Keratins are intermediate filament-forming proteins that provide mechanical support and fulfill a variety of additional functions in epithelial cells. In 1982, a nomenclature was devised to name the ...keratin proteins that were known at that point. The systematic sequencing of the human genome in recent years uncovered the existence of several novel keratin genes and their encoded proteins. Their naming could not be adequately handled in the context of the original system. We propose a new consensus nomenclature for keratin genes and proteins that relies upon and extends the 1982 system and adheres to the guidelines issued by the Human and Mouse Genome Nomenclature Committees. This revised nomenclature accommodates functional genes and pseudogenes, and although designed specifically for the full complement of human keratins, it offers the flexibility needed to incorporate additional keratins from other mammalian species.
In this issue, Israeli and colleagues confirm that homozygous mutations in corneodesmosin (CDSN) cause type B peeling skin syndrome (PSS), an autosomal recessive skin disorder. The deletion mutation ...described resulted in a frameshift, producing a downstream premature stop codon and early truncation of the protein. The recently described CDSN nonsense mutation in another PSS family also resulted in protein truncation and nonsense-mediated mRNA decay. Type B generalized PSS can now be clearly distinguished from acral PSS, caused by mutations in transglutaminase 5. This directly affects cornified envelope cross-linking rather than corneodesmosome adherence. These observations provide new insight into the molecular defects underlying two closely related forms of PSS.
: A novel missense mutation (p.Thr198Ser) in the 1A helix of keratin 5 (K5) has been identified in a four‐generation family with a history of the localized variant of epidermolysis bullosa simplex ...(EBS‐loc), a genetic skin fragility disorder caused by K5 or K14 mutations. Genomic DNA was isolated from blood samples of patients and their healthy relatives, and all exons of the genes encoding K5 and K14 (KRT5 and KRT14) were amplified by PCR and directly sequenced. The identified mutation was confirmed by mismatch allele‐specific (MM‐AS)‐PCR and restriction enzyme digestion with RsaI. K5 p.Thr198Ser lies at the C‐terminal end of the 1A helical domain and is considered to be outside of the main mutation hotspot region. This is the first reported mutation to affect position 30 of the 1A helix (1A:T30S) in any of the 54 known keratins.
D'Alessandro and colleagues have investigated stress responses in keratinocyte cell lines lacking keratin 14 (K14-null mutation). In this issue, they describe the use of this model to assess the ...extent of phenotypic rescue achievable by wild-type K14 in the absence of a dominant negative mutation. This work provides proof that, in principle, transfection of wild-type K14 on a null background can significantly normalize the cell and reduce stress responses. However, hurdles to gene therapy in vivo persist because the majority of patients with keratin genodermatoses have heterozygous dominant negative mutations, which are more disruptive than those of the null state. Although correction in the laboratory is now relatively routine, gene delivery to the skin of patients and stable correction of mutations remain major challenges.
Twenty years have elapsed since keratin mutations were linked to cutaneous genodermatoses, and we now know that they cause 40 different genetic disorders. In this issue, Wilson et al. have identified ...KRT6C mutations in patients with focal palmoplantar keratoderma (FPPK), but debate concerning overlapping phenotypes between FPPK and pachyonychia congenita (PC) will continue because only one family has nail involvement. Furthermore, screening of control DNA samples identified 3 in 335 individuals (1%) who had a mutation (K6c p.Asn172del), but the phenotype was not ascertained. However, this raises the question as to whether individuals with sensitive feet bear specific KRT6C mutations and whether a general population screen should be considered.
Pachyonychia congenita (PC) is a rare autosomal dominant condition characterized by multiple ectodermal abnormalities. Patients with Jadassohn-Lewandowsky Syndrome (MIM #167200; PC-1) have nail ...defects (onchyogryposis), palmoplantar hyperkeratosis, follicular hyperkeratosis and oral leukokeratosis. Those with the rarer Jackson-Lawler Syndrome (MIM #167210; PC-2) lack oral involvement but have natal teeth and cutaneous cysts. Ultra-structural studies have identified abnormal keratin tonofilaments and linkage to the keratin gene cluster on chromosome 17 has been found in PC families. Keratins are the major structural proteins of the epidermis and associated appendages and the nail, hair follicle, palm, sole and tongue are the main sites of constitutive K6, K16 and K17 expression. Furthermore, mutations in K16 and K17 have recently been identified in some PC patients. Although we did not detect K16 or K17 mutations in PC families from Slovenia, we have found a heterozygous deletion in a K6 isoform (K6a) in the affected members of one family. This 3 bp deletion (AAC) in exon 1 of K6a removes a highly conserved asparagine residue (delta N170) from position 8 of the 1A helical domain (delta N8). This is the first K6a mutation to be described and this heterozygous K6a deletion is sufficient to explain the pathology observed in this PC-1 family.
The expression of different keratin intermediate filaments has been used to define keratinocyte maturation and different phenotypic subtypes involved in acute wound (AW) healing. Immunohistochemistry ...with specific anti-keratin monoclonal and polyclonal antibodies was used to examine AW in normal healthy volunteers (n=16). In all wounds examined, basal keratinocytes and cells at the leading edge of the wound expressed keratins K5 and K14. However, suprabasal cells had a more complex pattern of keratin expression, which was dependent on their position relative to the wound and location within the suprabasal compartment of the epidermis. In general, K10 was expressed in suprabasal keratinocytes at the wound edge, but not in keratinocytes covering the wound center, which expressed K6, K16, and K17 in a complex fashion. Ki67 expression, a marker of cell proliferation, was restricted to basal and immediate suprabasal layers at the wound edge. Keratinocytes populated the wound bed below the scab by migration, which was supported by keratinocyte proliferation in the surrounding epidermis both at and adjacent to the wound edge.
Canine claws are complex epithelial structures resembling the mammalian hair fibre, and human nail plate, in terms of tissue‐specific differentiation. They are composed of several distinct epithelial ...cell lineages undergoing either hard or soft keratinization. The claw plate has three distinct regions: stratum externum, stratum medium (SM) and stratum internum and the underside and tip are cushioned by a soft keratinizing epithelium, the sole. We have examined keratin expression in the canine claw and associated epithelia. Digits from German shepherd dogs were decalcified, processed and sectioned by sledge microtome. Sections were stained with haematoxylin and eosin or treated with specific antibodies to various keratins (immunohistochemistry). Proteins were extracted from claw components and analysed by SDS‐PAGE and Western blotting. The keratinized canine claw plate expressed hair‐specific keratins (type I, K25‐K38 and type II, K71‐K86) but only the inner region of the SM contained K6‐ and K16‐positive tubules, soft epithelia running through the hard keratinized claw plate. The soft keratinaceous sole epithelium expressed keratins K5, K6, K14, K16 and K17 and contained cells with abundant envelopes. The canine claw had two slippage zones, the inner claw bed, between the claw plate and ungula process, which expressed K17 and the region between the inner and outer claw sheath, equivalent to the hair follicle companion layer, which expressed K6, K77, K16 and K17. In conclusion, several different cell types have been defined in the canine claw presenting a complex mechanism of cellular differentiation.
Résumé
Les griffes canines sont des structures épithéliales complexes ressemblant en terme de différentiation tissulaire spécifique, aux follicules pileux des mammifères et aux ongles humains. Elles sont constituées de plusieurs lignées distinctes de cellules épithéliales à l’origine de kératinisation molle ou dure. La base de la griffe a trois régions : le stratum externum (SE), le stratum medium (SM) et le stratum internum (SI) et la face inférieure et l’extrémité sont protégés par un épithélium kératinisé mou, la sole. Nous avons examinés l’expression de la kératine de la griffe du chien et les épithélia associés. Les doigts de Bergers Allemands ont été décalcifiés, traités et sectionnés par microtome à traîneau. Les coupes ont été colorées à l’hématoxyline et éosine ou traitées par immunohistochimie avec des anticorps spécifiques de différentes kératines. Les protéines ont été extraites des griffes et analysées par SDS‐PAGE et western blot. Le plat de la griffe kératinisée exprimait des kératines spécifiques du poil (type I, K25‐K38 et type II, K71‐K86) mais seul SM2 contenait des tubules positifs pour K6 et K16, épithélium souple traversant le plat de la griffe kératinisée. L’épithélium de la sole kératinisée molle exprimait K5, K6, K14, K16 et K17 et contenait des cellules avec d’abondantes enveloppes. La griffe canine a deux zones d’attache, la face interne du lit de la griffe, entre le plat de la griffe et le processus unguéal, qui exprime K17 et la région entre la gaine intérieure (ICS) et extérieure (OCS) de la griffe qui exprime K6, K77, K16 et K17. En conclusion, plusieurs types cellulaires différents ont été identifiés dans la griffe canine qui représente ainsi un mécanisme complexe de différentiation cellulaire.
Resumen
Las uñas caninas son estructuras epiteliales complejas que asemejan folículos pilosos de mamíferos y uñas humanas, en términos de diferenciación tisular específica. Están compuestas por distintas líneas celulares epiteliales que progresan con queratinización blanda o dura. La lámina de la uña tiene tres regiones distintas: el estrato externo (SE), el estrato medio (SM) y el estrato interno (SI) y la parte inferior y la punta están almohadilladas por epitelio queratinizado blando, la suela. Hemos examinado la expresión de citoqueratinas en la uña canina y el epitelio asociado a ella. Dedos de perros Pastor Alemán fueron decalcificados, procesados y seccionados en microtomo horizontal. Las secciones se tiñeron con hematoxilina y eosina o se trataron con anticuerpos específicos para varias citoqueratinas (inmunohistoquímica). Las proteínas fueron extraídas de los componentes de la uña y se analizaron mediante SDS‐PAGE y western blotting. La lámina queratinizada de la uña expresaba queratinas específicas del pelo (tipo I, K25‐K38 y tipo II, K71‐K86) pero sólo el SM2 contenía túbulos positivos para K6 y K16, epitelio blando que corre a lo largo de la lámina queratinizada de la uña. El epitelio blando queratinizado de la suela expresaba K5, K6, K14, K16 y K17 y contenía células con abundante envuelta. La uña canina tenía dos zonas de deslizamiento, la base interna de la uña, entre la lámina de la uña y el proceso ungular, que expresaba K17 y la región entre las vainas interna y externa de la uña, equivalente al estrato del folículo entre las vainas externa e interna (estrato de acompañamiento), que expresaba K6, K77, K16 y K17. En conclusión, se definen varios tipos celulares en la uña canina que presentan un mecanismo complejo de diferenciación celular.
Zusammenfassung
Die Krallen des Hundes sind komplexe epitheliale Strukturen, die den Haarfollikeln der Säugetiere und den menschlichen Nägeln im Bezug auf die Gewebe‐spezifische Differenzierung ähnlich sind. Sie bestehen aus mehreren deutlich unterschiedlichen epithelialen Zelllinien, die entweder eine harte oder weiche Verhornung durchmachen. Das Krallenbein hat drei deutlich unterschiedliche Bereiche: Stratum externum (SE), Stratum medium (SM) und Stratum internum (SI) und die Unterseite und Spitze, die durch weiches keratinisierendes Epithel, die Sohle, eingepolstert sind. Wir haben die Expression von Keratin in der Hundekralle und in benachbarten Epithelien untersucht. Es wurden Zehen von Deutschen Schäferhunden entkalzifiziert, verarbeitet und mittels Schlittenmikrotom geschnitten. Die Schnitte wurden mit Hämatoxylin‐Eosin gefärbt oder mit spezifischen Antikörpern zu verschiedenen Keratinen behandelt (Immunhistochemie). Es wurden Proteine von den verschiedenen Bestandteilen der Krallen extrahiert und mittels SDS‐PAGE und Western Blotting analysiert. Das keratinisierte Krallenbein drückte Haar‐spezifische Keratine (Typ I, K25‐K38 und Typ II, K71‐K86) aus, aber nur SM2 besaß K6 und K16 positive Tubuli, weiche Epithelien, die durch das keratinisierte Krallenbein laufen. Das weiche, keratinöse Epithel zeigte K5, K6, K14, K16 und K17 Expression und beinhaltete Zellen mit mächtigen Umhüllungen. Die Hundekralle hatte zwei Gleitstellen, das innere Krallenbett, zwischen dem Krallenbein und dem Processus unguicularis, der K17 Expression zeigte und die Region zwischen der inneren (ICS) und äußeren (OCS) Krallenhülle, die gleichzusetzen ist mit dem Companion layer des Haarfollikels (CL), welche K6, K77, K16 und K17 Expression zeigte. Zusammenfassend kann man sagen, dass einige verschiedene Zelltypen in der Hundekralle definiert werden konnten, die einen komplexen Mechanismus der Zelldifferenzierung zeigten.
Epidermolytic hyperkeratosis is a rare autosomal dominant inherited skin disorder caused by keratin 1 or keratin 10 mutations. Keratins are major structural proteins of the epidermis, and in ...keratinocytes committed to terminal differentiation the intermediate filaments are composed of keratin 1 and keratin 10 heterodimers. The majority of reported mutations (86.6%) are heterozygous single point mutations and most of these are located in the 1A and 2B regions of the highly conserved keratin α-helical rod domain. We have studied eight Scandinavian families with epidermolytic hyperkeratosis and identified three point mutations, two codon deletions, two splice site mutations, and a complex deletion/insertion. Two of the point mutations were in the KRT1 gene (F191C and K177N) and the other was in KRT10 (L453P). All three patients had associated palmoplantar keratoderma. The splice site mutations in KRT1 both caused a large deletion removing 22 codons (Δ176–197) from the 1A helical domain. Codon deletions were found in KRT1 (Δ170–173) and in KRT10 (Δ161–162) in two patients with a severe phenotype. A final patient had a more complex mutation with a large deletion (442 bp) together with a large insertion (214 bp) of unknown origin that caused deletion of exon 6 in KRT1. In conclusion, we have found eight novel keratin mutations that cause epidermolytic hyperkeratosis with differing phenotypes. Even when a large part of keratin 1 (46 amino acids) is deleted, surprisingly mild phenotypes can result, suggesting that genotype-phenotype relationships in epidermolytic hyperkeratosis are complex and do not solely depend on the type of mutation but also depend on interactions between the behavior of the mutant protein and the cellular environment.
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