Human epidermal embryogenesis

Prenatal diagnosis of bullous ichthyosiform erythroderma: detection of tonofilament clumps in fetal epidermal and amniotic fluid cells

The prenatal diagnosis of bullous ichthyosiform erythroderma (BIE) has been achieved at 20 weeks' gestation by electron microscopic identification of a pathognomonic cytoskeletal abnormality within fetal epidermal cells obtained by fetoscopic skin biopsy. The same abnormality was also observed in skin derived amniotic fluid cells. The question whether amniocentesis might be used instead of fetoscopy for future prenatal detection of BIE is discussed.

Problems in prenatal diagnosis of the ichthyosis congenita group

The late onset of normal keratinization after week 24 menstrual age (MA) of fetal life is the cause of considerable problems with the prenatal diagnosis of congenital ichthyosis. This paper summarizes the experiences with prenatal diagnosis in nine pregnancies at risk of congenital ichthyosis and one at risk of chondrodysplasia punctata, rhizomelic type. An important prerequisite--and the main problem--is the manifestation of the mutant genes early enough in fetal life to allow a safe exclusion. Continuous precocious keratinization of the interfollicular epidermis, hyperkeratosis, and/or specific markers of congenital ichthyosis such as various types of lipid inclusions had been expected. With a normal ultrastructure and development of fetal epidermis no evidence of ichthyosis was present in eight cases; all eight children were born healthy. Regional variations of the onset of keratinization of the interfollicular epidermis, observed in one of these eight fetuses as well as in one fetus at risk (but normal for) recessive dystrophic epidermolysis bullosa, posed considerable problems and might lead to a false-positive diagnosis. Examination after birth allowed one to localize these regions to areas close to the mamillae. Regional variations in addition to the well-known cranio-caudal gradient thus are normal findings: both children have normal skin. One fetus at risk of non-bullous congenital ichthyosiform erythroderma (type II) was involved without prenatal manifestation of interfollicular keratinization, specific markers, or increased numbers of cornified cells in the pilosebaceous follicles at 20 weeks MA. A slightly more irregular pattern of the horn cell contents was not regarded as sufficient evidence alone to indicate congenital ichthyosis. A severely affected boy was born in week 34 MA. Similarly the fetus at risk of chondrodysplasia punctata showed no skin abnormalities, neither at fetoscopy (week 22 MA) nor after abortion (week 24 MA) although based on other clinical features it was clearly affected. Thus, this genodermatosis cannot be diagnosed prenatally by its keratinization disturbances. In future cases, precocious keratinization and hyperkeratosis cannot be expected to be expressed before week 24 MA, and minor signs, such as irregularities of horn cell contents, have to be taken as an indication of involvement. Multiple biopsies are required, and a safe exclusion may be impossible before week 22 MA.

Epidermal morphogenesis and induction of the 67 kD keratin polypeptide by culture of human keratinocytes at the liquid-air interface

Culture in the presence of delipidized serum (i.e., in the absence of vitamin A) has been shown to allow terminal differentiation of human keratinocytes, both in terms of morphological appearance and in terms of 67 kD keratin polypeptide synthesis (Fuchs, E & Green, H, Cell 25 (1981) 617) [2]. Culture at the liquid-air interface is known to induce morphological differentiation in a variety of culture systems designed for keratinocytes (Pruniéras, M et al., J invest dermatol 81 (1983) 28s) [3]. We report here that human keratinocytes grown on a dermal equivalent (or lattice) in the presence of total serum are able to express the 67 kD keratin polypeptide, provided that the culture is raised at the liquid-air interface. Loss of contact with air results in switching off this synthesis.

Congenital neoplasia--a stem cell pathology

The theory presented herewith provides a unified explanation for neoplasia and teratogenesis, both regarded here as stem cell disorders. Proliferating cells in the organism form two mutually exclusive classes, immortal stem cells and transitional cells whose life span is limited. Any lasting change in the organism e.g. tissue differentiation or neoplasia, is determined by stem cells. Congenital as well as adult neoplasms exhibit three key features: maturation arrest, stem cell pool expansion and increased cell turnover and they progress through the following states: dysplasia, neoplasia in situ, benign stage (e.g. polyp) and overt neoplasia. The neoplasm is regarded here as an organ with a purpose intended to supply the organism with a missing substance. Besides serving as tissue progenitors, stem cells are postulated here to secrete a substance 'A' necessary for a proper tissue function. Carcinogens interfere with the substance production mainly by depleting stem cells so that less 'A' is produced. The capacity of the adult to replenish the depleted stem cells is limited, and the missing substance has to be formed by an alternative way i.e. by Neoplasia. The 'A' substitute formed by the neoplasm denominated as 'B' is however less efficient than 'A'. Neoplastic growth thus depends upon the relative abundance of substances 'A' and 'B'. Since in the growing organism, stem cells multiply, some of the missing 'A' is replenished by them and the neoplasm may regress.

Prenatal diagnosis of anhidrotic ectodermal dysplasia

This paper reports on successful prenatal diagnosis of X-linked anhidrotic ectodermal dysplasia (AED) by means of light and electron microscopy on fetal skin biopsies obtained under fetoscopy. In the present family two brothers of the proband were severely affected with the full symptomatology of AED, the pregnant female and her mother revealed minor symptoms with patches of skin lacking vellus hair. Control of lesional skin of the affected family members by electron microscopy revealed no ultrastructural abnormalities. However, all biopsies lacked skin appendages including hair follicles, sebaceous glands, and sweat glands. The lack of pilosebaceous follicles can be used as a diagnostic criterion since these structures are fully developed in normal fetuses of 20 weeks whereas the development of sweat glands does not start before week 20 to 24 of fetal life. Skin biopsies were taken from various regions of the fetus at risk via fetoscopy in week 20 and processed for light and electron microscopy. All samples revealed complete absence of all skin appendages in contrast to a total of 61 non-AED fetuses. Thus positive prenatal diagnosis of AED was made and the pregnancy was terminated. Control investigations after abortion confirmed the diagnosis.

The biology of human fetal skin at ages related to prenatal diagnosis

It is the goal of the present article to review the state of knowledge of human skin development and to indicate some of the questions being approached in current studies of human fetal skin. Because of the breadth of the topic, the discussion will be limited to two ages during gestation that correspond to periods when samples of fetal skin or amniotic fluid cells (which in part are derived from the skin) are used to evaluate the condition of the fetus. These periods correspond to ages when amniocentesis (14-16 weeks) and fetoscopy accompanied by fetal skin biopsy (19-20 weeks) are performed.

Genetically induced abnormalities of epidermal differentiation and ultrastructure in ichthyoses and epidermolyses: pathogenesis, heterogeneity, fetal manifestation, and prenatal diagnosis

Comparative ultrastructural investigations on the pathomorphogenesis of inherited ichthyoses and epidermolyses have shown that such heterogeneous skin disorders may serve as model systems for genetic interactions with developmental processes, such as keratinization, or functional systems, such as dermal-epidermal junctional integrity. Most interesting from the morphologic point of view are dominantly inherited skin disorders in the ichthyosis and epidermolysis bullosa groups in which primary structural defects of structural proteins have been demonstrated that seem to be under the direct control of the mutant gene. Such structural abnormalities concern keratohyalin in autosomal-dominant ichthyosis vulgaris, the tonofilament system in hystrix-like ichthyoses, and the anchoring fibrils in dominant dystrophic epidermolyses. Taking bullous congenital ichthyosiform erythroderma (epidermolytic hyperkeratosis) as a central example, we discuss the stability of such structural defects, the heterogeneity in the ultrastructural abnormalities of clinically closely similar entities (ichthyosis hystrix Curth-Macklin, congenital reticulate ichthyosiform erythroderma), and, in the latter keratinization disorder, the presence of an unusual filament system of unknown biochemical composition in the abnormal keratinocytes. Expression of mutant genes during fetal life and fetal manifestation of such abnormalities are a precondition for the prenatal diagnosis of genetic skin disorders (bullous ichthyosiform erythroderma, epidermolysis bullosa dystrophica Hallopeau-Siemens, Herlitz syndrome). Finally, problems related to the differentiation of mutant keratinocytes and of amniotic fluid cells of fetuses at risk of genetic skin disorders under the in vitro conditions of primary cell cultures are briefly discussed.

Phenotypic expression of epidermal cells in vitro: a review

Disaggregated epidermal cells, sheets of epidermis, and explants of partial and full-thickness skin have been grown in cell, organ, and explant cultures. Each type of epidermal sample has also been "cultured" as a graft on a living animal host. The extent of tissue-specific phenotypic expression by the epidermal cell varies with the type of culture and the culture conditions: medium, biologic and pharmacologic additives, substrate, cell density, pH, and temperature. Specific culture conditions can be chosen to select for certain phenotypic traits. In spite of the diversity of conditions that may be used for culture, keratinocytes in cell, explant, and organ cultures undergo a similar pattern of differentiation. They stratify and keratinize, but rarely express a complete program of keratinization. Many of the characteristics associated with this pattern of differentiation are also observed in fetal epidermis during development. In culture, normal tissue architecture is usually absent; cells organize in flattened, loosely associated layers, synthesize a different pattern of keratin polypeptides, form keratohyalin granules only sporadically, and rarely contain lamellar granules. Epidermal differentiation in explant and organ cultures can be evaluated in regions of the explant, epibolic zone, and outgrowth apron. The epidermis of the original explant undergoes hyperproliferation, degeneration, sloughing, and then regeneration of a thin tissue. The cells in the epithelial outgrowth zone stratify and differentiate almost identically with those in cell culture. Neogenesis of structures in the basement-membrane zone can be followed in all three regions of the explant culture. Sheets of epidermis or epidermal cells transplanted onto or into a host animal show the most complete expression of the epidermal phenotype. After a period of hyperplastic growth, the cell layers become established in a pattern nearly identical to that in vivo. A complete granular layer is formed and stratum corneum cells, which are structurally and biochemically equivalent to those in tissue, differentiate. In some instances, the epidermis reconstructed from cells or tissue is indistinguishable from adjacent host epidermis. Experiments that include serial transfer from one culture system to another demonstrate the plasticity of the epidermal cell and its ability to respond variously to its environment.

Antenatal diagnosis of genodermatoses

The technics of fetoscopy and fetal skin biopsy have expanded our capabilities for antenatal diagnosis of certain hereditary skin disorders (genodermatoses). The fetus and placenta can be visualized directly and skin biopsy specimens can be obtained for light and electron microscopic studies, tissue culture, and biochemical analysis. These technics have been utilized successfully in the prenatal diagnosis or exclusion of epidermolysis bullosa, epidermolytic hyperkeratosis, and harlequin ichthyosis in fetuses known to be at risk for these disorders, and they offer tremendous potential for prenatal diagnosis in a variety of other genodermatoses. Studies of tissue obtained by this procedure will undoubtedly expand our knowledge of the morphogenesis and biochemistry of fetal skin and will provide needed baseline data for the further development of these technics.

Barrier properties of the newborn infant's skin

The barrier properties of the skin were examined in 223 studies in 70 newborn infants of 25 to 41 weeks' gestation, aged from 1 hour to 26 days. Percutaneous drug absorption was studied by observing the blanching response to solutions of 1% and 10% phenylephrine applied to a small area of abdominal skin. Skin water loss was measured at the same site using an evaporimeter. Infants of 37 weeks' gestation or more showed little or no drug absorption and had low skin water losses, indicating that their skin is an effective barrier. By contrast, infants of 32 weeks' gestation or less showed marked drug absorption and high skin water losses in the early neonatal period, indicating that their skin is defective as a barrier. Both drug absorption and water loss in these infants fell steadily; by about 2 weeks of age the skin of the most immature infants functioned like that of mature infants. The varying barrier properties can be explained by the poor development of the stratum corneum in the more premature infants at birth and its rapid maturation after birth. The trauma caused to the skin by use of adhesive tape and the fixation of transcutaneous oxygen electrodes resulted in increased drug absorption and water loss from the damaged area.

Prenatal diagnosis of oculocutaneous albinism by electron microscopy of fetal skin

Oculocutaneous albinism was diagnosed prenatally by electron microscopic examination of fetal skin samples taken during fetoscopy at 20 weeks of gestation. Melanosome development in hair bulb melanocytes progressed no further than stage II, indicating a lack of melanin synthesis. In 4 age-matched control fetuses, numerous stage IV melanosomes, signifying active melanin synthesis, were identified. The diagnosis was confirmed after the pregnancy was terminated at 22 weeks. Examination of the fetal eye showed absence of pigment in the retinal epithelium and uvea at a stage when ocular melanogenesis would normally be active. This study shows that oculocutaneous albinism can be detected in the second trimester using similar techniques to those employed in the prenatal diagnosis of epidermolysis bullosa and ichthyosis.

The sequence of events in the differentiation of the epidermis in fetal rats with particular reference to membrane-coating granules

The sequence of events in the establishment of a keratinised epidermis has been related to age and crown rump length in fetal rats. Differentiation of the epidermis occurs under cover of the periderm throughout gestation. Ten stages are defined between 12d intra-uterine life and birth. Membrane-coating granules (MCGs) appeared at 18d (Stage 4) after the appearance of tonofilaments but before the appearance of the first "fetal" keratohyaline granules (KHGs) at 19d (Stage 5). Measurement of the position of MCGs within the cells showed a less marked concentration near the superficial border of the cells than that found at later stages. As KHGs formed, exocytosis of MCGs occurred into the intercellular space immediately deep to the periderm. It is suggested that after 19d (Stage 5) the periderm serves to retain the contents of the MCGs in this space so providing the permeability barrier and that prior to that stage the periderm itself probably provides the permeability barrier of fetal skin.

Regional development of the human epidermis in the first trimester embryo and the second trimester fetus (ages related to the timing of amniocentesis and fetal biopsy)

The epidermis was sampled from multiple body sites of whole human embryos and fetuses of 45- and 65-days, 16- and 21-weeks estimated gestation age to determine whether a regionally dependent, variable rate of interfollicular epidermal development exists. Surface characteristics and thickness of the epidermis were evaluated by scanning electron and light microscopy, respectively. It was concluded that all epidermal development proceeded simultaneously during the first trimester with the exception of the foot which was more advanced in both thickness and state of differentiation. During the second trimester the epidermis of both the head and the foot showed more precocious development, particularly in relation to the special sense organs and to the plantar surface. The interfollicular epidermis of the majority of the body, however, was approximately equivalent in the state of development. These data have potential relevance to prenatal diagnosis of inherited skin disease from amniocentesis and/or fetal biopsy specimens; the present survey of the total epidermal surface will allow one to predict the types of skin-derived cells that should be present in the amniotic fluid at a given age, and to evaluate a fetal biopsy from one region and be confident that it is an accurate index of fetal skin development, age and status in general.