Mutant cone cells (purple) that lack N-cadherin show patterning defects.


A century ago, scientists noted a similarity between the patterns that cells and soap bubbles adopt. Now, this nearly forgotten parallel is recalled by Takashi Hayashi and Richard Carthew (Northwestern University, Evanston, IL). Their results show that the same physical mechanism that drives bubbles to coalesce in forms that minimize their total surface area (and thus their surface free energy) also governs cell patterning.

Like bubbles, cone cells in the fly eye assembled in shapes that minimize surface area. Parameters that help specify this minimization include the number of intersection points between cells or bubbles, the number of interfaces that link these points, and the angles between them. Ommatidia containing abnormal numbers of cone cells still retained these minimizing characteristics. But those that lacked cadherins, and thus intercellular adhesion, did not. Presumably the lack of adhesion makes these cells act as independently energy-minimizing units rather than a single unit.

As well as controlling cone cell packing, cadherins and surface mechanics also organize cone cells within an ommatidia. Only cone cells expressed N-cadherin; other ommatidial cell types, such as pigment cells, expressed E-cadherin. Cone cells thus aggregated in the midst of the other cells to minimize contact between cells of different adhesion strengths (N-cadherin adheres more strongly than does E-cadherin). By altering the adhesion differential through misexpressed or mutant cadherins, the authors perturbed the shape of the cone cell group and thus increased its area of contact with other cells.


Hayashi, T., and R.W. Carthew.