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XB-ART-58288
Curr Biol October 11, 2021; 31 (19): 4269-4281.e8.
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The DNA-to-cytoplasm ratio broadly activates zygotic gene expression in Xenopus.

Jukam D , Kapoor RR , Straight AF , Skotheim JM .


Abstract
In multicellular animals, the first major event after fertilization is the switch from maternal to zygotic control of development. During this transition, zygotic gene transcription is broadly activated in an otherwise quiescent genome in a process known as zygotic genome activation (ZGA). In fast-developing embryos, ZGA often overlaps with the slowing of initially synchronous cell divisions at the mid-blastula transition (MBT). Initial studies of the MBT led to the nuclear-to-cytoplasmic ratio model where MBT timing is regulated by the exponentially increasing amounts of some nuclear component "N" titrated against a fixed cytoplasmic component "C." However, more recent experiments have been interpreted to suggest that ZGA is independent of the N/C ratio. To determine the role of the N/C ratio in ZGA, we generated Xenopus frog embryos with ∼3-fold differences in genomic DNA (i.e., N) by using X. tropicalis sperm to fertilize X. laevis eggs with or without their maternal genome. Resulting embryos have otherwise identical X. tropicalis genome template amounts, embryo sizes, and X. laevis maternal environments. We generated transcriptomic time series across the MBT in both conditions and used X. tropicalis paternally derived mRNA to identify a high-confidence set of exclusively zygotic transcripts. Both ZGA and the increase in cell-cycle duration are delayed in embryos with ∼3-fold less DNA per cell. Thus, DNA is an important component of the N/C ratio, which is a critical regulator of zygotic genome activation in Xenopus embryos.

PubMed ID: 34388374
PMC ID: PMC8511243
Article link: Curr Biol
Grant support: [+]

Species referenced: Xenopus tropicalis Xenopus laevis
Genes referenced: cdk9 eef1a1o eomes ets2 fgf8 foxi4.2 gata6 gs17 klf17 pou5f3.3 sox3 srsf6 vegt znf44
GO keywords: regulation of gene expression
Antibodies: Cenpa Ab1


Article Images: [+] show captions