Fly centrioles – different after all

In contrast to vertebrate centriole pairs, where the mother and daughter centriole can easily be distinguished from each other by examining their morphology, Drosophila centrioles lack structural differences and can only be recognised by identifying specific protein markers. Here (p. 2437), Marco Gottardo, Giuliano Callaini and Maria Giovanna Riparbelli used electron microscopy to examine mother and daughter centrioles in a range of fly tissues. They found that mature centrioles of somatic cells comprised doublets with a distinct cartwheel structure, whereas differentiating male germ cells had centrioles that comprised triplets. However, no structural differences between the mother and daughter centrioles could be found in any of the tissues examined. By contrast, male germline stem cells (GSCs) contained centrioles that comprised doublets, triplets or a mix thereof. Upon careful examination of the GSC niche, the authors observed that the mother centriole comprised triplets and that the daughter centriole was made up of doublets that matured into triplets. In addition, the authors showed that the mother centriole extended projections to the apical plasma membrane, which could function as an anchor to keep the mother centriole stationary during centrosome separation. This study is the first demonstration of a structural asymmetry between mother and daughter centrioles in Drosophila, which might reflect an unequal distribution of centrosomal proteins, thereby providing important insights into centrosome biology in flies.