Down the road to skin ....Down the road to skin . . . Among the first genes to "turn on' in development, the most active are several that encode proteins making up the filaments that give structure to skin, report Thomas Sargent, Igor Dawid and colleagues at NICHD NICHD National Institute of Child Health and Human Development. . "These keratin keratin (kĕr`ətĭn), any one of a class of fibrous protein molecules that serve as structural units for various living tissues. The keratins are the major protein components of hair, wool, nails, horn, hoofs, and the quills of feathers. genes are the earliest tissue-specific gene expressed in Xenopus,' says Sargent. "And skin is the first organ to differentiate.' Because these early keratin genes are expressed even in dissociated dis·so·ci·ate v. dis·so·ci·at·ed, dis·so·ci·at·ing, dis·so·ci·ates v.tr. 1. To remove from association; separate: embryonic cells, they are not triggered by contact with other cells. Instead, the major means of differentiation seems to be suppression of gene activity. These keratin genes are turned off in the areas that develop into neural tissue, Sargent reports. In addition, they are inactivated inactivated rendered inactive; the activity is destroyed. inactivated viruses treated so that they are no longer able to produce evidence of growth or damaging effect on tissue. by experimentally introduced contact with certain other embryonic cells. But even in the cells that become skin, by the time a tadpole develops into a frog, other genes take over their role. "No gene first turned on in the blastula blastula /blas·tu·la/ (blas´tu-lah) pl. blas´tulae [L.] the usually spherical structure produced by cleavage of a zygote, consisting of a single layer of cells (blastoderm) surrounding a fluid-filled cavity (blastocoele). . . . is also expressed in the adult,' Sargent says. |
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