Developmental gene expression profile of axon guidance cues in Purkinje cells during cerebellar circuit formation.

The establishment of precise neural circuits during development involves a variety of contact-mediated and secreted guidance molecules that are expressed in a complementary fashion by different cell types. To build a functional circuit, each cell type must first trigger an intrinsic genetic program that is led by their environment at a key time point. It is therefore essential to identify the different cell-specific and stage-specific transcriptional profiles expressed by neurons. However, very few studies have been done to address this issue thus far. Herein, we have carried out a large-scale quantitative real-time PCR analysis of all classical axon guidance molecules (i.e., Semaphorins, Netrins, Ephrins, and Slits) and their receptors expressed by Purkinje cells (PCs) at specific stages of postnatal cerebellar development in vivo. Most cerebellar connections are setup in a well-characterized sequential manner during postnatal development and lead to the fine regulation of the PC, the sole output of the structure. Our analysis of the relative expression of these guidance cues has uncovered a dynamic expression pattern corresponding to specific stages of cerebellar development, thus providing a starting point for studying the role of these axon guidance molecules in cerebellar wiring.