Journal
DEVELOPMENT
Volume 142, Issue 10, Pages 1785-1793Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/dev.119057
Keywords
Two-segment periodicity; Segmentation clock; Zebrafish; In vivo imaging; her1; Somite; Oscillations
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Funding
- Association Francaise contre les Myopathies
- Marie Curie Outgoing International Fellowship
- National Institutes of Health (NIH) [1-R01-GM061952]
- Natural Science and Engineering Research Council of Canada, Discovery Grant program, Fonds de recherche du Quebec - Nature et technologies
- Human Frontier Science Program
- Simons Foundation Investigator Award in the Mathematical Modeling of Living Systems
- NIH Training Grant [GM007127]
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The formation of reiterated somites along the vertebrate body axis is controlled by the segmentation clock, a molecular oscillator expressed within presomitic mesoderm (PSM) cells. Although PSM cells oscillate autonomously, they coordinate with neighboring cells to generate a sweeping wave of cyclic gene expression through the PSM that has a periodicity equal to that of somite formation. The velocity of each wave slows as it moves anteriorly through the PSM, although the dynamics of clock slowing have not been well characterized. Here, we investigate segmentation clock dynamics in the anterior PSM in developing zebrafish embryos using an in vivo clock reporter, her1: her1-venus. The her1: her1-venus reporter has single-cell resolution, allowing us to follow segmentation clock oscillations in individual cells in real-time. By retrospectively tracking oscillations of future somite boundary cells, we find that clock reporter signal increases in anterior PSM cells and that the periodicity of reporter oscillations slows to about similar to 1.5 times the periodicity in posterior PSM cells. This gradual slowing of the clock in the anterior PSM creates peaks of clock expression that are separated at a two-segment periodicity both spatially and temporally, a phenomenon we observe in single cells and in tissue-wide analyses. These results differ from previous predictions that clock oscillations stop or are stabilized in the anterior PSM. Instead, PSM cells oscillate until they incorporate into somites. Our findings suggest that the segmentation clock may signal somite formation using a phase gradient with a two-somite periodicity.
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