Epidermal Appendages Research Articles

Evolution of an Epidermal Differentiation Complex (EDC) Gene Family in Birds.

The transition of amniotes to a fully terrestrial lifestyle involved the adaptation of major molecular innovations to the epidermis, often in the form of epidermal appendages such as hair, scales and feathers. Feathers are diverse epidermal structures of birds, and their evolution has played a key role in the expansion of avian species to a wide range of lifestyles and habitats. As with other epidermal appendages, feather development is a complex process which involves many different genetic and protein elements. In mammals, many of the genetic elements involved in epidermal development are located at a specific genetic locus known as the epidermal differentiation complex (EDC). Studies have identified a homologous EDC locus in birds, which contains several genes expressed throughout epidermal and feather development. A family of avian EDC genes rich in aromatic amino acids that also contain MTF amino acid motifs (EDAAs/EDMTFs), that includes the previously reported histidine-rich or fast-protein (HRP/fp), an important marker in feather development, has expanded significantly in birds. Here, we characterize the EDAA gene family in birds and investigate the evolutionary history and possible functions of EDAA genes using phylogenetic and sequence analyses. We provide evidence that the EDAA gene family originated in an early archosaur ancestor, and has since expanded in birds, crocodiles and turtles, respectively. Furthermore, this study shows that the respective amino acid compositions of avian EDAAs are characteristic of structural functions associated with EDC genes and feather development. Finally, these results support the hypothesis that the genes of the EDC have evolved through tandem duplication and diversification, which has contributed to the evolution of the intricate avian epidermis and epidermal appendages.

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.

Water conservation strategies through anatomical traits in the endangered arid zone species Salvadora oleoides Decne.

Salvadora oleoides Decne. (Salvadoraceae) is a facultative and mesomorphic xerophyte, well adapted to arid and semi-arid regions. Twelve populations were selected from different ecological regions of Punjab to investigate structural modifications that are essential for water conservation, by either improving water-storing capacity or preventing water loss from the plant body, hence, enabling this species to cope with environmental extremities. We observed significant plasticity in structural features, which ensures ecological success in a variety of environmental conditions. Huge variation was seen in various tissue systems, i.e., epidermis and epidermal appendages, collenchyma, size of internal oil glands, storage parenchyma, shape, size and arrangement of vascular tissue, intensity of sclerification, and stomatal size, shape and orientation. The desert populations showed additional parenchymatous layer under multilayered epidermis, xylem completely surrounded by phloem, broad metaxylem vessels, intensive sclerification in and outside vascular tissue, and numerous and small sized stomata on abaxial leaf surface. Population from salt-affected areas showed greater stem cross-sectional area, enlarge palisade parenchymatous cells, multilayered epidermis, large storage parenchyma, and sclerified vascular bundles. Roadside populations possessed sclerified vascular bundles and dense hairiness on leaf surface.

HOMEODOMAIN PROTEIN8 mediates jasmonate-triggered trichome elongation in tomato.

Plant hormones can adjust the physiology and development of plants to enhance their adaptation to biotic and abiotic challenges. Jasmonic acid (JA), one of the immunity hormones in plants, triggers genome-wide transcriptional changes in response to insect attack and wounding. Although JA is known to affect the development of trichomes, epidermal appendages that form a protective barrier against various stresses, it remains unclear how JA interacts with developmental programs that regulate trichome development. In this study, we show that JA affects trichome length in tomato by releasing the transcriptional repression mediated by Jasmonate ZIM (JAZ) proteins. We identified SlJAZ4, a negative regulator preferentially expressed in trichomes, as the critical component in JA signaling in tomato trichomes. We also identified a homeodomain-leucine zipper gene, SlHD8, as the downstream regulator of JA signaling that promotes trichome elongation. SlHD8 is also highly expressed in trichomes and physically interacts with SlJAZ4. Loss-of-function mutations in SlHD8 caused shorter trichomes, a phenotype that was only partially rescued by methyl jasmonate treatment. Our dual-luciferase and chromatin immunoprecipitation-quantitative PCR assays revealed that SlHD8 regulates trichome elongation by directly binding to the promoters of a set of cell-wall-loosening protein genes and activating their transcription. Together, our findings define SlHD8-SlJAZ4 as a key module mediating JA-induced trichome elongation in tomato.

Spinal Dysraphism- A Histopathological Study of 45 Cases

Introduction: Dysraphic conditions of spine resulting from non closure of the neural groove, consists of different types of malformations and they are called spina bifida, which have been classified into several types. Myelomeningocele (MMC) and Meningocele (MC) come under spina bifida cystica. Aim: To review the clinical and pathological findings of congenital spinal dysraphism and discuss the pathological diagnosis Materials and Methods: A descriptive cross-sectional type of study was conducted in 45 cases of spinal dysraphism during the period from October 2012 to February 2016, in the Department of Pathology of a tertiary care hospital, Hyderabad, India. Cases which were diagnosed as spinal dysraphism by clinical and radiological examination, tissue specimens were sent to the department of pathology along with clinical and radiological findings. Haematoxylin and Eosin (H&E) staining was done in all cases, followed by detailed microscopic study of slides. Histopathological findings such as epithelial, mesodermal, neuroectodermal changes were elucidated in detail and findings were compared with literature. Results: In a total of 45 cases there were 30 cases of MMC, nine cases of MC and six cases of encephalocele. Loss of epidermal appendages were seen in 91% of cases and neuropil like matrix was present in 76% cases. Conclusion: The embryogenesis of spina bifida involves ectoderm, neuroectoderm and mesoderm. A detailed definition of histopathological aspects will help in understanding these anomalies and should be a part of a detailed histopathology report.

Mammary development in the embryo and adult: new insights into the journey of morphogenesis and commitment.

The mammary gland is a unique tissue and the defining feature of the class Mammalia. It is a late-evolving epidermal appendage that has the primary function of providing nutrition for the young, although recent studies have highlighted additional benefits of milk including the provision of passive immunity and a microbiome and, in humans, the psychosocial benefits of breastfeeding. In this Review, we outline the various stages of mammary gland development in the mouse, with a particular focus on lineage specification and the new insights that have been gained by the application of recent technological advances in imaging in both real-time and three-dimensions, and in single cell RNA sequencing. These studies have revealed the complexity of subpopulations of cells that contribute to the mammary stem and progenitor cell hierarchy and we suggest a new terminology to distinguish these cells.

Star-nose-inspired multi-mode sensor for anisotropic motion monitoring

Stretchable and twistable sensors attract much attention due to their excellent flexibility, stability, and sensitivity for most wearable devices. Star nasal moles in nature possess a flexible and highly sensitive nose that is composed of dozens of epidermal appendages or rays densely covered with small organs, which provides us inspiration for fabricating highly sensitive sensors. Herein, we present a strategy to build a star-nose-inspired sensor with stretchable and twistable structure, where the nose’s ray-like parallel polyimide films were fabricated by electrospinning and chemical silver coating. The sensor is finally encapsulated in PDMS and its sensitivity is significantly improved due to the design of bio-inspired parallel films. The bio-inspired sensor finally exhibits ultra-light, ultra-thin, and high sensitivity (Gauge Factor (GF) ~ 4000) characteristics, ensuring a perfect fit for human skin to achieve stretch, twist, and pressure detection functions. At last, an anisotropic sensor for omnidirectionally sensing human motions was built by crosswise assembling two of functional layers. This study highlights interesting possibilities for bioinspired sensors, with integrated light, thin, stretchable, twistable, and anisotropic features for wearable devices for monitoring human movement and personal health.

Calreticulin exploits TGF-β for extracellular matrix induction engineering a tissue regenerative process.

Topical application of extracellular calreticulin (eCRT), an ER chaperone protein, in animal models enhances wound healing and induces tissue regeneration evidenced by epidermal appendage neogenesis and lack of scarring. In addition to chemoattraction of cells critical to the wound healing process, eCRT induces abundant neo-dermal extracellular matrix (ECM) formation by 3days post-wounding. The purpose of this study was to determine the mechanisms involved in eCRT induction of ECM. In vitro, eCRT strongly induces collagen I, fibronectin, elastin, α-smooth muscle actin in human adult dermal (HDFs) and neonatal fibroblasts (HFFs) mainly via TGF-β canonical signaling and Smad2/3 activation; RAP, an inhibitor of LRP1 blocked eCRT ECM induction. Conversely, eCRT induction of α5 and β1 integrins was not mediated by TGF-β signaling nor inhibited by RAP. Whereas eCRT strongly induces ECM and integrin α5 proteins in K41 wild-type mouse embryo fibroblasts (MEFs), CRT null MEFs were unresponsive. The data show that eCRT induces the synthesis and release of TGF-β3 first via LRP1 or other receptor signaling and later induces ECM proteins via LRP1 signaling subsequently initiating TGF-β receptor signaling for intracellular CRT (iCRT)-dependent induction of TGF-β1 and ECM proteins. In addition, TGF-β1 induces 2-3-fold higher level of ECM proteins than eCRT. Whereas eCRT and iCRT converge for ECM induction, we propose that eCRT attenuates TGF-β-mediated fibrosis/scarring to achieve tissue regeneration.

The HD-Zip IV transcription factor SlHDZIV8 controls multicellular trichome morphology by regulating the expression of Hairless-2.

Trichomes are specialized epidermal appendages that serve as excellent models to study cell morphogenesis. Although the molecular mechanism underlying trichome morphogenesis in Arabidopsis has been well characterized, most of the regulators essential for multicellular trichome morphology remain unknown in tomato. In this study, we determined that the recessive hairless-2 (hl-2) mutation in tomato causes severe distortion of all trichome types, along with increased stem fragility. Using map-based cloning, we found that the hl-2 phenotype was associated with a 100 bp insertion in the coding region of Nck-associated protein 1, a component of the SCAR/WAVE complex. Direct protein-protein interaction was detected between Hl-2 and Hl (SRA1, specifically Rac1-associated protein) using yeast two-hybrid and co-immunoprecipitation assays, suggesting that these proteins may work together during trichome formation. In addition, knock-down of a HD-Zip IV transcription factor, HDZIPIV8, distorted trichomes similar to the hl-2 mutant. HDZIPIV8 regulates the expression of Hl-2 by binding to the L1-box in the Hl-2 promoter region, and is involved in organizing actin filaments. The brittleness of hl-2 stems was found to result from decreased cellulose content. Taken together, these findings suggest that the Hl-2 gene plays an important role in controlling multicellular trichome morphogenesis and mechanical properties of stems in tomato plants.

A study of clinical pattern of acne vulgaris – In a tertiary care hospital in India

Acne vulgaris is a chronic inflammatory disease of the pilosebaceous units. Sebaceous gland is an important epidermal appendage involved in its pathogenesis. It is one of the most common skin condition of adolescents and adults. In this disease it develops multiple lesions like comedones, papules, nodules, cysts and scars. Factors like androgenetic hormones, amount of sebum secretion, follicular microbial flora, and fat rich diets are responsible for its cause. With this background we conducted this study of clinical pattern of acne vulgaris in a tertiary care hospital in India. To study about the clinical pattern of acne vulgaris in patients attending dermatology OPD in a tertiary care hospital in India.A total of 200 consecutive patients attending the dermatology OPD with clinical features of Acne vulgaris was included in the study. Pregnant women and patients with drug induced acne vulgaris were excluded from the study. This hospital based observational study was carried out from November 2019 to January 2020. The datas were collected in a predesigned proforma which includes age, gender, marital status, age of onset, duration, body sites involved, number and severity of acne lesions, menstrual history, features of androgenicity, post inflammatory hyperpigmentation and scarring of skin.A total of 200 Acne vulgaris patients were studied with 59% males and 41% females. Age group wise, patients above 18 years (51%) followed by 14 to 18 years (38%) were affected. The common body sites involvement were face (45%), trunk (18%) and neck (13%) are mainly involved. Acne grading shows, grade 3(53%), grade 2(21%) were involved. Males with androgenetic features were 20 patients (38%) and females were 33 patients (62%). Total number of patients having androgenetic features were 53(26.5%).

Biotransformation of keratin waste to amino acids and active peptides based on cell-free catalysis

BackgroundKeratin is the primary constituent of the vertebrate epidermis and epidermal appendages, as well as the main waste product generated during poultry processing from feathers, hair, scales, nails, etc. Keratin is generally hard, stubborn and difficult to hydrolyze; however, it is also inexpensive and contains more than 85% protein. Currently, tens of millions of tons of keratin waste are produced each year worldwide; however, no effective methods for the recovery of keratin waste have been reported thus far, making such research urgent. Keratinase has been reported to be useful for keratin waste recovery; however, nearly all keratinases are unable to hydrolyze keratin after they are detached from living cell systems. This may be due to low keratinase activity and lack of synergistic factors.ResultsHerein, the keratinase gene from Bacillus licheniformis BBE11-1 was successfully expressed in Bacillus subtilis WB600, allowing for improved activity of the recombinant keratinase KerZ1 to 45.14 KU/mL via promoter substitution and screening of the ribosome-binding sites. Further, real-time control of temperature, pH, dissolved oxygen, and feed strategy allowed the activity of KerZ1 to reach 426.60 KU/mL in a 15-L fermenter, accounting for a 3552-fold increase compared to the wild-type keratinase (120.1 U/mL). Most importantly, we proposed a method based on the synergistic action of keratinase KerZ1 and sodium sulfite, to hydrolyze feathers into amino acids. In specific, 100 g/L of feather waste can be successfully converted into 56.6% amino acids within 12 h, while supporting the production of dozens of bioactive peptides.ConclusionsThe activity of recombinant keratinase can be greatly enhanced via transcription and translational regulation in Bacillus subtilis. The synergistic action of keratinase and sulfite can rapidly degrade feather waste and produce amino acids and polypeptides.

Epidermal structure and differentiation.

In this Primer, Moreci and Lechler follow the lifetime of an epidermal cell from its birth to its ultimate death, and detail how this journey is necessary for epidermal function.

Lepidosaur ß-keratin chains with four 34-residue repeats: Modelling reveals a potential filament-crosslinking role

ß-keratin chains contain a characteristic and homologous 34-residue sequence, which is believed to adopt a twisted ß-sheet conformation that assembles in an antiparallel manner with a similar sheet in a second chain to form a ß-sandwich. These sandwiches are, in turn, related to one another by a left-handed four-fold screw axis to generate a helical structure that forms the core of the 3.4 nm diameter filaments observed by electron microscopy and deduced from X-ray fibre diffraction. Recently, it has been shown that one ß-keratin chain, with a molecular weight approximately twice that of the majority of ß-keratin chains, is conserved across the lepidosaurs (lizards, snakes and tuatara). Uniquely, it contains four 34-residue repeats. Although this chain is a minor component the observation that the entire chain shows a high degree of sequence conservation between species suggests an important structural/functional role in vivo. Modelling shows that only six families of structures are physically possible. In three of these the repeats exist within a single filament and might therefore act in a filament nucleation role. In the second three families the repeats exist in two, three or four filaments, implying that their function may be to act as an inter-filament crosslinker, thereby providing lateral reinforcement to the epidermal appendage. The favoured model is one in which the first two repeats form a β-sandwich in one filament and the second two repeats form a β-sandwich in a neighbouring filament. Links between alternating up- and down-pointing β-sheets would provide optimum connectivity.

Epidermal micromorphology and venation patterns of Microlicieae (Melastomataceae) leaves: Looking for new characters for the taxonomy of this neotropical tribe

Species belonging to the family Melastomataceae are typically recognized by their leaves with acrodromous venation exhibiting a wide variety of trichomes and epidermal appendages. The tribe Microlicieae is one of the major clades in this family and its intergeneric delimitation is still imprecise. We analyzed the epidermal micromorphology and venation patterns of 25 Microlicieae species. The type and distribution of epidermal appendages can be useful characteristics for species delimitation in Microlicieae. The acrodromous venation was found to be constant in the tribe and the number of primary veins was correlated with leaf size. The genus Lavoisiera was more constant in having a smooth epidermis, acrodromous venation with one primary vein, and sclereids at the veinlets. The genera Trembleya and Microlicia were highly variable with respect to the epidermis of the leaves. The investigated characteristics can be explored in a phylogenetic context and could be useful for future taxonomic investigations of Microlicieae.

INITIAL STAGES OF INFECTIOUS PROCESS OF Pseudomonas syringae pv. garcae IN COFFEE LEAVES

<p>Bacterial blight of coffee (<em>Pseudomonas</em> <em>syringae</em> pv. <em>garcae</em>) (PSG) has been causing damage and losses to coffee growing. However, initial stages of the infectious process<em> </em>should be described in order to understand the relationship cycle and to propose efficient management strategies. This study described the initial stages of<strong> </strong>infectious process of the PSG in coffee leaves over time. The bacterial penetration sites studied were stomata, leaf margins, and wounds. Coffee seedlings received 50μL inoculum suspension at marked points on the abaxial face and leaf margins, and around wounds. By 30 minutes, 1, 3, 6, and 12 hours after inoculation, leaf disks collected at inoculated points were analyzed with scanning electron microscopy. One hour after inoculation, bacterial groups could be seen as result of cell multiplication. Subsequently, the number of grouped bacteria increased proportionally over time. A growing population concentration was found near stomata, wounds, epidermal appendages, and wax layer on leaf margins and leaf tip. Bacteria were positioned in their long axis starting from structures, thus creating a population gradient and displacement flow toward penetration pathways. Initial stages of infectious process occurred in all penetration sites, thus it was not possible to determine a preferred pathway.</p>

Phospholipase Cγ1 is required for normal irritant contact dermatitis responses and sebaceous gland homeostasis.

Differentiation and proliferation of keratinocyte are controlled by various signalling pathways. The epidermal growth factor receptor (EGFR) is known to be an important regulator of multiple epidermal functions. Inhibition of EGFR signalling disturbs keratinocyte proliferation, differentiation and migration. Previous studies have revealed that one of the EGFR downstream signalling molecules, phospholipase Cγ1 (PLCγ1), regulates differentiation, proliferation and migration of keratinocytes in in vitro cell culture system. However, the role of PLCγ1 in the regulation of keratinocyte functions in animal epidermis remains unexplored. In this study, we generated keratinocyte-specific PLCγ1 knockout (KO) mice (PLCγ1 cKO mice). Contrary to our expectations, loss of PLCγ1 did not affect differentiation, proliferation and migration of interfollicular keratinocytes. We further examined the role of PLCγ1 in irritant contact dermatitis (ICD), in which epidermal cells play a pivotal role. Upon irritant stimulation, PLCγ1 cKO mice showed exaggerated ICD responses. Further study revealed that epidermal loss of PLCγ1 induced sebaceous gland hyperplasia, indicating that PLCγ1 regulates homeostasis of one of the epidermal appendages. Taken together, our results indicate that, although PLCγ1 is dispensable in interfollicular keratinocyte for normal differentiation, proliferation and migration, it is required for normal ICD responses. Our results also indicate that PLCγ1 regulates homeostasis of sebaceous glands.

Nail Anatomy, Nail Psoriasis, and Nail Extensor Enthesitis Theory: What Is the Link?

The concept of the nail unit as a musculoskeletal appendage has become popular in the dermatological and rheumatological literature. However, an exact knowledge of the characteristics of mesenchyme surrounding the nail such as the composition of the collagen and elastic fibers and their arrangement is fundamental before one can propose a constitutive model. To the best of my knowledge, there is no study in the literature concerning the elastic network of the ligamentous connective tissue of the base of the distal phalanx. This study by means of elastic stains demonstrates that the so-called superficial, deep, and lateral laminae of the extensor tendon correspond to 3 different microanatomic structures: the nail dermis and its fibrous root, the subcutaneous proximal nail fold, and the periosteum. The complex fascial and adipose connective tissue of the proximal nail fold surrounds the matrical dermis and could viewed as a kind of suspensory system for the proximal nail unit. Such suspensory system protects the nail matrix epithelium from the biomechanical strain of the extensor mechanism. Near the ulnar and radial edge of the base of the phalanx, focal interconnections between the fibrous root of the apex of the matrix and the periosteum through a fascia-like structure are visible. In its most lateral zone, the matrical horns lie on a thick dermis connected to the interosseous ligament. Such lateral laminar system serves as anchoring ropes for the vault of the nail plate. The nail-extensor enthesitis theory relies on an oversimplified anatomy because the nail unit is an epidermal appendage with a specialized connection with the lateral periosteum, but not a musculoskeletal appendage. Finally, I would like to emphasize, the practical importance of recognizing the matrical hypoderm. In nail surgery, the interface between the matrical nail dermis and its submatrical loose connective tissue is potentially a new, relatively superficial, surgical cleaving plane, beside the classical deep surgical procedure usually extending to the periosteum. Recognition of this additional cleaving plane leads to an optimal nail tangential biopsy.

Transcription factor Blimp-1 regulates sebocyte homeostasis and cytokine production

Abstract Blimp-1, encoded by Prdm1, is a master transcriptional factor that governs the differentiation fate of many cell types, including epidermal keratinocytes. Previous results from our laboratory showed that inducible deletion of Prdm1 in mouse epidermis spontaneously induces skin inflammation. Epidermis composes of not only epidermal keratinocytes, but also epidermal appendages, including hair follicles, sebaceous glands and sweat glands. Sebaceous glands release the “oil” contents that lubricate the skin. Our previous results also showed that Blimp-1 is required for the maintenance of the homeostasis of terminally differentiated sebocytes. Here, we aim to investigate the potential function of Blimp-1 in inflammation and lipid metabolism in sebocytes. We depleted Blimp-1 by siRNA in SZ95, the immortalized human sebocyte cells. We found accumulated and enlarged lipid droplets in Blimp-1 depleted cells. Consistently, gas chromatography–mass spectrometry (GC-MS) analyses showed that the levels of several long-chain fatty acids, including 1,3-dipalmitoyl-2oleoylglycerol, 1-palmitoyl-2oleoyl-3-lineoleoyl-rac-glycerol, and triolein, were accumulated in Blimp-1-depleted SZ95 cells, linking with the significant increases in the production of pro-inflammatory cytokines, including IL-1β, IL-6, IL-8 and IL-18. Thus, Blimp-1 served as a pivotal mediator in the regulation of the inflammatory responses in epidermis, likely also through affecting the lipid metabolism and cytokine production in sebocytes.

Size fractionated phytomonitoring of airborne particulate matter (PM) and speciation of PM bound toxic metals pollution through Calotropis procera in an urban environment

Abstract Phytomonitoring of airborne toxic metals (e.g., Pb, Cd, Cu, and Ni) at urban roadsides was conducted by studying accumulation patterns in the leaves of Calotropis procera through foliar dust, leaf samples, road dust, and soil samples. These samples were collected at four roadside sites over three consecutive months (March through May 2017). The results show that the leaves of C. procera can accumulate selected airborne toxic metals. The uptake pattern of ambient particulate matter (PM) on leaf surfaces was also examined by scanning electron microscopy (SEM), coupled with energy dispersive spectroscopy. Particle density analysis based on SEM images quantified and distinguished PM accumulation in a range of different sizes (0.2–100 µm) on both sides of the leaves. PM throughout the leaf (e.g., in stomata, trichomes, and epidermal appendages) was found to contain 12 airborne metals, including Pb, Cd, Cu, Ni, and Zn. The overall results support the use of C. procera as a phytomonitoring tool to assess interactions between plants and metals.

Molecular structure of sauropsid β-keratins from tuatara (Sphenodon punctatus)

The birds and reptiles, collectively known as the sauropsids, can be subdivided phylogenetically into the archosaurs (birds, crocodiles), the testudines (turtles), the squamates (lizards, snakes) and the rhynchocephalia (tuatara). The structural framework of the epidermal appendages from the sauropsids, which include feathers, claws and scales, has previously been characterised by electron microscopy, infrared spectroscopy and X-ray diffraction analyses, as well as by studies of the amino acid sequences of the constituent β-keratin proteins (also referred to as the corneous β-proteins). An important omission in this work, however, was the lack of sequence and structural data relating to the epidermal appendages of the rhynchocephalia (tuatara), one of the two branches of the lepidosaurs. Considerable effort has gone into sequencing the tuatara genome and while this is not yet complete, there are now sufficient sequence data for conclusions to be drawn on the similarity of the β-keratins from the tuatara to those of other members of the sauropsids. These results, together with a comparison of the X-ray diffraction pattern of tuatara claw with those from seagull feather and goanna claw, confirm that there is a common structural plan in the β-keratins of all of the sauropsids, and not just those that comprise the archosaurs (birds and crocodiles), the testudines (turtles) and the squamates (lizards and snakes).