Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 2012 | Published + Supplemental Material
Journal Article Open

Pulsed Feedback Defers Cellular Differentiation

Abstract

Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable "polyphasic" positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a "timer" that operates over timescales much longer than a cell cycle.

Additional Information

© 2012 Levine et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Received July 8, 2011; Accepted December 19, 2011; Published January 31, 2012. This work was supported by US NIH grant R01GM079771, NSF grant 0644463, and the Packard Foundation. JL was supported in part by a Rosen Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. We thank Shaunak Sen, Avigdor Eldar, Jon Young, James Locke, and Jordi Garcia-Ojalvo for help and critical feedback during the course of this work, and members of the Elowitz Lab for general discussions. We also thank the Burkholder, Fujita, Grossman, Hoch, Lazazzera, Losick, and Rudner labs for the generous gift of B. subtilis strains. Author Contributions: The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: JHL MBE JD. Performed the experiments: JHL MEF. Analyzed the data: JHL MBE. Contributed reagents/materials/analysis tools: JHL MEF MBE. Wrote the paper: JHL MBE.

Attached Files

Published - Levine2012p17380Plos_Biol.pdf

Supplemental Material - journal.pbio.1001252.s001.pdf

Supplemental Material - journal.pbio.1001252.s002.pdf

Supplemental Material - journal.pbio.1001252.s003.pdf

Supplemental Material - journal.pbio.1001252.s004.pdf

Supplemental Material - journal.pbio.1001252.s005.pdf

Supplemental Material - journal.pbio.1001252.s006.pdf

Supplemental Material - journal.pbio.1001252.s007.pdf

Supplemental Material - journal.pbio.1001252.s008.pdf

Supplemental Material - journal.pbio.1001252.s009.pdf

Supplemental Material - journal.pbio.1001252.s010.pdf

Supplemental Material - journal.pbio.1001252.s011.pdf

Supplemental Material - journal.pbio.1001252.s012.pdf

Supplemental Material - journal.pbio.1001252.s013.pdf

Supplemental Material - journal.pbio.1001252.s014.doc

Files

journal.pbio.1001252.s012.pdf
Files (2.8 MB)
Name Size Download all
md5:7a64205da55cb775b61546c8b3b4b4b0
118.5 kB Preview Download
md5:d1c6af31a49b37b50953a429b77ff833
113.6 kB Preview Download
md5:8b9f44289e1e3699cd7268f7f308775e
370.7 kB Download
md5:be712b49bfca5d7ba20c9aaffdfc75e2
62.9 kB Preview Download
md5:126b7a4cf82977671ed051fa836ff71d
251.0 kB Preview Download
md5:036fb7265b2dc751b8423a003753c9bf
136.7 kB Preview Download
md5:61edaf6687f98cc6cc786473afaf0b44
108.4 kB Preview Download
md5:3d6e9a988036f900f821c7906ceac61e
65.1 kB Preview Download
md5:4f0cbe11beb1f89c18953f87cb0621b6
132.4 kB Preview Download
md5:2f4f3d685890dd2541f7bea3cdd67f99
866.7 kB Preview Download
md5:dbf3c81cac7ffd2a151f0e973991b1d3
64.9 kB Preview Download
md5:b39228e607b27cd2cb9c2baa5db5a768
114.8 kB Preview Download
md5:45e7e1cf3b642394f3f8319ef0a3794e
90.9 kB Preview Download
md5:49b8a5e88bbe1bdf7b88a0ff40734bda
120.5 kB Preview Download
md5:8503b841ddc2bbf266446c15ef8c32d7
201.3 kB Preview Download

Additional details

Created:
August 19, 2023
Modified:
October 24, 2023