Poodry C A & Schneiderman H A. The ultrastrucrure of the developing leg of Drosophila melanogaster. Roux Arch. Devel. Bird. 166:1-44, 1970

In the 1960s the fruitfly, Drosophila melanogaster, experienced a resurgence as an organism of choice for research in developmental genetics, thanks to the insightful and meticulousprobing of Ernest 1-ladorn and his students. They focused on the development of the imaginal discs found in the body of the larvae. These discs are the primordia of adult (imaginal) structures such as legs or eyes. The culture and bioassay of imaginal disc tissues had revealed principles of determination and regen. eration as well as a puzzling change in the determined state called transdetermination. Genetic and physical mosaics were employed to decipher rules of pattern formation and intercellular communication. We needed to understand the detailed anatomy of imaginal disc tissues to build a conceptual framework to explain the experimental observations. We undertook our study of the uitrastructure of the developing leg imaginal disc to fill that need. The paper has been widely cited mainly for two reasons. It was the first comprehensive and welkiocumented ultrastructural study of an imaginal disc. Thus, it explored a number of aspects of develop. ment, summarized below, that have been carried further by many subsequent studies. Second, its timely appearance provided a bridge between the experimental work and the explanations ofthe underlying cell biology. We reaffirmed that the precursor of the adult integument is a single-layered, secretory epithelium. I say reaffirmed because the same conclusion had been reached in histological studies of similar structures from houseflies and blowflies some 80 years earlier. However, the high resolution of electron microscopy can also lead to a myopic view, and pinneering ultrastructural studieshad depicted the imaginal discs as multilayered. Thisdistinction is important because patterning of a single-layered structure can be viewed as a problem ofordering differentiations in two dimensions rather than three.’ A comparison of the disc through the early stage of metamorphosis (the prepupal period) suggested that morphogenesis is accompanied by and perhaps driven by a change in cell shape from tall columnar to cuboidal. Dianne Fristrom extended this finding to show that cells not only change shape but also undergo a limited rearrangementduring this morphogenesis. 2