Ghost in the machine: The peripodial epithelium

Abstract

A fundamental feature of early animal development is that fate specification and the morphogenesis of one tissue is often induced by signals emanating from a neighboring population of cells. H. Spemann and H. Mangold introduced this concept when they showed that a transplanted blastopore lip of an early gastrulating newt could induce the formation of a full axis after it was transplanted into a second newt species. C.H. Waddington later demonstrated that the process of induction is not restricted to amphibians but rather is a general mechanism that applies broadly to many different organisms including mammals. Extirpation and transplantation studies of the vertebrate eye and lens indicate that these two tissues influence aspects of each other’s development. Likewise, several studies have shown that the development of the developing eye field in Drosophila is influenced by an overlying tissue called the peripodial epithelium. While the vertebrate lens and the peripodial epithelium of the Drosophila eye-antennal disc are non-homologous structures, these two tissues use common elements such as the Pax6 transcription factor and the TGFβ/BMP4 signaling pathway to influence the growth, specification, and patterning of the adjacent retinas. In this chapter, we will describe what is known about the role that the peripodial epithelium plays in the development of the eye-antennal disc of Drosophila.