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Manuel Irimia @mirimiam.bsky.social · 20/04/2026

We analyzed these datasets within a unified framework, using three main data types to identify ZGA onset across species (PCA distances, newly expressed genes and intron/exon read ratio). The result was the first systematic atlas of ZGA onset across animals. 4/15

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Manuel Irimia @mirimiam.bsky.social · 20/04/2026

We found the timing of ZGA onset to be highly variable across species, covering every possible cell cycle from 1 (rodents) to 14 (flies). While the most common stages were 3-5 cell cycles, we could not really infer an ancestral ZGA stage due to its high variability. 5/15

Distribution of ZGA onsets and attempt to reconstruct ancestral state

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Manuel Irimia @mirimiam.bsky.social · 20/04/2026

What determines this variability? First, ZGA onset in cell cycles is not at all correlated with onset in hours of development, against some hypotheses in the field. Second, ZGA nearly always occurs before gastrulation, as expected, suggesting they impose constraints on each other's onset. 6/15

No correlation between ZGA onset in hours and cycle and association with gastrulation

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