XENOPUS GAMMA-CRYSTALLIN GENE-EXPRESSION - EVIDENCE THAT THE GAMMA-CRYSTALLIN GENE FAMILY IS TRANSCRIBED IN LENS AND NONLENS TISSUES

Crystallins, the major gene products of the lens, accumulate to high l evels during the differentiation of the vertebrate lens. Although crys tallins were traditionally thought to be lens specific, it has recentl y been shown that some are also expressed at very low levels in nonlen s tissues. We have examined the embryonic expression pattern of gamma- crystallins, the most abundant crystallins of the embryonic lens in Xe nopus laevis. The expression profile of five Xenopus gamma-crystallin genes mirrors the pattern of lens differentiation in X. laevis, exhibi ting on average a 100-fold increase between tailbud and tadpole stages . Four of these genes are also ubiquitously expressed outside the lens at a very low level, the first demonstration of nonlens expression of any gamma-crystallin gene; expression of the remaining gene was not d etected outside the head region, thus suggesting that there may be two classes of gamma-crystallin genes in X. laevis. Predictions regarding control mechanisms responsible for this dual mode of expression are d iscussed. This study raises the question of whether any crystallin, on stringent examination, will be found exclusively in the lens.