Early anterior/posterior patterning of the midbrain and cerebellum

Transplantation studies performed in chicken embryos indicated that early a nterior/posterior patterning of the vertebrate midbrain and cerebellum migh t be regulated by an organizing center at the junction between the midbrain and hindbrain. More than a decade of molecular and genetic studies have sh own that such an organizer is indeed central to development of the midbrain and anterior hindbrain. Furthermore, a complicated molecular network that includes multiple positive and negative feedback loops underlies the establ ishment and refinement of a mid/hindbrain organizer, as well as the subsequ ent function of the organizer. In this review, we first introduce the expre ssion patterns of the genes known to be involved in this patterning process and the quail-chick transplantation experiments that have provided the fou ndation for understanding the genetic pathways regulating mid/hindbrain pat terning. Subsequently, we discuss the molecular genetic studies that have r evealed the roles for many genes in normal early patterning of this region. Finally, some of the remaining questions and future directions are discuss ed.