Argininosuccinate lyase (ASL)/δ-crystallin
Polymerase chain reaction
Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
Chicken argininosuccinate lyase (ASL)/δ-crystallin, a lens enzyme-crystallin, is encoded in two linked genes (δ1 and δ2); only the δ2 polypeptide contains ASL activity. Here we have quantified δ1- and δ2-crystallin mRNA in the lens, cornea, neural retina, heart, and brain at different stages of embryonic development and in 1-wk-old and 1-yr-old chickens by the polymerase chain reaction using internal δ1 and δ2 RNA standards. The δ1/δ2 mRNA ratio differed for every tissue and was regulated during development. In the embryo there was more δ1 than δ2 mRNA in the lens (50-100 times), cornea (3-4 times), and neural retina (2-20 times), about equal amounts of δ1 and δ2 mRNA in the heart, and more δ2 mRNA in the brain (15 times). δ1-Crystallin mRNA differentially decreased in every tissue after hatching; by contrast, the δ2 mRNA remained about the same except for the lens, where it decreased 50-fold between 1 wk and 1 yr after hatching. In the 1-yr-old chicken, the δ2/δ1 mRNA ratios were 7 in the lens, 175 in the cornea, 22 in the neural retina, 107 in the heart, and 136 in the brain, indicating that δ2-crystallin is strongly favored in all adult tissues of the chicken. The excess of δ1 to δ2 mRNA in the embryonic lens, cornea, and neural retina is intriguing, and suggests some connection with developing transparent eye tissues. Finally, we raise the possibility that expression of both δ-crystallin genes may create tetrameric ASL isoenzymes (perhaps with different specific activities). The unexpected predominance of δ2 mRNA in the 1-yr-old lens suggests that both the enzymatic and refractive functions of ASL/δ-crystallin are operative and spatially separated, with the enzymatic role present in the cortical fibers and the refractive role in the center of the lens. © 1993 wiley-Liss, Inc.
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