The aim of this year's lecture is to examine some of the temporal referents at work during embryonic development in Drosophila flies and mammals. Embryonic development is an accumulation of diverse molecular and cellular mechanisms, all with their own temporalities. Where do these different times come from? How are they coded ? How can the embryo both generate and follow its own time frames ?
These questions will be addressed through a few examples of biological clocks and timers operating during development. The aim is to understand how these molecular clocks can be translated into biological spaces, cellular and tissue arrangements, and how these different times can ultimately organize the spatialities of the embryo.
In this first lesson, the general content and objectives of the lecture are outlined. Then, after a few general definitions of terms and concepts, the question of the differentiation in time of the neuroblasts of the nervous system of the Drosophila embryo is tackled with the original publication of 2001. At the origin of this temporal mechanism lies an asymmetrical mitotic division of a neuroblast that each time produces a daughter cell that will differentiate, and another neuroblast (self-renewing) that will contain a different genetic " address ", carried by a series of transcription factors that are activated by intrinsic regulatory mechanisms following a precise genetic hierarchy (epistasis). This chain of events sets the tempo for neuron production in this embryonic nervous system (the ventral cord).
