Developmental timing and cell fate maintenance in Caenorhabditis elegans

The development of a multi-cellular organism begins with a single fertilized egg cell, and ends with a fully-grown adult with all kinds of specialized cell types. During this complex developmental process, cells undergo several important developmental events, such as cell fate differentiation, movement and growth. The correct timing of the occurrence and duration of those developmental events is one of the key challenges during development, in order to prevent malformation of tissues. After cells have reached their terminal cell fate, a new important challenge appears, that is the maintenance of their obtained terminally differentiated state, to prevent loss of their specialized functions. Robust maintenance of terminal cell fate is particularly important in cell types that are hardly renewed during the lifetime of an animal, such as neuronal cells. In this thesis, we focused on these two complementary key challenges, of correct developmental timing and long-term cell fate maintenance, that cells face during their lifetime. With the help of the model system Caenorhabditis elegans, we studied how cell growth is timed by gene expression oscillators during development, and what mechanism lies behind the long-term maintenance of terminal cell fate that is controlled by terminal selector genes.