Fig. 3. 3′UTR control of survivin isoform expression.

A: Canonical and ΔEx3 survivin mRNA isoforms showing exons, possible polyadenylation sites, 3′ UTR lengths. B: RT-PCR showing RNA corresponding to all three survivin polyadenylation sites are detected in H9 cells cultured for 1 and 3 days in both media. Expression of medium- and long-poly(A) tail mRNAs is lower at day 1 in differentiating vs. pluripotency media. At day 3, only expression of the long-poly(A) tail mRNA is reduced in differentiation medium compared to in pluripotency medium. C: Luciferase reporter (pMIR-Report) constructs containing 3′ UTR sequences from canonical and ΔEx3 survivin isoforms (left). Normalized luciferase signal in cells transiently co-transfected with the constructs shown at left and a Renilla luciferase construct, cultured for 24 h post-transfection in either pluripotency or differentiation medium (right). Short 3′ UTR constructs from both survivin isoforms showed increased expression regardless of culture media, whereas constructs containing only medium and long poly(A) tail 3′ UTR constructs from canonical survivin showed upregulation in the presence of RA (differentiation medium). ΔEx3-derived medium and long poly(A) tail 3′ UTRs were not upregulated in the presence of RA.