Lens crystallins and their genes: diversity and tissue-specific expression

Multiomic analysis implicates FOXO4 in genetic regulation of chick lens fiber cell differentiation

A classic model for identification of novel differentiation mechanisms and pathways is the eye lens that consists of a monolayer of quiescent epithelial cells that are the progenitors of a core of mature fully differentiated fiber cells. The differentiation of lens epithelial cells into fiber cells follows a coordinated program involving cell cycle exit, expression of key structural proteins and the hallmark elimination of organelles to achieve transparency. Although multiple mechanisms and pathways have been identified to play key roles in lens differentiation, the entirety of mechanisms governing lens differentiation remain to be discovered. A previous study established that specific chromatin accessibility changes were directly associated with the expression of essential lens fiber cell genes, suggesting that the activity of transcription factors needed for expression of these genes could be regulated through binding access to the identified chromatin regions. Sequence analysis of the identified chromatin accessible regions revealed enhanced representation of the binding sequence for the transcription factor FOXO4 suggesting a direct role for FOXO4 in expression of these genes. FOXO4 is known to regulate a variety of cellular processes including cellular response to metabolic and oxidative stress, cell cycle withdrawal, and homeostasis, suggesting a previously unidentified role for FOXO4 in the regulation of lens cell differentiation. To further evaluate the role of FOXO4 we employed a multiomics approach to analyze the relationship between genome-wide FOXO4 binding, the differentiation-specific expression of key genes, and chromatin accessibility. To better identify active promoters and enhancers we also examined histone modification through analysis of H3K27ac. Specific methods included CUT&RUN (FOXO4 binding and H3K27ac modification), RNA-seq (differentiation state specific gene expression), and ATAC-seq (chromatin accessibility). CUT&RUN identified 20,966 FOXO4 binding sites and 33,921 H3K27ac marked regions across the lens fiber cell genome. RNA-seq identified 956 genes with significantly greater expression levels in fiber cells compared to epithelial cells (log2FC > 0.7, q < 0.05) and 2548 genes with significantly lower expression levels (log2FC < -0.7, q < 0.05). Integrated analysis identified 1727 differentiation-state specific genes that were nearest neighbors to at least one FOXO4 binding site, including genes encoding lens gap junctions (GJA1, GJA3), lens structural proteins (BFSP1, CRYBB1, ASL1), and genes required for lens transparency (HSF4, NRCAM). Multiomics analysis comparing the identified FOXO4 binding sites in published ATAC-seq data revealed that chromatin accessibility was associated with FOXO4-dependent gene expression during lens differentiation. The results provide evidence for an important requirement for FOXO4 in the regulated expression of key genes required for lens differentiation and link epigenetic regulation of chromatin accessibility and H3K27ac histone modification with the function of FOXO4 in controlling lens gene expression during lens fiber cell differentiation.

Moonlighting enzymes: when cellular context defines specificity

It is not often realized that the absolute protein specificity is an exception rather than a rule. Two major kinds of protein multi-specificities are promiscuity and moonlighting. This review discusses the idea of enzyme specificity and then focusses on moonlighting. Some important examples of protein moonlighting, such as crystallins, ceruloplasmin, metallothioniens, macrophage migration inhibitory factor, and enzymes of carbohydrate metabolism are discussed. How protein plasticity and intrinsic disorder enable the removing the distinction between enzymes and other biologically active proteins are outlined. Finally, information on important roles of moonlighting in human diseases is updated.

Multiomics Analysis Reveals Novel Genetic Determinants for Lens Differentiation, Structure, and Transparency

Recent advances in next-generation sequencing and data analysis have provided new gateways for identification of novel genome-wide genetic determinants governing tissue development and disease. These advances have revolutionized our understanding of cellular differentiation, homeostasis, and specialized function in multiple tissues. Bioinformatic and functional analysis of these genetic determinants and the pathways they regulate have provided a novel basis for the design of functional experiments to answer a wide range of long-sought biological questions. A well-characterized model for the application of these emerging technologies is the development and differentiation of the ocular lens and how individual pathways regulate lens morphogenesis, gene expression, transparency, and refraction. Recent applications of next-generation sequencing analysis on well-characterized chicken and mouse lens differentiation models using a variety of omics techniques including RNA-seq, ATAC-seq, whole-genome bisulfite sequencing (WGBS), chip-seq, and CUT&RUN have revealed a wide range of essential biological pathways and chromatin features governing lens structure and function. Multiomics integration of these data has established new gene functions and cellular processes essential for lens formation, homeostasis, and transparency including the identification of novel transcription control pathways, autophagy remodeling pathways, and signal transduction pathways, among others. This review summarizes recent omics technologies applied to the lens, methods for integrating multiomics data, and how these recent technologies have advanced our understanding ocular biology and function. The approach and analysis are relevant to identifying the features and functional requirements of more complex tissues and disease states.

Proteomic analysis of retinal pigment epithelium cells after exposure to UVA radiation

Background

Age-related macular degeneration (AMD) is the primary cause of blindness and severe vision loss in developed countries and is responsible for 8.7% of blindness globally. Ultraviolet radiation can induce DNA breakdown, produce reactive oxygen species, and has been implicated as a risk factor for AMD. This study investigated the effects of UVA radiation on Human retinal pigment epithelial cell (ARPE-19) growth and protein expression.

Methods

ARPE-19 cells were irradiated with a UVA lamp at different doses (5, 10, 20, 30 and 40 J/cm²) from 10 cm. Cell viability was determined by MTT assay. Visual inspection was first achieved with inverted light microscopy and then the DeadEnd™ Fluorometric TUNEL System was used to observe nuclear DNA fragmentation. Flow cytometry based-Annexin V-FITC/PI double-staining was used to further quantify cellular viability. Mitochondrial membrane potential was assessed with JC-1 staining. 2D electrophoresis maps of exposed cells were compared to nonexposed cells and gel images analyzed with PDQuest 2-D Analysis Software. Spots with greater than a 1.5-fold difference were selected for LC-MS/MS analysis and some confirmed by western blot. We further investigated whether caspase activation, apoptotic-related mitochondrial proteins, and regulators of ER stress sensors were involved in UVA-induced apoptosis.

Results

We detected 29 differentially expressed proteins (9 up-regulated and 20 down-regulated) in the exposed cells. Some of these proteins such as CALR, GRP78, NPM, Hsp27, PDI, ATP synthase subunit alpha, PRDX1, and GAPDH are associated with anti-proliferation, induction of apoptosis, and oxidative-stress protection. We also detected altered protein expression levels among caspases (caspase 3 and 9) and in the mitochondrial (cytosolic cytochrome C, AIF, Mcl-1, Bcl-2, Bcl-xl, Bax, Bad, and p-Bad) and ER stress-related (p-PERK, p-eIF2α, ATF4 and CHOP) apoptotic pathways.

Conclusions

UVA irradiation suppressed the proliferation of ARPE-19 cells in a dose-dependent manner, caused quantitative loses in transmembrane potential (ΔΨm), and induced both early and late apoptosis.

Lipid-derived and other oxidative modifications of retinal proteins in a rat model of Smith-Lemli-Opitz syndrome

Oxidative modification of proteins can perturb their structure and function, often compromising cellular viability. Such modifications include lipid-derived adducts (e.g., 4-hydroxynonenal (HNE) and carboxyethylpyrrole (CEP)) as well as nitrotyrosine (NTyr). We compared the retinal proteome and levels of such modifications in the AY9944-treated rat model of Smith-Lemli-Opitz syndrome (SLOS), in comparison to age-matched controls. Retinas harvested at 3 months of age were either subjected to proteomic analysis or to immuno-slot blot analysis, the latter probing blots with antibodies raised against HNE, CEP, and NTyr, followed by quantitative densitometry. HNE modification of retinal proteins was markedly (>9-fold) higher in AY9944-treated rats compared to controls, whereas CEP modification was only modestly (≤2-fold) greater, and NTyr modification was minimal and exhibited no difference as a function of AY9944 treatment. Anti-HNE immunoreactivity was greatest in the plexiform and ganglion cell layers, but also present in the RPE, choroid, and photoreceptor outer segment layer in AY9944-treated rats; control retinas showed minimal HNE labeling. 1D-PAGE/Western blot analysis of rod outer segment (ROS) membranes revealed HNE modification of both opsin and β-transducin. Proteomic analysis revealed the differential expression of several retinal proteins as a consequence of AY9944 treatment. Upregulated proteins included those involved in chaperone/protein folding, oxidative and cellular stress responses, transcriptional regulation, and energy production. βA3/A1 Crystallin, which has a role in regulation of lysosomal acidification, was down-regulated. Hence, oxidative modification of retinal proteins occurs in the SLOS rat model, in addition to the previously described oxidation of lipids. The results are discussed in the context of the histological and physiological changes that occur in the retina in the SLOS rat model.

The small heat shock protein αA-crystallin negatively regulates pancreatic tumorigenesis

Our recent study has shown that αA-crystallin appears to act as a tumor suppressor in pancreas. Here, we analyzed expression patterns of αA-crystallin in the pancreatic tumor tissue and the neighbor normal tissue from 74 pancreatic cancer patients and also pancreatic cancer cell lines. Immunocytochemistry revealed that αA-crystallin was highly expressed in the normal tissue from 56 patients, but barely detectable in the pancreatic tumor tissue. Moreover, a low level of αA-crystallin predicts poor prognosis for patients with pancreatic duct adenocarcinoma (PDAC). In the 12 pancreatic cell lines analyzed, except for Capan-1 and Miapaca-2 where the level of αA-crystallin was about 80% and 65% of that in the control cell line, HPNE, the remaining pancreatic cancer cells have much lower αA-crystallin levels. Overexpression of αA-crystallin in MiaPaca-1 cells lacking endogenous αA-crystallin significantly decreased its tumorigenicity ability as shown in the colony formation and wound healing assays. In contrast, knockdown of αA-crystallin in the Capan-1 cells significantly increased its tumorigenicity ability as demonstrated in the above assays. Together, our results further demonstrate that αA-crystallin negatively regulates pancreatic tumorigenesis and appears to be a prognosis biomarker for PDAC.

Physical Features of Intracellular Proteins that Moonlight on the Cell Surface

Moonlighting proteins comprise a subset of multifunctional proteins that perform two or more biochemical functions that are not due to gene fusions, multiple splice variants, proteolytic fragments, or promiscuous enzyme activities. The project described herein focuses on a sub-set of moonlighting proteins that have a canonical biochemical function inside the cell and perform a second biochemical function on the cell surface in at least one species. The goal of this project is to consider the biophysical features of these moonlighting proteins to determine whether they have shared characteristics or defining features that might suggest why these particular proteins were adopted for a second function on the cell surface, or if these proteins resemble typical intracellular proteins. The latter might suggest that many other normally intracellular proteins found on the cell surface might also be moonlighting in this fashion. We have identified 30 types of proteins that have different functions inside the cell and on the cell surface. Some of these proteins are found to moonlight on the surface of multiple species, sometimes with different extracellular functions in different species, so there are a total of 98 proteins in the study set. Although a variety of intracellular proteins (enzymes, chaperones, etc.) are observed to be re-used on the cell surface, for the most part, these proteins were found to have physical characteristics typical of intracellular proteins. Many other intracellular proteins have also been found on the surface of bacterial pathogens and other organisms in proteomics experiments. It is quite possible that many of those proteins also have a moonlighting function on the cell surface. The increasing number and variety of known moonlighting proteins suggest that there may be more moonlighting proteins than previously thought, and moonlighting might be a common feature of many more proteins.

UV-induced retinal proteome changes in the rat model of age-related macular degeneration

Age-related macular degeneration (AMD) is characterized by irreversible damage of photoreceptors in the central posterior part of the retina, called the macula and is the most common cause of vision loss in those aged over 50. A growing body of evidence shows that cumulative long-term exposure to UV radiation may be harmful to the retina and possibly leads to AMD irrespective of age. In spite of many research efforts, cellular and molecular mechanisms leading to UV-induced retinal damage and possibly retinal diseases such as AMD are not completely understood. In the present study we explored damage mechanisms accounting for UV-induced retinal phototoxicity in the rats exposed to UVA and UVB irradiation using a proteomics approach. Our study showed that UV irradiation induces profound changes in the retinal proteomes of the rats associated with the disruption of energy homeostasis, oxidative stress, DNA damage response and structural and functional impairments of the interphotoreceptor matrix components and their cell surface receptors such as galectins. Two small leucine-rich proteoglycans, biglycan and lumican, were identified as phototoxicity biomarkers associated with UV-induced disruption of interphotoreceptor matrix (IPM). In addition, UVB induced activation of Src kinase, which could account for cytoskeletal rearrangements in the retina was observed at the proteomics level. Pharmacological intervention either to target Src kinase with the aim of preventing cytoskeletal rearrangements in the retinal pigment epithelium (RPE) and neuronal retina or to help rebuild damaged IPM may provide fresh avenues of treatment for patients suffering from AMD.

Exon-level expression profiling of ocular tissues

The normal gene expression profiles of the tissues in the eye are a valuable resource for considering genes likely to be involved with disease processes. We profiled gene expression in ten ocular tissues from human donor eyes using Affymetrix Human Exon 1.0 ST arrays. Ten different tissues were obtained from six different individuals and RNA was pooled. The tissues included: retina, optic nerve head (ONH), optic nerve (ON), ciliary body (CB), trabecular meshwork (TM), sclera, lens, cornea, choroid/retinal pigment epithelium (RPE) and iris. Expression values were compared with publically available Expressed Sequence Tag (EST) and RNA-sequencing resources. Known tissue-specific genes were examined and they demonstrated correspondence of expression with the representative ocular tissues. The estimated gene and exon level abundances are available online at the Ocular Tissue Database.

Crystallin distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei lenses

The eye lens remains transparent because of soluble lens proteins known as crystallins. For years γ-crystallins have been known as the main lens proteins in lower vertebrates such as fish and amphibians. The unique growth features of the lens render it an ideal structure to study ageing; few studies have examined such changes in anuran lenses. This study aimed to investigate protein distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei species. Lenses were fractionated into concentric layers by controlled dissolution. Water-soluble proteins were separated into high (HMW), middle (MMW) and low molecular weight (LMW) fractions by size-exclusion HPLC and constituents of each protein class revealed by 1DE and 2DE. Spots were selected from 2DE gels on the basis of known ranges of subunit molecular weights and pH ranges and were identified by MALDI-TOF/TOF MS following trypsin digestion. Comparable lens distribution patterns were found for each species studied. Common crystallins were detected in both species; the most prominent of these was γ-crystallin. Towards the lens centre, there was a decrease in α- and β-crystallin proportions and an increase in γ-crystallins. Subunits representing taxon-specific crystallins demonstrating strong sequence homology with ζ-crystallin/quinone oxidoreductase were found in both L. infrafrenata and P. sauvagei lenses. Further work is needed to determine which amphibians have taxon-specific crystallins, their evolutionary origins, and their function.

Differential response of lens crystallins and corneal crystallins in degenerative corneas

Corneal degenerations, occurring either spontaneously or as a complication to other diseases, cause vision problems by endangering corneal transparency. Our past cornea research projects involving mice revealed that some recruited mice presented corneal problems similar to human corneal degeneration. The present study examines the histology of diseased mice corneas, including ultrastructure. Genome-wide microarray and proteomic methods were utilized to screen for molecular changes in the diseased corneas. It was found that abnormalities affected mainly anterior layers of the corneas. The most often observed histological abnormalities included neoplasm or detachment of the epithelial layer, erosion or breakage of Bowman membranes, blood vessel formation, and bleeding in the stroma. Microarray assay showed that among the 46 up-regulated probes in diseased corneas, 13 were for lens crystallins. However, all corneal crystallins genes remained unchanged. αA-crystallin was among the proteins that showed the greatest increase in diseased corneas, as detected by gel electrophoresis. We propose that lens crystallins, rather than corneal crystallins, are involved in the pathological process of corneal degeneration. Further study along these lines would provide insight into the mechanism of corneal transparency.

The congenital cataract-linked G61C mutation destabilizes γD-crystallin and promotes non-native aggregation

γD-crystallin is one of the major structural proteins in human eye lens. The solubility and stability of γD-crystallin play a crucial role in maintaining the optical properties of the lens during the life span of an individual. Previous study has shown that the inherited mutation G61C results in autosomal dominant congenital cataract. In this research, we studied the effects of the G61C mutation on γD-crystallin structure, stability and aggregation via biophysical methods. CD, intrinsic and extrinsic fluorescence spectroscopy indicated that the G61C mutation did not affect the native structure of γD-crystallin. The stability of γD-crystallin against heat- or GdnHCl-induced denaturation was significantly decreased by the mutation, while no influence was observed on the acid-induced unfolding. The mutation mainly affected the transition from the native state to the intermediate but not that from the intermediate to the unfolded or aggregated states. At high temperatures, both proteins were able to form aggregates, and the aggregation of the mutant was much more serious than the wild type protein at the same temperature. At body temperature and acidic conditions, the mutant was more prone to form amyloid-like fibrils. The aggregation-prone property of the mutant was not altered by the addition of reductive reagent. These results suggested that the decrease in protein stability followed by aggregation-prone property might be the major cause in the hereditary cataract induced by the G61C mutation.

Expression of βA3/A1-crystallin in the developing and adult rat eye

Crystallins are very abundant structural proteins of the lens and are also expressed in other tissues. We have previously reported a spontaneous mutation in the rat βA3/A1-crystallin gene, termed Nuc1, which has a novel, complex, ocular phenotype. The current study was undertaken to compare the expression pattern of this gene during eye development in wild type and Nuc1 rats by in situ hybridization (ISH) and immunohistochemistry (IHC). βA3/A1-crystallin expression was first detected in the eyes of both wild type and Nuc1 rats at embryonic (E) day 12.5 in the posterior portion of the lens vesicle, and remained limited to the lens fibers throughout fetal life. After birth, βA3/A1-crystallin expression was also detected in the neural retina (specifically in the astrocytes and ganglion cells) and in the retinal pigmented epithelium (RPE). This suggested that βA3/A1-crystallin is not only a structural protein of the lens, but has cellular function(s) in other ocular tissues. In summary, expression of βA3/A1-crystallin is controlled differentially in various eye tissues with lens being the site of greatest expression. Similar staining patterns, detected by ISH and IHC, in wild type and Nuc1 animals suggest that functional differences in the protein, rather than changes in mRNA/protein level of expression, likely account for developmental abnormalities in Nuc1.

Selective degradation of aggregate-prone CryAB mutants by HSPB1 is mediated by ubiquitin-proteasome pathways

Disease-causing mutations of genes encoding small MW heat shock proteins (sHSPs) constitute a growing family of inherited myofibrillar disorders. In the present work, we found that three structurally-distinct CryAB mutants R120G, 450delA and 464delCT are mostly present in the detergent-insoluble fractions when overexpressed in H9c2 rat heart cells. We found that either over-expression or knockdown of HSPB1, a related sHSP, affects the solubility, stability, and degradation of aggregation-prone CryAB mutants. HSPB1 overexpression has negligible effects on the solubility and protein aggregates of either R120G and/or 450delA but increased the solubility and prevented formation of 464delCT aggregates. HSPB1 knockdown decreased solubility and increased protein aggregates of all CryAB mutants, indicating a key role for HSPB1 in clearance of CryAB mutants under basal conditions. We provide four lines of evidence that such selective clearance of R120G, 450delA and 464delCT mutants by HSPB1 is mediated by the ubiquitin-proteasome system (UPS). First, we found that treatment with the proteasome inhibitors increased the levels of all CryAB mutants. Second, R120G and 450delA overexpression corresponded to the accumulation of their specific ubiquitin conjugates in H9c2 cells. Third, HSPB1 knockdown directly increased the levels of all polyubiquitin conjugates. And fourth, the selective attenuation of 464delCT expression by HSPB1 over-expression was abrogated by the proteasome inhibition. We conclude that such selective interactions between CryAB mutants and HSPB1 overexpression might have important implications for the clinical manifestations and potential treatment.

Explosive expansion of betagamma-crystallin genes in the ancestral vertebrate

In jawed vertebrates, βγ-crystallins are restricted to the eye lens and thus excellent markers of lens evolution. These βγ-crystallins are four Greek key motifs/two domain proteins, whereas the urochordate βγ-crystallin has a single domain. To trace the origin of the vertebrate βγ-crystallin genes, we searched for homologues in the genomes of a jawless vertebrate (lamprey) and of a cephalochordate (lancelet). The lamprey genome contains orthologs of the gnathostome βB1-, βA2- and γN-crystallin genes and a single domain γN-crystallin-like gene. It contains at least two γ-crystallin genes, but lacks the gnathostome γS-crystallin gene. The genome also encodes a non-lenticular protein containing βγ-crystallin motifs, AIM1, also found in gnathostomes but not detectable in the uro- or cephalochordate genome. The four cephalochordate βγ-crystallin genes found encode two-domain proteins. Unlike the vertebrate βγ-crystallins but like the urochordate βγ-crystallin, three of the predicted proteins contain calcium-binding sites. In the cephalochordate βγ-crystallin genes, the introns are located within motif-encoding region, while in the urochordate and in the vertebrate βγ-crystallin genes the introns are between motif- and/or domain encoding regions. Coincident with the evolution of the vertebrate lens an ancestral urochordate type βγ-crystallin gene rapidly expanded and diverged in the ancestral vertebrate before the cyclostomes/gnathostomes split. The β- and γN-crystallin genes were maintained in subsequent evolution, and, given the selection pressure imposed by accurate vision, must be essential for lens function. The γ-crystallin genes show lineage specific expansion and contraction, presumably in adaptation to the demands on vision resulting from (changes in) lifestyle.

The small heat shock protein alphaA-crystallin is expressed in pancreas and acts as a negative regulator of carcinogenesis

The small heat shock protein alphaA-crystallin is a structural protein in the ocular lens. In addition, recent studies have also revealed that it is a molecular chaperone, an autokinase and a strong anti-apoptotic regulator. Besides its lenticular distribution, a previous study demonstrates that a detectable level of alphaA-crystallin is found in other tissues including thymus and spleen. In the present study, we have re-examined the distribution of alphaA-crystallin in various normal human and mouse tissues and found that the normal pancreas expresses a moderate level of alphaA-crystallin. Moreover, alphaA-crystallin is found significantly downregulated in 60 cases of pancreatic carcinoma of different types than it is in 11 normal human pancreas samples. In addition, we demonstrate that alphaA-crystallin can enhance the activity of the activating protein-1 (AP-1) through modulating the function of the MAP kinase, and also upregulates components of TGFbeta pathway. Finally, expression of alphaA-crystallin in a pancreatic cancer cell line, MiaPaCa, results in retarded cell migration. Together, these results suggest that alphaA-crystallin seems to negatively regulate pancreatic carcinogenesis.

cDNA, genomic sequence and overexpression of crystallin alpha-B Gene (CRYAB) of the Giant Panda

AlphaB-crystallin, a small heat-shock protein, has been shown to prevent the aggregation of other proteins under various stress conditions. Here we have cloned the cDNA and the genomic sequence of CRYAB gene from the Giant Panda (Ailuropoda melanoleuca) using RT-PCR technology and Touchdown-PCR, respectively. The length of cDNA fragment cloned contains an open reading frame of 528bp encoding 175 amino acids and the length of the genomic sequence is 3189bp, containing three exons and two introns. Alignment analysis indicated that the nucleotide sequence and the deduced amino acid sequence are highly conserved to other four species studied, including Homo sapiens, Mus musculus, Rattus norvegicus and Bos taurus. The homologies for nucleotide sequences of Giant Panda CRYAB to that of these species are 93.9%, 91.5%, 91.5% and 95.3%, respectively, and the homologies for amino acid sequences are 98.3%, 97.1%,97.7% and 99.4%, respectively. Topology prediction shows that there are only four Casein kinase II phosphorylation sites in the CRYAB protein of the Giant Panda. The cDNA of CRYAB was transfected into E. coli, and the CRYAB fused with the N-terminally His-tagged protein gave rise to the accumulation of an expected 24KDa polypeptide, which accorded with the predicted protein. The expression product obtained could be used for purification and study of its function further.

Novel immunocontraceptive targets in mammals: uterine secretions and the conceptus; a marsupial approach

We report the first immunocontraceptive trial in mammals using a uterine-secreted protein, the marsupial shell coat protein 4 (CP4). The marsupial shell coat, which surrounds the conceptus for 60–80% of gestation, is secreted by the uterine epithelium. Following immunization against glutathione S-transferase (GST)-CP4, the fertility of female common brushtail possums (n=6) was significantly reduced (P=0.000), and this reduction in fertility was positively correlated with the maximum GST-CP4 humoral immune response (P=0.025). Ultrastructural examination of the reproductive tract indicated that the cell-mediated immune response against GST-CP4 targeted the shell coat, the shell-free conceptus and the uterine glandular epithelium, thus preventing normal conceptus development and uterine secretion of shell coat proteins and nutrients. These results show that uterine-secreted proteins are promising immunocontraceptive targets, especially in pest mammal species, e.g. possum, rabbit and horse, that have uterine-secreted additions to embryonic coats, or that have late implantation requiring uterine nutrient provisioning from secretions.

Dual roles for Prox1 in the regulation of the chicken betaB1-crystallin promoter

PURPOSE

Lens fiber cell differentiation is marked by the onset of betaB1-crystallin expression and is controlled by the cooperative action of a set of transcription factors including Prox1, an atypical homeodomain protein. Previously, the authors reported that Prox1 directly interacts with the OL2 element found in the chicken betaB1-crystallin basal promoter to activate the expression of this gene. Here they mapped the location of activating and repressing sequences of the full-length chicken betaB1-crystallin promoter (-432/+30) in lens epithelial cells, annular pad cells, and intact lens and characterized Prox1-binding sites found in this region.

METHODS

Transfection analysis and transgenic mice were used to characterize upstream regions of the chicken betaB1-crystallin gene. DNaseI footprinting and chromatin immunoprecipitation was performed to identify Prox1-binding sites, and transfection analyses were used to characterize these sites functionally.

RESULTS

Sequences between -152 and -432 of the chicken betaB1-crystallin promoter mediated either promoter activation or repression, depending on the stage of lens differentiation tested. Two new Prox1-binding sites were found in this region that bound Prox1 more avidly than the OL2 element. However, neither binding site conferred Prox1-mediated activation on a heterologous promoter; instead, each allowed Prox1 to repress promoter function.

CONCLUSIONS

The function of the upstream region of the chicken betaB1-crystallin promoter changes depending on cellular context. These data suggest that Prox1 function as a transcriptional activator could be regulated at the DNA level based on the characteristics of the responsive elements.

Unlike mammalian GRIFIN, the zebrafish homologue (DrGRIFIN) represents a functional carbohydrate-binding galectin

Galectins, a family of beta-galactoside-binding proteins, participate in a variety of biological processes, such as early development, tissue organization, immune regulation, and tumor evasion and metastasis. Although as many as fifteen bona fide galectins have been identified in mammals, but the detailed mechanisms of their biological roles still remain unclear for most. This fragmentary knowledge extends to galectin-like proteins such as the rat lens crystallin protein GRIFIN (Galectin-related inter fiber protein) and the galectin-related protein GRP (previously HSPC159; hematopoietic stem cell precursor) that lack carbohydrate-binding activity. Their inclusion in the galectin family has been debated, as they are considered products of evolutionary co-option. We have identified a homologue of the GRIFIN in zebrafish (Danio rerio) (designated DrGRIFIN), which like the mammalian equivalent is expressed in the lens, particularly in the fiber cells, as revealed by whole mount in situ hybridization and immunostaining of 2 dpf (days post fertilization) embryos. As evidenced by RT-PCR, it is weakly expressed in the embryos as early as 21 hpf (hour post fertilization) but strongly at all later stages tested (30 hpf and 3, 4, 6, and 7 dpf). In adult zebrafish tissues, however, DrGRIFIN is also expressed in oocytes, brain, and intestine. Unlike the mammalian homologue, DrGRIFIN contains all amino acids critical for binding to carbohydrate ligands and its activity was confirmed as the recombinant DrGRIFIN could be purified to homogeneity by affinity chromatography on a lactosyl-Sepharose column. Therefore, DrGRIFIN is a bona fide galectin family member that in addition to its carbohydrate-binding properties, may also function as a crystallin.

GAD isoforms exhibit distinct spatiotemporal expression patterns in the developing mouse lens: correlation with Dlx2 and Dlx5

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter of the adult nervous system and its biosynthetic enzyme glutamic acid decarboxylase (GAD) are abundantly expressed in the embryonic nervous system and are involved in the modulation of cell proliferation, migration, and differentiation. Here we describe for the first time the expression of GABA and embryonic and adult GAD isoforms in the developing mouse lens. We show that the GAD isoforms are sequentially induced with specific spatiotemporal profiles: GAD65 and embryonic GAD isoforms prevail in primary fibers, while GAD67 is the predominant GAD expressed in the postnatal secondary fibers. This pattern correlates well with the expression of Dlx2 and Dlx5, known as upstream regulators of GAD. GABA and GAD are most abundant at the tips of elongating fibers and are absent from organelle-free cells, suggesting their involvement is primarily in shaping of the cytoskeleton during fiber elongation stages.

The eyes have it: A Problem-Based Learning Exercise in Molecular Evolution

Molecular evolution provides an interesting context in which to use problem-based learning because it integrates a variety of topics in biology, biochemistry, and molecular biology. This three-stage problem for advanced students deals with the structure, multiple functions, and properties of lactate dehydrogenase isozymes, and the related evolutionary trade offs of gene sharing versus gene duplication among their corresponding genes. It has directive elements that require students to find and read classic articles, review thermodynamic principles, and apply their understanding to a mythical world wherein dinosaurs continued to evolve. The science fiction writing assignment that brings closure to the problem transformed the problem with respect to student interest and engagement.

The function of the beta3 interactive domain in the small heat shock protein and molecular chaperone, human alphaB crystallin

Knowledge of the interactive domains on the surface of small heat shock proteins (sHSPs) is necessary for understanding the assembly of complexes and the activity as molecular chaperones. The primary sequences of 26 sHSP molecular chaperones were aligned and compared. In the interactive beta3 sequence, 73DRFSVNLDVKHFS85 of human alphaB crystallin, Ser-76, Asn-78, Lys-82, and His-83 were identified as nonconserved residues on the exposed surface of the alpha crystallin core domain. Site-directed mutagenesis produced the mutant alphaB crystallins: S76E, N78G, K82Q, and H83F. Domain swapping with homologous beta3 sequences, 32EKFEVGLDVQFFT44 from Caenorhabditis elegans sHSP12.2 or 69DKFVIFLDVKHFS81 from alphaA crystallin, resulted in the mutant alphaB crystallins, CE1 and alphaA1, respectively. Decreased chaperone activity was observed with the point mutants N78G, K82Q, and H83F and with the mutant, CE1, in aggregation assays using betaL crystallin, alcohol dehydrogenase (ADH), or citrate synthase (CS). The S76E mutant had minimal effect on chaperone activity, and domain swapping with alphaA crystallin had no effect on chaperone activity. The mutations that resulted in altered chaperone activity, produced minimal modification to the secondary, tertiary, and quaternary structure of human alphaB crystallin as determined by ultraviolet circular dichroism spectroscopy, chymotrypsin proteolysis, and size exclusion chromatography. Chaperone activity was influenced by the amount of unfolding of the target proteins and independent of complex size. The results characterized the importance of the exposed side chains of Glu-78, Lys-82, and His-83 in the interactive beta3 sequence of the alpha crystallin core domain in alphaB crystallin for chaperone function.

In vivo heteromer formation. Expression of soluble betaA4-crystallin requires coexpression of a heteromeric partner

The beta-crystallins are a family of long-lived, abundant structural proteins that are coexpressed in the vertebrate lens. As beta-crystallins form heteromers, a process that involves transient exposure of hydrophobic interfaces, we have examined whether in vivobeta-crystallin assembly is enhanced by protein chaperones, either small heat shock proteins, Hsp27 or alphaB-crystallin, or Hsp70. We show here that betaA4-crystallin is abundantly expressed in HeLa cells, but rapidly degraded, irrespective of the presence of Hsp27, alphaB-crystallin or Hsp70. Degradation is even enhanced by Hsp70. Coexpression of betaA4-crystallin with betaB2-crystallin yielded abundant soluble betaA4-betaB2-crystallin heteromers; betaB1-crystallin was much less effective in solubilizing betaA4-crystallin. As betaB2-crystallin competed for betaA4-crystallin with Hsp70 and the proteasomal degradation pathway, betaB2-crystallin probably captures an unstable betaA4-crystallin intermediate. We suggest that the proper folding of betaA4-crystallin is not mediated by general chaperones but requires a heteromeric partner, which then also acts as a dedicated chaperone towards betaA4-crystallin.

Recapitulation of human betaB1-crystallin promoter activity in transgenic zebrafish

Development of the eye is morphologically similar among vertebrates, indicating that the underlying mechanism regulating the process may have been highly conserved during evolution. Herein we analyzed the promoter of the human betaB1-crytallin gene in zebrafish by transgenic experiments. To delineate the evolutionarily conserved regulatory elements, we performed serial deletion assays in the promoter region. The results demonstrated that the -90/+61-bp upstream proximal promoter region is sufficient to confer lens-tissue specificity to the human betaB1-crystallin gene in transgenic zebrafish. Through phylogenetic sequence comparisons and an electrophoretic mobility shift assay (EMSA), a highly conserved cis-element of a six-base pair sequence TG(A/C)TGA, the consensus sequence for the Maf protein binding site, within the proximal promoter region was revealed. Further, a site-mutational assay showed that this element is crucial for promoter activity. These data suggest that the fundamental transcriptional regulatory mechanism of the betaB1-crystallin gene has been well conserved between humans and zebrafish, and plausibly among all vertebrates, during evolution.

Insights into the domains required for dimerization and assembly of human alphaB crystallin

Protein pin array technology was used to identify subunit-subunit interaction sites in the small heat shock protein (sHSP) alphaB crystallin. Subunit-subunit interaction sites were defined as consensus sequences that interacted with both human alphaA crystallin and alphaB crystallin. The human alphaB crystallin protein pin array consisted of contiguous and overlapping peptides, eight amino acids in length, immobilized on pins that were in a 96-well ELISA plate format. The interaction of alphaB crystallin peptides with physiological partner proteins, alphaA crystallin and alphaB crystallin, was detected using antibodies and recorded using spectrophotometric absorbance. Five peptide sequences including 37LFPTSTSLSPFYLRPPSF54 in the N terminus, 75FSVNLDVK82)(beta3), 131LTITSSLS138 (beta8) and 141GVLTVNGP148 (beta9) that form beta strands in the conserved alpha crystallin core domain, and 155PERTIPITREEK166 in the C-terminal extension were identified as subunit-subunit interaction sites in human alphaB crystallin using the novel protein pin array assay. The subunit-subunit interaction sites were mapped to a three-dimensional (3D) homology model of wild-type human alphaB crystallin that was based on the crystal structure of wheat sHSP16.9 and Methanococcus jannaschi sHSP16.5 (Mj sHSP16.5). The subunit-subunit interaction sites identified and mapped onto the homology model were solvent-exposed and had variable secondary structures ranging from beta strands to random coils and short alpha helices. The subunit-subunit interaction sites formed a pattern of hydrophobic patches on the 3D surface of human alphaB crystallin.

Structural studies of duck delta2 crystallin mutants provide insight into the role of Thr161 and the 280s loop in catalysis

Delta crystallin, a taxon-specific crystallin present in avian eye lenses, is homologous to the urea cycle enzyme ASL (argininosuccinate lyase). Although there are two delta crystallin isoforms in duck lenses, ddeltac1 (duck delta1 crystallin) and ddeltac2 (duck delta2 crystallin), only ddeltac2 is catalytically active. Previous structural studies have suggested that residues Ser283 and His162 in the multi-subunit active site of ddeltac2/ASL are the putative catalytic acid/base, while the highly conserved, positively charged Lys289 is thought to help stabilize the carbanion intermediate. The strict conservation of a small hydroxy-containing residue (Thr or Ser) at position 161 adjacent to the putative catalytic base, as well as its proximity to the substrate in the S283A ddeltac2 enzyme-substrate complex, prompted us to investigate further the role this residue. Structures of the active T161S and inactive T161D ddeltac2 mutants, as well as T161D complexed with argininosuccinate, have been determined to 2.0 A resolution. The structures suggest that a hydroxy group is required at position 161 to help correctly position the side chain of Lys289 and the fumarate moiety of the substrate. Threonine is probably favoured over serine, because the interaction of its methyl group with Leu206 would restrict its conformational flexibility. Residues larger than Thr or Ser interfere with substrate binding, supporting previous suggestions that correct positioning of the substrate's fumarate moiety is essential for catalysis to occur. The presence of the 280s loop (i.e. a loop formed by residues 270-290) in the 'open' conformation suggests that loop closure, thought to be essential for sequestration of the substrate, may be triggered by the formation of the carbanion or aci-carboxylate intermediates, whose charge distribution more closely mimics that of the sulphate ion found in the active-site region of the inactive ddeltac1. The 280s loop in ddeltac1 is in the closed conformation.

Mutational analysis of duck delta 2 crystallin and the structure of an inactive mutant with bound substrate provide insight into the enzymatic mechanism of argininosuccinate lyase

The major soluble avian eye lens protein, delta crystallin, is highly homologous to the housekeeping enzyme argininosuccinate lyase (ASL). ASL is part of the urea and arginine-citrulline cycles and catalyzes the reversible breakdown of argininosuccinate to arginine and fumarate. In duck lenses, there are two delta crystallin isoforms that are 94% identical in amino acid sequence. Only the delta2 isoform has maintained ASL activity and has been used to investigate the enzymatic mechanism of ASL. The role of the active site residues Ser-29, Asp-33, Asp-89, Asn-116, Thr-161, His-162, Arg-238, Thr-281, Ser-283, Asn-291, Asp-293, Glu-296, Lys-325, Asp-330, and Lys-331 have been investigated by site-directed mutagenesis, and the structure of the inactive duck delta2 crystallin (ddeltac2) mutant S283A with bound argininosuccinate was determined at 1.96 A resolution. The S283A mutation does not interfere with substrate binding, because the 280's loop (residues 270-290) is in the open conformation and Ala-283 is more than 7 A from the substrate. The substrate is bound in a different conformation to that observed previously indicating a large degree of conformational flexibility in the fumarate moiety when the 280's loop is in the open conformation. The structure of the S283A ddeltac2 mutant and mutagenesis results reveal that a complex network of interactions of both protein residues and water molecules are involved in substrate binding and specificity. Small changes even to residues not involved directly in anchoring the argininosuccinate have a significant effect on catalysis. The results suggest that either His-162 or Thr-161 are responsible for proton abstraction and reinforce the putative role of Ser-283 as the catalytic acid, although we cannot eliminate the possibility that arginine is released in an uncharged form, with the solvent providing the required proton. A detailed enzymatic mechanism of ASL/ddeltac2 is presented.

Structural studies of duck delta 1 and delta 2 crystallin suggest conformational changes occur during catalysis

Duck delta1 and delta2 crystallin are 94% identical in amino acid sequence, and while delta2 crystallin is the duck orthologue of argininosuccinate lyase (ASL) and catalyzes the reversible breakdown of argininosuccinate to arginine and fumarate, the delta1 isoform is enzymatically inactive. The crystal structures of wild type duck delta1 and delta2 crystallin have been solved at 2.2 and 2.3 A resolution, respectively, and the refinement of the turkey delta1 crystallin has been completed. These structures have been compared with two mutant duck delta2 crystallin structures. Conformational changes were observed in two regions of the N-terminal domain with intraspecies differences between the active and inactive isoforms localized to residues 23-32 and both intra- and interspecies differences localized to the loop of residues 74-89. As the residues implicated in the catalytic mechanism of delta2/ASL are all conserved in delta1, the amino acid substitutions in these two regions are hypothesized to be critical for substrate binding. A sulfate anion was found in the active site of duck delta1 crystallin. This anion, which appears to mimic the fumarate moiety of the argininosuccinate substrate, induces a rigid body movement in domain 3 and a conformational change in the loop of residues 280-290, which together would sequester the substrate from the solvent. The duck delta1 crystallin structure suggests that Ser 281, a residue strictly conserved in all members of the superfamily, could be the catalytic acid in the delta2 crystallin/ASL enzymatic mechanism.

Evolutionary history of the enolase gene family

The enzyme enolase [EC 4.2.1.11] is found in all organisms, with vertebrates exhibiting tissue-specific isozymes encoded by three genes: alpha (alpha), beta (beta), and gamma (gamma) enolase. Limited taxonomic sampling of enolase has obscured the timing of gene duplication events. To help clarify the evolutionary history of the gene family, cDNAs were sequenced from six taxa representing major lineages of vertebrates: Chiloscyllium punctatum (shark), Amia calva (bowfin), Salmo trutta (trout), Latimeria chalumnae (coelacanth), Lepidosiren paradoxa (South American lungfish), and Neoceratodus forsteri (Australian lungfish). Phylogenetic analysis of all enolase and related gene sequences revealed an early gene duplication event prior to the last common ancestor of living organisms. Several distantly related archaebacterial sequences were designated as 'enolase-2', whereas all other enolase sequences were designated 'enolase-1'. Two of the three isozymes of enolase-1, alpha- and beta-enolase, were discovered in actinopterygian, sarcopterygian, and chondrichthian fishes. Phylogenetic analysis of vertebrate enolases revealed that the two gene duplications leading to the three isozymes of enolase-1 occurred subsequent to the divergence of living agnathans, near the Proterozoic/Phanerozoic boundary (approximately 550Mya). Two copies of enolase, designated alpha(1) and alpha(2), were found in the trout and are presumed to be the result of a genome duplication event.

Stabilization and remodeling of the membrane skeleton during lens fiber cell differentiation and maturation

Actin filaments are integral components of the plasma membrane-associated cytoskeleton (membrane skeleton) and are believed to play important roles in the determination of cell polarity, shape, and membrane mechanical properties, however the roles of actin regulatory proteins in controlling the assembly, stability, and organization of actin filaments in the membrane skeleton are not well understood. Tropomodulin is a tropomyosin and actin-binding protein that stabilizes tropomyosin-actin filaments by capping their pointed ends and is associated with the spectrin-actin membrane skeleton in erythrocytes, skeletal muscle cells, and lens fiber cells, a specialized epithelial cell type. In this study, we have investigated the role of tropomodulin and other membrane skeleton components in lens fiber cell differentiation and maturation. Our results demonstrate that tropomodulin is expressed concomitantly with lens fiber cell differentiation and assembles onto the plasma membrane only after fiber cells have begun to elongate and form apical-apical contacts with the undifferentiated epithelium. In contrast, other membrane skeleton components, spectrin, actin, and tropomyosin, are constitutively expressed and assembled on the plasma membranes of both undifferentiated and differentiated fiber cells. Tropomodulin, but not other membrane skeleton components, is also enriched at a novel structure at the apical and basal ends of newly elongated fiber cells at the fiber cell-epithelium and fiber cell-capsule interface, respectively. Once assembled, tropomodulin and its binding partners, tropomyosin and actin, remain membrane-associated and are not proteolyzed during fiber cell maturation and aging, despite proteolysis of alpha-spectrin and other cytoskeletal filament systems such as microtubules and intermediate filaments. We propose that actin filament stabilization by tropomodulin, coupled with partial proteolysis of other cytoskeletal components, represents a programmed remodeling of the lens membrane skeleton that may be essential to maintain plasma membrane integrity and transparency of the extremely elongated, long-lived cells of the lens. The unique localization of tropomodulin at fiber cell tips further suggests a new role for tropomodulin at cell-cell and cell-substratum contacts; this may be important for cell migration and/or adhesion during differentiation and morphogenesis.

Up-regulation of novel intermediate filament proteins in primary fiber cells: an indicator of all vertebrate lens fiber differentiation?

The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed "beaded filaments." CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up-regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49(INS), was also detected early in embryonic development and into adulthood. Peptide-specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49(INS) in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up-regulated expression of CP49 and CP95 could serve as pan-specific markers for all vertebrate lens fiber development.

Regulation of lens fiber cell differentiation by transcription factor c-Maf

To elucidate the regulatory mechanisms underlying lens development, we searched for members of the large Maf family, which are expressed in the mouse lens, and found three, c-Maf, MafB, and Nrl. Of these, the earliest factor expressed in the lens was c-Maf. The expression of c-Maf was most prominent in lens fiber cells and persisted throughout lens development. To examine the functional contribution of c-Maf to lens development, we isolated genomic clones encompassing the murine c-maf gene and carried out its targeted disruption. Insertion of the beta-galactosidase (lacZ) gene into the c-maf locus allowed visualization of c-Maf accumulation in heterozygous mutant mice by staining for LacZ activity. Homozygous mutant embryos and newborns lacked normal lenses. Histological examination of these mice revealed defective differentiation of lens fiber cells. The expression of crystallin genes was severely impaired in the c-maf-null mutant mouse lens. These results demonstrate that c-Maf is an indispensable regulator of lens differentiation during murine development.

Mutational analysis of amino acid residues involved in argininosuccinate lyase activity in duck delta II crystallin

Delta-crystallins are the major structural eye lens proteins of most birds and reptiles and are direct homologues of the urea cycle enzyme argininosuccinate lyase. There are two isoforms of delta-crystallin, delta Iota and delta IotaIota, but only delta IotaIota crystallin exhibits argininosuccinate lyase (ASL) activity. At the onset of this study, the structure of argininosuccinate lyase/delta IotaIota crystallin with bound inhibitor or substrate analogue was not available. Biochemical and X-ray crystallographic studies had suggested that H162 may function as the catalytic base in the argininosuccinate lyase/delta IotaIota crystallin reaction mechanism, either directly or indirectly through the activation of a water molecule. The identity of the catalytic acid was unknown. In this study, the argininosuccinate substrate was modeled into the active site of duck delta IotaIota crystallin, using the coordinates of an inhibitor-bound Escherichia coli fumarase C structure to orient the fumarate moiety of the substrate. The model served as a means of identifying active site residues which are positioned to potentially participate in substrate binding and/or catalysis. On the basis of the results of the modeling, site-directed mutagenesis was performed on several amino acids, and the kinetic and thermodynamic properties of each mutant were determined. Kinetic studies reveal that five residues, R115, N116, T161, S283, and E296, are essential for catalytic activity. Determination of the free energy of unfolding/refolding of wild-type and mutant delta II crystallins revealed that all constructs exhibit similar thermodynamic stabilities. During the course of this work, the structure of an inactive delta IotaIota crystallin mutant with bound substrate was solved [Vallee et al. (1999) Biochemistry 38, 2425-2434], which has allowed the kinetic data to be interpreted on a structural basis.

Cellular and molecular features of lens differentiation: a review of recent advances

In this paper, the more recent literature pertaining to differentiation in the developing vertebrate lens is reviewed in relation to previous work. The literature reviewed reveals that the developing lens has been, and will continue to be, a useful model system for the examination of many fundamental processes occurring during embryonic development. Areas of lens development reviewed here include: the induction and early embryology of the lens; lens cell culture techniques; the role of growth factors and cytokines; the involvement of gap junctions in lens cell-cell communication; the role of cell adhesion molecules, integrins, and the extracellular matrix; the role of the cytoskeleton; the processes of programmed cell death (apoptosis) and lens fibre cell denucleation; the involvement of Pax and Homeobox genes; and crystallin gene regulation. Finally, some speculation is provided as to possible directions for further research in lens development.

Distinctive immunohistochemical profiles of small heat shock proteins (heat shock protein 27 and alpha B-crystallin) in human brain tumors

BACKGROUND

Recent studies have described alpha B-crystallin as a member of the small heat shock protein (HSP) family, and the expressions of alpha-crystallin-related small heat shock proteins, namely HSP27 and alpha B-crystallin, in the brain appear to be regulated in a similar way by various stress conditions.

METHODS

A comparative immunohistochemical analysis was performed on 198 human brain tumors to examine the expressions of HSP27 and alpha B-crystallin.

RESULTS

Positive staining with HSP27 was frequently observed in schwannomas, craniopharyngiomas, epidermoid cysts, and metastatic tumors to the brain. The immunopositivity of HSP27 was relatively low in tumors originating from neuroepithelium as well as in meningiomas; however, a statistically significantly higher percentage of HSP27-positive cells was noted in their anaplastic counterparts, such as glioblastomas, anaplastic oligodendrogliomas, anaplastic ependymomas, and anaplastic meningiomas (P < 0.005). Conversely, a positive immunoexpression of alpha B-crystallin was frequently observed among astrocytic tumors, schwannomas, hemangioblastomas, and chordomas.

CONCLUSIONS

The immunohistochemical expression of HSP27 and alpha B-crystallin differed among histologic types of tumors. Furthermore, the immunopositivity of HSP27, which was considered to play a role not only in drug resistance but also in the regulation of cell proliferation, increased in proportion to the anaplasia of the tumors.

Multifactional glucanases

Diverse functional roles of multifunctional proteins arise from either their independent functional domains or dual activities mediated through a single active site. Presence of multifunctional proteins significantly enhances the metabolic efficiency of a cell. Microorganisms utilising complex substrates with extensive microheterogeneities, such as carbohydrates evolved batteries of multifunctional glucanases, facilitating parsimonious utilisation of these substrates. Various attempts have since been made to artificially construct these glucanases. Analysis of information on various glucanases would be helpful in understanding the evolutionary interrelationship between this class of enzymes and will give an insight into the structural features controlling different unrelated activities. This review examines the genesis, evolution and structural features of multifunctional glucanases.

Transgenic models for eye malformations

Several lines of transgenic mice developing eye malformations have been described in the literature and appear to be of increasing interest for the study of eye teratology in humans, since gene expression and regulation can be studied in the developing animal. Transgenic applications are briefly described here and an overview of existing transgenic mouse models carrying different eye abnormalities is given according to the major diagnosis (e.g., cataract, microphthalmia, anterior segment dysgenesis, retinal dysplasia). Interestingly, many transgenic models exhibit pathological findings similar to those observed in human pediatric ophthalmology. Unfortunately, detailed embryological studies in transgenic mice bearing congenital eye malformations are not available for all lines. Thus, the importance of creating further transgenic models to study the function of morphogenes and growth factors in eye development is also discussed.

Murine transcription factor alpha A-crystallin binding protein I. Complete sequence, gene structure, expression, and functional inhibition via antisense RNA

alpha A-crystallin binding protein I (alpha A-CRYBP1) is a ubiquitously expressed DNA binding protein that was previously identified by its ability to interact with a functionally important sequence in the mouse alpha A-crystallin gene promoter. Here, we have cloned a single copy gene with 10 exons spanning greater than 70 kb of genomic DNA that encodes alpha A-CRYBP1. The mouse alpha A-CRYBP1 gene specifies a 2,688-amino acid protein with 72% amino acid identity to its human homologue, PRDII-BF1. Both the human and the mouse proteins contain two sets of consensus C2H2 zinc fingers at each end as well a central nonconsensus zinc finger. The alpha A-CRYBP1 gene produces a 9.5-kb transcript in 11 different tissues as well as a testis-specific, 7.7-kb transcript. alpha A-CRYBP1 cDNA clones were isolated from adult mouse brain and testis as well as from cell lines derived from mouse lens (alpha TN4-1) and muscle (C2C12). A single clone isolated from the muscle C2C12 library contains an additional exon near the 5'-end that would prevent production of a functional protein if the normal translation start site were utilized; however, there is another potential initiation codon located downstream that is in frame with the rest of the coding region. In addition, we identified multiple cDNAs from the testis in which the final intron is still present. Finally, we used an antisense expression construct derived from an alpha A-CRYBP1 cDNA clone to provide the first functional evidence that alpha A-CRYBP1 regulates gene expression. When introduced into the alpha TN4-1 mouse lens cell line, the antisense construct significantly inhibited expression from a heterologous promoter that utilized the alpha A-CRYBP1 binding site as an enhancer.

Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology

alpha-Crystallin is a high-molecular-mass protein that for many decades was thought to be one of the rare real organ-specific proteins. This protein exists as an aggregate of about 800 kDa, but its composition is simple. Only two closely related subunits termed alpha A- and alpha B-crystallin, with molecular masses of approximately 20 kDa, form the building blocks of the aggregate. The idea of organ-specificity had to be abandoned when it was discovered that alpha-crystallin occurs in a great variety of nonlenticular tissues, notably heart, kidney, striated muscle and several tumors. Moreover alpha B-crystallin is a major component of ubiquinated inclusion bodies in human degenerative diseases. An earlier excitement arose when it was found that alpha B-crystallin, due to its very similar structural and functional properties, belongs to the heat-shock protein family. Eventually the chaperone nature of alpha-crystallin could be demonstrated unequivocally. All these unexpected findings make alpha-crystallin a subject of great interest far beyond the lens research field. A survey of structural data about alpha-crystallin is presented here. Since alpha-crystallin has resisted crystallization, only theoretical models of its three-dimensional structure are available. Due to its long life in the eye lens, alpha-crystallin is one of the best studied proteins with respect to post-translational modifications, including age-induced alterations. Because of its similarities with the small heat-shock proteins, the findings about alpha-crystallin are illuminative for the latter proteins as well. This review deals with: structural aspects, post-translational modifications (including deamidation, racemization, phosphorylation, acetylation, glycation, age-dependent truncation), the occurrence outside of the eye lens, the heat-shock relation and the chaperone activity of alpha-crystallin.

Close packing of an oligomeric eye lens beta-crystallin induces loss of symmetry and ordering of sequence extensions

beta-Crystallins are oligomeric eye lens proteins that are related to monomeric gamma-crystallins. The main sequence difference between the two families is the presence of sequence extensions in the beta-crystallins. A major question concerns the role that these extensions play in mediating interactions at the high protein concentrations found in the lens. The predominant beta-crystallin polypeptide, beta B2, can be crystallized in two different space groups, I222 and C222. The I222 crystal structure revealed that the protein packed as a tetramer with perfect 222 symmetry but that the extensions were disordered. The X-ray structure of the C222 lattice of beta B2 has now been refined at 3.3 A, the structure analysed and compared with the I222 lattice. The protein is also a tetramer with 222 symmetry in the C222 lattice but differs in that parts of the N-terminal extensions have been visualized. In the asymmetric unit of the C222 lattice there are four subunits, each comprising a single polypeptide chain, in which certain flexible loops in the N-terminal domains and the N-terminal extensions have various conformations. The tetramers in the C222 lattice are more tightly packed than in the I222 form. Analysis of the tetramer contacts shows that the sites of interaction break the 222 symmetry of the tetramers. The N-terminal extensions play a major role in directing interactions between tetramers. One of the N-terminal extensions interacts with a hydrophobic patch on the N-terminal domain of another tetramer. These crystallographic observations obtained over a physiological concentration range indicate how, in beta-crystallin oligomers, the N-terminal extensions of beta B2 can switch from interacting with water to interacting with protein depending on their relative concentrations. This could be useful in maintaining a gradient of refractive index.

Expression of alpha B-crystallin in human brain tumors

We have previously shown that alpha B-crystallin is a heat-shock protein which specifically accumulates in response to the expression of c-Ha-ras and v-mos oncogenes in mouse NIH 3T3 fibroblasts. Elevated levels of alpha B-crystallin mRNA or protein were shown to be associated with pathological conditions of the brain. Therefore, we have examined the expression of alpha B-crystallin in normal human brains and brain tumors by Western blot analysis. alpha B-crystallin is moderately expressed in adult but not fetal brain. Elevated levels of alpha B-crystallin expression are observed in glial tumors such as astrocytoma, glioblastoma multiforme, and oligodendroglioma. alpha B-crystallin in these tumors is predominately unphosphorylated. High amounts of accumulated alpha B-crystallin in astrocytic tumors are preferentially found in the more aggressive stages. Glioblastoma multiforme is exceptional in that high alpha B-crystallin expression is observed in only one half of the analyzed samples whereas no alpha B-crystallin could be detected in the other. These results indicate that alpha B-crystallin may be a useful biochemical marker for studying the pathogenesis of various human brain tumors.