Elsevier

Developmental Biology

Volume 397, Issue 2, 15 January 2015, Pages 248-256
Developmental Biology

Stochasticity and stereotypy in the Ciona notochord

https://doi.org/10.1016/j.ydbio.2014.11.016Get rights and content
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Highlights

  • We developed a new Ciona fate mapping method based on mosaic transgene expression.

  • This was used to extensively quantify the patterns of notochord cell intercalation.

  • Intercalation is not invariant but is far more stereotyped than previously believed.

  • Navigation of individual notochord cells is strongly influenced by neighbors.

  • Distinct cell behaviors are seen between the 1° and 2° notochord lineages.

Abstract

Fate mapping with single cell resolution has typically been confined to embryos with completely stereotyped development. The lineages giving rise to the 40 cells of the Ciona notochord are invariant, but the intercalation of those cells into a single-file column is not. Here we use genetic labeling methods to fate map the Ciona notochord with both high resolution and large sample sizes. We find that the ordering of notochord cells into a single column is not random, but instead shows a distinctive signature characteristic of mediolaterally-biased intercalation. We find that patterns of cell intercalation in the notochord are somewhat stochastic but far more stereotyped than previously believed. Cell behaviors vary by lineage, with the secondary notochord lineage being much more constrained than the primary lineage. Within the primary lineage, patterns of intercalation reflect the geometry of the intercalating tissue. We identify the latest point at which notochord morphogenesis is largely stereotyped, which is shortly before the onset of mediolateral intercalation and immediately after the final cell divisions in the primary lineage. These divisions are consistently oriented along the AP axis. Our results indicate that the interplay between stereotyped and stochastic cell behaviors in morphogenesis can only be assessed by fate mapping experiments that have both cellular resolution and large sample sizes.

Keywords

Ciona
Notochord
Fate map
Intercalation
Stochasticity
Morphogenesis

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