Differential expression of the two delta-crystallin genes in lens and non-lens tissues: shift favoring delta 2 expression from embryonic to adult chickens.
Chicken argininosuccinate lyase (ASL)/delta-crystallin, a lens enzyme-crystallin, is encoded in two linked genes (delta 1 and delta 2); only the delta 2 polypeptide contains ASL activity. Here we have quantified delta 1- and delta 2-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 delta 1 and delta 2 RNA standards. The delta 1/delta 2 mRNA ratio differed for every tissue and was regulated during development. In the embryo there was more delta 1 than delta 2 mRNA in the lens (50-100 times), cornea (3-4 times), and neural retina (2-20 times), about equal amounts of delta 1 and delta 2 mRNA in the heart, and more delta 2 mRNA in the brain (15 times). delta 1-Crystallin mRNA differentially decreased in every tissue after hatching; by contrast, the delta 2 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 delta 2/delta 1 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 delta 2-crystallin is strongly favored in all adult tissues of the chicken. The excess of delta 1 to delta 2 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 delta-crystallin genes may create tetrameric ASL isoenzymes (perhaps with different specific activities). The unexpected predominance of delta 2 mRNA in the 1-yr-old lens suggests that both the enzymatic and refractive functions of ASL/delta-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.
Li
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Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892.
Zelenka
P S
PS
Piatigorsky
J
J
D000375:Aging / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D000818:Animals; D001123:Argininosuccinate Lyase / Q000032:analysis / Q000502:physiology; D001483:Base Sequence; D001921:Brain / Q000196:embryology / Q000378:metabolism; D001923:Brain Chemistry; D002642:Chick Embryo; D002645:Chickens / Q000378:metabolism*; D003315:Cornea / Q000737:chemistry / Q000196:embryology / Q000378:metabolism*; D003459:Crystallins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000032:analysis / Q000235:genetics; D005314:Embryonic and Fetal Development; D015870:Gene Expression / Q000235:genetics*; D005796:Genes / Q000235:genetics; D006321:Heart / Q000196:embryology; D007908:Lens, Crystalline / Q000737:chemistry / Q000196:embryology* / Q000378:metabolism; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012160:Retina / Q000737:chemistry / Q000196:embryology / Q000378:metabolism*
D003459:Crystallins; D012333:RNA, Messenger; D004247:DNA; D001123:Argininosuccinate Lyase