Following the adverse outcome pathway from micronucleus to cancer using H2B-eGFP transgenic healthy stem cells.

In vitro assessment of genotoxicity as an early warning tool for carcinogenicity mainly relies on recording cytogenetic damages (micronuclei, nucleoplasmic bridges) in tumour-derived mammalian cell lines like V79 or CHO. The forecasting power of the corresponding standardised test is based on epidemiological evidence between micronuclei frequencies and cancer incidence. As an alternative to destructive staining of nuclear structures a fish stem cell line transgenic for a fusion protein of histone 2B (H2B) and enhanced green fluorescent protein (eGFP) was established. The cells are derived from koi carp brain (KCB) and distinguish from mammalian culturable cells by non-tumour-driven self-renewal. This technology enables the analysis of genotoxic- and malign downstream effects in situ in a combined approach. In proof-of concept-experiments, we used known carcinogens (4-Nitroquinoline 1-oxide, colchicine, diethylstilbestrol, ethyl methanesulfonate) and observed a significant increase in micronuclei (MNi) frequencies in a dose-dependent manner. The concentration ranges for MNi induction were comparable to human/mammalian cells (i.e. VH-16, CHL and HepG2). Cannabidiol caused the same specific cytogenetic damage pattern as observed in human cells, in particular nucleoplasmic bridges. Metabolic activation of aflatoxin B1 and cyclophosphamide could be demonstrated by pre-incubation of the test compounds using either conventional rat derived S9 mix as well as an in vitro generated biotechnological alternative product ewoS9R. The presented high throughput live H2B-eGFP imaging technology using non-transformed stem cells opens new perspectives in the field of in vitro toxicology. The technology offers experimental access to investigate the effects of carcinogens on cell cycle control, gene expression pattern and motility in the course of malign transformation. The new technology enables the definition of Adverse Outcome Pathways leading to malign cell transformation and contributes to the replacement of animal testing. Summary: Complementation of genotoxicity testing by addressing initiating events leading to malign transformation is suggested. A vertebrate cell model showing "healthy" stemness is recommended, in contrast to malign transformed cells used in toxicology/oncocology.

A novel and ancient group of type I keratins with members in bichir, sturgeon and gar.

BACKGROUND: Vertebrate epithelial cells typically express a specific set of keratins. In teleosts, keratins are also present in a variety of mesenchymal cells, which usually express vimentin. Significantly, our previous studies revealed that virtually all known teleost keratins evolved independently from those present in terrestrial vertebrates. To further elucidate the evolutionary scenario that led to the large variety of keratins and their complex expression patterns in present day teleosts, we have investigated their presence in bichir, sturgeon and gar. RESULTS: We have discovered a novel group of type I keratins with members in all three of these ancient ray-finned fish, but apparently no counterparts are present in any other vertebrate class so far investigated, including the modern teleost fish. From sturgeon and gar we sequenced one and from bichir two members of this novel keratin group. By complementary keratin blot-binding assays and peptide mass fingerprinting using MALDI-TOF mass spectrometry, in sturgeon we were able to assign the sequence to a prominent protein spot, present exclusively in a two-dimensionally separated cytoskeletal preparation of skin, thus identifying it as an epidermally expressed type I keratin. In contrast to the other keratins we have so far sequenced from bichir, sturgeon and gar, these new sequences occupy a rather basal position within the phylogenetic tree of type I keratins, in a close vicinity to the keratins we previously cloned from river lamprey. CONCLUSION: Thus, this new K14 group seem to belong to a very ancient keratin branch, whose functional role has still to be further elucidated. Furthermore, the exclusive presence of this keratin group in bichir, sturgeon and gar points to the close phylogenetic relationship of these ray- finned fish, an issue still under debate among taxonomists.

Evolution of tissue-specific keratins as deduced from novel cDNA sequences of the lungfish Protopterus aethiopicus.

Lungfishes are possibly the closest extant relatives of the land vertebrates (tetrapods). We report here the cDNA and predicted amino acid sequences of 13 different keratins (ten type I and three type II) of the lungfish Protopterus aethiopicus. These keratins include the orthologs of human K8 and K18. The lungfish keratins were also identified in tissue extracts using two-dimensional polyacrylamide gel electrophoresis, keratin blot binding assays and immunoblotting. The identified keratin spots were analyzed by peptide mass fingerprinting which assigned seven sequences (inclusively Protopterus K8 and K18) to their respective protein spot. The peptide mass fingerprints also revealed the fact that the major epidermal type I and type II keratins of this lungfish have not yet been sequenced. Nevertheless, phylogenetic trees constructed from multiple sequence alignments of keratins from lungfish and distantly related vertebrates such as lamprey, shark, trout, frog, and human reveal new insights into the evolution of K8 and K18, and unravel a variety of independent keratin radiation events.

Sequence, evolution and tissue expression patterns of an epidermal type I keratin from the shark Scyliorhinus stellaris.

From the shark Scyliorhinus stellaris we cloned and sequenced a cDNA encoding a novel type I keratin, termed SstK10. By MALDI-MS peptide mass fingerprinting of cytoskeletal proteins separated on polyacrylamide gels, we assigned SstK10 to a 46-kDa protein which is the major epidermal type I ("IE") keratin in this fish and is specifically expressed in stratified epithelia. In a phylogenetic tree based on type I keratin sequences and with lamprey keratins applied as outgroup, SstK10 branches off in a rather basal position. This tree strongly supports the concept that teleost keratins and tetrapod keratins resulted from two independent gene radiation processes. The only exception is human K18 because its orthologs have been found in all jawed vertebrates (Gnathostomata) studied; in the tree, they form a common, most early branch, with the shark version, SstK18, in the most basal position. Thus, the sequences of SstK10 and SstK18 also favor the classical view of vertebrate evolution that considers the cartilaginous fishes as the most ancient living Gnathostomata. To determine the overall expression patterns of epidermal ("E") and simple epithelial ("S") keratins in this shark, we furthermore tested a panel of monoclonal anti-keratin antibodies by immunofluorescence microscopy of frozen tissue sections, and in immunoblots of cytoskeletal preparations, demonstrating that immunodetection of specific keratins is a convenient method to characterize epithelial tissues in shark.

Genes coding for intermediate filament proteins closely related to the hagfish "thread keratins (TK)" alpha and gamma also exist in lamprey, teleosts and amphibians.

The "thread keratins (TK)" alpha and gamma so far have been considered highly specialized intermediate filament (IF) proteins restricted to hagfish. From lamprey, we now have sequenced five novel IF proteins closely related to TKalpha and TKgamma, respectively. Moreover, we have detected corresponding sequences in EST and genomic databases of teleosts and amphibians. The structure of the TKalpha genes and the positions of their deduced amino acid sequences in a phylogenetic tree clearly support their classification as type II keratins. The genes encoding TKgamma show a structure typical for type III IF proteins, whereas their positions in phylogenetic trees favor a close relationship to the type I keratins. Considering that most keratin-like sequences detected in the lancelet also exhibit a gene structure typical for type III IF proteins, it seems likely that the keratin gene(s) originated from an ancient type III IF protein gene. According to EST analyses, the expression of the thread keratins in teleost fish and amphibians may be particularly restricted to larval stages, which, in conjunction with the observed absence of TKalpha and TKgamma genes in any of the available Amniota databases, indicates a thread keratin function closely related to larval development in an aquatic environment.

Identification of keratins and analysis of their expression in carp and goldfish: comparison with the zebrafish and trout keratin catalog.

With more than 50 genes in human, keratins make up a large gene family, but the evolutionary pressure leading to their diversity remains largely unclear. Nevertheless, this diversity offers a means to examine the evolutionary relationships among organisms that express keratins. Here, we report the analysis of keratins expressed in two cyprinid fishes, goldfish and carp, by two-dimensional polyacrylamide gel electrophoresis, complementary keratin blot binding assay, and immunoblotting. We further explore the expression of keratins by immunofluorescence microscopy. Comparison is made with the keratin expression and catalogs of zebrafish and rainbow trout. The keratins among these fishes exhibit a similar range of molecular weights and isoelectric points, with a similar overall pattern on two-dimensional gels. In addition, immunofluorescence microscopy studies of goldfish and carp tissues have revealed the expression of keratins in both epithelial and mesenchymally derived tissues, as reported previously for zebrafish and trout. We conclude that keratin expression is qualitatively similar among these fishes, with goldfish and carp patterns being more similar to each other than to zebrafish, and the cyprinid fishes being more similar to each other than to the salmonid trout. Because of the detected similarity of keratin expression among the cyprinid fishes, we propose that, for certain experiments, they are interchangeable. Although the zebrafish distinguishes itself as being a developmental and genetic/genomic model organism, we have found that the goldfish, in particular, is a more suitable model for both biochemical and histological studies of the cytoskeleton, especially since goldfish cytoskeletal preparations seem to be more resistant to degradation than those from carp or zebrafish.

cDNA sequences of the authentic keratins 8 and 18 in zebrafish.

From the zebrafish Danio rerio, we have cDNA cloned and sequenced a novel type II and a novel type I keratin, termed DreK8 and DreK18, respectively. We identified DreK8/18 as the true orthologs of the human keratin pair K8/18 as follows: (i) MALDI-MS assignment to the biochemically identified K8 and K18 candidates that are co-expressed in simple epithelia and absent in epidermal keratinocytes; (ii) multiple sequence alignments and phylogenetic tree analysis, showing that DreK8, within the phylogenetic tree of type II keratins, forms a highly bootstrap-supported branch together with K8 from goldfish and rainbow trout, whereas DreK18, within the phylogenetic tree of type I keratins, groups with the K18 sequences from all other vertebrates studied; (iii) presence of a conserved motif in the tail domain of DreK8 (VxKxxETxDGxxVSESSxV) that is typical for all hitherto sequenced K8 orthologs. Moreover, several zebrafish type II keratin sequences published by other authors have now been assigned to epidermal keratins, previously identified biochemically.

Type I keratin cDNAs from the rainbow trout: independent radiation of keratins in fish.

Five different type I keratins from a teleost fish, the rainbow trout Oncorhynchus mykiss, have been sequenced by cDNA cloning and identified at the protein level by peptide mass mapping using MALDI-MS. This showed that the entire range of type I keratins detected biochemically in this fish has now been sequenced. Three of the keratins are expressed in the epidermis (subtype Ie), whereas the other two occur in simple epithelia and mesenchymal cells (subtype Is). Among the Is keratins is an ortholog of human K18; the second Is polypeptide is clearly distinct from K18. We raised a new monoclonal antibody (F1F2, subclass IgG1) that specifically recognizes trout Is keratins, with negative reactions on zebrafish. A phylogenetic tree has been constructed from a multiple alignment of the rod domains of the new sequences together with type I sequences from other vertebrates such as shark, zebrafish, and human; a recently sequenced lamprey Is keratin was applied as outgroup. This tree shows one branch defining the K18 orthologs and a second branch containing all other type I keratins (mostly subtype Ie). Within this second branch, the teleost keratins form a separate, highly bootstrap-supported twig. This tree leaves little doubt that the teleost Ie keratins diversified independently from the mammalian Ie keratins.

Type II keratin cDNAs from the rainbow trout: implications for keratin evolution.

From a teleost fish, the rainbow trout Oncorhynchus mykiss, we have cloned and sequenced cDNAs encoding five different type II keratins. The corresponding protein spots, as separated by 2D-PAGE of trout cytoskeletal preparations, have been identified by peptide mass mapping using MALDI mass spectrometry. Three of the sequenced keratins are expressed in the epidermis (subtype IIe), and two in simple epithelia and mesenchymal cells (subtype IIs). The IIs keratins are both orthologs of human K8. This leaves unsequenced only the trace component S3 of the biochemically established trout keratin catalog. A phylogenetic tree has been constructed from a multiple alignment of the rod domains of the new keratin sequences together with type II sequences from other vertebrates such as shark, zebrafish, and human; lamprey K8 (recently sequenced in our laboratory) has been used as outgroup. This tree suggests, in a highly bootstrap-supported manner, that the teleost IIe keratins diversified independently from the mammalian IIe keratins. In contrast, all the species investigated express K8-like keratins, suggesting that the different IIe branches evolved from K8-like progenitors. The tree also indicates that the published zebrafish sequences represent IIe keratins and that the biochemically identified K8 ortholog in zebrafish has not yet been sequenced.