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Limb development: how Drosophila genetics can be used to understand pattern formation

Published on September 29, 2008 Reviewed on May 31, 2018   30 min

A selection of talks on Genetics & Epigenetics

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0:00
Hi, I'd like to talk about limb development in drosophila with a particular emphasis on how drosophila genetics can be used to understand hedgehog signaling and pattern formation.
0:13
The embryonic development of higher organisms is precisely controlled. Body plans are impressively reproducible and they're stored to a large extent in the genome. For example, if you look at identical twins, which inherit the same set of chromosomes, you can witness how many details are written down in these plans and how carefully these plans are executed. But how does the development of a multicellular organism occur, such that animals that receive the identical genome also end up looking the same like Dolly the first cloned mammal that strikingly resembled her mother?
0:52
Pattern formation in animals is controlled by cell to cell signaling, cells communicate with each other during development by extracellular signals. Certain cells, for example, release signals that serve other cells to determine their position within a tissue. The information specified by such signals has been referred to as positional information.
1:17
The concept of positional information is around already for an entire century. It is based mainly on embryological evidence, such as transplantation experiments only relatively late in the 20th century. Also, genetic experiments supported the concept of positional information. Two classical experiments representative for many others are illustrated on this slide. An embryology experiment by Saunders revealed in the 1960s that there is a source of positional information in the posterior region of the developing chick limb bud. These cells referred to as ZPA, zone of polarizing activity are able to specify a precise anteroposterior digit pattern, if transplanted to an ectopic site in a host embryo. A representative example of a genetic approach is illustrated below. This drosophila embryo from the Nusslein-Volhard Wieschaus screen has lost a great deal of positional information in the patterning process that normally leads to the specification of precisely spaced and patterned denticle belts on the ventral side. The loss of a single gene here is responsible for the collapse of this patterning process. This gene has been termed hedgehog due to the hedgehog like appearance of these mutant embryos. Nobody would have guessed at the time that these two activities conferring positional information in vertebrate limbs above and in an insect embryo below represent one and the same secreted signaling molecule.

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Limb development: how Drosophila genetics can be used to understand pattern formation

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