Chicken lens crystallin DNA sequences show at least two delta-crystallin genes

Restriction analysis of chicken DNA using probes derived from a cloned cDNA and analysis of cloned genomic DNA fragments containing delta-crystallin gene sequences have indicated the presence of at least two non-allelic genes for delta-crystallin, the first and principal crystallin synthesised in the embryonic chicken lens. Electron microscopic analyses of three cloned genomic fragments revealed that the delta-crystallin mRNA gene sequences are interrupted at least 14 times in one of the delta-crystallin genes.

Developmental changes in proteins of purified membranes of chicken lenses and evidence for contamination by cytoplasmic delta-crystallin

Urea-washed membranes from embryonic chick lenses (15 days old) and from the cortical and nuclear regions of adult chicken lenses (1 year) have been prepared by repeated centrifugation through discontinuous density gradients. The protein components of the isolated membranes have been examined by electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate and urea. Proteins with molecular weights of 75 000, 56 000, 54 000, 48 000, 34 000, 32 000, 25 000, and 22 000 were present in all the membrane preparations, although their proportions changed during development. One additional protein, molecular weight 70 000, was seen only in the embryonic lens membranes. The greatest developmental change was the increase in 25 000 molecular weight protein from 12% in the embryonic lens to about 45% in the adult lens. Since it has been suggested that this protein is associated with gap junctions, its increase during development may reflect a corresponding increase in the number of gap junctions in the lens. The 50 000 molecular weight protein of embryonic lens membranes and membranes of adult nuclear lens fibers consisted at least partly of delta-crystallin, since delta-crystallin peptides could be identified in tryptic peptide maps of the isolated protein after in vitro radioiodination. Peptide maps of the 50 000 molecular weight protein of cortical lens fiber membranes contained no identifiable delta-crystallin peptides, although it is possible that modified delta-crystallin peptides may be present. The level of cytoplasmic contamination of the membrane fraction was estimated by preparing lens membranes in the presence of added delta-[35S]crystallin. The results indicated that cytoplasmic contamination contributes significantly to the presence of delta-crystallin in lens membrane preparations.

Molecular cloning and partial characterization of delta-crystallin cDNA sequences in a bacterial plasmid

Double-stranded cDNA synthesized from delta-crystallin mRNA isolated from lens fiber cells of 15-day-old embryonic chicken was cloned in Escherichia coli chi 1776 in the Pst I site of the plasmid pBR322 by using the oligo(dC) . oligo(dG) joining procedure. Twelve Amps Tetr transformants contained sequences complementary to purified delta-crystallin [32P]cDNA. One of the recombinant clones (p delta Cr-2) had an insert of 1241 +/- 240 base pairs, as judged by R-looping analysis with purified delta-crystallin mRNA. The inserted cDNA represents at least 69% of the delta-crystallin coding sequences. p delta Cr-2 was further characterized by restriction analysis, protection of delta-crystallin [3H]cDNA from digestion by S1 nuclease, and hybrid-mediated arrest of delta-crystallin mRNA translation in vitro. p delta Cr-2 provides an invaluable probe for additional analysis of the primary structure, gene organization, and regulated synthesis of delta-crystallin, the principal protein synthesized during lens differentiation in the chicken embryo.

Heterogeneity of delta-crystallins of the embryonic mallard lens. Correlation between subunit compositions and isoelectric points

delta-Crystallins from the lenses of embryonic mallards (Anas platyrhynchos) were analyzed with respect to native and subunit molecular weight, subunit composition, and isoelectric point. NaDodSO4-urea-polyacrylamide gel electrophoresis showed that unfractionated mallard delta-crystallins are composed of approximately equal amounts of subunits with molecular weights near 47 000 and 48 000. Agarose gel chromatography showed that the embryonic mallard delta-crystallins have native molecular weights slightly less than 200 000. Thus, embryonic mallard delta-crystallins appear to be tetramers. Five major and nine minor delta-crystallins were resolved by isoelectric focusing. The five predominant delta-crystallins each cross-reacted with antichick delta-crystallin antiserum, and each had a different proportion of the larger and smaller subunits, indicating a direct relationship between the isoelectric point and the subunit composition. The presence of numerous, minor species of native delta-crystallins with different isoelectric points suggested that the subunits possess charge heteogeneity as well as size heterogeneity.

Differential metabolism and leakage of protein in an inherited cataract and a normal lens cultured with ouabain

Ocular lenses in Nakano mice showed marked changes in synthesis, degradation and leakage of protein during cataractogenesis. The cataract-associated changes included the differential lowering of crystallin synthesis, the cleavage of crystallin polypeptides to lower molecular weight forms and the leakage of crystallins from cultured lenses. Ouabain treatment of normal lenses induced these alterations, suggesting that changes in the intracellular levels of Na+ and K+ affect the anabolism and catabolism of protein during cataract formation.

Regulation of protein synthesis, intracellular electrolytes and cataract formation in vitro

Control of protein synthesis is associated with changes in the ratio of intracellular Na+ to K+ in the cultured embryonic chick lens. Correlations of intracellular Na+/K+ ratios with crystallin synthesis and cataract formation in vitro suggest that the Na+/K+ ratio may have an important role in the regulation of protein synthesis during cataractogenesis.

Lens cataract formation and reversible alteration in crystallin synthesis in cultured lenses

Embryonic chick lenses developed cortical cataracts and altered their pattern of delta-crystallin synthesis within 3 hours, if cultured without their vitreous body or traumatized with their vitreous body attached. delta-Crystallin reverted to the normal pattern by 24 hours in the cataractous lenses. Thus, biochemical differences that are only observable during the initial stages of cataractogenesis can exist between opaque and normal lenses.

Partial dissociation and renaturation of embryonic chick delta-crystallin. Characterization by ultracentrifugation and circular dichroism

1. delta-Crystallin from 15-day-old embryonic chick lenses was characterized by circular dichrosim (CD) spectroscopy. Examination by CD spectroscopy in the far ultraviolet (190-250 nm) demonstrated that the secondary structure of delta-crystallin has at least 75% alpha-helix; the delta-crystallin subunits dissociated in sodium dodecyl sulfate retain their alpha-helical content. This appreciable alpha-helical content of delta-crystallin contrasts with the absence of alpha-helix in other lens crystallins. 2. As judged by CD spectroscopy in the near ultraviolet (250-320 nm) the tertiary structure of embryonic delta-crystallin is not readily disrupted by environmental changes, such as NaCl, KSCN or the non-ionic detergent Emulphogene BC 720, and is stable to temperature fluctuation between 2 and 56 degrees C. 3. Experiments were directed towards deaggregation and renaturation of the four subunits of embryonic delta-crystallin by treatment with urea or guanidine hydrochloride. The native tertiary structure of delta-crystallin was lost above 4 M urea or 2 M guanidine hydrochloride, as judged by CD spectroscopy in the near ultraviolet. Ultracentrifugation at sedimentation equilibrium showed that in 4 M urea delta-crystallin dissociates into dimeric subunits, while in 2 M guanidine hydrochloride delta-crystallin exists as a mixture of dimeric and tetrameric subunits. Dialysis of delta-crystallin from 4 M urea resulted in reaggregation of the subunits into tetramers, about 50% of which showed native tertiary structure. Dialysis from 2 M guanidine hydrochloride also resulted in tetramer formation, and about 35% was recovered with native conformation. Removal of denaturant by dialysis produced no native teritary structure after treatment with 8 M urea, but about 15% native conformation after treatment with 6 M guanidine hydrochloride.

Quantitation of delta-crystallin messenger RNA during lens induction in chick embryos

Embryonic chick cells of the presumptive lens ectoderm are induced to differentiate into a lens by the optic vesicle, an outgrowth from the developing brain. This lens induction involves formation of the lens placode by cell elongation between about 44 and 50 hr of development, followed by invagination of the placode between about 50 and 55 hr of development. The amount of delta-crystallin messenger RNA (mRNA) in heads of embryos between 48 and 72 hr of development was determined by molecular hybridization with [3H]DNA complementary to purified delta-crystallin mRNA. An average of approximately 0.5 pg of delta-crystallin mRNA was found per embryonic head at 48 hr of development. This leads to approximately 265 molecules of delta-crystallin mRNA per lens cell, if one assumes that the mRNA is confined to the lens rudiment, as is indicated by immunofluorescence studies of delta-crystallin performed by other investigators. Pulse-labeling experiments with [35S]methionine indicated that the delta-crystallin mRNA is being translated already at this time. delta-Crystallin mRNA accumulated at an average rate of 1 molecule per cell per minute between 48 and 72 hr of development. Thus, by extrapolation, the initiation of delta-crystallin mRNA accumulation coincides with the initiation of lens placode formation at approximately 43-44 hr of development, which is some 8-9 hr after the initiation of lens induction by the optic vesicle. These data suggest that delta-crystallin synthesis is regulated by the accumulation of delta-crystallin mRNA during lens induction in chick embryos.

Subunit composition of delta-crystallin from embryonic chick lens. Analysis of methionine-containing tryptic peptides and cyanogen bromide peptides

The predominant protein in the embryonic chick lens, delta-crystallin, is composed of four subunits with molecular weights near 50,000. The degree to which these 4 polypeptides are the same or dissimilar was explored in delta crystallin purified from 15-day-old embryonic chick lenses by relating the numbers of methionine-containing tryptic peptides and cyanogen bromide (CNBr) peptides derived from the native protein to the average number of methionine residues per subunit. Amino acid analyses indicated that 1 mol of native delta-crystallin contains approximately 32 methionine residues, leading to an average of 8 methionine residues per subunit. Approximately equal amounts of 8 methionine-containing tryptic peptides were resolved by two-dimensional thin layer separation on cellulose sheets and by isoelectric focusing in polyacrylamide gels. Nine CNBr peptides were resolved by a combination of electrophoresis in sodium dodecyl sulfate (SDS)-polyacrylamide gels and chromatography on SDS-hydroxylapatite columns. The additive molecular weight of the 9 CNBr peptides was very close to the delta-crystallin subunit molecular weight of 50,000. Thus, the subunits of 15-day-old embryonic chick delta-crystallin have similar sequence of encoded amino acids.

Reiteration frequency of delta-crystallin DNA in lens and non-lens tissues of chick embryos. delta-Crystallin gene is not amplified during lens cell differentiation

The differentiation of embryonic chick lens fibers is characterized by an increased rate of synthesis of the lens protein, delta-crystallin, and accumulation of delta-crystallin mRNA. In the present study, the number of delta-crystallin genes in lens and non-lens tissues of embryonic chicks has been determined to test whether the accumulation of delta-crystallin mRNA during lens fiber differentiation is associated with an amplification of delta-crystallin genes. DNA from embryonic chick lens fibers, embryonic chick lens epithelia, or whole chick embryos with the eyes removed, was annealed with [3H]DNA complementary to delta-crystallin mRNA. Analysis of the annealing reactions indicated that the sequences for delta-crystallin are in the unique fraction of the chick genome, and are not amplified in the lens during embryonic development.