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Curr Biol January 5, 2015; 25 (1): 45-52.

Nuclear size scaling during Xenopus early development contributes to midblastula transition timing.

Jevtić P , Levy DL .

Early Xenopus laevis embryogenesis is a robust system for investigating mechanisms of developmental timing. After a series of rapid cell divisions with concomitant reductions in cell size, the first major developmental transition is the midblastula transition (MBT), when zygotic transcription begins and cell cycles elongate. Whereas the maintenance of a constant nuclear-to-cytoplasmic (N/C) volume ratio is a conserved cellular property, it has long been recognized that the N/C volume ratio changes dramatically during early Xenopus development. We investigated how changes in nuclear size and the N/C volume ratio during early development contribute to the regulation of MBT timing. Whereas previous studies suggested a role for the N/C volume ratio in MBT timing, none directly tested the effects of altering nuclear size. In this study, we first quantify blastomere and nuclear sizes in X. laevis embryos, demonstrating that the N/C volume ratio increases prior to the MBT. We then manipulate nuclear volume in embryos by microinjecting different nuclear scaling factors, including import proteins, lamins, and reticulons. Using this approach, we show that increasing the N/C volume ratio in pre-MBT embryos leads to premature activation of zygotic gene transcription and early onset of longer cell cycles. Conversely, decreasing the N/C volume ratio delays zygotic transcription and leads to additional rapid cell divisions. Whereas the DNA-to-cytoplasmic ratio has been implicated in MBT timing, our data show that nuclear size also contributes to the regulation of MBT timing, demonstrating the functional significance of nuclear size during development.

PubMed ID: 25484296
PMC ID: PMC4286459
Article link: Curr Biol
Grant support: [+]
Genes referenced: bix1.1 bix1.3 brap gs17 kpna2 lmnb3 nodal3.1 nodal3.2 nodal5.2 nodal5.4 odc1 rtn4
Antibodies: Nuclear Pore Complex Ab1

Article Images: [+] show captions
References [+] :
Almouzni, Constraints on transcriptional activator function contribute to transcriptional quiescence during early Xenopus embryogenesis. 1995, Pubmed, Xenbase

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