Half pint couples transcription and splicing of eIF4E-1,2 gene during fly development

There are seven genes encoding eight protein isoforms of the translation initiation factor 4E (eIF4E) in Drosophila. One of these genes, eIF4E-1,2, gives rise to three mRNAs with different 5′-untranslated regions (5′UTRs) through alternative splicing regulated by Haf pint (Hfp) in the ovary. eIF4E-1a and eIF4E-1b mRNAs encode the eIF4E-I protein, whereas eIF4E-2 mRNA encodes the eIF4E-II protein. We report here that Hfp regulates alternative splicing of eIF4E-1,2 pre-mRNA during Drosophila development in a sex-independent way. Hfp RNA interference-mediated knockdown in Drosophila S2 cells reproduces the eIF4E-1,2 gene expression found in development. Interestingly, 5′UTRs of eIF4E-1a and -1b isoforms, unlike the eIF4E-2 5′UTR, promote a significant increase in the translation efficiency of a luciferase-encoding chimeric mRNA. Thus, these results suggest that the eIF4E-1,2 gene is regulated by Hfp through a mechanism linked to transcription control and 3′ splice site selection, which determines the pattern and translation efficiency of eIF4E-1,2 mRNAs.