POST-TRANSCRIPTIONAL REGULATION OF AFP AND IgM GENES Gene expression can be regulated at multiple steps once transcription is initiated. I have studied two different gene models, the α-Fetoprotein (AFP) and the immunoglobulin heavy chain (IgM) genes, to better understand post-transcriptional gene regulation mechanisms. The AFP gene is highly expressed during fetal liver development and dramatically repressed after birth. There is a mouse strain-specific difference between adult
... evels of AFP, with BALB/cJ mice expressing 10 to 20-fold higher levels compared to other mouse strains. BALB/cJ mice express low levels of Zhx2 and thus incompletely repress AFP. Despite differences in steady state AFP mRNA levels in the adult liver between Balb/cJ and wild-type mice, transcription rates across this gene were similar, indicating a post-transcriptional regulatory mechanism. I found accumulated unspliced RNA across multiple AFP introns in wild-type mice where mature AFP mRNA levels are low, suggesting overall AFP splicing is inefficient in the presence of Zhx2. The IgM gene is alternative processed to produce two mRNA isoforms through a competition between cleavage/polyadenylation (µspA) and splicing reactions and the pA/splice RNA expression ratio increases during B cell maturation. Cotranscriptional cleavage (CoTC) events, driven by specific cis-acting elements, are required downstream of some poly(A) signals to terminate transcription. In some cases, a pause site can produce similar effect. I explored whether there is a CoTC-like element within the IgM gene that may contribute to developmental changes in the mRNA ratio. In both a B cell and plasma cell line there was a gradual decrease in transcripts downstream from the µspA signal, suggesting that there is not evidence for a CoTC element within the IgM gene. To examine the effect a CoTC element would have on the competition between the splice and µspA reactions, we inserted the CoTC sequence of the β-globin gene into different locations downstream of the µspA signal. While the β-globin CoTC element caused cotranscriptional cleavage in all locations, it only affected the µspA/splice ratio when located close to the µspA site. This suggests there is a position effect of the inserted CoTC element on the competing polyadenylation and splicing reactions within the IgM transcripts.