Fruit fly research turns established dogma on its head

25 December 2013

Drosophila Illustration

Image: Drosophila melanogaster

The fruit fly Drosophila has been used by developmental biologists and geneticists for over a century as a model to study how development is controlled.

Now, research by scientists from the Medical Research Council's National Insitute for Medical Research (NIMR; now part of the Francis Crick Institute) has refuted a widely accepted notion about an important signalling protein that determines patterning and growth during the fly's development.

Dr Jean-Paul Vincent of NIMR explained: "During embryonic development, cells must acquire different fates in a coordinated manner. Certain cells become organisers by producing signals called morphogens that spread to surrounding cells, thus instructing them to grow into particular types of cell and tissue.

"Only a small number of morphogens have been identified. Among them is a class of proteins called Wnts. It has been widely assumed that Wnts need to spread  to control cell fate over large areas of tissues. Wingless, the main Wnt of flies, is normally produced from a stripe of cells across the prospective wing - known as the wing primordia - and has been assumed to spread throughout this tissue to organise the wing pattern."

To investigate this theory, the researchers used genomic engineering to develop fruit flies that still produced the Wingless protein, but in a form that was prevented from spreading by an artificial anchor to the cell membrane.

Unexpectedly, the resultant flies had normally patterned wings of nearly the right size - indicating that Wingless does not need to spread to control cell fate.

"We suggest that when wing primordia are still small, all the cells are either expressing Wingless or in direct contact with Wingless-expressing cells and that this activity suffices to stimulate growth and establish the wing blade fate. Later, signalling from the Wingless stripe locally activates genes required to make a wing margin. Thus two distinct fates can be specified without the need for the signalling protein to spread."

The work also has implications for stem cells - as Wnts also play a role in maintaining their state in stem cell niches.

Dr Vincent added: "Our results will come as a surprise to many, even though previous papers hinting that Wingless is not a morphogen can be found. Our ļ¬nding changes radically our expectation of how Wnts control growth, patterning, regeneration and possibly stem cell niches."

The paper, Patterning and growth control by membrane-tethered Wingless, by Cyrille Alexandre, Alberto Baena-Lopez and Jean-Paul Vincent, is published in Nature.

  • Wingless is the name of a protein that determines patterning and growth of fruit fly wings during larval development. New research has rebutted a widely accepted view about how Wingless operates.
  •  A team at the Medical Research Council's National Institute for Medical Research discovered that rather than sending signals to individual cells by spreading through the wing as it grows, Wingless can determine cell fates very early in development. They suggest that early Wingless signalling causes sustained expression of the relevant genes, which are 'remembered' by cells and their descendents.