(A) Use of microfabricated PDMS wells for manipulating the shape of sea urchin embryos. Fertilized eggs are placed into wells of different shapes that are designed all to be the volume of an egg. The depth of the chambers (h) is smaller than the egg diameter (d) so that the egg is slightly flattened into its new geometry.

(B) Differential interference contrast (DIC) pictures of eggs in chambers adopting different geometries.

(C) Division-plane positioning in cells with different geometries. Cells of different shapes were introduced into wells and then assayed for division-plane positioning. The “long axis rule” predicts that cells will divide at the center of cell mass at an axis perpendicular to the long axis at this center. The cells in the top row follow this rule, but the cells in the bottom row do not.

(D) Time-lapse sequence of an embryo shaped in a rectangular chamber, from 15 min after fertilization to completion of cytokinesis. DNA was stained with Hoechst. Note the early centering of the zygote nucleus after pronuclei migration and fusion, and the elongation of the interphase nucleus along the future division axis.

(E) The orientation of the interphase nucleus predicts the future spindle axis and division plane in these cells. The relative centering and orientation at metaphase (M), anaphase (A), and cytokinesis (C) relative to interphase (I) are computed as indicated in the figure from time-lapse sequences. Error bars represent standard deviations.