Epidermis: The external, nonvascular layer of the skin. It is made up, from within outward, of five layers of EPITHELIUM: (1) basal layer (stratum basale epidermidis); (2) spinous layer (stratum spinosum epidermidis); (3) granular layer (stratum granulosum epidermidis); (4) clear layer (stratum lucidum epidermidis); and (5) horny layer (stratum corneum epidermidis).Plant Epidermis: A thin layer of cells forming the outer integument of seed plants and ferns. (Random House Unabridged Dictionary, 2d ed)Keratinocytes: Epidermal cells which synthesize keratin and undergo characteristic changes as they move upward from the basal layers of the epidermis to the cornified (horny) layer of the skin. Successive stages of differentiation of the keratinocytes forming the epidermal layers are basal cell, spinous or prickle cell, and the granular cell.Skin: The outer covering of the body that protects it from the environment. It is composed of the DERMIS and the EPIDERMIS.Hair Follicle: A tube-like invagination of the EPIDERMIS from which the hair shaft develops and into which SEBACEOUS GLANDS open. The hair follicle is lined by a cellular inner and outer root sheath of epidermal origin and is invested with a fibrous sheath derived from the dermis. (Stedman, 26th ed) Follicles of very long hairs extend into the subcutaneous layer of tissue under the SKIN.Keratins: A class of fibrous proteins or scleroproteins that represents the principal constituent of EPIDERMIS; HAIR; NAILS; horny tissues, and the organic matrix of tooth ENAMEL. Two major conformational groups have been characterized, alpha-keratin, whose peptide backbone forms a coiled-coil alpha helical structure consisting of TYPE I KERATIN and a TYPE II KERATIN, and beta-keratin, whose backbone forms a zigzag or pleated sheet structure. alpha-Keratins have been classified into at least 20 subtypes. In addition multiple isoforms of subtypes have been found which may be due to GENE DUPLICATION.Mice, Hairless: Mutant strains of mice that produce little or no hair.Keratin-10: A type I keratin that is found associated with the KERATIN-1 in terminally differentiated epidermal cells such as those that form the stratum corneum. Mutations in the genes that encode keratin-10 have been associated with HYPERKERATOSIS, EPIDERMOLYTIC.Dermis: A layer of vascularized connective tissue underneath the EPIDERMIS. The surface of the dermis contains innervated papillae. Embedded in or beneath the dermis are SWEAT GLANDS; HAIR FOLLICLES; and SEBACEOUS GLANDS.Skin Physiological Phenomena: The functions of the skin in the human and animal body. It includes the pigmentation of the skin.Skin Neoplasms: Tumors or cancer of the SKIN.Langerhans Cells: Recirculating, dendritic, antigen-presenting cells containing characteristic racket-shaped granules (Birbeck granules). They are found principally in the stratum spinosum of the EPIDERMIS and are rich in Class II MAJOR HISTOCOMPATIBILITY COMPLEX molecules. Langerhans cells were the first dendritic cell to be described and have been a model of study for other dendritic cells (DCs), especially other migrating DCs such as dermal DCs and INTERSTITIAL DENDRITIC CELLS.Keratin-14: A type I keratin that is found associated with the KERATIN-5 in the internal stratified EPITHELIUM. Mutations in the gene for keratin-14 are associated with EPIDERMOLYSIS BULLOSA SIMPLEX.Sebaceous Glands: Small, sacculated organs found within the DERMIS. Each gland has a single duct that emerges from a cluster of oval alveoli. Each alveolus consists of a transparent BASEMENT MEMBRANE enclosing epithelial cells. The ducts from most sebaceous glands open into a HAIR FOLLICLE, but some open on the general surface of the SKIN. Sebaceous glands secrete SEBUM.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.Hair: A filament-like structure consisting of a shaft which projects to the surface of the SKIN from a root which is softer than the shaft and lodges in the cavity of a HAIR FOLLICLE. It is found on most surfaces of the body.Papilloma: A circumscribed benign epithelial tumor projecting from the surrounding surface; more precisely, a benign epithelial neoplasm consisting of villous or arborescent outgrowths of fibrovascular stroma covered by neoplastic cells. (Stedman, 25th ed)Dermatitis: Any inflammation of the skin.Wound Healing: Restoration of integrity to traumatized tissue.Skin DiseasesDesmosomes: A type of junction that attaches one cell to its neighbor. One of a number of differentiated regions which occur, for example, where the cytoplasmic membranes of adjacent epithelial cells are closely apposed. It consists of a circular region of each membrane together with associated intracellular microfilaments and an intercellular material which may include, for example, mucopolysaccharides. (From Glick, Glossary of Biochemistry and Molecular Biology, 1990; Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Keratosis: Any horny growth such as a wart or callus.Skin Aging: The process of aging due to changes in the structure and elasticity of the skin over time. It may be a part of physiological aging or it may be due to the effects of ultraviolet radiation, usually through exposure to sunlight.Skin Abnormalities: Congenital structural abnormalities of the skin.Intermediate Filament Proteins: Filaments 7-11 nm in diameter found in the cytoplasm of all cells. Many specific proteins belong to this group, e.g., desmin, vimentin, prekeratin, decamin, skeletin, neurofilin, neurofilament protein, and glial fibrillary acid protein.Mice, Transgenic: Laboratory mice that have been produced from a genetically manipulated EGG or EMBRYO, MAMMALIAN.Blister: Visible accumulations of fluid within or beneath the epidermis.Melanocytes: Mammalian pigment cells that produce MELANINS, pigments found mainly in the EPIDERMIS, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called MELANOSOMES. The large non-mammalian melanin-containing cells are called MELANOPHORES.Gene Expression Regulation, Developmental: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action during the developmental stages of an organism.Morphogenesis: The development of anatomical structures to create the form of a single- or multi-cell organism. Morphogenesis provides form changes of a part, parts, or the whole organism.Skin Absorption: Uptake of substances through the SKIN.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Skin Transplantation: The grafting of skin in humans or animals from one site to another to replace a lost portion of the body surface skin.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Skin, Artificial: Synthetic material used for the treatment of burns and other conditions involving large-scale loss of skin. It often consists of an outer (epidermal) layer of silicone and an inner (dermal) layer of collagen and chondroitin 6-sulfate. The dermal layer elicits new growth and vascular invasion and the outer layer is later removed and replaced by a graft.9,10-Dimethyl-1,2-benzanthracene: 7,12-Dimethylbenzanthracene. Polycyclic aromatic hydrocarbon found in tobacco smoke that is a potent carcinogen.Skin Pigmentation: Coloration of the skin.In Situ Hybridization: A technique that localizes specific nucleic acid sequences within intact chromosomes, eukaryotic cells, or bacterial cells through the use of specific nucleic acid-labeled probes.Cell Division: The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Feathers: Flat keratinous structures found on the skin surface of birds. Feathers are made partly of a hollow shaft fringed with barbs. They constitute the plumage.Administration, Topical: The application of drug preparations to the surfaces of the body, especially the skin (ADMINISTRATION, CUTANEOUS) or mucous membranes. This method of treatment is used to avoid systemic side effects when high doses are required at a localized area or as an alternative systemic administration route, to avoid hepatic processing for example.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Ectoderm: The outer of the three germ layers of an embryo.Mice, Inbred SENCAR: Mice selectively bred for hypersusceptibility to two-stage chemical skin carcinogenesis. They are also hypersusceptible to UV radiation tumorigenesis with single high-dose, but not chronic low-dose, exposures. SENCAR (SENsitive to CARcinogenesis) mice are used in research as an animal model for tumor production.Sweat Glands: Sweat-producing structures that are embedded in the DERMIS. Each gland consists of a single tube, a coiled body, and a superficial duct.Hyperplasia: An increase in the number of cells in a tissue or organ without tumor formation. It differs from HYPERTROPHY, which is an increase in bulk without an increase in the number of cells.Larva: Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals.Ichthyosis, Lamellar: A chronic, congenital ichthyosis inherited as an autosomal recessive trait. Infants are usually born encased in a collodion membrane which sheds within a few weeks. Scaling is generalized and marked with grayish-brown quadrilateral scales, adherent at their centers and free at the edges. In some cases, scales are so thick that they resemble armored plate.Metamorphosis, Biological: Profound physical changes during maturation of living organisms from the immature forms to the adult forms, such as from TADPOLES to frogs; caterpillars to BUTTERFLIES.Embryo, Nonmammalian: The developmental entity of a fertilized egg (ZYGOTE) in animal species other than MAMMALS. For chickens, use CHICK EMBRYO.Keratin-5: A type II keratin that is found associated with the KERATIN-14 in the internal stratified EPITHELIUM. Mutations in the gene for keratin-5 are associated with EPIDERMOLYSIS BULLOSA SIMPLEX.Ichthyosis: Any of several generalized skin disorders characterized by dryness, roughness, and scaliness, due to hypertrophy of the stratum corneum epidermis. Most are genetic, but some are acquired, developing in association with other systemic disease or genetic syndrome.Hyperkeratosis, Epidermolytic: A form of congenital ichthyosis inherited as an autosomal dominant trait and characterized by ERYTHRODERMA and severe hyperkeratosis. It is manifested at birth by blisters followed by the appearance of thickened, horny, verruciform scales over the entire body, but accentuated in flexural areas. Mutations in the genes that encode KERATIN-1 and KERATIN-10 have been associated with this disorder.Plant Roots: The usually underground portions of a plant that serve as support, store food, and through which water and mineral nutrients enter the plant. (From American Heritage Dictionary, 1982; Concise Dictionary of Biology, 1990)beta-Keratins: Keratins that form into a beta-pleated sheet structure. They are principle constituents of the corneous material of the carapace and plastron of turtles, the epidermis of snakes and the feathers of birds.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Skin Diseases, Genetic: Diseases of the skin with a genetic component, usually the result of various inborn errors of metabolism.Caspase 14: A short pro-domain caspase that is almost exclusively expressed in the EPIDERMIS and may play a role in the differentiation of epidermal KERATINOCYTES.Hoof and Claw: Highly keratinized processes that are sharp and curved, or flat with pointed margins. They are found especially at the end of the limbs in certain animals.Dermatitis, Contact: A type of acute or chronic skin reaction in which sensitivity is manifested by reactivity to materials or substances coming in contact with the skin. It may involve allergic or non-allergic mechanisms.Transglutaminases: Transglutaminases catalyze cross-linking of proteins at a GLUTAMINE in one chain with LYSINE in another chain. They include keratinocyte transglutaminase (TGM1 or TGK), tissue transglutaminase (TGM2 or TGC), plasma transglutaminase involved with coagulation (FACTOR XIII and FACTOR XIIIa), hair follicle transglutaminase, and prostate transglutaminase. Although structures differ, they share an active site (YGQCW) and strict CALCIUM dependence.Epithelium: One or more layers of EPITHELIAL CELLS, supported by the basal lamina, which covers the inner or outer surfaces of the body.Tetradecanoylphorbol Acetate: A phorbol ester found in CROTON OIL with very effective tumor promoting activity. It stimulates the synthesis of both DNA and RNA.Desmoplakins: Desmoplakins are cytoskeletal linker proteins that anchor INTERMEDIATE FILAMENTS to the PLASMA MEMBRANE at DESMOSOMES.Glucosylceramides: Cerebrosides which contain as their polar head group a glucose moiety bound in glycosidic linkage to the hydroxyl group of ceramides. Their accumulation in tissue, due to a defect in beta-glucosidase, is the cause of Gaucher's disease.Aquaporin 3: Aquaporin 3 is an aquaglyceroporin that is expressed in the KIDNEY COLLECTING DUCTS and is constitutively localized at the basolateral MEMBRANE.Integumentary System: The outer covering of the body composed of the SKIN and the skin appendages, which are the HAIR, the NAILS; and the SEBACEOUS GLANDS and the SWEAT GLANDS and their ducts.Carcinoma, Basal Cell: A malignant skin neoplasm that seldom metastasizes but has potentialities for local invasion and destruction. Clinically it is divided into types: nodular, cicatricial, morphaic, and erythematoid (pagetoid). They develop on hair-bearing skin, most commonly on sun-exposed areas. Approximately 85% are found on the head and neck area and the remaining 15% on the trunk and limbs. (From DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1471)Plant Leaves: Expanded structures, usually green, of vascular plants, characteristically consisting of a bladelike expansion attached to a stem, and functioning as the principal organ of photosynthesis and transpiration. (American Heritage Dictionary, 2d ed)Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Keratin-15: A type I keratin found in the basal layer of the adult epidermis and in other stratified epithelia.Stem Cells: Relatively undifferentiated cells that retain the ability to divide and proliferate throughout postnatal life to provide progenitor cells that can differentiate into specialized cells.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Desmoglein 1: A desmosomal cadherin that is an autoantigen in the acquired skin disorder PEMPHIGUS FOLIACEUS.Keratin-16: A type I keratin expressed in a variety of EPITHELIUM, including the ESOPHAGUS, the TONGUE, the HAIR FOLLICLE and NAILS. Keratin-16 is normally found associated with KERATIN-6. Mutations in the gene for keratin-6 have been associated with PACHYONYCHIA CONGENITA, TYPE 1.Signal Transduction: The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.Keratolytic Agents: Agents that soften, separate, and cause desquamation of the cornified epithelium or horny layer of skin. They are used to expose mycelia of infecting fungi or to treat corns, warts, and certain other skin diseases.Gene Expression: The phenotypic manifestation of a gene or genes by the processes of GENETIC TRANSCRIPTION and GENETIC TRANSLATION.Alopecia: Absence of hair from areas where it is normally present.Permeability: Property of membranes and other structures to permit passage of light, heat, gases, liquids, metabolites, and mineral ions.Desmogleins: A group of desmosomal cadherins with cytoplasmic tails that resemble those of classical CADHERINS.Regeneration: The physiological renewal, repair, or replacement of tissue.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Transcription Factors: Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Cell Proliferation: All of the processes involved in increasing CELL NUMBER including CELL DIVISION.Drosophila Proteins: Proteins that originate from insect species belonging to the genus DROSOPHILA. The proteins from the most intensely studied species of Drosophila, DROSOPHILA MELANOGASTER, are the subject of much interest in the area of MORPHOGENESIS and development.Drosophila: A genus of small, two-winged flies containing approximately 900 described species. These organisms are the most extensively studied of all genera from the standpoint of genetics and cytology.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Pemphigus: Group of chronic blistering diseases characterized histologically by ACANTHOLYSIS and blister formation within the EPIDERMIS.Administration, Cutaneous: The application of suitable drug dosage forms to the skin for either local or systemic effects.Ambystoma mexicanum: A salamander found in Mexican mountain lakes and accounting for about 30 percent of the urodeles used in research. The axolotl remains in larval form throughout its life, a phenomenon known as neoteny.Molting: Periodic casting off FEATHERS; HAIR; or cuticle. Molting is a process of sloughing or desquamation, especially the shedding of an outer covering and the development of a new one. This phenomenon permits growth in ARTHROPODS, skin renewal in AMPHIBIANS and REPTILES, and the shedding of winter coats in BIRDS and MAMMALS.Dermatitis, Atopic: A chronic inflammatory genetically determined disease of the skin marked by increased ability to form reagin (IgE), with increased susceptibility to allergic rhinitis and asthma, and hereditary disposition to a lowered threshold for pruritus. It is manifested by lichenification, excoriation, and crusting, mainly on the flexural surfaces of the elbow and knee. In infants it is known as infantile eczema.Embryonic Induction: The complex processes of initiating CELL DIFFERENTIATION in the embryo. The precise regulation by cell interactions leads to diversity of cell types and specific pattern of organization (EMBRYOGENESIS).Keratin-17: A type I keratin found associated with KERATIN-6 in rapidly proliferating squamous epithelial tissue. Mutations in the gene for keratin-17 have been associated with PACHYONYCHIA CONGENITA, TYPE 2.Cell Movement: The movement of cells from one location to another. Distinguish from CYTOKINESIS which is the process of dividing the CYTOPLASM of a cell.Body Patterning: The processes occurring in early development that direct morphogenesis. They specify the body plan ensuring that cells will proceed to differentiate, grow, and diversify in size and shape at the correct relative positions. Included are axial patterning, segmentation, compartment specification, limb position, organ boundary patterning, blood vessel patterning, etc.Arabidopsis: A plant genus of the family BRASSICACEAE that contains ARABIDOPSIS PROTEINS and MADS DOMAIN PROTEINS. The species A. thaliana is used for experiments in classical plant genetics as well as molecular genetic studies in plant physiology, biochemistry, and development.Pupa: An inactive stage between the larval and adult stages in the life cycle of insects.Vitiligo: A disorder consisting of areas of macular depigmentation, commonly on extensor aspects of extremities, on the face or neck, and in skin folds. Age of onset is often in young adulthood and the condition tends to progress gradually with lesions enlarging and extending until a quiescent state is reached.Netherton Syndrome: Rare autosomal recessive disease with variable expressions. Clinical features of the disease include variable ICHTHYOSIFORM ERYTHRODERMA, CONGENITAL; bamboo hair (trichorrhexis invaginata); and ATOPIC DERMATITIS. The disease is caused by mutations in the SPINK5 gene.Ichthyosis Vulgaris: Most common form of ICHTHYOSIS characterized by prominent scaling especially on the exterior surfaces of the extremities. It is inherited as an autosomal dominant trait.Ecdysterone: A steroid hormone that regulates the processes of MOLTING or ecdysis in insects. Ecdysterone is the 20-hydroxylated ECDYSONE.Skin Physiological Processes: Biological activities and functions of the SKIN.Keratin-9: A type II keratin found predominantly expressed in the terminally differentiated EPIDERMIS of palms and soles. Mutations in the gene for keratin 9 are associated with KERATODERMA, PALMOPLANTAR, EPIDERMOLYTIC.Mice, Inbred C57BLHair Diseases: Diseases affecting the orderly growth and persistence of hair.Animals, Newborn: Refers to animals in the period of time just after birth.Mice, Knockout: Strains of mice in which certain GENES of their GENOMES have been disrupted, or "knocked-out". To produce knockouts, using RECOMBINANT DNA technology, the normal DNA sequence of the gene being studied is altered to prevent synthesis of a normal gene product. Cloned cells in which this DNA alteration is successful are then injected into mouse EMBRYOS to produce chimeric mice. The chimeric mice are then bred to yield a strain in which all the cells of the mouse contain the disrupted gene. Knockout mice are used as EXPERIMENTAL ANIMAL MODELS for diseases (DISEASE MODELS, ANIMAL) and to clarify the functions of the genes.Onions: Herbaceous biennial plants and their edible bulbs, belonging to the Liliaceae.Carcinogens: Substances that increase the risk of NEOPLASMS in humans or animals. Both genotoxic chemicals, which affect DNA directly, and nongenotoxic chemicals, which induce neoplasms by other mechanism, are included.Gene Expression Regulation: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.Protein PrecursorsMembrane Proteins: Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.Urochordata: A subphylum of chordates intermediate between the invertebrates and the true vertebrates. It includes the Ascidians.Desmoglein 3: A desmosomal cadherin that is an autoantigen in the acquired skin disorder PEMPHIGUS VULGARIS.Gene Expression Regulation, Plant: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action in plants.Arabidopsis Proteins: Proteins that originate from plants species belonging to the genus ARABIDOPSIS. The most intensely studied species of Arabidopsis, Arabidopsis thaliana, is commonly used in laboratory experiments.