Abstract
Abstract The transcription factor Bicoid (Bcd) establishes patterning in the early Drosophila blastocyst through its graded concentration along the anterior-posterior (AP) axis. bcd mRNA is maternally deposited during oogenesis, yet precisely when and where bcd mRNA is translated remains an open problem. Here, we take advantage of the SunTag reporter system to quantitatively examine the spatiotemporal profile of bcd mRNA translation in vivo . We demonstrate that Processing body (P body) localisation in the oocyte suppresses premature bcd mRNA translation. Upon egg laying, bcd mRNA disassociates from P bodies and translation is observed exclusively in the anterior pole of the embryo. Accompanying nuclear migration to the embryo cortex at nuclear cycle (n.c.) 9, bcd mRNA relocates to the apical domain of the nuclear environment and translation continues near the embryo surface. In n.c. 14, bcd mRNA localises to newly formed P bodies and further translation is not detected. We use these observations to build a modified source-diffusion-degradation model of Bcd gradient formation that leads to an exponential gradient by n.c. 12 and is consistent with other experimental measurements of Bcd dynamics. Consequently, we see that the spatiotemporal dynamics of bcd mRNA translation are highly regulated throughout oogenesis and early embryo development.