An egg is packed with its mother’s mRNAs and proteins, and the young embryo runs on them while its own genes are mostly silent. Then control passes over: maternal mRNAs are cleared and the embryo switches on its own genes. This maternal-to-zygotic transition happens in every animal studied (Tadros & Lipshitz 2009; Vastenhouw et al. 2019), at different times: after about 12 cell divisions in frogs (Newport & Kirschner 1982), at the 2-cell stage in mice and around the 4–8-cell stage in humans. Established: Replicated many times; textbook knowledge.
In the fruit fly, the embryo’s nuclei divide 13 times in about two hours, then form cells at stage 5, when its own genes switch on strongly. Open data from FlyBase show the hand-over:
- oskar (mother’s)
- bicoid (mother’s)
- even-skipped (embryo’s own)
- fushi tarazu (embryo’s own)
- zerknüllt (embryo’s own)
Source: FlyBase gene RPKM matrix (modENCODE developmental RNA-seq; Graveley et al. 2011), CC BY 4.0, retrieved 2026-10-03. Each gene scaled to its own maximum.
Show the numbers
| Stage | oskar (mother’s) | bicoid (mother’s) | even-skipped (embryo’s own) | fushi tarazu (embryo’s own) | zerknüllt (embryo’s own) |
|---|---|---|---|---|---|
| 0–2 h | 100 | 100 | 5 | 5 | 13 |
| 2–4 h | 6 | 47 | 100 | 100 | 100 |
| 4–6 h | 2 | 18 | 11 | 16 | 4 |
| 6–8 h | 1 | 14 | 6 | 18 | 0 |
| 8–10 h | 1 | 19 | 6 | 14 | 2 |
| 10–12 h | 1 | 10 | 6 | 3 | 0 |
Stage 5: the embryo takes over. In stage 5, membranes grow between about 6,000 nuclei at once and the embryo strongly switches on its own genes. The future eggs and sperm, the pole cells, sit at the back. This hand-over is the maternal-to-zygotic transition.
My question
In mouse embryos, lactate and a lactyl tag on histones help the first genes switch on (Li et al. 2024). Emerging: A few studies so far; an active research area. I am asking whether metabolism shapes histone marks at this moment in the fly embryo. Hypothesis: An idea being tested. No answer yet. More on my current project.
In my research: The fly from egg chamber to stage 5, step by step →
Sources
- Tadros W, Lipshitz HD (2009) The maternal-to-zygotic transition: a play in two acts. Development 136:3033–3042. doi:10.1242/dev.033183
- Vastenhouw NL, Cao WX, Lipshitz HD (2019) The maternal-to-zygotic transition revisited. Development 146:dev161471. doi:10.1242/dev.161471
- Newport J, Kirschner M (1982) A major developmental transition in early Xenopus embryos: I. Characterization and timing of cellular changes at the midblastula stage. Cell 30:675–686. doi:10.1016/0092-8674(82)90272-0
- Graveley BR, et al. (2011) The developmental transcriptome of Drosophila melanogaster. Nature 471:473–479 (via FlyBase, CC BY 4.0). doi:10.1038/nature09715
- Li J, et al. (2024) Lactate regulates major zygotic genome activation by H3K18 lactylation in mammals. National Science Review 11:nwad295. doi:10.1093/nsr/nwad295