On the wing
The location of a signal molecule called Dpp controls how fruit fly wings develop.
From the wings of a butterfly to the fingers of a human hand, living tissues often have complex and intricate patterns. Developmental biologists have long been fascinated by the signals — called morphogens — that guide how these kinds of pattern develop. Morphogens are substances that are produced by groups of cells and spread to the rest of the tissue to form a gradient. Depending on where they sit along this gradient, cells in the tissue activate different sets of genes, and the resulting pattern of gene activity ultimately defines the position of the different parts of the tissue.
Decades worth of studies into how limbs develop in animals from mice to fruit flies have revealed common principles of morphogen gradients that regulate the development of tissue patterns. Morphogens have been shown to help regulate the growth of tissues in a number of different animals as well. However, how the morphogens regulate tissue size and what role their gradients play in this process remain topics of intense debate in the field of developmental biology.
In the developing wing of a fruit fly, a morphogen called Dpp is expressed in a thin stripe located in the centre and spreads to the rest of the tissue to form a gradient. Shinya Matsuda and Marcus Affolter have now characterized where and when the Dpp morphogen must be produced to regulate both the final size of the fly’s wing and the number of cells the wing eventually contains. The experiments involved preventing the production of Dpp in the developing wing in specific cells and at specific stages of development. This approach confirmed that Dpp must be produced in the central stripe for the wing to grow. Pablo Bosch, Ruta Ziukaite, Cyrille Alexandre and colleagues and, independently, Lara Barrio and Marco Milán report the same findings in two related studies, and also conclude that the gradient of Dpp throughout the wing is not required for growth.
Further work will be needed to explain how the Dpp signal regulates the growth of the wing. The answer to this question will contribute to a better understanding of the role of morphogens in regulating the size of human organs and how a failure to do so might cause developmental disorders.
To find out more
Read the eLife research papers on which this eLife digest is based: Dpp controls growth and patterning in Drosophila wing precursors through distinct modes of action, Boundary Dpp promotes growth of medial and lateral regions of the Drosophila wing and Dpp from the anterior stripe of cells is crucial for the growth of the Drosophila wing disc (Jul 4, 2017).