Differential expression of the two delta-crystallin/argininosuccinate lyase genes in lens, heart, and brain of chicken embryos.
Chicken delta-crystallin/argininosuccinate lyase (ASL), a major enzyme-crystallin of the embryonic lens, is encoded by two similar, tandemly arranged genes (delta 1 and delta 2). We show here by the polymerase chain reaction (PCR) and in situ hybridization that although the amount of mRNA for each of the delta-crystallins increases in the lens epithelial and fiber cells during development of the embryonic chicken, the delta 1 mRNA accumulates preferentially in the fiber cells. The delta 1/delta 2 mRNA ratio actually decreased from 16.5 +/- 7 to 6.5 +/- 1 in the central epithelial cells while it increased from 20 +/- 10 to 95 +/- 5 in the fibers between 6 and 14 days of development. By contrast, the heart and brain of 4- to 8-day-old embryonic chickens showed 10(3) to 10(4) times less delta-crystallin mRNA per microgram of total RNA than the lens, with a delta 1/delta 2 mRNA ratio of only 0.20 to 0.30. The tissue-specific differences in the relative expression of the two delta-crystallin genes suggest that the delta 2 polypeptide is principally responsible for ASL activity and that the delta 1 polypeptide is specialized for lens transparency. The trace amounts of delta 1 mRNA in the heart and brain raise the possibility that the delta 1 polypeptide contributes to or modulates ASL activity of the native tetrameric protein. Transfection experiments in which we used the pSVOCAT plasmid demonstrated that both delta-crystallin genes contain an enhancer in their third intron. The promoter and enhancer of each delta-crystallin gene were functionally comparable in the pSVOCAT plasmid when tested in primary embryonic lens epithelial cells, suggesting that the differential expression of the two delta-crystallin genes in the lens requires additional cis-regulatory sequences, post-transcriptional mechanisms, or both.
Thomas
G
G
Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892.
Zelenka
P S
PS
Cuthbertson
R A
RA
Norman
B L
BL
Piatigorsky
J
J
D000818:Animals; D001123:Argininosuccinate Lyase / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D001921:Brain / Q000196:embryology / Q000378:metabolism*; D002642:Chick Embryo; D003459:Crystallins / Q000096:biosynthesis / Q000235:genetics*; D005796:Genes; D005807:Genes, Overlapping; D006321:Heart / Q000196:embryology; D007908:Lens, Crystalline / Q000196:embryology / Q000378:metabolism*; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D012689:Sequence Homology, Nucleic Acid
D003459:Crystallins; D012333:RNA, Messenger; D001123:Argininosuccinate Lyase