Association of IRF5 polymorphisms with increased risk for systemic lupus erythematosus in population of Crete, a southern-eastern European Greek island.

Interferon regulatory factor 5 (IRF5) regulates type I interferon (IFN)-responsive genes, and has been one of the most consistently associated genes with systemic lupus erythematosus (SLE). We sought to investigate whether IRF5 haplotypes are associated with risk for SLE in the genetically homogeneous Greek population of the island of Crete, as well as whether these haplotypes are associated with increased type I IFN. 322 SLE patients and 247 healthy controls from Crete were genotyped for rs2004640, rs3807306, rs10488631 and rs2280714 SNPs of IRF5 gene by using Taqman primer-probe sets. Type I IFN levels were measured using a functional reporter cell assay. All IRF5 SNPs examined were found to be associated with SLE in univariate case-control analysis. The 4 SNPs formed 5 major haplotypes and the Neanderthal-derived TACA risk haplotype was present in Crete and enriched in the SLE cases (OR=2.01, P=0.0003). Serum IFN levels were measured in a subset of the SLE patients, and carriage of the TACA haplotype was associated with higher circulating type I IFN levels (P=0.037). This study demonstrates the association of IRF5 with an increased susceptibility for SLE in the population of Crete and emphasizes the association of the Neanderthal-derived IRF5 haplotype with SLE susceptibility. Patients carrying allele the Neanderthal allele C had greater type I IFN, supporting a functional consequence of this polymorphism.

Investigation of the genetic overlap between rheumatoid arthritis and psoriatic arthritis in a Greek population.

OBJECTIVES: Several rheumatoid arthritis (RA) susceptibility loci have also been found to be associated with psoriatic arthritis (PsA), demonstrating that there is a degree of genetic overlap between various autoimmune diseases. We sought to investigate whether single nucleotide polymorphisms (SNPs) mapping to previously reported RA and/or PsA susceptibility loci, including PLCL2, CCL21, REL, STAT4, CD226, PTPN22, and TYK2, are associated with risk for the two diseases in a genetically homogeneous Greek population. METHOD: This study included 392 RA patients, 126 PsA patients, and 521 healthy age- and sex-matched controls from Greece. Genotyping of the SNPs was performed with Taqman primer/probe sets. Bioinformatic analysis was performed using BlastP, PyMOL, and Maestro and Desmond. RESULTS: A significant association was detected between the GC genotype of rs34536443 (TYK2) in both the PsA and RA cohorts. The C allele of this SNP was associated with PsA only. Evidence for association with PsA was also found for the GG genotype and G allele of the rs10181656 SNP of STAT4. The TC genotype of the rs763361 SNP of CD226 was associated with PsA only. CONCLUSIONS: Genetic overlap between PsA and RA was detected for the rs34536443 SNP of the TYK2 gene within a Greek population. An association of STAT4 (rs10181656) with PsA was confirmed whereas CD226 (rs763361) was associated with PsA but not with RA, in contrast to previous reports. The different findings of this study compared to previous ones highlights the importance of comparative studies that include various ethnic or racial populations.

Association of juvenile idiopathic arthritis with PTPN22 rs2476601 is specific to females in a Greek population.

BACKGROUND: Juvenile idiopathic arthritis (JIA) is an autoimmune disease characterized by persistent chronic arthritis. Disease risk is believed to be influenced by both genetic and environmental factors. It is well established that the PTPN22 single nucleotide polymorphism (SNP) rs2476601 is associated with JIA susceptibility. It was recently reported in an Australian study that this association is restricted to females and is not observed in males. A significant source of inconsistency amongst the literature on autoimmune disease susceptibility genes stems from an inability to replicate genetic findings across different racial or ethnic groups. We therefore attempted to generate further evidence of the female-specific association of rs2476601 in a homogeneous Greek population. FINDINGS: We genotyped rs2476601 in 128 Caucasian JIA patients (70.3 % female) and 221 healthy controls (28.1 % female) from Northern Greece. Overall, PTPN22 was associated with increased risk of JIA in this Greek sample (OR = 2.3, 95 % CI 1.1 - 5.1, p = 0.038). Sex-stratified analyses showed that, once again, the risk association was restricted to females (Female: OR = 19.9, 95 % CI 1.2 - 342, p = 0.0016; Male: OR = 1.1, 95 % CI 0.3 - 3.1, p = 0.94) supporting the prior findings. CONCLUSIONS: Our data demonstrates that this sex-specific pattern of association is broadly applicable to different populations, and provides further impetus to undertake mechanistic studies to understand the impact of sex on PTPN22 in JIA.

Gene expression analysis in RA: towards personalized medicine.

Gene expression has recently been at the forefront of advance in personalized medicine, notably in the field of cancer and transplantation, providing a rational for a similar approach in rheumatoid arthritis (RA). RA is a prototypic inflammatory autoimmune disease with a poorly understood etiopathogenesis. Inflammation is the main feature of RA; however, many biological processes are involved at different stages of the disease. Gene expression signatures offer management tools to meet the current needs for personalization of RA patients' care. This review analyses currently available information with respect to RA diagnostic, prognostic and prediction of response to therapy with a view to highlight the abundance of data, whose comparison is often inconclusive due to the mixed use of material source, experimental methodologies and analysis tools, reinforcing the need for harmonization if gene expression signatures are to become a useful clinical tool in personalized medicine for RA patients.

The effect of RFC G80A polymorphism in Cretan children with acute lymphoblastic leukemia and its interaction with MTHFR C677T and A1298C polymorphisms.

INTRODUCTION: The association between the risk of acute lymphoblastic leukemia (ALL) in children and enzymes involved in the folate metabolism has been under investigation lately. The reduced folate carrier gene (RFC) encodes reduced folate carrier, a protein that transports into the cell both folate and methotrexate, a commonly used chemotherapeutic drug, has been proved polymorphic at position 80 (G→A). The role of this polymorphism in childhood ALL and its interaction with other enzymes of the folate metabolic pathway, including MTHFR, has been examined in different populations with diverse results. METHODS: In the present case-control study, 35 children with ALL and 48 healthy adult blood donors, all originating from the island of Crete (Greece), were screened for the presence of the RFC G80A polymorphism, using PCR/RFLP techniques. The effect on ALL risk and methotrexate-induced toxicities, along with the role of gene-gene interactions in our population, were examined. RESULTS: No significant association was observed between the RFC G80A genotypes and either the development of ALL or the presence of adverse events. However, a significant association was detected between the MTHFR A1298C/ RFC G80A genotype and a nonpredisposition for ALL (P = 0.035). CONCLUSION: This study suggests that gene-gene interactions in childhood ALL may be of prognostic value in our population.

Genetic variation near IRF8 is associated with serologic and cytokine profiles in systemic lupus erythematosus and multiple sclerosis.

Alleles of interferon (IFN) regulatory factor 8 (IRF8) are associated with susceptibility to both systemic lupus erythematosus (SLE) and multiple sclerosis (MS). Although high-type I IFN is thought to be causal in SLE, type I IFN is used as a therapy in MS. We investigated whether IRF8 alleles were associated with type I IFN levels or serologic profiles in SLE and MS. Alleles that have been previously associated with SLE or MS were genotyped in SLE and MS patients. The MS-associated rs17445836G allele was associated with anti-double-stranded DNA (dsDNA) autoantibodies in SLE patients (meta-analysis odds ratio=1.92). The same allele was associated with decreased serum IFN activity in SLE patients with anti-dsDNA antibodies, and with decreased type I IFN-induced gene expression in peripheral blood mononuclear cell from anti-dsDNA-negative SLE patients. In secondary progressive MS patients, rs17445836G was associated with decreased serum type I IFN. Rs17445836G was associated with increased IRF8 expression in SLE patient B cells. In summary, IRF8 rs17445836G is associated with human autoimmune disease characterized by low-type I IFN levels, and this may have pharmacogenetic relevance as type I IFN is modulated in SLE and MS. The association with autoantibodies and increased IRF8 expression in B cells supports a role for rs17445836G in humoral tolerance.

Investigation of juvenile idiopathic arthritis susceptibility loci: results from a Greek population.

The strategy of studying the putative role of RA susceptibility genetic factors in the development of juvenile idiopathic arthritis (JIA), an autoimmune disease characterized by persistent chronic arthritis, has been proven highly successful so far. Moreover, accumulated evidence indicates that an ethnic heterogeneity of genetic factors exists for rheumatic disorders. We investigated whether five single nucleotide polymorphisms (SNPs), previously found to be associated with JIA in various populations so far, are also associated with JIA in Greece. The sample set consisted of 128 Caucasian JIA patients and 221 healthy controls from Northern Greece. Five Single Nucleotide Polymorphisms (SNPs) markers, namely TRAF1/C5 rs10818488, PTPN22 rs2476601, STAT4 rs7574865, CD247 rs1773560 and PTPN2 rs7234029 SNPs were genotyped in a case-control study with Restriction Fragment Length Polymorphisms (RFLPs) or Taqman primer-probe sets. This study demonstrated for the first time in a Greek population that the PTPN22, TRAF1/C5 and CD247 polymorphisms examined are associated with an increased susceptibility to JIA, thus suggesting that the respective risk alleles may confer susceptibility to clinically distinct disorders. However, our results did not demonstrate any association of STAT4 and PTPN2 SNPs with the disease in our population, thus highlighting the importance of comparative studies in different ethnic populations.

Genetic variants in the region of the C1q genes are associated with rheumatoid arthritis.

Rodent models for arthritis implicate a role for complement in disease development and progression. In humans, complement deposition has been observed in inflamed synovia of rheumatoid arthritis (RA) patients. In this study we analysed whether genetic variants of complement component C1q predispose to RA. We genotyped single nucleotide polymorphisms (SNPs) in and around the C1q genes, C1qA, C1qB and C1qC, in a Dutch set of 845 RA cases and 1046 controls. Replication was sought in a sample set from North America (868 cases/1193 controls), and a meta-analysis was performed in a combined samples set of 8000 cases and 23 262 controls of European descent. We determined C1q serum levels in relation to C1q genotypes. In the discovery phase, five of the 13 SNPs tested in the C1q genes showed a significant association with RA. Additional analysis of the genomic area around the C1q genes revealed that the strongest associating SNPs were confined to the C1q locus. Within the C1q locus we observed no additional signal independent of the strongest associating SNP, rs292001 [odds ratio (OR) = 0·72 (0·58-0·88), P = 0·0006]. The variants of this SNP were associated with different C1q serum levels in healthy controls (P = 0·006). Interestingly, this SNP was also associated significantly in genome-wide association studies (GWAS) from the North American Rheumatoid Arthritis Consortium study, confirming the association with RA [OR = 0·83 (0·69-1·00), P = 0·043]. Combined analysis, including integrated data from six GWAS studies, provides support for the genetic association. Genetic variants in C1q are correlated with C1q levels and may be a risk for the development of RA.

Polymorphisms of genes related to endothelial cells are associated with primary biliary cirrhosis patients of Cretan origin.

BACKGROUND: Primary biliary cirrhosis (PBC) is an organ specific autoimmune disease of still unidentified genetic etiology. We have shown that endothelins (ETs), produced by the liver endothelial cells are increased in PBC and may play a major pathogenetic role. AIMS: To study gene polymorphisms related to the endothelial cells (eNOS, EDN-1 genes) and, to investigate whether the previously reported association of CTLA4 gene polymorphisms is replicated in a genetically homogeneous Greek population. PATIENTS AND METHODS: Genomic DNA was extracted from 100 PBC patients (83 females, 93% AMA+, 74/100 Ludwig stage I-II) and 158 healthy controls. eNOS, CTLA4 and ET1 polymorphisms were determined by PCR-RFLPs analysis. RESULTS: Both eNOS intron4 VNTR and eNOS exon7 G894T SNP were significantly associated with increased risk in PBC. EDN-11 rs2071942 "A" and rs5370 "T" alleles appeared a tendency for association with disease progression. No association was found between PBC and the CTLA4 SNPs analyzed. CONCLUSIONS: We demonstrated that eNOS, a gene related to the liver endothelium function is associated with PBC. Contrarily, the important in adaptive immunity gene CTLA4 was not associated with the disease in the homogeneous population analyzed. These results are compatible partially with our previous hypothesis that defects of the liver endothelial system, leading to endothelin overproduction, may be a fundamental early pathogenetic mechanism in PBC.

Association of the PTPN22 R620W polymorphism with increased risk for SLE in the genetically homogeneous population of Crete.

Autoimmune diseases affect approximately 5% of the population, but much work remains to define the genetic risk factors and pathogenic mechanisms underlying these conditions. There is accumulating evidence that common genetic factors might predispose to multiple autoimmune disorders. Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are complex autoimmune disorders with multiple susceptibility genes. The functional R620W (C1858T) polymorphism of the protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene, a member of the PTPs that negatively regulate T-cell activation, has been recently associated with susceptibility to various autoimmune diseases. The aim of this study was to assess whether the C1858T polymorphism of PTPN22 also confers increased risk for SLE and RA in the genetically homogeneous population of Crete. It was found that the minor T allele of the PTPN22 C1858T SNP was more common in SLE patients than in control individuals (odds ratio [OR] = 1.91, 95% confidence interval [CI] = 1.11 to 3.9, p = 0.017). No significant difference was observed in the frequency of this allele when RA patients were compared with controls (OR = 1.14, 95% CI = 0.65 to 1.9, p = 0.64). Although the PTPN22 1858 T allele is found at decreased frequency in Southern Europe, including Crete, an association was found between this allele and SLE in the population studied.

Intron 4 polymorphism of the endothelial nitric oxide synthase eNOS gene and early microangiopathy in type 1 diabetes.

Nitric oxide (NO) is an endogenous vasodilator involved in inflammatory and autoimmune response, and in the pathophysiology of diabetic vascular disease. Endothelium-derived NO is formed from L-arginine by endothelial NO synthase (eNOS), and earlier studies have provided evidence for altered NO metabolism and impaired endothelial function in diabetes, probably due to polymorphisms in eNOS gene. In the present study we investigated the association of the eNOS gene intron 4 a/b VNTR polymorphism with diabetic microangiopathy in 61 young individuals with type 1 diabetes (T1D), 35 male and 26 female, aged 5.0-29.1 (mean 15.6) years, and followed up for 3.24-11.4 (mean 7.44) years. Ten patients (16.4%) had developed microalbuminuria, three hypertension and two retinopathy. Wild-type b/b homozygosity for eNOS gene intron 4 VNTR was found in 37 (60.7%) and a/b polymorphism in 24 (39.3%). No significant relationship was demonstrated between eNOS gene intron 4 polymorphisms and microalbuminuria, hypertension or retinopathy in these young individuals. Our findings suggest that a/b polymorphism of the intron 4 eNOS gene is not associated with early onset diabetic microangiopathy.

Familial Mediterranean Fever in Crete: a genetic and structural biological approach in a population of 'intermediate risk'.

Familial Mediterranean Fever (FMF) is an autosomal, recessively inherited disease, characterized by recurrent and short attacks of fever with serosal inflammation that are caused by mutations in MEFV gene that encodes pyrin protein. To date, more than 70 disease-associated mutations have been identified, almost all of them representing missense nucleotide changes. FMF is very common among patients with Mediterranean ancestry, although the exact prevalence is not yet known, Greeks are considered to be at 'intermediate risk'. In the present study, we studied FMF patients in natives of Crete, a population sharing a common genetic and cultural background. The spectrum of MEFV gene mutations in 71 patients as well as 158 healthy controls was studied by performing a molecular analysis focused on the 12 most frequent FMF-associated mutations. We found that 59 of 71 (83.1%) FMF patients had at least one MEFV mutation, five patients were homozygotes and 54 heterozygotes for FMF-associated mutations. No mutations were detected in 12 patients (16.9%). As in high-risk populations, common MEFV mutations were found in Cretan FMF patients, with the M694V being the most penetrant. M694V and M694I mutations were associated with severe phenotypes, with many patients presenting with uncommon clinical manifestations such as erysipelas-like erythema or renal disturbances. Of interest, 20 (37%) of our heterozygous FMF patients presented with a severe phenotype. Population genetics analysis showed an FMF carrier frequency in healthy Cretan population of approximately 6% (1:17) and places Cretans closer to the Western rather than Eastern populations of the Mediterranean basin. Finally, we constructed a three-dimensional model showing the interaction of the PRYSPRY domain of pyrin with caspase-1 onto which we mapped MEFV mutations, classified according to disease severity. In this model, the 'flexible loops' of caspase-1 appear to have no access to some positions that have been previously associated with mild disease, suggesting that alternative pathogenic pathways leading to FMF need to be explored.

Inflammasomes and rheumatic diseases: evolving concepts.

The realisation that the production of inflammatory cytokines in inflammatory rheumatic diseases may be induced by non-infectious endogenous signals has encouraged researchers to explore mechanisms of innate immunity and their contribution to the pathogenesis of these diseases. The nucleotide-binding and oligomerisation domain (NOD)-like receptors (NLRs) sense pathogens, products of damaged cells or endogenous metabolites and could potentially be involved in the initiation, amplification and progression of the inflammatory response in rheumatic diseases. NLRs are involved in the regulation of innate immune responses with some of them promoting the activation of inflammatory caspases within multiprotein complexes, called inflammasomes. A typical inflammasome consists of a sensor, an NLR protein, an adaptor protein such as ASC (for apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) and an effector protein that is a caspase that activates pro-inflammatory cytokines such as interleukin (IL)1beta and IL18. Recent data suggest a role of the inflammasome in the pathogenesis of autoinflammatory as well as inflammatory rheumatic diseases such as juvenile chronic arthritis, adult onset Still disease, rheumatoid arthritis and gout. Modulation of these pathways may be a potential therapeutic target for inflammatory rheumatic diseases.

Association of the nitric oxide synthase (eNOS) gene polymorphism with increased risk for both lupus glomerulonephritis and rheumatoid arthritis in a single genetically homogeneous population.

Nitric oxide (NO), a short-lived gaseous free radical, synthesized from L-arginine by NO synthases (NOS), is a potent mediator of biologic responses involved in the pathogenesis of autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Most biological necessary NO is produced by the family of three NOS. To date, several functionally relevant genetic polymorphisms in the eNOS gene have been associated with various vascular, infectious and autoimmune diseases. To our knowledge, no study has explored these polymorphisms for both SLE and RA in the same population. The objective of this study was to investigate the influence of the eNOS gene intron 4 a/b VNTR polymorphism (a 27-base-pair tandem repeat-based polymorphism) on susceptibility to SLE and RA in patients living in the island of Crete, a genetically homogeneous population. A group of 145 healthy subjects and 190 SLE patients were included in this study. Similarly, a second group of 235 healthy controls and 202 RA patients were analysed. In both cases, patients and controls were sex- and age-matched. Herein we report that the presence of a/b genotype of the eNOS gene may act as a risk factor not for the presence of SLE but for the development of glomerulonephritis (OR 2.71, 95% CI: 1.4-5.2), while it may be a susceptibility gene for RA (OR: 2.005, 95% CI: 1.31-3.07). Thus, in our population, the a/b genotype of the eNOS gene represents a severity rather than a susceptibility genotype for SLE.

Mutational analysis of the PRYSPRY domain of pyrin and implications for familial mediterranean fever (FMF).

Familial Mediterranean fever (FMF) is an autosomal, recessively inherited disease, characterized by recurrent fever and serositis that affects mainly patients of the Mediterranean basin. The gene responsible for FMF, named MEFV, was cloned and several missense mutations were found to be responsible for the disease. Based on a recent molecular analysis of MEFV gene mutations in 43 patients from Crete aiming to correlate specific genotypes and clinical manifestations of FMF, we were prompted to construct a three-dimensional model (3-D model) of the PRYSPRY domain of pyrin. The majority of the known MEFV mutations located on this domain have been classified, according to disease severity, and localized on this 3-D model. The functional consequences of these mutations and their implications on disease severity are discussed. Moreover, we report a putative novel missense mutation, S702C, which we identified in exon 10 of the MEFV gene and localized on the constructed 3-D model.

Effect of acetone feeding on alcohol dehydrogenase activity in the olive fruit fly, Bactrocera oleae.

The purpose of this study is to demonstrate a clear connection between the presence of acetone in larval diet and alcohol dehydrogenase (ADH) activity in laboratory raised populations of Bactrocera oleae. ADH activity of B. oleae is depressed in acetone-impregnated diets. At the same time the change of activity is accompanied by a change in the relative proportions of the multiple forms of ADH. The bulk of activity in the most cathodally migrating form is lost, and all the activity becomes localized in the less cathodally migrating forms of the enzyme. Moreover, ADH activity, expressed in vivo, appears to drop after exposure to acetone, as shown by the fact that larvae become less sensitive to pentenol poisoning. Our results show clear selective differences imposed by acetone on three homozygous genotypes involving the ADH alleles F, S and I in B. oleae. The directions of these differences were found to vary with the fitness component under test. Acetone treatment seems to affect developmental time and larva's viability as well as allele frequencies of ADH under artificial rearing. The effect of acetone on the maintenance of ADH polymorphism in artificially reared populations of B. oleae is further discussed.

Characterization of two alcohol dehydrogenase (Adh) loci from the olive fruit fly, Bactrocera (Dacus) oleae and implications for Adh duplication in dipteran insects.

We report the cloning and structural characterization of two Adh loci of the olive fruit fly, Bactrocera oleae. Each of the two genes, named Adh1 and Adh2, consists of three exons and two introns for a total length of 1981 and 988 nucleotides, respectively. Their deduced amino acid sequences of 257 and 258 residues exhibit a 77% identity and display the characteristics of the insect ADH enzymes, which belong to the short-chain dehydrogenases/reductases family. The Adh genes of B. oleae are compared to the two genes of the Mediterranean fly, Ceratitis capitata, the only other species of the Tephritidae family in which the Adh genes have been studied. On the basis of amino acid divergence the four genes form two clusters each containing one gene from each species, as expected if there was one duplication event before speciation. On the basis of nucleotide sequence the four sequences form two clusters each containing the two sequences from the same species, as expected if there was a separate duplication event in each species. To help decide between the two alternatives, we compared at both the amino acid and DNA level the Adh genes of five Drosophila species that are known to carry two such genes and observed that, with only one exception at the amino acid level, conspecific loci cluster together. We conclude that the information we have at present does not allow a firm choice between the hypothesis of a single duplication event that occurred before the split of Bactrocera and Ceratitis from their common ancestor and the hypothesis of two independent duplication events, one in each of the two genera.

The actin loci in the genus Drosophila: establishment of chromosomal homologies among five palearctic species of the Drosophila obscura group by in situ hybridization.

Chromosomal homologies among the four palearctic Drosophila obscura group species D. ambigua, D. tristis, D. obscura, and D. subsilvestris and the "trans-palearctic" species D. bifasciata were established by in situ hybridization using the 5C actin gene of D. melanogaster as a probe. In all species two labeling sites were detected in each of chromosomal elements C and E and one in each of chromosomal elements A and D. In addition one labeling site was detected on element B for the species D. subsilvestris and D. bifasciata. The conservative distribution pattern of the genes of the actin multigene family, the similarities of the locations of the actin genes in the chromosomes of the five species studied, together with the concordant evidence of synteny of visible and other genetic markers as well as the similarities in banding patterns, all agree with the conclusion that the chromosomal elements have retained their essential identity throughout the evolution of these species. Using in situ hybridization detailed information of some homologous regions of chromosomes can also be established.

Essential role for gamma-tubulin in the acentriolar female meiotic spindle of Drosophila.

Microtubule nucleation in vivo requires gamma-tubulin, a highly conserved component of microtubule-organizing centers. In Drosophila melanogaster there are two gamma-tubulin genes, gammaTUB23C and gammaTUB37C. Here we report the cytological and molecular characterization of the 37C isoform. By Western blotting, this protein can only be detected in ovaries and embryos. Antibodies against this isoform predominantly label the centrosomes in embryos from early cleavage divisions until cycle 15, but fail to reveal any particular localization of gamma-tubulin in the developing egg chambers. The loss of function of this gene results in female sterility and has no effect on viability or male fertility. Early stages of oogenesis are unaffected by mutations in this gene, as judged both by morphological criteria and by localization of reporter genes, but the female meiotic spindle is extremely disrupted. Nuclear proliferation within the eggs laid by mutant females is also impaired. We conclude that the expression of the 37C gamma-tubulin isoform of D. melanogaster is under strict developmental regulation and that the organization of the female meiotic spindle requires gamma-tubulin.

To bead or not to bead? Lens-specific intermediate filaments revisited.

For nearly three decades cytoplasmic intermediate filaments (IFs) have been described as 10 nm thick, unbranched ropes radiating from the cell nucleus and extending to the plasma membrane. This stereotype is now being challenged by the discovery and molecular characterization of the beaded filaments (BFs), a novel class of IFs composed of the lens-specific proteins filensin and phakinin. In contrast to 'mainstream' IFs, BFs have a distinctly nodular appearance and form a meshwork underneath the plasma membrane of the lens fiber cells. In vitro assembly studies, expression of filensin and phakinin in cultured cells, and analysis of the corresponding genes reveal that these proteins have evolved from two different subfamilies of IF proteins, thus yielding a unique structure. The new information provides a basis for understanding how the various forms of tissue-specific IF proteins might have developed adopting to the constraints of a specialized environment.