Tests of hypotheses and parameters for zebrafish cleavage patterns.

(A) 4-cell stage zebrafish embryo expressing the MT marker ensconsin-GFP, fixed and labeled for actin and DNA, and imaged parallel to the A-V axis. Yolk granules fluoresce in the actin channel, and appear to exclude MTs. Scale bar: 50 μm, 10 μm (inset). (B and C) Predictions of the model, under the hypothesis that MT forces orienting the division axis arise from sites of cell-cell adhesion. Pulling interfaces (arrows) are depicted in darker blue. (D) The predicted cell division orientation lineage under this hypothesis. Note the absence of orientation switch at the 5^th Cleavage.