Magazine article Science News

Getting from the Egg to the Chicken

Magazine article Science News

Getting from the Egg to the Chicken

Article excerpt

Getting from the egg to the chicken

Every chicken, toad or person starts as a single cell that multiplies and differentiates into spatially organized structures such as digits on a limb. This developmental process remains one of the great unsolved mysteries of biology. Scientists have conjectured that chemicals called morphogens may help orchestrate embryonic development by turning on or off genes in specific sets of cells at different times.

That conjecture got an experimental thumbs-up several years ago when Christina Thaller and Gregor Eichele of the Harvard Medicl School found that retinoic acid -- a member of the "retinoid" class of chemicals, which also includes vitamin A -- induces the finger-like projections, or digits, to sprout from the wing buds of chick embryos. They measured higher amounts of retinoic acid in the posterior portion of the wing, where digits normally develop, than in the anterior part. But they found that a dab of retinoic acid on the front part of the wing bud leads to the growth of an additional, though misplaced, set of well-formed digits there (SN: 6/27/87, p.406).

In the June 28 NATURE, the Boston researchers report evidence for another potential morphogen. They found that the retinoid 3,4-didehydroretinoic acid (ddRA) also induces digit duplication on the wing bud. Moreover, they measured five to six times more ddRA than retinoic acid in the wing buds--a hint that ddRA may be even more important in development. …

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