Two type II keratin genes are localized on human chromosome 12

Epidermolytic hyperkeratosis: clinical update

Epidermolytic hyperkeratosis (EHK), earlier termed as bullous congenital ichthyosiform erythroderma is a skin disorder characterized as an autosomal dominant and rare disorder which has been observed to affect 1 in over 200,000 infants as a consequence of a significant mutation in the genes responsible for the keratin proteins, mostly keratin 1 and 10. The features present at birth include erythema and blistering. In adults, the hallmarks include hyperkeratosis, erosions, and blisters. The major symptoms including xerosis, pruritus, and painful fissuring lead not only to cosmetic problems but also stress, inferiority complex and other psychological conditions. While clinical inspection followed by confirmatory tests including histopathology and electron microscopic assessment is used for diagnosis, treatment modalities can be further improved for better diagnosis. This article reviews subtypes of ichthyosis, with a focus on EHK, genetics behind the disease, recently reported mutations, the existing diagnostics and treatments for the same and potential of new modalities in diagnosis/treatment.

Keratin expression in breast cancers

Cytokeratin (CK) immunohistochemistry can play an important role in breast carcinoma evaluation. We evaluated the expression of a panel of commonly used CKs in a large cohort of breast cancers and assessed its correlation with other biomarkers and breast cancer subtypes. Expression of CK7, CK8, CK18 and CK19 was observed in more than 90 % of all breast carcinomas in this study, confirming their efficacy in immunohistochemical identification of breast cancer. A combination of CK8 and CK7 gave the highest sensitivity for detection of a minute number of breast cancer cells. Expression of other CKs, including CK5/6, CK14 and CK20, correlated positively with high tumour grade. The expression of CK5/6 and CK14 in a significant number of high-grade tumours raised concern regarding the use of absence of their expression to identify breast carcinoma. For identification of the basal subtype, CK5/6 gave a higher detection rate than CK14. CK20 expression was found more frequently than reported in previous studies, might constitute an indicator of poor prognosis and may be associated with the molecular apocrine subtype. This study highlights the diagnostic and prognostic relevance of the unique CK expression patterns in breast cancer.

Defining the complex epithelia that comprise the canine claw with molecular markers of differentiation

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.

Analysis of gene expression profiles in cholesteatoma using oligonucleotide microarray

CONCLUSION

Microarray analysis may be a useful tool to identify some candidate genes related to the pathogenesis of cholesteatoma.

OBJECTIVE

The aim of this study was to investigate gene expression profiles in human cholesteatoma using an oligonucleotide chip including 10,115 genes.

MATERIALS AND METHODS

Gene expression from five cholesteatoma matrices and five normal retroauricular skins was analyzed by Macrogen human oligo-chip and the expression levels of some selected genes were also confirmed by RT-PCR.

RESULTS

In all, 1327 up-regulated or 767 down-regulated genes that were over 3 times more prominent in cholesteatoma than in skin were identified by 5 samples of microarray data. Among these up-regulated or down-regulated genes in cholesteatoma, 291 genes were identified in 3 samples or more out of 5 samples as up-regulated expression more than threefold in density and 191 genes were down-regulated more than threefold in density. RT-PCR of 21 selected genes revealed that those expression levels were higher in choleasteatoma than retroauricular skin.

Characterization of new members of the human type II keratin gene family and a general evaluation of the keratin gene domain on chromosome 12q13.13

The recent completion of a reference sequence of the human genome now allows a complete characterization of the type II keratin gene domain on chromosome 12q13.13. This, domain, approximately 780 kb in size, is present on nine bacterial artificial chromosome clones sequenced by the Human Genome Sequencing Project. The type II keratin domain contains 27 keratin genes and eight pseudogenes. Twenty-three of these genes and four pseudogenes have been previously reported. This study describes, in addition to the genomic sequencing of the K2p gene and the bioinformatic identification of four keratin pseudogenes, the characterization of cDNA corresponding to three previously undescribed keratin genes K1b, K6l, and Kb20, as well as cDNA sequences for the previously described keratin genes hHb2, hHb4, and K3. Northern analysis of the new keratins K1b, K6l, K5b, and Kb20 using mRNA of major organs as well as of specific epithelial subtypes shows singular expression of these keratins in skin, hair follicles and, for K5b and Kb20, in tongue, respectively. In addition, the obvious discrepancies between the current reference sequence of the human genome and the previously described gene/cDNA sequences for K6c, K6d, K6e, K6f, K6h are investigated, leading to the conclusion that K6c, K6d as well as K6e, K6f are probably polymorphic variants of K6a and K6h, respectively. All 26 human type II keratins found on this domain as well as K18, dtype 1 Keratin, are identified at the genomic and transcriptional level. This appears to be the total complement of functional type II keratins in humans.

A cluster of 21 keratin-associated protein genes within introns of another gene on human chromosome 21q22.3

Recently, we identified multiple unique sequences in the 21q22.3 region and predicted them to be a cluster of genes encoding hair-specific keratin-associated proteins (KAPs). Detailed computer-aided analysis of these clustered genes revealed that the cluster spans over 165 kb and consists of 21 KAP-related sequences including 16 putative genes and 5 pseudogenes. These were further divided into two subfamilies, KRTAP12 (KRTAP12.1-12.4 and KRTAP12.5P) and KRTAP18 (KRTAP18.1-18.12 and KRTAP18.13P-18.16P). All 16 putative genes possess several intragenic repeat sequences and apparently belong to the high-sulfur KAP gene family (16-30% cysteine content) known for nonhuman mammalian species. Transcripts were detected by RT-PCR analysis for all 16 putative KAP genes and their expression was restricted to hair root cells (radix pili cells) and not found in 28 other tissues, including skin. All 16 KAP genes produced unspliced transcripts, indicating their nature to be that of active intronless genes. Interestingly, all these KAP-related genes are located within introns of the recently identified gene TSPEAR (approved gene symbol C21orf29), 214 kb in size. Surprisingly, the transcriptional direction of 8 of the 16 active genes is the same as that of C21orf29/TSPEAR. This finding suggests a novel transcription mechanism in which C21orf29/TSPEAR gene transcription passes over the multiple transcriptional termination sites of the KAP genes.

Molecular advances in genetic skin diseases

The genes for several genetic skin diseases have been identified in recent years. This development improves diagnostic capabilities and genetic counseling, and investigators can now turn to the molecular mechanisms involved in the pathogenesis of these diseases. The identification of the causative genes has led to the generation of mouse models for some genetic skin diseases. A study of the keratin 10 deficient mouse, a model for epidermolytic hyperkeratosis, and a mouse model for Bloom syndrome are reviewed in this article. Several studies also evaluate the relation between genotype and phenotype. In this article, the clinical findings and molecular advances in tuberous sclerosis complex, neurofibromatosis type 1, Bloom syndrome, epidermolytic hyperkeratosis, X-linked ichthyosis, Netherton syndrome, and Hermansky-Pudlak syndrome are reviewed.

Keratin expression in human tissues and neoplasms

Keratin expression in human tissues and neoplasms Keratin filaments constitute type I and type II intermediate filaments (IFs), with at least 20 subtypes named keratin 1-20. Since certain keratin subtypes are only expressed in some normal human tissues but not others, and vice versa, various tissues have been subclassified according to the pattern of keratin staining. Simple epithelia generally express the simple epithelial keratins 7, 18, 19, and 20, while complex epithelia express complex epithelial keratins 5/6, 10, 14, and 15. When an epithelium undergoes malignant transformation, its keratin profile usually remains constant. The constitution and expression patterns of keratin filaments in human epithelial neoplasms are complex and often distinctive. In this article, we first briefly review the molecular and cell biology of keratin filaments. We then focus on the expression patterns of keratin filaments in various human neoplasms.

The mouse keratin 6 isoforms are differentially expressed in the hair follicle, footpad, tongue and activated epidermis

Keratin 6 (K6) is expressed constitutively in a variety of internal stratified epithelia as well as in palmoplantar epidermis and in specialized cells of the hair follicle. K6 expression can also be induced by hyperproliferative conditions as in wound healing or by conditions that perturb normal keratinocyte function. The functional significance of the expression of K6 on keratinocyte biology under these disparate conditions is not known. Here we report on the characterization of two isoforms of mouse K6 that are encoded by separate genes. The two genes (denoted K6a and K6b) are linked, have the same orientation and are actively transcribed. Sequence analysis revealed, that although they encode almost identical products, they have distinctly different regulatory regions, suggesting that the two K6 genes would be differentially expressed. In an attempt to define the expression characteristics of the K6 isoforms, we produced transgenic mice with each gene after modifying the C-terminal sequences to enable detection of the transgenic proteins with specific antibodies. The constitutive expression of the K6a transgene paralleled that of the endogenous genes in all K6 expressing tissues, except in the tongue. The K6b transgene was also expressed in these tissues but, in contrast to K6a, was only expressed in suprabasal cells. Both K6 transgenes were also induced in the interfollicular epidermis in response to phorbol esters, with K6a induced in all layers of the treated epidermis, while K6b was expressed only in suprabasal cells. These studies suggest that the K6 isoforms have overlapping yet distinct expression profiles.

Identification of novel and known mutations in the genes for keratin 5 and 14 in Danish patients with epidermolysis bullosa simplex: correlation between genotype and phenotype

Epidermolysis bullosa simplex (EBS) is a group of autosomal dominant inherited skin diseases caused by mutations in either the keratin 5 (K5) or the keratin 14 (K14) genes and characterized by development of intraepidermal skin blisters. The three major subtypes of EBS are Weber-Cockayne, Koebner, and Dowling-Meara, of which the Dowling-Meara form is the most severe. We have investigated five large Danish families with EBS and two sporadic patients with the Dowling-Meara form of EBS. In the sporadic Dowling-Meara EBS patients, a novel K14 mutation (N123S) and a previously published K5 mutation (N176S) were identified, respectively. A novel K14 mutation (K116N) was found in three seemingly unrelated families, whereas another family harbored a different novel K14 mutation (L143P). The last family harbored a novel K5 mutation (L325P). The identified mutations were not present in more than 100 normal chromosomes. Six polymorphisms were identified in the K14 gene and their frequencies were determined in normal controls. These polymorphisms were used to show that the K14 K116N mutation was located in chromosomes with the same haplotype in all three families, suggesting a common ancestor. We observed a strict genotype-phenotype correlation in the investigated patients as the same mutation always resulted in a similar phenotype in all individuals with the mutation, but our results also show that it is not possible to predict the EBS phenotype merely by the location (i.e., head, rod, or linker domains) of a mutation. The nature of the amino acid substitution must also be taken into account.

Characterization and chromosomal localization of human hair-specific keratin genes and comparative expression during the hair growth cycle

During anagen, cell proliferation in the germinative matrix of the hair follicle gives rise to the fiber and inner root sheath. The hair fiber is constructed from structural proteins belonging to four multigene families: keratin intermediate filaments, high-sulfur matrix proteins, ultra high-sulfur matrix proteins, and high glycine-tyrosine proteins. Several hair-specific keratin intermediate filament proteins have been characterized, and all have relatively cysteine-rich N- and C-terminal domains, a specialization that allows extensive disulfide cross-linking to matrix proteins. We have cloned two complete type II hair-specific keratin genes (ghHb1 and ghHb6). Both genes have nine exons and eight introns spanning about 7 kb and lying about 10 kb apart. The structure of both genes is highly conserved in the regions that encode the central rod domain but differs considerably in the C-terminal coding and noncoding sequences, although some conservation of introns does exist. These genes have been localized to the type II keratin cluster on chromosome 12q13 by fluorescence in situ hybridization. They, and their type I partner ghHa1, are expressed in differentiating hair cortical cells during anagen. In cultured follicles, ghHa1 expression declined in cortical cells and was no longer visible after 6 d, whereas the basal epidermal keratin hK14 appeared in the regressing matrix. The transition from anagen to telogen is marked by downregulation of hair cortical specific keratins and the appearance of hK14 in the epithelial sac to which the telogen hair fiber is anchored. Further studies of the regulation of these genes will improve our understanding of the cyclical molecular changes that occur as the hair follicle grows, regresses, and rests.

The role of keratin proteins and their genes in the growth, structure and properties of hair

The importance of wool in the textile industry has inspired extensive research into its structure since the 1960s. Over the past several years, however, the hair follicle has increased in significance as a system for studying developmental events and the process of terminal differentiation. The present chapter seeks to integrate the expanding literature and present a broad picture of what we know of the structure and formation of hair at the cellular and molecular level. We describe in detail the hair keratin proteins and their genes, their structure, function and regulation in the hair follicle, and also the major proteins and genes of the inner and outer root sheaths. We discuss hair follicle development with an emphasis on the factors involved and describe some hair genetic diseases and transgenic and gene knockout models because, in some cases, they stimulate natural mutations that are advancing our understanding of cellular interactions in the formation of hair.

A transgenic mouse model that recapitulates the clinical features of both neonatal and adult forms of the skin disease epidermolytic hyperkeratosis

Keratins are the major structural proteins of keratinocytes, which are the most abundant cell type in the mammalian epidermis. Mutations in epidermal keratin genes have been shown to cause severe blistering skin abnormalities. One such disease, epidermolytic hyperkeratosis (EHK), also known as bullous congenital ichthyosiform erythroderma, occurs as a result of mutations in highly conserved regions of keratins K1 and K10. Patients with EHK first exhibit erythroderma with severe blistering, which later is replaced by thick patches of scaly skin. To assess the effect of a mutated K1 gene on skin biology and to produce an animal model for EHK, we removed 60 residues from the 2B segment of HK1 and observed the effects of its expression in the epidermis of transgenic mice. Phenotypes of the resultant mice closely resembled those observed in the human disease, first with epidermal blisters, then later with hyperkeratotic lesions. In neonatal mice homozygous for the transgene, the skin was thicker, with an increased labeling index, and the spinous cells showed a collapse of the keratin filament network around the nuclei, suggesting that a critical concentration of the mutant HK1, over the endogenous MK1, was required to disrupt the structural integrity of the spinous cells. Additionally, footpad epithelium, which is devoid of hair follicles, showed blistering in the spinous layer, suggesting that hair follicles can stabilize or protect the epidermis from trauma. Blisters were not evident in adult mice, but instead they showed a thick, scaly hyperkeratotic skin with increased mitosis, resulting in an increased number of corneocytes and granular cells. Irregularly shaped keratohyalin granules were also observed. To date, this is the only transgenic model to show the typical morphology found in the adult form of EHK.

Peripherin gene is linked to keratin 18 gene on human chromosome 12

Peripherin is a neuron-specific intermediate filament (IF) protein, found primarily in phylogenetically old regions of the nervous system. Whereas other neuronal IF genes have only two to three introns and are scattered in the genome, the peripherin gene (PRPH) has a complex intron-exon structure like nonneuronal IF genes that are clustered in tandem arrays, e.g., those encoding the keratins. We used a cosmid containing the human peripherin gene (PRPH) to determine its chromosomal location in relationship to nonneuronal IF genes. Using a rodent-human mapping panel, we localized the PRPH gene to human chromosome 12. Since a cluster of keratin genes maps to 12q12-13, polymorphic markers were developed for PRPH and for one of the keratin genes presumed to be in the cluster, keratin 18 (KRT18). Both markers were typed in CEPH reference families. Pairwise and multipoint analyses of the CEPH data revealed that KRT18 is tightly linked to DNA markers D12S4, D12S22, D12S90, D12S96 and D12S103, which lie between D12S18 and D12S8, with odds greater than 1000:1. These markers are physically located at 12q11-13, thus supporting the fine localization of KRT18 in or near the group of type II keratins in this region. Furthermore, linkage analysis showed that the peripherin gene (PRPH) is tightly linked to KRT18 (Z = 15.73, theta = 0.013), and therefore appears to be in close proximity to the cluster.

Sequence and expression of human hair keratin genes

Normal hair growth and differentiation requires co-ordinate expression of many hair specific structural protein genes. It has been established that one of the 4 major groups of hair structural proteins, low-sulphur hair keratins, belongs to the intermediate filament (IF) multigene family. Hair keratin IF proteins differ from those of other epithelia as they contain cysteine-rich terminal domains allowing more extensive disulphide bonding to the high-sulphur hair matrix proteins. Until recently, little information concerning the primary sequence of hair keratins was available but cloning of some mouse hair and sheep wool keratins has now been reported. Using these sequences, we have polymerase chain reaction (PCR) amplified genomic fragments of human hair-specific keratin IF genes and isolated cosmid clones containing full length genes. We have sequenced part of these genes and studied their expression in human hair follicles. Hair specific keratin fragments were amplified from placental gDNA by PCR primed with synthetic oligonucleotides. Fragments were cloned and sequenced after ligation into pGEM-3Z and labelled riboprobes were generated for in situ hybridization on human skin sections. A human cosmid library was screened with PCR fragments and clones encoding human hair keratin genes were characterised by southern hybridization and sequencing. The type I human hair-specific keratin clones obtained (HaKA1-b2, 386 bp; hHaKA1-XH1, 1202 bp) encoded 2B helix, C-terminal and 3'nc regions and were 65% homologous to mouse sequences. The type II hair keratin clone (hHaKB2-1, 829 bp) also encoded 2B helix and C-terminal regions and was 95% homologous to mouse. In situ hybridization on human skin sections showed a specific reaction with precortical cells of the hair follicle. One human cosmid clone, isolated with the hHaKB2-1 probe, contained two type II hair keratin genes about 7 kb apart, each of which had 9 exons spanning approximately 6 kb. The coding sequences were homologous to mouse cDNA (77-88%). These human hair-specific keratin clones are useful molecular tools for studies of hair differentiation.

Organization and expression of hair follicle genes

Several families of proteins are expressed in the growth of hair and an estimated 50-100 proteins constitute the final hair fiber. The cumbersome nomenclature for naming these different proteins has led to a proposal to modify that which is currently used for epidermal keratins. Investigations of the organization of hair genes indicate that the members of each family are clustered in the genome and their expression could be under some general control. Interestingly, the protein called trichohyalin, markedly distinct from the hair proteins, is produced in the inner root sheath cells and the gene for it has been found to be located at the same human chromosome locus as the genes for profilaggrin, involucrin, and loricrin. A mainstream objective is to identify controls responsible for the production in the hair cortex of keratin intermediate filaments (IFs) and two large groups of keratin-associated proteins (KAPs) rich in the amino acids cysteine or glycine/tyrosine. A specific family of cysteine-rich proteins is expressed in the hair cuticle. Comparisons of promoter regions of IF genes and KAP genes, including a recently characterized gene for a glycine/tyrosine-rich protein, have revealed putative hair-specific motifs in addition to known elements that regulate gene expression. In the sheep, the patterns of expression in hair differentiation are particularly interesting insofar as there are distinct segments of para- and orthocortical type cells that have significantly different pathways of expression. The testing of candidate hair-specific regulatory sequences by mouse transgenesis has produced several interesting hair phenotypes. Transgenic sheep over-expressing keratin genes but showing no hair growth change have been obtained and compared with the equivalent transgenic hair-loss mice. Studies of the effects of amino acid supply on the rate of hair growth have demonstrated that with cysteine supplementation of sheep a perturbation occurs in which there is a markedly increased level of only one type of mRNA and the ration of para- to orthocortical cells is increased. A molecular explanation of this phenomenon is being sought.

A mutation (Met-->Arg) in the type I keratin (K14) gene responsible for autosomal dominant epidermolysis bullosa simplex

We have identified a single base change in exon 4 of the type I keratin gene which results in the replacement of a methionine for an arginine residue at codon 272 in an Irish family displaying an autosomal dominant simplex (Koebner) form of epidermolysis bullosa (EB). This family had previously provided tentative evidence for linkage to genetic markers on chromosome 1q. The mutation cosegregates with the disease, producing a lod score of 4.8 at theta = 0.

Squamous cell metaplasia in the human lung: molecular characteristics of epithelial stratification

Squamous cell metaplasia (SCM) is a frequent epithelial alteration of the human tracheobronchial mucosa. This review pays particular attention to the fact that SCM can mimic esophageal, and in some instances even skin-type differentiation, showing striking similarities not only in morphology but also in terms of gene expression. Therefore, characterization of this dynamic process lends insight into the process of stratification, squamous cell formation, and "keratinization" in a pathologically relevant in vivo situation in man. First, the concept of metaplasia is presented with certain historical viewpoints on histogenesis. Then, the morphological characteristics of normal bronchial epithelium are compared with the altered phenotype of cells in SCM. These changes are described as a disturbance of the finely tuned balance of differentiation and proliferation through the action of a variety of extrinsic and intrinsic factors. Molecular aspects of altered cell/cell and cell/extracellular matrix interactions in stratified compared with single-layered epithelia are discussed with reference to SCM in the lung. Intracellular organizational and compositional changes are then summarized with special emphasis on the differential distribution of the cytokeratin (CK) polypeptides. Finally, the still unresolved problems of the histogenetic relationships between normal bronchial mucosa, SCM, and pulmonary neoplasms are addressed. As these questions remain open, examples for detection of well defined "markers" are provided that may be employed as objective criteria for determining clinically important cellular differentiation features.

Linkage of the epidermolytic hyperkeratosis phenotype and the region of the type II keratin gene cluster on chromosome 12

Bullous congenital ichthyosiform erythroderma (epidermolytic hyperkeratosis) is a severe, generalized, lifelong disease of the skin. As in epidermolysis bullosa simplex, intraepidermal blisters and clumping of keratin intermediate filaments are characteristic. We report here linkage of the inheritance of this disease to the region of chromosome 12q containing the genes encoding type II keratins. This suggests that keratin gene mutations may underlie this complex hyperproliferative and hyperkeratotic phenotype.

Mapping of the trichohyalin gene: co-localization with the profilaggrin, involucrin, and loricrin genes

The chromosomal location of the gene encoding the human hair follicle protein trichohyalin has been determined by in situ hybridization. The human gene has been localized to the region 1q21.1-1q23 (probably 1q21.3) using a sheep trichohyalin cDNA probe. The genes encoding three other epithelial proteins, namely, profilaggrin, involucrin, and loricrin, are also located in the same region of chromosome 1, which, together with their similar gene and protein structures, suggests that the four proteins form a novel superfamily of epithelial structural proteins.

Mutations in the rod domains of keratins 1 and 10 in epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis is a hereditary skin disorder characterized by blistering and a marked thickening of the stratum corneum. In one family, affected individuals exhibited a mutation in the highly conserved carboxyl terminal of the rod domain of keratin 1. In two other families, affected individuals had mutations in the highly conserved amino terminal of the rod domain of keratin 10. Structural analysis of these mutations predicts that heterodimer formation would be unaffected, although filament assembly and elongation would be severely compromised. These data imply that an intact keratin intermediate filament network is required for the maintenance of both cellular and tissue integrity.

Regional assignment of the human keratin 5 (KRT5) gene to chromosome 12q near D12S14 by PCR analysis of somatic cell hybrids and multicolor in situ hybridization

Keratin 5 is the major type II keratin of the basal cells of epidermis and of other stratified epithelia. With its type I partner, keratin 14, it constitutes a major fraction of the cytoskeleton of the basal cells. Because the inheritance of epidermolysis bullosa simplex, a disease of epidermal basal cell fragility, was mapped in one family to chromosome 12q close to D12S14, we undertook to localize the gene for keratin 5. Polymerase chain reaction analysis of somatic cell hybrids mapped the keratin 5 gene to chromosome 12, and multicolor fluorescence in situ hybridization localized it to 12q very near D12S14. This sublocalization exemplifies the utility of in situ physical localization in assessing the candidacy of genes thought to underlie inherited disorders.

Chromosomal localisation of the mouse and human peripherin genes

Using a mouse cDNA probe encoding for the major part of peripherin, a type III intermediate filament protein, we have assigned, by in situ hybridization, the mouse and human peripherin genes, Prph, to the E-F region of chromosome 15 and to the q12-q13 region of chromosome 12, respectively. These regions are known as homologous chromosomal segments containing other intermediate filament genes (keratins) and also other genes which could be co-ordinately regulated.

Close linkage of retinoic acid receptor genes with homeobox- and keratin-encoding genes on paralogous segments of mouse chromosomes 11 and 15

Retinoic acid is essential for normal development and growth of structures such as head and limbs, and it can act as morphogen or teratogen. Retinoic acid induces expression of genes such as the homeobox genes and keratin type I and type II genes. Retinoic acid receptors are nuclear transcription factors that play a key role in retinoid physiology. As part of the characterization of retinoic acid receptor gene family, linkage of genes encoding the three receptors was determined by using interspecific backcross and recombinant inbred strain analysis of restriction fragment variants. Retinoic acid receptor alpha is located on mouse Chromosome (Chr) 11 near the homeobox-2 complex and the keratin type I gene complex, whereas retinoic acid receptor gamma is on mouse Chr 15 near the homeobox-3 complex and the keratin type II complex. Close genetic proximity of these functionally related genes may be significant. We confirmed assignment of retinoic acid receptor beta to the centromeric portion of Chr 14. These linkage assignments provide further evidence for duplicated segments in the mouse genome.

Chromosomal localization of mouse hair keratin genes

Many genetic defects are known to cause abnormal development of the coat in mice. Hair keratin genes would seem to be particularly promising candidates among the potential targets of these mutations in mice and of inherited hair-related abnormalities in humans as well. We used specific probes from cloned and sequenced mouse hair keratin cDNAs (MHKA-2, MHKB-1, and MHKB-2) to assess linkage of hair keratin genes and mouse mutations. We analyzed DNA from the progeny of interspecies backcrossed mice for segregation of hair mutations, hair ("hard") keratin alleles, and epidermal ("soft") keratin alleles (Krt-1 and Krt-2 loci). The results suggest that most, if not all, hair keratin genes (types Ia and IIa) are part of the Krt-1 locus on chromosome 11 and Krt-2 locus on chromosome 15, respectively. Linkage of the hair keratin genes and the mutations Re, Den, and Bsk on chromosome 11, and Ca, Sha, and Ve on chromosome 15 suggests that these mutations may possibly involve altered hair keratin expression or structure. In addition, the nondispersion of homologous keratin genes in the mammalian genome suggests that a domain organization of the genes has influenced evolution of the keratin gene family and that the organization may play a significant role in tissue-specific and developmental regulation of keratin gene expression as well.

Epidermolysis bullosa simplex: evidence in two families for keratin gene abnormalities

Epidermolysis bullosa simplex (EBS) is characterized by skin blistering due to basal keratinocyte fragility. In one family studied, inheritance of EBS is linked to the gene encoding keratin 14, and a thymine to cytosine mutation in exon 6 of keratin 14 has introduced a proline in the middle of an alpha-helical region. In a second family, inheritance of EBS is linked to loci that map near the keratin 5 gene. These data indicate that abnormalities of either of the components of the keratin intermediate filament heterodipolymer can impair the mechanical stability of these epithelial cells.

The peripherin gene maps to mouse chromosome 15

We have mapped the mouse peripherin gene, Prph, to chromosome 15 by means of Southern analysis of a panel of Chinese hamster/mouse somatic cell hybrids using a rat peripherin cDNA probe. Peripherin is a recently characterized type III intermediate filament expressed in the peripheral and the central nervous system. Although its exact function is not known, peripherin is likely to be involved in the neuronal cytoskeleton, a role it shares with other intermediate filaments, such as the neurofilament proteins. The intermediate filament gene family is believed to have evolved via gene duplication and dispersal throughout the genome; these processes have resulted in clusters of intermediate filament genes on specific chromosomes and conservation of these chromosomal locations among mammalian species.

Mutant keratin expression in transgenic mice causes marked abnormalities resembling a human genetic skin disease

To explore the relationship between keratin gene mutations and genetic disease, we made transgenic mice expressing a mutant keratin in the basal layer of their stratified squamous epithelia. These mice exhibited abnormalities in epidermal architecture and often died prematurely. Blistering occurred easily, and basal cell cytolysis was evidence at the light and electron microscopy levels. Keratin filament formation was markedly altered, with keratin aggregates in basal cells. In contrast, terminally differentiating cells made keratin filaments and formed a stratum corneum. Recovery of outer layer cells was attributed to down-regulation of mutant keratin expression and concomitant induction of differentiation-specific keratins as cells terminally differentiate, and the fact that these cells arose from basal cells developing at a time when keratin expression was relatively low. Collectively, the pathobiology and biochemistry of the transgenic mice and their cultured keratinocytes bore a resemblance to a group of genetic disorders known as epidermolysis bullosa simplex.

Cell type-specific and efficient synthesis of human cytokeratin 19 in transgenic mice

In studies designed to identify cis-regulatory elements involved in the cell-type-specific expression of human cytokeratin (CK) genes we have dissected from the major type I CK gene locus on chromosome 17 a region containing the gene that encodes CK 19, with flanking segments of different lengths, and have examined the expression of related gene constructs in transgenic mice. Adult transgenic mice have been characterized by immunohistochemistry, gel-electrophoretic analyses of cytoskeletal proteins and genomic DNA (Southern blots). We have found that a construct harbouring the transcriptional unit plus approximately 0.7 kb downstream from the polyA-addition site and an immediately adjacent 5' upstream segment of approximately 3.6 kb, when combined with a further 5' upstream element of -6.4 - -8.6 kb, is sufficient to guarantee the synthesis of human CK 19 in the same cells and to a similar extent as the murine genome expresses its endogenous CK 19 gene. The findings demonstrate that all cis-elements necessary for the specific and efficient expression of a single type I CK gene, in the context of epithelial differentiation, can be located in the vicinity of the gene itself and that more-distant elements are not required.

Localization of the gene for human simple epithelial keratin 18 to chromosome 12 using polymerase chain reaction

Many human genes encoding keratin intermediate filament proteins are clustered on chromosomes 17 (the type I genes) and 12 (the type II genes). Some have not yet been localized, notably the genes for the primary embryonic keratins 8 and 18, normally expressed in simple epithelia: this is because the numerous pseudogenes for these keratins have made it difficult to identify the true functional gene in each case. Through the use of human-specific primers from within introns of the published gene sequence for human type I keratin 18, human genomic DNA has been specifically amplified using the polymerase chain reaction. A single reaction product was obtained. DNA from a characterized series of mouse-human somatic cell hybrid lines was tested for the presence of sequences able to initiate the chain reaction from these primers, and the presence or absence of this genomic DNA PCR product allowed us to assign a gene for human keratin 18 to chromosome 12 unambiguously. This differs from the location of other human type I keratins on chromosome 17 and may indicate the early divergence of the genes for stratifying cell keratins from that of simple, or embryonic, keratin 18.

Human papillomavirus type 16 DNA is integrated into chromosome region 12q14-q15 in a cell line derived from a vulvar intraepithelial neoplasia

The SK-v cell line, established from a precancerous lesion (a vulvar intraepithelial neoplasia), contains 10 to 20 copies of the human papillomavirus type 16 (HPV16) genome, and was previously shown to derive from a clone of cells present in the patient's lesions. By in situ hybridization the integrated HPV16 DNA sequences were localized to a single site in chromosome region 12q14-q15. The localization of viral sequences to a single nonrearranged chromosome 12 suggests that integration occurred at this site in the patient's premalignant lesions. The INT1 and GLI protooncogenes are located in this chromosomal region. No detectable modification of the structure and expression of these genes was observed by blot hybridization experiments.

Isolation and characterization of ERBB3, a third member of the ERBB/epidermal growth factor receptor family: evidence for overexpression in a subset of human mammary tumors

A related DNA fragment distinct from the epidermal growth factor receptor and ERBB2 genes was detected by reduced stringency hybridization of v-erbB to normal genomic human DNA. Characterization of the cloned DNA fragment mapped the region of v-erbB homology to three exons with closest identity of 64% and 67% to a contiguous region within the tyrosine kinase domains of the epidermal growth factor receptor and ERBB2 proteins, respectively. cDNA cloning revealed a predicted 148-kDa transmembrane polypeptide with structural features identifying it as a member of the ERBB gene family, prompting us to designate the gene as ERBB3. It was mapped to human chromosome 12q13 and was shown to be expressed as a 6.2-kilobase transcript in a variety of normal tissues of epithelial origin. Markedly elevated ERBB3 mRNA levels were demonstrated in certain human mammary tumor cell lines. These findings suggest that increased ERBB3 expression, as in the case of epidermal growth factor receptor and ERBB2, may play a role in some human malignancies.

Preferential sites for viral integration on mammalian genome

Chromosomal localization of human papillomavirus (HPV) 16 and 18 on human cervical carcinomas and epithelial cell lines obtained after HPV transfection has uncovered a nonrandom association of viral integration and specific genome sites. Fragile sites appear to be preferential targets for viral integration because of their structural and functional characteristics through which chromosomal anomalies, alterations in protooncogene activity, and gene amplification can occur. Individually or in association, such changes lead to the acquisition of an unlimited cell growth potential but not tumorigenicity. Genetic instability and uncontrolled cell division resulting from HPV integration increase the cell's susceptibility to other exogenous carcinogenic factors that may complete the process of neoplastic development.