It only takes two genes to make the difference between an ordinary embryo and one that develops without a head.
At least, that is the case in the zebrafish, a team of geneticists from Vanderbilt University report in the Dec. 15 issue of the journal Genes & Development. According to the papers senior author, Lilianna Solnica-Krezel, something similar is likely to hold true for mammals and humans. One of these genes has an equivalent in human development; the other one were not sure of, says the assistant professor of biological sciences at Vanderbilt.
This is the latest in a series of recent studies that have begun to unravel the mysteries of development at the molecular level. For hundreds of years scientists have wondered how an early embryo that is made up of identical, undifferentiated cells, can develop into nerves, muscles, lungs and other organs. Answers to this question may lead to new treatments for birth defects and other illnesses caused by defective development.
The picture that is emerging is one of elegant simplicity. The cells in the embryo secrete a protein called bone morphogenetic protein, or BMP. A structure, called the (Spemann) gastrula organizer, forms on the eggs surface in what will become the dorsal, or backside of the animal. The organizer becomes a source of negative regulators of BMPproteins that reduce its production or function. This interaction produces variations in the concentration of BMP in different parts of the embryo, providing instructions that effectively determine top and bottom, left and right, front and back. The cells then use this information to begin differentiating into various types of tissue and to move to appropriate locations within the developing embryo.
Where BMP concentrations are lowest, cells develop into nervous tissue and backbone and where they are highest cells tend to become skin, blood and tail, Solnica-Krezel observes.
(In 1992, Brigid L. M. Hogan, the Hortense B. Ingram Chair in Molecula
Contact: David F. Salisbury