Localization of Bicoid mRNA is divided into three phases. In the previtellogenic stage, Bicoid mRNA is localized to the apex of each of the 15 nurse cells of the ovule. In vitellogenesis, the contents of the nurse cells are transported into the oocyte by a cytoskeletal based mechanism of cytoplasmic streaming. In a third process, Bicoid mRNA is transported along the microtubule network of the oocyte to its anterior pole. The latter process requires direction action of Exuperantia, Exuperantia-like, Swallow and Staufen, and involves binding of Exu-like to cis-acting localization signals within the 3' untranslated region of Bicoid mRNA. Staufen also binds to the 3' UTR of BCD mRNA.

Maternally transcribed genes

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