Tissue interactions in the induction of anterior pituitary: Role of the ventral diencephalon, mesenchyme, and notochord

Rathke's pouch, the epithelial primordium of the anterior pituitary, differ entiates in close topographical and functional association with the ventral diencephalon. It is stilt not known whether the ventral diencephalon acts as the initial inducer of pituitary development. The roles of the adjacent mesenchyme and notochord, two other tissues located in close proximity to R athke's pouch, in this process are even less clear. In this report we descr ibe an in vitro experimental system that reproduces the earliest steps of a nterior pituitary development. We provide evidence that the ventral diencep halon from 2- to 4-day-old chick embryos is able to function as an inducer of pituitary development and can convert early chick embryonic head ectoder m, which is not involved normally in pituitary development, into typical an terior pituitary tissue. This induction is contact-dependent. In our experi mental system, there is a requirement for the supporting action of mesenchy me, which is independent of the mesenchyme source. Transplantation of the n otochord into the lateral head region of a six-somite chick embryo induces an epithelial invagination, suggesting that the notochord induces the outpo uching of the roof of the stomodeal ectoderm that results in formation of R athke's pouch and causes the close contact between this ectoderm and the ve ntral diencephalon. finally, we demonstrate that the ventral diencephalon f rom e9.5-e11.5 mouse embryos is also an efficient inducer of anterior pitui tary differentiation in chick embryonic lateral head ectoderm, suggesting t hat the mechanism of anterior pituitary induction is conserved between mamm als and birds, using the same, or similar, signaling pathways. (C) 1999 Aca demic Press.