F-BAR proteins form crescent-shaped dimers that link actin dynamics and membrane remodelling. Despite this crucial function, however, recent single-knockout studies indicate that many F-BAR proteins are not essential for development, suggesting redundant or cooperative functions in vivo. On page 499, Sven Bogdan and colleagues present a functional analysis of nostrin, an uncharacterised Drosophila melanogaster F-BAR protein that is related to Cdc42-interacting protein 4 (Cip4). The authors' genetic analyses show strong synergistic functions between nostrin and cip4. Single mutant flies had no obvious phenotype, but loss of both nostrin and cip4 gene functions resulted in reduced fertility and viability. Furthermore, double-mutant escaper flies had increased wing epithelium polarisation defects, and egg chambers showed strong encapsulation defects owing to impaired turnover of E-cadherin at the membrane. Interestingly, Cip4 and Nostrin prefer similar membrane curvatures in vitro, but assemble different forms of membrane-bound coats and do not heterooligomerise. The authors, therefore, propose a cooperative, non-redundant function for Cip4 and Nostrin in the regulation of membrane dynamics in Drosophila epithelial morphogenesis.