Morphogenesis of the lens placode

For over 100 years, the vertebrate eye has been an important model system to understand cell induction, cell shape change, and morphogenesis during development. In the past, most of the studies examined histological changes to detect the presence of induction mechanisms, but the advancement of molecular biology techniques has made exploring the genetic mechanisms behind lens development possible. Despite the particular emphasis given to the induction of the lens placode, there are still many aspects of the cell biology of lens morphogenesis to be explored. Here, we will revisit the classical detailed description of early lens morphological changes, correlating it with the cell biology mechanisms and with the molecules and signaling pathways identified up to now in chick and mouse embryos. A detailed description of lens development stages helps better understand the timeline of the events involved in early lens morphogenesis. We then point to some key questions that are still open. (AU)