Limbs: a pattern emerges

Article Abstract:

In a developing embryo, all limbs are constructed from the same set of cells; however, the factors which determine whether these cells become an arm or a leg and whether they are positioned in the front or back have remained a mystery. Recent studies indicate that the positioning of a limb is dependent on activation of a group of genes called the homoeotic selector gene complex (HOM). Studies in the mouse show that activation of the HOM genes, Hox-2 and Hox-5, may be involved in determining whether cells will be in the head or tail. Additionally, cells farthest away from the body (fingertips) and on the back surface of a limb activate the Hox-5 gene first and as the limb grows, the cells move farther away from this region and become inactivated. Thus, in the developing limb there is a zone of rapid growth and as the cells move farther away from this region, their growth decreases and their position becomes determined. This pattern has been found to occur in both insects and animals. Chemical signals called morphogens determine whether a cell becomes a thumb or a little finger. A high dose of morphogen is thought to produce a little finger whereas a low dose would produce a thumb. It is thought that retinoic acid might activate the Hox-5 gene. In spite of these suggestive observations, there is still no proof that Hox-5 activation controls the positioning of a limb. Such knowledge would have drastic implications in the treatment of amputees. (Consumer Summary produced by Reliance Medical Information, Inc.)

Medical examination, Morphogenesis, Embryology, Animal embryology

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Actin cables and epidermal movement in embryonic wound healing

Article Abstract:

The epidermis closes over lesions inflicted on a chick embryo, migrating not by lamellipodia as in adult wounds, but by another mechanism. A cable of filamentous actin, residing in a single layer of basal cells at the exposed edge of the epidermis, circumscribes the margin of the wound. This cable then contracts, drawing the epidermis together under tension. The tension in the cable may be positively reinforced by intracellular chemical signals.

Physiological aspects, Embryology, Experimental, Embryological research, Wound healing, Epidermis

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Giving limbs a hand

Article Abstract:

Researchers have described dHAND, a gene that plays an important part in early limb development.

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