Developmental Regulation of bicoid mRNA Stability Is Mediated by the First 43 Nucleotides of the 3′ Untranslated Region

ABSTRACT

During the transition from the maternal to the zygotic developmental program, the expression of genes important for pattern formation or cell cycle regulation changes dramatically. Rapid changes in gene expression are achieved in part through the control of mRNA stability. This report focuses on bicoid, a gene essential for formation of anterior embryonic structures in Drosophila melanogaster. bicoid mRNA is synthesized exclusively during oogenesis. Here, we show that bicoid mRNA stability is regulated. While bicoid mRNA is stable in retained oocytes, in unfertilized eggs, and during the first 2 h of embryogenesis, specific degradation is activated at cellularization of the blastoderm. To identify cis-acting sequences required for bicoid mRNA’s regulated stability, fusions betweenbicoid and genes producing stable mRNAs were introduced into the Drosophila germ line by P-element-mediated transformation. The analysis of the fusion mRNAs identified abicoid instability element (BIE) contained within a 43-nucleotide sequence immediately following the stop codon. The BIE is sufficient to destabilize the otherwise-stable ribosomal protein A1 mRNA and is separable from the previously identified bicoidmRNA localization signals and from the “nanos response element.” Similar mechanisms may regulate a class of developmentally important maternal genes whose mRNA has a temporal profile similar to that of bicoid.

ACKNOWLEDGMENTS

We thank Robert Cohen and Kam Cheung (Columbia University) for providing a plasmid containing the sgs3 promoter and the nurse cell-specific enhancer from hsp26. We thank Paul Macdonald (Stanford University) for flies transformed with the BBT construct and for the plasmid p1122, containing the bicoidcDNA. We thank Robin Wharton (Duke University) for flies transformed with the ΔNRE construct. P.S. is very grateful to Lukas Kuehn (ISREC, Epalinges, Switzerland) for giving him the opportunity to finish this study in his laboratory and for his continuous support. We thank Claude Bonnard for his help in use of the Genetics Computer Group package. We thank Marilyn Doman, Ann Riedl, and Maria Goreti Freitas-Sibajev for their comments on the manuscript.

This work was supported by a grant from the National Institutes of Health.