Slippery slopes: understanding gradients and asymmetries in development

The joint meeting of the Society for Developmental Biology and the Inter- national Society of Developmental Biologists gave a rich look at the cur- rer,t state of developmental biology*. Wi~.h approximately one thousand par- ticipants and a huge diversity of talks and posters of very high quality, it is difficult to do anything here but skim the surface of the interesting work presented (see Box 1 ). This review will focus therefore primarily on one broad theme of the meetiqg - the impor- tance of asymmetries in development. Understanding how asymmetries are established, maintained and read out is a central subject in developmental biology. Asymmetries are essential at the levels of the unicellular organism (for example to compartmentalize cel- lular processes and mediate asymmet- ric cell division), of the single cell in multicellular organisms (for example to maintain stem cells ~and apical-basal polarity in epithelia) and of the whole organism (in orienting the basic body axes and defining organ primordia).