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Differential nuclear import sets the timing of protein access to the embryonic genome.

ABSTRACT: The development of a fertilized egg to an embryo requires the proper temporal control of gene expression. During cell differentiation, timing is often controlled via cascades of transcription factors (TFs). However, in early development, transcription is often inactive, and many TF levels stay constant, suggesting that alternative mechanisms govern the observed rapid and ordered onset of gene expression. Here, we find that in early embryonic development access of maternally deposited nuclear proteins to the genome is temporally ordered via importin affinities, thereby timing the expression of downstream targets. We quantify changes in the nuclear proteome during early development and find that nuclear proteins, such as TFs and RNA polymerases, enter the nucleus sequentially. Moreover, we find that the timing of nuclear proteins' access to the genome corresponds to the timing of downstream gene activation. We show that the affinity of proteins to importin is a major determinant in the timing of protein entry into embryonic nuclei. Thus, we propose a mechanism by which embryos encode the timing of gene expression in early development via biochemical affinities. This process could be critical for embryos to organize themselves before deploying the regulatory cascades that control cell identities.

SUBMITTER: Nguyen T

PROVIDER: S-EPMC9537182 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

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Differential nuclear import sets the timing of protein access to the embryonic genome.

Nguyen Thao T Costa Eli J EJ Deibert Tim T Reyes Jose J Keber Felix C FC Tomschik Miroslav M Stadlmeier Michael M Gupta Meera M Kumar Chirag K CK Cruz Edward R ER Amodeo Amanda A Gatlin Jesse C JC Wühr Martin M

Nature communications 20221006 1

The development of a fertilized egg to an embryo requires the proper temporal control of gene expression. During cell differentiation, timing is often controlled via cascades of transcription factors (TFs). However, in early development, transcription is often inactive, and many TF levels stay constant, suggesting that alternative mechanisms govern the observed rapid and ordered onset of gene expression. Here, we find that in early embryonic development access of maternally deposited nuclear pro ...[more]

PMID: 36202846

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Project description:During early embryonic cell divisions, the total nuclear volume doubles with each cycle. At a critical volume ratio between the nucleus and cytoplasm, embryos start transcribing their genome in a reproducible and sequential manner. However, the underlying molecular mechanism for these well-timed events remains unclear. Previous studies proposed that titration of a regulatory factor by the exponentially increasing DNA content of the system triggers the onset of the first transcripts. Nevertheless, a systematic investigation of nuclear proteome changes during development is still missing. In this study, we perform this investigation and find that differential nuclear import timing can largely explain the sequential onset of transcription. First, we investigated nuclear proteome changes in early development. We found that nuclear proteins sequentially titrate into the embryonic nuclei. Interestingly, transcription factors and RNA polymerases enter the nucleus at different times, which correspond to the activation of their nuclear functions. Notably, we observed a high correlation between when transcription factors enter the nucleus and the order in which they activate downstream transcription. Time-lapse imaging of protein import into nuclei encapsulated in droplets of cytoplasmic extract validated our discovery of the sequential nuclear import by mass spectrometry. Lastly, we investigated the underlying molecular mechanism responsible for the differential timing of protein entry into embryonic nuclei. To this end, we quantified the relative affinity of substrates to importin and observe that high-affinity substrates tend to enter the nucleus earlier than low-affinity substrates. Notably, we can explain > 36% of the observed time-variation of when proteins enter the nucleus in the embryo with this simple affinity assay. Together, our results suggest that embryos control protein entry into the nucleus by modulating importin affinities, which then determines the timing of essential nuclear processes in early development.

Dataset Information

Differential nuclear import sets the timing of protein access to the embryonic genome.

Publications

Differential nuclear import sets the timing of protein access to the embryonic genome.

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