PTB Regulates the Processing of a 3′-Terminal Exon by Repressing both Splicing and Polyadenylation

Abstract

The polypyrimidine tract binding protein (PTB) has been described as a global repressor of regulated exons. To investigate PTB functions in a physiological context, we used a combination of morpholino-mediated knockdown and transgenic overexpression strategies in Xenopus laevis embryos. We show that embryonic endoderm and skin deficient in PTB displayed a switch of the α-tropomyosin pre-mRNA 3′ end processing to the somite-specific pattern that results from the utilization of an upstream 3′-terminal exon designed exon 9A9′. Conversely, somitic targeted overexpression of PTB resulted in the repression of the somite-specific exon 9A9′ and a switch towards the nonmuscle pattern. These results validate PTB as a key physiological regulator of the 3′ end processing of the α-tropomyosin pre-mRNA. Moreover, using a minigene strategy in the Xenopus oocyte, we show that in addition to repressing the splicing of exon 9A9′, PTB regulates the cleavage/polyadenylation of this 3′-terminal exon.

ACKNOWLEDGMENTS

We thank Nick Proudfoot for the β-globin construct used to derive pSV40βglobinβpA and David Bentley for the VA reporter plasmid. We thank Chris Smith for critically reading the manuscript. We also thank Beverley Osborne for helpful suggestions and his continual support.

This work was supported by grants to S.H. from the Association Française contre les Myopathies.