Specification of the meso-isthmo-cerebellar region: the Otx2/Gbx2 boundary.

The midbrain/hindbrain (MH) territory containing the mesencephalic and isthmocerebellar primordial is characterized by the expression of several families of regulatory genes including transcription factors (Otx, Gbx, En, and Pax) and signaling molecules (Fgf and Wnt). At earlier stages of avian neural tube, those genes present a dynamic expression pattern and only at HH18-20 onwards, when the mesencephalic/metencephalic constriction is coincident with the Otx2/Gbx2 boundary, their expression domains become more defined. This review summarizes experimental data concerning the genetic mechanisms involved in the specification of the midbrain/hindbrain territory emphasizing the chick/quail chimeric experiments leading to the discovery of a secondary isthmic organizer.

Morphogenetic and cellular movements that shape the mouse cerebellum; insights from genetic fate mapping.

We used the cerebellum as a model to study the morphogenetic and cellular processes underlying the formation of elaborate brain structures from a simple neural tube, using an inducible genetic fate mapping approach in mouse. We demonstrate how a 90 degrees rotation between embryonic days 9 and 12 converts the rostral-caudal axis of dorsal rhombomere 1 into the medial-lateral axis of the wing-like bilateral cerebellar primordium. With the appropriate use of promoters, we marked specific medial-lateral domains of the cerebellar primordium and derived a positional fate map of the murine cerebellum.

Cell behaviors and genetic lineages of the mesencephalon and rhombomere 1.

Brain structures derived from the mesencephalon (mes) and rhombomere 1 (r1) modulate distinct motor and sensory modalities. The precise origin and cellular behaviors underpinning the cytoarchitectural organization of the mes and r1, however, are unknown. Using a novel inducible genetic fate mapping approach in mouse, we determined the fate and lineage relationships of mes/r1 cells with fine temporal and spatial resolution.