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Axis Specification in Zebrafish Is Robust to Cell Mixing and Reveals a Regulation of Pattern Formation by Morphogenesis.

Current biology : CB (2020-06-20)
Timothy Fulton, Vikas Trivedi, Andrea Attardi, Kerim Anlas, Chaitanya Dingare, Alfonso Martinez Arias, Benjamin Steventon
ABSTRACT

A fundamental question in developmental biology is how the early embryo establishes the spatial coordinate system that is later important for the organization of the embryonic body plan. Although we know a lot about the signaling and gene-regulatory networks required for this process, much less is understood about how these can operate to pattern tissues in the context of the extensive cell movements that drive gastrulation. In zebrafish, germ layer specification depends on the inheritance of maternal mRNAs [1-3], cortical rotation to generate a dorsal pole of β-catenin activity [4-8], and the release of Nodal signals from the yolk syncytial layer (YSL) [9-12]. To determine whether germ layer specification is robust to altered cell-to-cell positioning, we separated embryonic cells from the yolk and allowed them to develop as spherical aggregates. These aggregates break symmetry autonomously to form elongated structures with an anterior-posterior pattern. Both forced reaggregation and endogenous cell mixing reveals how robust early axis specification is to spatial disruption of maternal pre-patterning. During these movements, a pole of Nodal signaling emerges that is required for explant elongation via the planar cell polarity (PCP) pathway. Blocking of PCP-dependent elongation disrupts the shaping of opposing poles of BMP and Wnt/TCF activity and the anterior-posterior patterning of neural tissue. These results lead us to suggest that embryo elongation plays a causal role in timing the exposure of cells to changes in BMP and Wnt signal activity during zebrafish gastrulation. VIDEO ABSTRACT.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Penicillin-Streptomycin, Solution stabilized, with 10,000 units penicillin and 10 mg streptomycin/mL, 0.1 μm filtered, BioReagent, suitable for cell culture
Sigma-Aldrich
Fluorescein isothiocyanate–dextran, average mol wt 70,000, (FITC:Glucose = 1:250)
Sigma-Aldrich
(−)-Blebbistatin, solid, synthetic
Sigma-Aldrich
Monoclonal Anti-β-Catenin antibody produced in mouse, clone 15B8, ascites fluid