Scale keratin in lizard epidermis reveals amino acid regions homologous with avian and mammalian epidermal proteins

Cysteine Enrichment Mediates Co-Option of Uricase in Reptilian Skin and Transition to Uricotelism

Uric acid is the main means of nitrogen excretion in uricotelic vertebrates (birds and reptiles) and the end product of purine catabolism in humans and a few other mammals. While uricase is inactivated in mammals unable to degrade urate, the presence of orthologous genes without inactivating mutations in avian and reptilian genomes is unexplained. Here we show that the Gallus gallus gene we name cysteine-rich urate oxidase (CRUOX) encodes a functional protein representing a unique case of cysteine enrichment in the evolution of vertebrate orthologous genes. CRUOX retains the ability to catalyze urate oxidation to hydrogen peroxide and 5-hydroxyisourate (HIU), albeit with a 100-fold reduced efficiency. However, differently from all uricases hitherto characterized, it can also facilitate urate regeneration from HIU, a catalytic property that we propose depends on its enrichment in cysteine residues. X-ray structural analysis highlights differences in the active site compared to known orthologs and suggests a mechanism for cysteine-mediated self-aggregation under H2O2-oxidative conditions. Cysteine enrichment was concurrent with the transition to uricotelism and a shift in gene expression from the liver to the skin where CRUOX is co-expressed with β-keratins. Therefore, the loss of urate degradation in amniotes has followed opposite evolutionary trajectories: while uricase has been eliminated by pseudogenization in some mammals, it has been repurposed as a redox-sensitive enzyme in the reptilian skin.

Histological Variants of Squamous and Basal Cell Carcinoma in Squamates and Chelonians: A Comprehensive Classification

In the present study, the histological characteristics of squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs) obtained from 22 squamate and 13 chelonian species were retrospectively evaluated. While the examined tissues were originally diagnosed as 28 SCCs and 7 BCCs based on histological evaluation by a specialty diagnostic service, eight SCCs could be re-classified as BCCs and three SCCs proved to be non-neoplastic lesions. In addition, all SCCs and BCCs were classified into distinct histological variants. The SCCs could be categorized as one SCC in situ, three moderately differentiated SCCs, seven well-differentiated SCCs, and six keratoacanthomas. BCCs were classified as five solid BCCs, four infiltrating BCCs, five keratotic BCCs, and one basosquamous cell carcinoma. In addition, the present study reports the occurrence of BCCs in seven reptile species for the first time. In contrast to what has been documented in humans, IHC staining with the commercially available epithelial membrane antigen and epithelial antigen clone Ber-EP4 does not allow differentiation of SCCs from BCCs in reptiles, while cyclooxygenase-2 and E-cadherin staining seem to have discriminating potential. Although the gross pathological features of the examined SCCs and BCCs were highly similar, each tumor could be unequivocally assigned to a distinct histological variant according to the observed histological characteristics. Based on the results of this study, a histopathological classification for SCCs and BCCs is proposed, allowing accurate identification and differentiation of SCCs and BCCs and their histological variants in the examined reptile species. Presumably, BCCs are severely underdiagnosed in squamates and chelonians.

Ancient lineages of the keratin-associated protein (KRTAP) genes and their co-option in the evolution of the hair follicle

BLAST searches against the human genome showed that of the 93 keratin-associated proteins (KRTAPs) of Homo sapiens, 53 can be linked by sequence similarity to an H. sapiens metallothionein and 16 others can be linked similarly to occludin, while the remaining KRTAPs can themselves be linked to one or other of those 69 directly-linked proteins. The metallothionein-linked KRTAPs comprise the high-sulphur and ultrahigh-sulphur KRTAPs and are larger than the occludin-linked set, which includes the tyrosine- and glycine-containing KRTAPs. KRTAPs linked to metallothionein appeared in increasing numbers as evolution advanced from the deuterostomia, where KRTAP-like proteins with strong sequence similarity to their mammalian congeners were found in a sea anemone and a starfish. Those linked to occludins arose only with the later-evolved mollusca, where a KRTAP homologous with its mammalian congener was found in snails. The presence of antecedents of the mammalian KRTAPs in a starfish, a sea anemone, snails, fish, amphibia, reptiles and birds, all of them animals that lack hair, suggests that some KRTAPs may have a physiological role beyond that of determining the characteristics of hair fibres. We suggest that homologues of these KRTAPs found in non-hairy animals were co-opted by placodes, formed by the ectodysplasin pathway, to produce the first hair-producing cells, the trichocytes of the hair follicles.

Structures of the ß-Keratin Filaments and Keratin Intermediate Filaments in the Epidermal Appendages of Birds and Reptiles (Sauropsids)

The epidermal appendages of birds and reptiles (the sauropsids) include claws, scales, and feathers. Each has specialized physical properties that facilitate movement, thermal insulation, defence mechanisms, and/or the catching of prey. The mechanical attributes of each of these appendages originate from its fibril-matrix texture, where the two filamentous structures present, i.e., the corneous ß-proteins (CBP or ß-keratins) that form 3.4 nm diameter filaments and the α-fibrous molecules that form the 7-10 nm diameter keratin intermediate filaments (KIF), provide much of the required tensile properties. The matrix, which is composed of the terminal domains of the KIF molecules and the proteins of the epidermal differentiation complex (EDC) (and which include the terminal domains of the CBP), provides the appendages, with their ability to resist compression and torsion. Only by knowing the detailed structures of the individual components and the manner in which they interact with one another will a full understanding be gained of the physical properties of the tissues as a whole. Towards that end, newly-derived aspects of the detailed conformations of the two filamentous structures will be discussed and then placed in the context of former knowledge.

The molecular evolution of feathers with direct evidence from fossils

Dinosaur fossils possessing integumentary appendages of various morphologies, interpreted as feathers, have greatly enhanced our understanding of the evolutionary link between birds and dinosaurs, as well as the origins of feathers and avian flight. In extant birds, the unique expression and amino acid composition of proteins in mature feathers have been shown to determine their biomechanical properties, such as hardness, resilience, and plasticity. Here, we provide molecular and ultrastructural evidence that the pennaceous feathers of the Jurassic nonavian dinosaur Anchiornis were composed of both feather β-keratins and α-keratins. This is significant, because mature feathers in extant birds are dominated by β-keratins, particularly in the barbs and barbules forming the vane. We confirm here that feathers were modified at both molecular and morphological levels to obtain the biomechanical properties for flight during the dinosaur-bird transition, and we show that the patterns and timing of adaptive change at the molecular level can be directly addressed in exceptionally preserved fossils in deep time.

Filamentous Structure of Hard β-Keratins in the Epidermal Appendages of Birds and Reptiles

The structures of avian and reptilian epidermal appendages, such as feathers, claws and scales, have been modelled using X-ray diffraction and electron microscopy data, combined with sequence analyses. In most cases, a family of closely related molecules makes up the bulk of the appendage, and each of these molecules contains a central β-rich 34-residue segment, which has been identified as the principal component of the framework of the 3.4 nm diameter filaments. The N- and C-terminal segments form the matrix component of the filament/matrix complex. The 34-residue β-rich central domains occur in pairs, related by either a parallel dyad or a perpendicular dyad axis, and form a β-sandwich stabilized by apolar interactions. They are also twisted in a right-handed manner. In feather, the filaments are packed into small sheets and it is possible to determine their likely orientation within the sheets from the low-angle X-ray diffraction data. The physical properties of the various epidermal appendages can be related to the amino acid sequence and composition of defined molecular segments characteristic of the chains concerned.

Molecular evidence of keratin and melanosomes in feathers of the Early Cretaceous bird Eoconfuciusornis

Microbodies associated with feathers of both nonavian dinosaurs and early birds were first identified as bacteria but have been reinterpreted as melanosomes. Whereas melanosomes in modern feathers are always surrounded by and embedded in keratin, melanosomes embedded in keratin in fossils has not been demonstrated. Here we provide multiple independent molecular analyses of both microbodies and the associated matrix recovered from feathers of a new specimen of the basal bird Eoconfuciusornis from the Early Cretaceous Jehol Biota of China. Our work represents the oldest ultrastructural and immunological recognition of avian beta-keratin from an Early Cretaceous (∼130-Ma) bird. We apply immunogold to identify protein epitopes at high resolution, by localizing antibody-antigen complexes to specific fossil ultrastructures. Retention of original keratinous proteins in the matrix surrounding electron-opaque microbodies supports their assignment as melanosomes and adds to the criteria employable to distinguish melanosomes from microbial bodies. Our work sheds new light on molecular preservation within normally labile tissues preserved in fossils.

Comparative Investigations of the Sandfish’s β-Keratin (Reptilia: Scincidae: Scincus scincus). Part 1: Surface and Molecular Examinations

The Sandfish (Scincidae: Scincus Scincus) Is a Lizard Capable of Moving through Desert Sand in a Swimming-Like Fashion. the Epidermis of this Lizard Shows a High Resistance against Abrasion Together with a Low Friction to Sand as an Adaption to a Subterranean Life below the Desert’s Surface, Outperforming even Steel. the Low Friction Is Mainly Caused by Chemical Composition of the Scales, which Consist of Glycosylated β-Keratins. in this Study, the Friction, the Micro-Structure, the Glycosylation of the β-Keratin Proteins and β-Keratin Coding DNA of the Sandfish in Comparison to other Reptilian Species Was Investigated, Mainly with the Closely Related Berber Skink (Scincidae: Eumeces Schneideri) and another Sand Swimming Species, the Not Closer Related Shovel-Snouted Lizard (Lacertidae: Meroles Anchietae). Glycosylated β-Keratins of the Sandfish, Visualized with Different Lectins Resulted in O-Linked Glycans through PNA Employed as Carbohydrate Marker. Furthermore, the Glycosylation of β-Keratins in Various Squamatean Species Was Investigated and All Species Tested Were Found Positive; however, it Seems Like both Sand Swimming Species Examined Have a much Stronger Glycosylation of their β-Keratins. in Order to Prove this Finding through a Genetic Foundation, DNA of a β-Keratin Coding Gene of the Sandfish Was Sequenced and Compared with a Homologue Gene of Eumeces Schneideri. by Comparison of the Protein Sequence, a Higher Abundance of O-Glycosylation Sites Was Found in the Sandfish (enabled through the Amino Acids Serine and Threonine), Giving Molecular Support for a Higher Glycosylation of the β-Keratins in this Species.

Cross-immunoreactivity between the LH1 antibody and cytokeratin epitopes in the differentiating epidermis of embryos of the grass snake Natrix natrix L. during the end stages of embryogenesis

The monoclonal anti-cytokeratin 1/10 (LH1) antibody recognizing K1/K10 keratin epitopes that characterizes a keratinized epidermis of mammals cross-reacts with the beta and Oberhäutchen layers covering the scales and gastrosteges of grass snake embryos during the final period of epidermis differentiation. The immunolocalization of the anti-cytokeratin 1/10 (LH1) antibody appears in the beta layer of the epidermis, covering the outer surface of the gastrosteges at the beginning of developmental stage XI, and in the beta layer of the epidermis, covering the outer surface of the scales at the end of developmental stage XI. This antibody cross-reacts with the Oberhäutchen layers in the epidermis covering the outer surface of both scales and gastrosteges at developmental stages XI and XII just before its fusion with the beta layers. After fusion of the Oberhäutchen and beta layers, LH1 immunolabeling is weaker than before. This might suggest that alpha-keratins in these layers of the epidermis are masked by beta-keratins, modified, or degraded. The anti-cytokeratin 1/10 (LH1) antibody stains the Oberhäutchen layer in the epidermis covering the inner surface of the gastrosteges and the hinge regions between gastrosteges at the end of developmental stage XI. However, the Oberhäutchen of the epidermis covering the inner surfaces of the scales and the hinge regions between scales does not show cytokeratin 1/10 (LH1) immunolabeling until hatching. This cross-reactivity suggests that the beta and Oberhäutchen layers probably contain some alpha-keratins that react with the LH1 antibody. It is possible that these alpha-keratins create specific scaffolding for the latest beta-keratin deposition. It is also possible that the LH1 antibody cross-reacts with other epidermal proteins such as filament-associated proteins, i.e., filaggrin-like. The anti-cytokeratin 1/10 (LH1) antibody does not stain the alpha and mesos layers until hatching. We suppose that the differentiation of these layers will begin just after the first postnatal sloughing.

Evolution of hard proteins in the sauropsid integument in relation to the cornification of skin derivatives in amniotes

Hard skin appendages in amniotes comprise scales, feathers and hairs. The cell organization of these appendages probably derived from the localization of specialized areas of dermal-epidermal interaction in the integument. The horny scales and the other derivatives were formed from large areas of dermal-epidermal interaction. The evolution of these skin appendages was characterized by the production of specific coiled-coil keratins and associated proteins in the inter-filament matrix. Unlike mammalian keratin-associated proteins, those of sauropsids contain a double beta-folded sequence of about 20 amino acids, known as the core-box. The core-box shows 60%-95% sequence identity with known reptilian and avian proteins. The core-box determines the polymerization of these proteins into filaments indicated as beta-keratin filaments. The nucleotide and derived amino acid sequences for these sauropsid keratin-associated proteins are presented in conjunction with a hypothesis about their evolution in reptiles-birds compared to mammalian keratin-associated proteins. It is suggested that genes coding for ancestral glycine-serine-rich sequences of alpha-keratins produced a new class of small matrix proteins. In sauropsids, matrix proteins may have originated after mutation and enrichment in proline, probably in a central region of the ancestral protein. This mutation gave rise to the core-box, and other regions of the original protein evolved differently in the various reptilians orders. In lepidosaurians, two main groups, the high glycine proline and the high cysteine proline proteins, were formed. In archosaurians and chelonians two main groups later diversified into the high glycine proline tyrosine, non-feather proteins, and into the glycine-tyrosine-poor group of feather proteins, which evolved in birds. The latter proteins were particularly suited for making the elongated barb/barbule cells of feathers. In therapsids-mammals, mutations of the ancestral proteins formed the high glycine-tyrosine or the high cysteine proteins but no core-box was produced in the matrix proteins of the hard corneous material of mammalian derivatives.

Beta-keratins of turtle shell are glycine-proline-tyrosine rich proteins similar to those of crocodilians and birds

This study presents, for the first time, sequences of five beta-keratin cDNAs from turtle epidermis obtained by means of 5'- and 3'-rapid amplification of cDNA ends (RACE) analyses. The deduced amino acid sequences correspond to distinct glycine-proline-serine-tyrosine rich proteins containing 122-174 amino acids. In situ hybridization shows that beta-keratin mRNAs are expressed in cells of the differentiating beta-layers of the shell scutes. Southern blotting analysis reveals that turtle beta-keratins belong to a well-conserved multigene family. This result was confirmed by the amplification and sequencing of 13 genomic fragments corresponding to beta-keratin genes. Like snake, crocodile and avian beta-keratin genes, turtle beta-keratins contain an intron that interrupts the 5'-untranslated region. The length of the intron is variable, ranging from 0.35 to 1.00 kb. One of the sequences obtained from genomic amplifications corresponds to one of the five sequences obtained from cDNA cloning; thus, sequences of a total of 17 turtle beta-keratins were determined in the present study. The predicted molecular weight of the 17 different deduced proteins range from 11.9 to 17.0 kDa with a predicted isoelectric point of 6.8-8.4; therefore, they are neutral to basic proteins. A central region rich in proline and with beta-strand conformation shows high conservation with other reptilian and avian beta-keratins, and it is likely involved in their polymerization. Glycine repeat regions, often containing tyrosine, are localized toward the C-terminus. Phylogenetic analysis shows that turtle beta-keratins are more similar to crocodilian and avian beta-keratins than to those of lizards and snakes.

beta-Keratins in crocodiles reveal amino acid homology with avian keratins

The DNA sequences encoding beta-keratin have been obtained from Marsh Mugger (Crocodylus palustris) and Orinoco Crocodiles (Crocodylus intermedius). Through the deduced amino acid sequence, these proteins are rich in glycine, proline and serine. The central region of the proteins are composed of two beta-folded regions and show a high degree of identity with beta-keratins of aves and squamates. This central part is thought to be the site of polymerization to build the framework of beta-keratin filaments. It is believed that the beta-keratins in reptiles and birds share a common ancestry. Near the C-terminal, these beta-keratins contain a peptide rich in glycine-X and glycine-X-X, and the distinctive feature of the region is some 12-amino acid repeats, which are similar to the 13-amino acid repeats in chick scale keratin but absent from avian feather keratin. From our phylogenetic analysis, the beta-keratins in crocodile have a closer relationship with avian keratins than the other keratins in reptiles.

Beta-keratins of the crocodilian epidermis: composition, structure, and phylogenetic relationships

Nucleotide and deduced amino acid sequences of three beta-keratins of Nile crocodile scales are presented. Using 5'- and 3'-RACE analysis, two cDNA sequences of 1 kb (Cr-gptrp-1) and 1.5 kb (Cr-gptrp-2) were determined, corresponding to 17.4 and 19.3 kDa proteins, respectively, and a pI of 8.0. In genomic DNA amplifications, we determined that the 5'-UTR of Cr-gptrp-2 contains an intron of 621 nucleotides. In addition, we isolated a third gene (Cr-gptrp-3) in genomic DNA amplifications that exhibits seven amino acid differences with Cr-gptrp-2. Genomic organization of the sequenced crocodilian beta-keratin genes is similar to avian beta-keratin genes. Deduced proteins are rich in glycine, proline, serine, and tyrosine, and contain cysteines toward the N- and C-terminal regions, likely for the formation of disulfide bonds. Prediction of the secondary structure suggests that the central core box of 20 amino acids contains two beta-strands and has 75-90% identity with chick beta-keratins. Toward the C-terminus, numerous glycine-glycine-tyrosine and glycine-glycine-leucine repeats are present, which may contribute to making crocodile scales hard. In situ hybridization shows expression of beta-keratin genes in differentiating beta-cells of epidermal transitional layers. Phylogenetic analysis of the available archosaurian and lepidosaurian beta-keratins suggests that feather keratins diversified early from nonfeather keratins, deep in archosaur evolution. However, only the complete knowledge of all crocodilian beta-keratins will confirm whether feather keratins have an origin independent of those in bird scales, which preceded the split between birds and crocodiles.

Hard cornification in reptilian epidermis in comparison to cornification in mammalian epidermis

The structure of reptilian hard (beta)-keratins, their nucleotide and amino acid sequence, and the organization of their genes are presented. These 13-19 kDa proteins are basic, rich in glycine, proline and serine, and different from cytokeratins. Their mRNAs are expressed in beta-cells. The central part of beta-keratins (this region has been previously termed 'core-box' and is peculiar of all sauropsid proteins) is composed of two beta-folded regions and shows a high identity with avian beta-keratins. This central part present in all beta-keratins, including feather keratins, is the site of polymerization to build the framework of beta-keratin filaments. Beta-keratins appear cytokeratin-associated proteins. Their central region might have originated in an ancestral glycine-rich protein present in stem reptiles from which beta-keratins evolved and diversified into reptiles and birds. Stem reptiles of the Carboniferous period might have possessed glycine-rich proteins derived from exons/domains corresponding to the variable, glycine-rich region of cytokeratins. Beta-keratins might have derived from a gene coding for small glycine-rich keratin-associated proteins. The glycine-rich regions evolved differently in the lineage leading to modern reptiles and birds versus that leading to mammals. In the reptilian lineage some amino acid regions produced by point mutations and amino acid changes might have given rise to originate the central beta-pleated region. The latter allowed the formation of filamentous proteins (beta-keratins) associated with intermediate filament keratins and replaced them in beta-keratin cells. In the mammalian lineage no beta-pleated region was generated in their matrix proteins, the glycine-rich keratin-associated proteins. The latter evolved as glycine-tyrosine-rich, sulphur-rich, and ultra-sulphur-rich proteins that are used for building hairs, horns and nails.

Characterization of keratins and associated proteins involved in the corneification of crocodilian epidermis

Crocodilian keratinocytes accumulate keratin and form a corneous cell envelope of which the composition is poorly known. The present immunological study characterizes the molecular weight, isoelectric point (pI) and the protein pattern of alpha- and beta-keratins in the epidermis of crocodilians. Some acidic alpha-keratins of 47-68 kDa are present. Cross-reactive bands for loricrin (70, 66, 55 kDa), sciellin (66, 55-57 kDa), and filaggrin-AE2-positive keratins (67, 55 kDa) are detected while caveolin is absent. These proteins may participate in the formation of the cornified cell membranes, especially in hinge regions among scales. Beta-keratins of 17-20 kDa and of prevalent basic pI (7.0-8.4) are also present. Acidic beta-keratins of 10-16 kDa are scarce and may represent altered forms of the original basic proteins. Crocodilian beta-keratins are not recognized by a lizard beta-keratin antibody (A68B), and by a turtle beta-keratin antibody (A685). This result indicates that these antibodies recognize specific epitopes in different reptiles. Conversely, crocodilian beta-keratins cross-react with the Beta-universal antibody indicating they share a specific 20 amino acid epitope with avian beta-keratins. Although crocodilian beta-keratins are larger proteins than those present in birds our results indicate presence of shared epitopes between avian and crocodilian beta-keratins which give good indication for the future determination of the sequence of these proteins.

Expression of beta-keratin mRNAs and proline uptake in epidermal cells of growing scales and pad lamellae of gecko lizards

Beta-keratins form a large part of the proteins contained in the hard beta layer of reptilian scales. The expression of genes encoding glycine-proline-rich beta-keratins in normal and regenerating epidermis of two species of gecko lizards has been studied by in situ hybridization. The probes localize mRNAs in differentiating oberhautchen and beta cells of growing scales and in modified scales, termed pad lamellae, on the digits of gecko lizards. In situ localization at the ultrastructural level shows clusters of gold particles in the cytoplasm among beta-keratin filaments of oberhautchen and beta cells. They are also present in the differentiating elongation or setae of oberhautchen cells present in pad lamellae. Setae allow geckos to adhere and climb vertical surfaces. Oberhautchen and beta cells also incorporate tritiated proline. The fine localization of the beta-keratin mRNAs and the uptake of proline confirms the biomolecular data that identified glycine-proline-rich beta-keratin in differentiating beta cells of gecko epidermis. The present study also shows the presence of differentiating and metabolically active cells in both inner and outer oberhautchen/beta cells at the base of the outer setae localized at the tip of pad lamellae. The addition of new beta and alpha cells to the corneous layer near the tip of the outer setae explains the anterior movement of the setae along the apical free-margin of pad lamellae. The rapid replacement of setae ensures the continuous usage of the gecko's adhesive devices, the pad lamellae, during most of their active life.

Cloning and characterization of scale beta-keratins in the differentiating epidermis of geckoes show they are glycine-proline-serine-rich proteins with a central motif homologous to avian beta-keratins

The beta-keratins constitute the hard epidermis and adhesive setae of gecko lizards. Nucleotide and amino acid sequences of beta-keratins in epidermis of gecko lizards were cloned from mRNAs. Specific oligonucleotides were used to amplify by 3'- and 5'-rapid amplification of cDNA ends analyses five specific gecko beta-keratin cDNA sequences. The cDNA coding sequences encoded putative glycine-proline-serine-rich proteins of 16.8-18 kDa containing 169-191 amino acids, especially 17.8-23% glycine, 8.4-14.8% proline, 14.2-18.1% serine. Glycine-rich repeats are localized toward the initial and end regions of the protein, while a central region, rich in proline, has a strand conformation (beta-pleated fold) likely responsible for the formation of beta-keratin filaments. It shows high homology with a core region of other lizard keratins, avian scale, and feather keratins. Northern blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis show a higher beta-keratin gene expression in regenerating epidermis compared with normal epidermis. In situ hybridization confirms that mRNAs for these proteins are expressed in cells of the differentiating oberhautchen cells and beta-cells. Expression in adhesive setae of climbing lamellae was shown by RT-PCR. Southern blotting analysis revealed that the proteins are encoded by a multigene family. PCR analysis showed that the genes are presumably located in tandem along the DNA and are transcribed from the same DNA strand like in avian beta-keratins.

Immunological characterization of a newly developed antibody for localization of a beta-keratin in turtle epidermis

Turtle scutes are made of hard (beta)-keratins. In order to study size and localization of beta-keratins in turtle shell, we produced a rat polyclonal antiserum against a turtle scute beta-keratin of 13-16 kDa, which allowed the immunolocalization of the protein in the epidermis. In immunoblots the antiserum recognized turtle beta-keratins but showed variable cross-reactivity with lizard, snake, and avian beta-keratins. The turtle antiserum appears less cross-reactive than a chicken scale antiserum (Beta-1). In bidimensional immunoblots, three main protein spots at 15-16 kDa with pI at 7.3, 6.8, 6.4, and an unresolved large spot at 40-45 kDa with pI around 5 were more constantly obtained. The latter may result from the aggregation of the smaller beta-keratin protein. The corneous layer of the carapace and plastron of various species of chelonians appeared immunofluorescent. The ultrastructural immunolocalization showed sparse labeling over beta-keratin filaments of cells of the horny layer of both carapace and plastron. The study for the first time shows that the isolated protein band derived from a component of the beta-keratin filaments of the corneous layer of turtles. This antibody can be used for further studies on beta-keratin expression and sequencing in chelonian shell. No labeling was present over other cell organelles or layers of turtle epidermis and it was absent in non-epidermal cells. The specificity for turtle beta-keratin suggests that the antiserum recognizes some epitope/s specific for chelonians beta-keratins, and that it also variably recognizes other reptilian and avian beta-keratins.

Alpha- and beta-keratins of the snake epidermis

Snake scales contain specialized hard keratins (beta-keratins) and alpha- or cyto-keratins in their epidermis. The number, isoelectric point, and the evolution of these proteins in snakes and their similarity with those of other vertebrates are not known. In the present study, alpha- and beta-keratins of snake molts and of the whole epidermis have been studied by using two-dimensional electrophoresis and immunocytochemistry. Specific keratins in snake epidermis have been identified by using antibodies that recognize acidic and basic cytokeratins and avian or lizard scale beta-keratin. Alpha keratins of 40-70 kDa and isoelectric point (pI) at 4.5-7.0 are present in molts. The study suggests that cytokeratins in snakes are acidic or neutral, in contrast to mammals and birds where basic keratins are also present. Beta keratins of 10-15 kDa and a pI of 6.5-8.5 are found in molts. Some beta-keratins appear as basic proteins (pI 8.2) comparable to those present in the epidermis of other reptiles. Some basic "beta-keratins" associate with cytokeratins as matrix proteins and replace cytokeratins forming the corneous material of the mature beta-layer of snake scales, as in other reptiles. The study also suggests that more forms of beta-keratins (more than three different types) are present in the epidermis of snakes.

Characterization of beta-keratins in lizard epidermis: electrophoresis, immunocytochemical and in situ-hybridization study

Lizard scales are composed of alpha-(cyto-) keratins and beta-keratins. The characterization of the molecular weight and isoelectric point (pI) of alpha- and beta-keratins of lizard epidermis (Podarcis sicula) has been done by using two-dimensional electrophoresis, immunoblotting, and immunocytochemistry. Antibodies against cytokeratins, against a chicken scale beta-keratin or against lizard beta-keratin bands of 15-16kDa, have been used to recognize alpha- and beta-keratins. Acid and basic cytokeratins of 42-67kDa show a pI from 5.0 to 8.9. This indicates the presence of specific keratins for the formation of the stratum corneum. Main protein spots of beta-keratin at 15-17kDa, and pI at 8.5, 8.2, and 6.7, and one spot at 10kDa and pI at 7.3 were recognized. Therefore, beta-keratins are mainly basic proteins, and are used for the formation of the hard corneous layer of the epidermis. Ultrastructural immunocytochemistry confirms that beta-keratin is packed into large and dense bundles of beta-keratin cells of lizard epidermis. The use of a probe against a lizard beta-keratin in situ-hybridization studies confirms that the mRNA for beta-keratins is present in beta-cells and is localized around or even associated with beta-keratin filaments.