Molecular weight and subunit structure of delta-crystallin from embryonic chick lens fibers

Simultaneous separation of taxon-specific crystallins from Mule duck and characterization of their enzymatic activities and structures

Methods to obtain pure proteins in large amounts are indispensible in protein research. We report here a large-scale/simultaneous isolation of taxon-specific crystallins (ɛ- and δ-crystallin) from the eye lenses of Mule duck. We also investigate the compositions, enzymatic activities, and structures of these purified taxon-specific proteins. A relatively mild method of ion-exchange chromatography was developed to fractionate ɛ-crystallin and δ-crystallin in large amount, ca. ∼6.60mg/g-lens and ∼41.0mg/g-lens, respectively. Both crystallins were identified by electrophoresis, HPLC, and MALDI-TOF-MS. ɛ-Crystallin, with native composition of M_r 142kDa, consisted of two subunits of 35kDa and 36kDa, while δ-Crystallin, with native molecular mass of 200kDa, comprised single subunit of M_r ∼50kDa. Both ɛ- and δ-crystallin were tetramers. The former showed lactate dehydrogenase (LDH) activity, while the latter appeared slightly active in an argininosuccinate lyase (ASL) assay. Raman spectroscopic results indicated that the secondary structures of ɛ- and δ-crystallin were predominantly α-helix as evidenced by the vibrational stretching of amide III over 1260cm^-1 and amide I at 1255cm^-1, in greatly contrast to the anti-parallel β-sheet of α- and β-crystallin as demonstrated by amide III at 1238cm^-1 and amide I at 1672cm^-1. The microenvironments of aromatic amino acids and the status of thiol groups also vary in different crystallins. The compositions, enzyme activities, and structures of the ɛ- and δ-crystalline of Mule duck are different from those of Muscovy duck (Cairina moschata) or Kaiya duck (Anas Platyrhynchos var. domestica), which reflect faithfully species specificity.

The gradient index lens of the eye: an opto-biological synchrony

The refractive power of a lens is determined largely by its surface curvatures and the refractive index of its medium. These properties can also be used to control the sharpness of focus and hence the image quality. One of the most effective ways of doing this is with a gradient index. Eye lenses of all species, thus far, measured, are gradient index (GRIN) structures. The index gradation is one that increases from the periphery of the lens to its centre but the steepness of the gradient and the magnitudes of the refractive index vary so that the optics of the lens accords with visual demands. The structural proteins, the crystallins, which create the index gradient, also vary from species to species, in type and relative distribution across the tissue. The crystallin classes do not contribute equally to the refractive index, and this may be related to their structure and amino acid content. This article compares GRIN forms in eye lenses of varying species, the relevance of these forms to visual requirements, and the relationship between refractive index and the structural proteins. Consideration is given to the dynamics of a living lens, potential variations in the GRIN form with physiological changes and the possible link between discontinuities in the gradient and growth. Finally, the property of birefringence and the characteristic polarisation patterns seen in highly ordered crystals that have also been observed in specially prepared eye lenses are described and discussed.

Distribution and pattern of water-soluble proteins of lens as revealed by gel filtration chromatography in fish (Catla catla) of different age groups

The water soluble proteins of the lens collected from different age group of the fish Catla catla were subjected to Sephadex G 200 gel filtration to fractionate and to characterize the protein and further to determine the elution volume (Ve) of different fractions. The relative proportion of each fraction was also calculated. Total number of fractions F1 to F4 was discernible through gel filtration. The molecular weight of these varied from 35,000 Da to 640,000 Da. Three subfractions were also noted in F1 fraction. Interesting observations were, presence of alpha, betaH betaL crystallins in all age groups and LMW proteins in older age group. a-crystallin present in major amounts in comparison to betaH & betaL crystallins. Decrease of alpha-crystallins (except in age group II) with the increase of age, counter balanced by the increase of betaH crystallins. Increase of betaH crystallins was followed by the decrease of betaL crystallins. Results suggest that proportionate distribution of different classes of proteins determined by column chromatography is widely variable.

Guanidine hydrochloride induced reversible dissociation and denaturation of duck delta2-crystallin

The tetrameric delta2-crystallin from duck lens exhibits a reversible dissociation-denaturation process in solutions containing guanidine hydrochloride (GdnHCl). Sigmoidal or biphasic curves for the dissociation/denaturation processes, obtained using different methods of structural analysis, as a function of GdnHCl concentration were not coincidental with each other. delta2-crystallin in 0.91 M GdnHCl existed primarily as a monomer, which had no endogenous argininosuccinate lyase activity. After dilution of the GdnHCl-treated protein, the monomers reassociated into tetramers with concomitant recovery of enzyme activity. The sigmoidal recovery of enzyme activity demonstrates a cooperative hysteretic reactivation process. When the concentration of GdnHCl was higher than 1.2 M, various partially unfolded soluble forms of delta2-crystallin were produced from the dissociated monomers as shown by size-exclusion chromatography. The formation of a partially unfolded intermediate during the dissociation-denaturation process is proposed.

Characterization and enzyme activity of argininosuccinate lyase/delta-crystallin of the embryonic duck lens

Argininosuccinate lyase (ASL)/delta-crystallin, a major soluble protein of the transparent eye lens of birds and reptiles, is a mixture of tetramers comprising all possible combinations of two similar polypeptides (delta 1 and delta 2). Only the delta 2 polypeptide has ASL activity. In the present investigation we have purified each of the 5 major isoforms (delta A to delta E, pI 5.2 to 5.8) of delta-crystallin tetramers from the embryonic duck lens by isoelectric focussing and established by peptide sequencing that the delta 1 and delta 2 polypeptides are encoded in the previously identified, linked delta 1 and delta 2 genes, respectively. The relative amounts of the different tetramers in the 14-day-old embryonic lens were consistent with equal expression of the 2 delta-crystallin genes and no preference for assembly of the 2 delta polypeptides. The relative amount of ASL activity of the tetramers was a linear function of the relative amount of their delta 2 polypeptides, with delta A (only delta 1) lacking enzymatic activity altogether. delta B (3 delta 1:1 delta 2), delta C (2 delta 1:2 delta 2), delta D (1 delta 1:3 delta 2) and delta E (4 delta 2) all gave normal Michaelis-Menten kinetics for fumarate production from argininosuccinate at 40 degrees C and had a similar Km (average Km for mixture was 0.15 mM). delta E had a Km of 0.187 mM and a Vmax of 9 mumol/min per mg protein. Unlike bovine and like human ASL, both reported previously, embryonic duck ASL/delta-crystallin showed no evidence of cooperativity or activation by GTP. Each isoform had a similar far ultraviolet circular dichroism spectrum and thermal stability between 20 degrees C and 60 degrees C, with denaturation occurring at 65 degrees C. Our data suggest that gene duplication, structural modifications leading to greater thermal stability of the delta 1 and delta 2 polypeptides, and selective loss of ASL activity in the delta 1 polypeptide all occurred during the recruitment of ASL for a refractive role in the duck lens, resulting in the generation of ASL isoenzymes.

A comparative study of vertebrate eye lens crystallins using isoelectric focusing and densitometry

1. The crystallin proteins of numerous species belonging to different classes of vertebrates have been studied. 2. Species-specific crystallin patterns are revealed which unequivocally characterize the different species. 3. A marked variability in the number and percentage of alpha-, beta- and gamma-crystallins were found in the various species. 4. The gamma-crystallin family, with a meagre number of common bands, has proved to be most representative of the species. The beta-crystallins, with their greater number of common bands, have been best preserved throughout vertebrate evolution. 5. From the similarity coefficient matrix a dendrogram is drawn up, a visual phylogenetic summary of the interrelationships between the vertebrates considered. 6. In the Discussion, other aspects are considered, such as lens morphology, functionality, animal age, post-synthetic modifications and genetic factors.

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.

Expression of the chicken 'delta 2-crystallin' gene in mouse cells: evidence for encoding of argininosuccinate lyase

In the chicken genome, downstream from the delta 1 gene, encoding delta-crystallin, a highly homologous gene called delta 2 is found, but neither its expression nor its function has been clarified. Close similarity of the delta 2 gene to mammalian argininosuccinate lyase (ASL)-encoding genes in organization and deduced amino acid sequence of the encoded protein suggested that this gene may encode chicken ASL. To test this possibility, we cloned the delta 2 gene on a plasmid, introduced it into mouse cells, and assessed expression and ASL activity in comparison with delta 1. We found that delta 2 was expressed well in fibroblastic L cells, which resulted in synthesis of a protein with a size (50 kDa) and antigenicity very close to delta-crystallin, but it was repressed in lens cells in which expression of delta 1 was activated. Transfectant L cell lines expressing delta 2 exhibited significantly higher ASL activity than those without. We conclude that the delta 2 gene codes for chicken ASL, but has a tissue specificity distinct from delta 1 in its expression.

Zeta-crystallin, a novel protein from the guinea pig lens is related to alcohol dehydrogenases

zeta-Crystallin is a major component of the water-soluble proteins of the guinea pig lens. We have constructed a lens cDNA library from one- to seven-day-old guinea pigs in the plasmid Bluescript KS+ and used the 16 amino acid (aa) sequence of a CNBr peptide to design an oligodeoxyribonucleotide probe. Analysis of two positive clones and direct sequence of the 5' end of the RNA resulted in the completion of a most probably full-length mRNA comprising 1842 nucleotides (nt). The ATG start codon occurs 83 nt downstream from the 5' end. The open reading frame, ending with a stop codon at nt position 1070, predicts a protein of 328 aa with a calculated Mr of 35,071. Comparison of the amino acid sequence with the National Biomedical Research Foundation protein data base reveals a significant similarity of zeta-crystallin with the enzyme of the alcohol dehydrogenase family.

Gene sharing by delta-crystallin and argininosuccinate lyase

The lens structural protein delta-crystallin and the metabolic enzyme argininosuccinate lyase (ASL; L-argininosuccinate arginine-lyase, EC 4.3.2.1) have striking sequence similarity. We have demonstrated that duck delta-crystallin has enormously high ASL activity, while chicken delta-crystallin has lower but significant activity. The lenses of these birds had much greater ASL activity than other tissues, suggesting that ASL is being expressed at unusually high levels as a structural component. In Southern blots of human genomic DNA, chicken delta 1-crystallin cDNA hybridized only to the human ASL gene; moreover, the two chicken delta-crystallin genes accounted for all the sequences in the chicken genome able to cross-hybridize with a human ASL cDNA, with preferential hybridization to the delta 2 gene. Correlations of enzymatic activity and recent data on mRNA levels in the chicken lens suggest that ASL activity depends on expression of the delta 2-crystallin gene. The data indicate that the same gene, at least in ducks, encodes two different functions, an enzyme (ASL) and a structural protein (delta-crystallin), although in chickens specialization and separation of functions may have occurred.

Transdifferentiated embryonic neuroretina cells: an in vitro system to study crystallin aggregation process

Transdifferentiated embryonic quail neuroretina cells synthesize in vitro crystallins (the lens-specific proteins) and form lentoid bodies (structures that mimic lens fiber cells) which also contain crystallins. A comparative study on the size of crystallins is reported in 7-day-old embryonic quail lenses, in 7-day-old embryonic quail transdifferentiated neuroretina cells (normal and MH2 transformed), and in isolated lentoid bodies. Analyses are performed using Superose FPLC in combination with SDS-PAGE and Western blot procedures. In quail lenses, an apparent 560-580-kDa alpha crystallin homopolymer is found and delta crystallin, the major avian lens protein, is detected as a 180-kDa tetramer. beta Crystallins, present in low amount within the 180-kDa peak, are a heterogeneous population composed of subunits of molecular weight identical to those found in chick lenses. In addition, an apparent 46-kDa monomeric delta crystallin is found. Normal and MH2-transformed neuroretina cultures produce an alpha crystallin polymer of lower molecular weight (450 kDa) and delta crystallin in a monomeric or dimeric form. The Western blot pattern of beta crystallins from MH2-transformed neuroretina cultures is strictly identical to that of quail lens beta crystallins. In particular, the beta B1 crystallin, which is specific to lens fiber cell differentiation, and the major beta 25-kDa crystallin are present. However, analysis of isolated lentoid bodies from normal transdifferentiated quail neuroretina cultures showed alpha and delta crystallins of comparable size to those found in lens extract, in particular the delta crystallin in tetrameric form. The lentoid body lens-like structure could favour the crystallin aggregation process.

Immunohistochemical characterization of delta crystallin-containing retina/optic nerve "boundary" cells in the chick embryo

The term "transdifferentiation" has been used to describe the apparent phenotypic conversion of chick embryo neural retina Müller glial cells into lens-like cells in vitro. This phenotypic conversion is characterized by expression of such lens-specific proteins as delta crystallin and has been viewed as an example of cells transforming from the phenotype of a given tissue to that of another. We have identified a population of neuroglia-like cells in the embryonic chick retina which express high levels of delta crystallin as a function of normal development. The position and morphology of these cells is quite distinctive in that they form a loose meshwork which defines the boundary between the neural retina and the optic nerve head. These "boundary" cells are detectable as early as Day 5 of development through hatching. However, the meshwork structure formed by the cells is only readily observed between Days 8 and 9 of development. Double-immunolabeling procedures comparing delta crystallin staining to that of glial and neuronal markers suggest that these cells are a form of retinal Müller glial cell. The results show that under appropriate microenvironmental conditions, expression of delta crystallin falls into the normal repertoire of retinoblast cells. The results also demonstrate the presence of a cellular boundary defining the junction between the neural retina and the optic nerve, tissues that are ontogenetically and structurally continuous but functionally distinct.

Phylogenetic comparison of lens crystallins from the vertebrate and invertebrate--convergent or divergent evolution?

A systematic biochemical comparison has been made of the crystallins isolated from the lenses of five different species belonging to the five major classes of vertebrates. Gel-permeation chromatography of the lens homogenates on Fractogel TSK HW-55(S) revealed well-defined elution patterns with a characteristic distribution of different classes of crystallins from each species. SDS gel electrophoresis and statistical comparison of the amino acid contents indicated that all crystallin groups from different classes share some common subunits and similarity in their amino acid compositions. The results coupled with the relatedness shown in the amino acid compositions of fish gamma-crystallin with those of mammalian gamma-crystallin and the squid crystallin from the invertebrate pointed to the possibility of the existence of a common ancestral protein for all crystallins. This is in favor of the divergent rather than convergent evolution of lens crystallins as commonly assumed in the literature.

Nucleotide sequence of a chicken delta-crystallin gene

We have determined the complete nucleotide sequence of one of the two non-allelic delta-crystallin genes in the chicken, arbitrarily designated delta-gene 1, using a genomic clone (lambda g delta 106) containing the entire gene sequence. By comparison of the genomic sequence and the delta-crystallin cDNA sequence previously determined, we have identified exon sequences in the genomic sequence. Thus, the presence of 17 exons and 16 introns in the gene has been clarified. The delta-crystallin polypeptide deduced from the exon sequences consists of 465 amino acids which is larger, by 19 amino acid residues, than the polypeptide deduced from the cDNA sequence previously reported. Re-examination of the cDNA sequence using the same cDNA clone previously used shows that the present exon sequences are correct and the molecular weight of the deduced delta-crystallin polypeptide is 50,615 daltons instead of the previously reported value of 48,447 daltons. In addition, some structural features of the delta-crystallin gene including putative expression signals are discussed.

Characterization and crystallization of delta-crystallin from the eye lens of adult turkey: comparison with delta-crystallin from adult quail and young chick

delta-Crystallin, purified from either adult turkey or quail lenses, and characterized by amino acid composition and circular dichroism spectroscopy, is shown to be similar to delta-crystallin purified from 3-day-old chick lenses. Crystallization of turkey delta-crystallin is reported along with the characterization of the crystal unit cell by X-ray diffraction techniques. Variation in unit cell parameters is observed and is correlated with hydration.

Immunochemical characterization and quantitative distribution of crystallins in the epithelium and differentiating fibre cell populations of chick embryonic lens

Lenses from 19-day chick embryos are fractionated by a double punch method to obtain the epithelium-annular pad complex (EP), outer fibres (OF), middle fibres (MF) and central fibres (CF). Water-soluble crystallins are characterized by SDS PAGE, isoelectric focusing (IEF) and two-dimensional IEF-SDS PAGE. Crystallins are also characterized by immunoelectrophoresis (IE), rocket IE, IEF-immunoblotting, and quantified by two-dimensional antigen-antibody crossed electrophoresis using antibodies to total 19-day embryonic as well as adult crystallins. In the adult lens, alpha-, beta- and delta-crystallins are 19%, 67% and 14%, respectively, while these are present at concentrations of 9%, 27% and 64%, respectively, in 19-day embryonic lens. In absolute amounts, delta-crystallin increases only by 1.23-fold between 19-day embryonic age and 6 months post-hatching, while total lens protein increases 12.5-fold. The predominance of delta-crystallin in central fibres, located along the optical axis, suggests that this protein is of embryonic origin. delta-Crystallin from fibres is electrofocused as 12 distinct molecular classes (pI 5.2-5.42) which react against anti-delta-crystallin on an immunoblot. Of these, the three most anodal species are not detected in EP. Fibres contain 50 000, 48 000 and 45 000 dalton delta-crystallin subunits while only 50 000 and 48 000 dalton subunits are present in EP.

Sequence of a complete chicken delta-crystallin cDNA

A full-length chicken delta-crystallin cDNA (p delta Cr17) was cloned and subjected to sequence analysis. The cDNA was shown to be full-length by both primer extension and S1 and mung bean nuclease experiments. Thus, the complete amino acid sequence of delta-crystallin is now available. The delta-crystallin polypeptide has a molecular mass of 48,542 daltons, as expected from its behavior on NaDodSO4/polyacrylamide gels. delta-Crystallin has one tryptophan, no cysteines, a prevalence of leucines (15%), and a paucity of aromatic residues. High alpha-helical content throughout the protein was predicted from the amino acid sequence. Nucleic acid sequence analysis suggests that delta-crystallin gene 1 encodes the mRNA that gave rise to the cDNA clone. These data provide a basis for the detailed analysis of the two delta-crystallin genes.

Direct observation of delta-crystallin accumulation by laser light-scattering spectroscopy in the chicken embryo lens

By using the technique of laser light-scattering spectroscopy, direct observation has been made on the intracellular accumulation of a crystallin protein within the cells of chicken embryo lens during the process of development. Appearance of delta-crystallin has been detected as early as day 4, and its concentration reaches a plateau at day 19. The measurements constitute a noninvasive determination of accumulation of protein molecules that specifically characterize the process of cell differentiation.

Delta crystallins and their nucleic acids

delta-Crystallin is a major structural protein of avian and reptilian lenses that is absent from the lenses of fish, amphibia and mammals. It appears to be a tetrameric protein with a native molecular weight near 200 000 (200K) and polypeptide molecular weight near 50K and 48K) (see Note added in proof). The alpha-crystallin polypeptides are extremely similar, associate in various combinations of four and are held together by hydrophobic interactions. Although principally cytoplasmic, delta-crystallin may associate with the cell membrane. delta-Crystallin differs from other lens crystallins in its alpha-helical content, native and subunit molecular weights, antigenicity, low wavelength of maximum fluorescence emission (315 nm) after excitation at 280 nm and amino acid composition (high in leucine; low in aromatic residues en no cysteine). Analyses of peptides, native and subunit molecular weights, and circular dichroism spectra indicate that the primary, secondary, tertiary and subunit structures of delta-crystallin have been generally conserved during evolution. There are at least two tandemly arranged delta-crystallin containing 13-15 introns in the chicken; a similar structure exists for a cloned delta-crystallin gene in the duck. Experiments with chicken show that delta-crystallin synthesis occurs principally in the embryo, especially during lens fiber cell differentiation. delta-Crystallin synthesis also takes place during lens fiber cell differentiation in culture. There is evidence for both transcriptional and post-transcriptional regulation of delta-crystallin synthesis. Current studies on the crystallographic and primary structures of delta-crystallin, on the structure, evolution and expression of the delta-crystallin genes, and on the translation of delta-crystallin mRNAs make this specialized lens protein an active area of investigation.

Lamprey 48-kDa lens protein represents a novel class of crystallins

SDS-PAGE revealed a major Mr 48 000 polypeptide of pI around 8 in the water-soluble fraction of lamprey lenses. It occurs as a monomeric protein, and its amino acid composition and tryptic peptides show no resemblances to alpha-, beta-, gamma- or delta-crystallin. Immunoblotting with antiserum against the 48-kDa protein revealed an immunologically related polypeptide of similar Mr in reptiles, several birds and a fish, but showed no cross-reactivity with any other water-soluble lens component. The 48-kDa protein is not detected in many birds and fishes, and in the investigated mammals and amphibians.

Gene and protein structure of a beta-crystallin polypeptide in murine lens: relationship of exons and structural motifs

A 23,000 molecular weight beta-crystallin (beta 23) of the murine eye lens is encoded in a 4.1 +/- 0.3-kilobase gene containing three introns. Each of the four exons seems to code for a separate structural motif of the protein, whose tertiary structure was predicted by an interactive computer graphics technique based on the crystallographic structure of bovine gamma II-crystallin. The first exon also encodes a hydrophobic N-terminal peptide resembling membrane anchor sequences of other proteins. Our results indicate structural homology among the beta- and gamma-crystallin polypeptides, and link gene structure with protein structure in this superfamily of lens proteins.

Comparative and age-dependent aspects of crystallin size and distribution in human, rabbit, bovine, rat, chicken, duck, frog and dogfish lenses

Lens extracts obtained from eight vertebrate species were analyzed using high-performance gel permeation chromatography with differential refractive index and low-angle laser light scattering detection. The elution patterns enabled the direct determination of the proportions of the crystallin classes as well as the molecular weights of the numerous size fractions in a more rapid and accurate way than previously. Concerning the mammalian species, also age-dependent aspects could be assessed by comparing the data obtained from the extracts of differently aged lenses and/or lens parts.

Studies on the water-soluble lens proteins of the lizard, Calotes versicolor. II. Electrophoretic and immunological characterization

The Sephadex G-200 gel filtration fractions C1 to C6 of the water-soluble lens proteins of Calotes versicolor have been characterized by polyacrylamide gel electrophoresis (PAGE), 7 M urea PAGE, SDS PAGE, and immunological tests. C1 fraction, an alpha-crystallin which cross-reacts with chick alpha, has very low amount of B chains. It shows two bands in SDS PAGE, one strong and another weak. C2 and C3 fractions, both of which partially cross-react with chick beta-crystallins, are largely similar but not identical. C2 in SDS PAGE produces a faint band with a molecular weight of 54,500, which suggests that C2 may either contain a small amount of delta-crystallin in addition to beta H crystallin or that Calotes beta H has a high molecular weight subunit like human beta H; however, in immunological tests no material cross-reacting with chick delta was seen. C4 and C5 are low molecular weight, monomeric, and basic proteins which in all probability are not gamma-crystallins.

The measurement and interpretation of Brillouin scattering in the lens of the eye

Brillouin scattering from hypersonic waves in the eye lenses of many animals has been observed with a multipass Fabry Perot interferometer. The measured values of speed and attenuation range widely among the different species and in different parts of any one lens. These variations correlate broadly with the observed stiffness and the densities that have been measured with a graded column. From the spectroscopic and density measurements high-frequency elastic moduli may be derived. The results are also evaluated at a macromolecular level in terms of scattering of hypersonic waves from spherical entities composed of the crystallins and their aggregates. Reasonable agreement is obtained for the hypersonic speed for lower protein concentration; the hypersonic attenuation and variation with scattering vector are consistent with the presence of large aggregates (of order 100 nm radius) in certain of the materials.

[Synthesis of a lens-specific antigen (delta-crystallin) in rudimentary chicken adenohypophysis]

The synthesis of two lens-specific proteins, delta- and beta-crystallins, by adenohypophyseal anlage of 4-day chick embryos was studied by the immunofluorescence technique in conjunction with autoradiography. Isolated anlages were incubated for 16 hours in a culture medium containing 14c-leucine. The synthesis was determined with the use of an unlabelled carrier, extract of chick lens, as well as of antisera against delta- and beta-crystallins. 14C-Leucine incorporation was found to occur only in delta-crystalline precipitation line rather than in beta-crystallin line. This evidence attests to the synthesis of delta-crystalline by the chick embryo adenohypophyseal anlage. The results are in agreement with the previously obtained immunohistochemical data on delta-crystalline localization in cells of the developing adenohypophysis.

Structural and functional similarities of delta-crystallin messenger ribonucleic acids from duck and chicken lenses

delta-Crystallin of the embryonic duck lens was compared with that of the embryonic chicken lens with respect to polypeptide composition, synthesis, and messenger ribonucleic acid (mRNA) sequences. Labeling experiments with [35S]methionine revealed that the duck delta-crystallin is composed of minor amounts of polypeptides with molecular weights near 50000 (50K) and 49000 (49K) and much greater amounts of polypeptides with molecular weights near 48000 (48K) and 47000 (47K), as judged by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis. All four sizes of polypeptides were synthesized in similar relative proportions as found in vivo in a rabbit reticulocytes lysate supplemented with delta-crystallin mRNA isolated from the embryonic duck lens. Synthesis of the 48K and 47K delta-crystallin polypeptides was differentially reduced in duck lenses cultured in the presence of ouabain. This is similar to the differential reduction of synthesis of the lower molecular weight delta-crystallin peptides in embryonic chicken lenses demonstrated previously. R loops formed between duck or chicken delta-crystallin mRNA and a cloned chicken delta-crystallin cDNA and heteroduplexes formed between duck or chicken delta-crystallin mRNA and cloned chicken genomic DNAs containing delta-crystallin sequences showed that, except for the putative 5' leader sequence, the duck and chicken delta-crystallin mRNAs have extremely similar nucleotide sequences. These data indicate considerable conservation of delta-crystallin throughout the approximately 100 million years of divergence between ducks and chickens. The findings also suggest a possible relationship between the structure of delta-crystallin mRNA and the differential reduction in synthesis of the lower molecular weight delta-crystallin polypeptides in ouabain-treated lenses of ducks and chickens.

Comparison of two delta-crystallin genes in the chicken

Restriction endonuclease mapping and electron microscopy established that there are at least two nonallelic delta-crystallin genes in the chicken. The structure of a complete delta-crystallin gene has been deduced by analysis of five cloned fragments from the chicken genome. Fifteen intervening sequences compose approximately 80% of this gene; the other gene contains at least 14 intervening sequences. The mRNA gene sequences appear to be similar; at least 60% divergence was found between the intervening sequences of the two delta-crystallin genes. Insertions or deletions or both appear to be major events responsible for these differences.

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.