Transport of mRNA in Drosophila eggs and embryos. The building blocks of anterior-posterior axis patterning in Drosophila are laid out during egg formation (oogenesis), well before the egg is fertilized and deposited. The developing egg (oocyte) is polarized by differentially localized mRNA molecules. In each oocyte shown, a different mRNA is labeled with a blue fluorescent marker. Nuclear DNA is labeled with a red marker. Each mRNA contributes to pattern formation in the developing embryo.