To understand development, we need to understand the genetic interactions that transform a fertilized oocyte into a multicellular organism with distinct and specialized tissue types and organs. Although we understand something about the complexities of early embryogenesis, we know relatively little about later embryonic events, most notably organ formation, because they are less amenable to genetic and embryological analysis. Fortunately, however, advances in genetics techniques are helping researchers to overcome this obstacle. This special issue celebrates their recent achievements with a collection of articles on different aspects of organogenesis. What emerges from each article is that, by studying individual organs, we can learn about the principles that govern organogenesis. So, from Kenneth Zaret, we learn how transcriptional control sets cell-fate choices in early liver formation. Helena Edlund discusses stem-cell specification in pancreatic development and draws our attention to the importance of carefully choosing cell-type markers to define cell populations. The need to integrate developmental signals in organogenesis is illustrated by Richard Harvey in his discussion of heart development. During organogenesis, migration, induction, patterning and morphogenesis all need to be combined to produce a “pattern of patterns”. Seppo Vainio and Yanfeng Lin show that the kidney is an ideal model organ to investigate branching morphogenesis. And Brigid Hogan and Peter Kolodziej discuss a related issue — strategies and evolution of tube formation — a process that accompanies organogenesis in all organisms.
These reviews are accompanied by highlights on related topics, including one on recent data on male gonadogenesis. They are also available, together with related articles previously published by us and other Nature Publishing Group journals, in a Web Focus at http://www.nature.com/nrg/focus/organogen
