Histone titration by DNA sets the threshold for the mid-blastula transition in Xenopus
Abstract/Contents
- Abstract
- During early development, animal embryos depend upon maternally deposited RNA until zygotic genes become transcriptionally active. Prior to this maternal-to-zygotic transition (MZT), many species execute rapid and synchronous cell divisions without growth phases or cell cycle checkpoints. In Xenopus laevis embryos, the MZT coincides with cell cycle lengthening, cellular motility onset, and the addition of cell cycle checkpoints at a stage termed the mid-blastula transition (MBT). A long standing model is that the timing of the MBT is controlled by a maternally loaded inhibitory factor that is titrated against the exponentially increasing amount of DNA(Newport and Kirschner, 1982b). To identify the inhibitory factor(s), we developed an assay using Xenopus egg extract that recapitulates the activation of transcription only above the DNA-to-cytoplasm ratio found in embryos at the MBT. We used this system to biochemically purify the factor responsible for inhibiting transcription below the threshold DNA-to-cytoplasm ratio. This unbiased approach identified histones H3 and H4 as inhibitory factors. Addition of exogenous H3/H4 tetramers to the extract increased the threshold concentration of DNA required for transcriptional activation. Non-specific removal of endogenous histones reduced the threshold DNA concentration required for transcription, and the addition of histone H3/H4 tetramers was sufficient to restore the threshold in depleted extracts. Finally, reduction of H3 protein in embryos induced a premature MBT. Our observations support a model for MBT regulation by a maternally loaded titratable factor and provide an identity for this long-sought molecule. More broadly, our work demonstrates how a constant concentration DNA binding molecule can be used to measure the amount of cytoplasm per genome, a surrogate for cell size.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Copyright date | 2014 |
| Publication date | 2013, c2014; 2013 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Amodeo, Amanda A |
|---|---|
| Associated with | Stanford University, Department of Biology. |
| Primary advisor | Skotheim, Jan, 1977- |
| Thesis advisor | Skotheim, Jan, 1977- |
| Thesis advisor | Simon, Michael, (Biology professor) |
| Thesis advisor | Stearns, Tim |
| Advisor | Simon, Michael, (Biology professor) |
| Advisor | Stearns, Tim |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Amanda A. Amodeo. |
|---|---|
| Note | Submitted to the Department of Biology. |
| Thesis | Ph.D. Stanford University 2014 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Amanda Anne Amodeo
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