Blastoderm Formation and Cellularisation in Drosophila melanogaster

Immediately following fertilisation in Drosophila and many other arthropods, the embryo undergoes a series of rapid syncytial nuclear divisions. These divisions are driven by maternally supplied components and occur in the absence of zygotic transcription. Unlike typical cell divisions, these divisions alternate between S and M phases, resulting in cell cycles that last only from 10 to 25 min. After four rounds of division, the nuclei undergo axial expansion, a process that relies on microfilaments. Subsequently migration of the nuclei to the cortex relies on microtubules. Once at the cortex, the nuclear divisions occur on a single plane and rely on partial cleavage furrows to maintain an even distribution. The cortical nuclear divisions continue until the mid-blastula transition (MBT), at which time cellularisation results in the formation of a multicellular embryo.