Human epidermal embryogenesis

Human skin through the ages

As the largest organ of the human body the skin offers a protective role, providing a tough but pliable covering that provides the major barrier between the internal organs and the environment. It actively regulates water loss and is both oxygen and carbon dioxide permeable, and influences temperature regulation and immunological functions through its sensory properties. Both intrinsic and enhanced environmental factors contribute to the progressive deterioration of the skin with increasing age. Cutaneous problems are therefore an unavoidable and inevitable consequence of aging skin, which can prove to be both cosmetically unacceptable to those who succumb to these problems, as well as even life threatening if skin breakdown becomes chronic as is case with leg ulceration. This in turn has major implications for long-term impact on those looking after them (e.g., family, carers, etc.) and a huge burden on the health care system.

What Do We Know about Pruritus in Very Young Infants? A Literature Review

In infants, pruritus is frequently considered as absent because they do not scratch themselves. Because pruritus could induce severe adverse effects in this vulnerable population, we aimed to review existing evidence on the ability of young infants to experience itch and on how to assess itch-related discomfort in this population. A literature review was performed (Pubmed, Google Scholar). Neurological itch pathways are well described. Skin development starts early during gestation. At 34 weeks of gestation, skin is almost complete while skin adaptations occur after birth. Newborn skin is neurologically functional, including the ability for young infants to feel pain. Similarities and interactions between pain and pruritus support the hypothesis that infants could feel pruritus. However, the existence of pruritus in infants has never been evidenced. Many itchy conditions can affect them, suggesting non-negligible prevalence of infant pruritus among which atopic dermatitis (AD) is the most studied disease. Studies reported a negative impact of AD on children and their families. There is no existing validated method to assess pruritus in infants, although they may feel pruritus and chronic pruritus can lead to serious adverse effects. To appropriately diagnose pruritus appears of great interest among young infants. Development of a method is required to this aim.

Understanding the formidable nail barrier: A review of the nail microstructure, composition and diseases

The topical treatment of nail fungal infections has been a focal point of nail research in the past few decades as it offers a much safer and focused alternative to conventional oral therapy. Although the current focus remains on exploring the ways of enhancing permeation through the formidable nail barrier, the understanding of the nail microstructure and composition is far from complete. This article reviews our current understanding of the nail microstructure, composition and diseases. A few of the parameters affecting the nail permeability and potential causes of the recurrence of fungal nail infection are also discussed.

Development, structure, and keratin expression in C57BL/6J mouse eccrine glands

Eccrine sweat glands in the mouse are found only on the footpads and, when mature, resemble human eccrine glands. Eccrine gland anlagen were first apparent at 16.5 days postconception (DPC) in mouse embryos as small accumulations of cells in the mesenchymal tissue beneath the developing epidermis resembling hair follicle placodes. These cells extended into the dermis where significant cell organization, duct development, and evidence of the acrosyringium were observed in 6- to 7-postpartum day (PPD) mice. Mouse-specific keratin 1 (K1) and 10 (K10) expression was confined to the strata spinosum and granulosum. In 16.5 and 18.5 DPC embryos, K14 and K17 were both expressed in the stratum basale and diffusely in the gland anlagen. K5 expression closely mimicked K17 throughout gland development. K6 expression was not observed in the developing glands of the embryo but was apparent in the luminal cell layer of the duct by 6 to 7 PPD. By 21 PPD, the gland apertures appeared as depressions in the surface surrounded by cornified squames, and the footpad surface lacked the organized ridge and crease system seen in human fingers. These data serve as a valuable reference for investigators who use genetically engineered mice for skin research.

Hsp27 Expression Coincides with Epidermal Stratification during Human Epidermal Morphogenesis

Heat shock protein 27 (Hsp27), apart from its protective function in response to stress, is implicated in the regulation of cell growth, differentiation and apoptosis. Data on the expression of Hsp27 in the developing human epidermis are sparse and partially conflicting. Thus, the purpose of the present study was to investigate Hsp27 expression during the morphogenesis of human epidermis. Skin biopsies and dispase-separated epidermal sheets obtained from 7 human embryos (7 and 8 weeks estimated gestational age, EGA), from 79 human fetuses (9-23 weeks EGA) and from 10 healthy adult volunteers were investigated by immunohistochemistry and Western blotting, respectively. The earliest detection of Hsp27 expression was found by immunohistochemistry at the 12th week EGA (basal and intermediate layer) and by Western blotting at the 9th week EGA. From the 16th to the 23rd week EGA immunoreactivity was not detectable in the basal layer, whereas in the overlying layers it revealed a differentiation-related pattern. The simultaneous onset of epidermal stratification and Hsp27 expression (9th week EGA) and the alterations of the latter in the subsequent stages of development, suggest that this stress protein may be involved in the molecular events underlying human epidermal morphogenesis.

Qualitative and quantitative alterations of cell surface carbohydrate residues during epidermal morphogenesis

The purpose of this study was to investigate the carbohydrate residue composition of cell surface in the developing epidermis and to define the chronological sequence of its alterations in human fetuses from the 10th to the 20th weeks of gestation and at the 23rd week of gestation, using a panel of six biotinylated lectins: Concanavalin A, Ulex europaeus agglutinin-I, Ricinus communis agglutinin-I, Peanut agglutinin, Wheat germ agglutinin, and Dolichos biflorus agglutinin. Distinct qualitative and quantitative alterations in the expression of cell surface carbohydrate residues were found during epidermal morphogenesis prior to keratinization (10th to 20th weeks). At the 23rd week of gestation, the already keratinized fetal human epidermis revealed a pattern of cell surface glycosylation very similar to that of the adult human epidermis. Further studies are now warranted to answer the question regarding whether the glycosylation pattern in the developing human epidermis is disturbed in fetuses with genodermatoses and whether these disturbances might be important for prenatally diagnosing the latter.

Gap junction development in the human fetal hair follicle and bulge region

BACKGROUND

Gap junctions, composed of connexin (Cx) subunits, are channels that allow intercellular communication between adjacent cells and are thought to play a key role in the regulation of cell proliferation and differentiation. The Cx expression pattern and formation of gap junctions in human fetal hair follicles has yet to be clarified, including the prominent follicular bulge region that is believed to be a site rich in stem cells.

OBJECTIVES

To study the expression of two major Cxs, Cx26 and Cx43, in developing hair follicles in skin samples from a series of human fetuses of estimated gestational age (EGA) 88-163 days, and to determine quantitatively the presence of gap junctions.

METHODS

We used immunofluorescence labelling to investigate the sequential expression pattern of Cx26 and Cx43 in developing human hair follicles. Gap junction formation was observed by electron microscopy and the numbers of gap junctions were analysed quantitatively. Results Both Cx26 and Cx43 expression were observed at 88 days' EGA in the inner part of the hair peg. At 135 days' EGA, Cx26 was expressed in the outer root sheath (ORS) and the inner root sheath (IRS), while Cx43 was expressed chiefly in the IRS, hair matrix and sebaceous glands. At 163 days' EGA, Cx26 expression was most intense in the outermost layer of the ORS, in contrast to Cx43 expression which was in the inner part of the ORS. In the bulge region, only Cx43 was expressed in a subset of cells in the bulge. Ultrastructurally, gap junctions were observed at 102 days' EGA in the hair peg, and the number of gap junctions increased as the hair follicle matured. Gap junctions were also observed between the bulge cells in considerable numbers.

CONCLUSIONS

The changing expression patterns of Cx26 and Cx43 and the increasing gap junction numbers suggest a close association of Cx expression and gap junction formation with hair follicle morphogenesis. In addition, the present ultrastructural observations demonstrate that considerable numbers of the bulge cells, a putative site rich in hair follicle stem cells, form gap junctions during human hair follicle development.

Changing pattern of deiminated proteins in developing human epidermis

Peptidylarginine deiminases are widely distributed, calcium-ion-dependent enzymes that convert arginine residues of proteins into citrulline residues. This reaction, deimination, is thought to be an important event during the final stage of epidermal differentiation, possibly associated with integration and disintegration of keratin filaments. To elucidate the possible roles of protein deimination during human epidermal development we investigated localization of deiminated proteins using anti-citrulline peptide antibody, which preferentially recognizes citrulline residues in the V subdomains of keratin 1, and anti-chemically modified citrulline antibody, which enables detection of citrulline residues independent of amino acid sequences. Anti-chemically modified citrulline antibody, but not anti-citrulline peptide antibody stained the periderm in two-layered epidermis of 49 d and 57 d estimated gestational age. In the stratified epidermis of 88 d, 96 d, and 108 d estimated gestational age fetal skin, anti-citrulline peptide antibody and anti-chemically modified citrulline antibody staining was seen in the periderm and intermediate cell layers. After periderm cells regressed and keratinization began in the interfollicular epidermis, anti-citrulline peptide antibody and anti-chemically modified citrulline antibody were restricted to the cornified cell layers of the interfollicular epidermis, similar to the distribution patterns of that in adult epidermis. Postembedding immunoelectron microscopy showed anti-citrulline peptide antibody immunogold labeling over the cytoplasmic intermediate filament network in the periderm and the intermediate cell layers. These results demonstrate an orderly formation of deiminated proteins in different layers of embryonic epidermis and suggest important roles for peptidylarginine deiminases in human epidermal morphogenesis.

Changes in gap junction distribution and connexin expression pattern during human fetal skin development

Gap junctions are intercellular channels composed of connexin subunits that mediate cell-cell communication. The functions of gap junctions are believed to be associated with cell proliferation and differentiation and to be important in maintaining tissue homeostasis. We therefore investigated the expression of connexins (Cx)26 and 43, the two major connexins in human epidermis, and examined the formation of gap junctions during human fetal epidermal development. By immunofluorescence, Cx26 expression was observed between 49 and 96 days' estimated gestational age (EGA) but was not present from 108 days' EGA onwards. Conversely, Cx43 expression was observed from 88 days' EGA onwards. Using electron microscopy, the typical structure of gap junctions was observed from 120 days' EGA. The number of gap junctions increased over time and they were more common in the upper layers, within the periderm and intermediate keratinocyte layers rather than the basal layer. Immunoelectron microscopy revealed Cx43 labeling on the gap junction structures after 105 days' EGA. Formation of gap junctions increased as skin developed, suggesting that gap junctions may play an important role in fetal skin development. Furthermore, the changing patterns of connexin expression suggest that Cx26 is important for early fetal epidermal development.

Formation of cornified cell envelope in human hair follicle development

BACKGROUND

Cornified cell envelope (CCE) formation is an important step in the final stage of keratinization, in which CCE precursor proteins including involucrin and loricrin are cross-linked by keratinocyte transglutaminases (TGases) to the inner surface of the plasma membrane of cornified cells, while the outer surface is coated with material derived from secreted lamellar granules.

OBJECTIVES

Skin samples from human fetuses of a series of estimated gestational age (EGA) (49-163 days) were studied for the prescence of precursor proteins. Methods TGase activity was studied by in situ TGase activity assay, and ultrastructural features of CCE formation were observed at each stage of hair follicle development. We used immunofluorescent labelling to investigate the time and site of expression of CCE precursor proteins involucrin and loricrin, TGases 1, 2 and 3, and a 25-kDa lamellar granule-associated protein (LGP) in developing human hair follicles.

RESULTS

In the hair germ (65-84 days EGA) (corresponding to the stages 1-2 of murine hair follicle morphogenesis), only TGase 2 was observed in the entire hair germ, where in situ TGase activity was weakly positive, although thickening of cell membrane was not seen ultrastructurally. In the hair peg (85-104 days EGA) (corresponding to the stage 3 of murine hair follicle morphogenesis), loricrin and TGase 2 were seen in cells of the upper part of the hair peg while TGase 1, 3 and LGP were observed in the inner cells of the hair peg. In situ TGase activity was weakly positive in the upper part and inner cells of the hair peg. In the bulbous hair peg (105-135 days EGA) (corresponding to the stages 4-6 of murine hair follicle morphogenesis) and differentiated lanugo hair follicle (> 135 days EGA) (corresponding to the stages 7-8 of murine hair follicle morphogenesis), immunoreactivities of involucrin, loricrin, TGase 1, 2, 3, in situ TGase activity and LGP were detected in the inner root sheath cells, hair canals and inner cells of the outer root sheath in the region of the isthmus. Ultrastructurally, thickening of cell membrane was already seen in the inner root sheath cells of the bulbous hair peg and electron-dense, thick CCE was observed in the hair cuticle and hair canal of differentiated lanugo hair follicle.

CONCLUSIONS

These data indicate that, in terms of CCE formation, certain portions of the developing human hair follicle have already been determined in differentiation of the hair canal and cuticle at the hair peg stage.

Kdap, a novel gene associated with the stratification of the epithelium

The skin develops and differentiates during embryogenesis, which is concertedly regulated by a variety of genes. The present study isolated from the rat embryonic skin a novel differentiation-associated gene named Kdap (keratinocyte differentiation-associated protein) by suppression subtractive hybridization between the skin of 14day postcoitus (dpc) embryo (the prehair-germ stage) and that of 17dpc embryo (the hair-germ stage). Its mRNA contained four spliced forms in these tissues. The gene encoded a protein of total 98 amino acids with a calculated molecular mass of 11kDa and an isoelectric point of 6.1 as an unspliced form. The two splicing zones were well conserved among rat, mouse, and human. This protein had a high hydrophobic N-terminal region, a possible signal sequence, and contained two putative N-myristoylation sites and two casein kinase II phosphorylation sites. In situ hybridization experiments detected Kdap transcripts exclusively in the suprabasal cell layers of the embryonic epidermis. Intense expression was also seen in suprabasal cells in regions of infundibulum of the hair follicle. These results indicated that Kdap provides a new insight into the mechanism of differentiation and the maintenance of stratified epithelia.

Influence of antenatal steroids and sex on maturation of the epidermal barrier in the preterm infant

BACKGROUND

The epidermal barrier is well developed in term infants but defective in the immature infant with important clinical consequences. The development of the barrier shares similarities with production of pulmonary surfactant. Studies in the rat have shown that barrier maturation is accelerated by antenatal steroids, both structurally and functionally. Females have a more mature barrier than males at the same gestational age. These factors have not been studied in the human.

AIM

To examine the influence of antenatal steroids and sex on maturation of the epidermal barrier in the preterm infant.

SUBJECTS

A total of 137 infants born before 34 weeks gestation, 80 boys and 57 girls, were studied: 87 had been exposed to antenatal steroids, and 50 had not; 99 were studied prospectively, and 38 had been studied previously.

METHOD

Barrier function was measured as transepidermal water loss from abdominal skin by evaporimetry. Measurements were made within the first 48 hours and corrected to a standard relative humidity of 50% (TEWL(50)).

RESULTS

The relation between TEWL(50) and gestation was exponential with very high levels in the most immature infants. No influence of antenatal steroids or sex could be shown. When infants who were optimally exposed to antenatal steroids were considered alone, no effect could be shown.

CONCLUSION

Epidermal maturation in the preterm infant does not appear to be influenced by antenatal steroids or sex, suggesting that the mechanism of maturation differs from that of the rat.

Expression of transglutaminase activity in developing human epidermis

Epidermal transglutaminase (TGase) is known to catalyse cross-linking of several precursor proteins in the formation of cornified cell envelope at the terminal differentiation of keratinocytes. Expression of TGase activity was studied using an in situ TGase activity assay in human fetal skin samples of 49-163 days estimated gestational age (EGA). In the early two-layered epidermis (49-56 days EGA), in situ TGase activity was not observed in the periderm cells or the basal cells. In the late two-layered epidermis (57-65 days EGA), in situ TGase activity became weakly positive in the periderm cells, but not in the basal cells. In the three-layered (66-95 days EGA) and in four- or more layered (96-135 days EGA) stratified epidermis, in situ TGase activity was still restricted only to the periderm cells. After keratinization occurred in the interfollicular epidermis (163 days EGA), in situ TGase activity was expressed in the granular and cornified layers. This unique localization of TGase activity further support the hypothesis that periderm cells form cornified cell envelope during their regression process in human fetal skin development.

Changing patterns of localization of putative stem cells in developing human hair follicles

In rodents, the hair follicle stem cells lie in a well-defined bulge in the outer root sheath; however, the bulge as a stem cell site of human hair follicle epithelium is still controversial. Epidermal stem cells are thought to express high levels of beta1 integrin and low levels of E-cadherin and beta- and gamma-catenin. In order to clarify the ontogenic distribution of possible stem cells during hair follicle development, the expression patterns of beta1 integrin subunits, E-cadherin, and beta- and gamma-catenins in the skin samples from human fetuses of a series of estimated gestational ages (EGA) were examined. beta1 integrin-rich, E-cadherin-, and beta- and gamma-catenin-poor cells, possible stem cells, were localized to the entire hair germ (65-84 d EGA) and later to the outermost cells of hair peg (85-104 d EGA). In the bulbous hair peg (105-135 d EGA) and in the differentiated lanugo hair follicle (>135 d EGA), they were settled in the bulge and the outermost layer of the outer root sheath. This sequential localization was similar to that of cells rich in epidermal growth factor receptor expression and positive with keratin 19, a putative marker of epidermal stem cells. In addition, these beta1 integrin-rich, E-cadherin-, and beta- and gamma-catenin-poor cells showed similar, undifferentiated morphologic features by electron microscopy. This information of ontogenic localization of possible hair follicle stem cells contributes to the further understanding of mechanisms of human hair follicle morphogenesis and supports the idea that the human fetal hair follicle bulge is a site of stem cells for follicular epithelium.

Epimorphin expression during human foetal hair follicle development

Epimorphin is a mesenchymal protein expressed in several organs and known to have an essential role in epithelial tissue organization, including hair follicle morphogenesis, in mice. Although about 90% homology has been reported between human and mouse epimorphin exon sequences, there is no information about expression and function of epimorphin in hair follicle development in humans. In order to elucidate the expression pattern of epimorphin in human hair follicle morphogenesis and to compare it with the distribution of tenascin and neural cell adhesion molecule (NCAM), skin samples from human foetuses of a series of estimated gestational ages (EGAs) (46-168 days EGA) were studied using monoclonal anti-epimorphin antibody MC-1, anti-tenascin antibody and anti-human NCAM antibody. Epimorphin was detected in the mesenchymal cell condensation at the pregerm stage (< 75 days EGA), and there was strong expression of epimorphin in the perifollicular mesenchymal cells around the hair germ (75-84 days EGA). At the hair peg stage (85-104 days EGA), epimorphin was around the hair peg with the strongest staining in the neck portion. This sequence of staining patterns was similar to that of tenascin. In the bulbous hair peg (105-134 days EGA), the perifollicular dermal mesenchymal cells were evenly positive for epimorphin. Mesenchymal cells underneath the follicle bulb prior to formation of the dermal papilla were also positive for epimorphin. In the lanugo hair follicle (> 134 days EGA), dermal papilla cells expressed epimorphin as well as tenascin and NCAM. These results indicate that epimorphin expression is closely linked to developing hair follicles in human foetuses. This suggests that epimorphin may have an important part in induction of morphogenesis during human foetal hair follicle development.

Periderm cells form cornified cell envelope in their regression process during human epidermal development

Terminally differentiated stratified squamous epithelium forms a lining of the plasma membrane called the cornified cell envelope, a thick layer of several covalently cross-linked precursor proteins including involucrin, small proline-rich proteins, and loricrin. Their cross-linking isodipeptide bonds are formed by epidermal transglutaminases 1-3. Material from lamellar granules is attached on the extracellular surface of corneocytes during the keratinization process. The formation of cornified cell envelope and sequential expression of major cornified cell envelope precursor proteins, transglutaminases, and 25 kDa lamellar granule-associated protein were studied in human embryonic and fetal skin. Ultrastructurally, membrane thickening has already started in periderm cells of the two-layered epidermis and an electron-dense, thickened cell envelope similar to cornified cell envelope in adult epidermis is observed in periderm cells at the three-layered and later stages of skin development. In the two-layered epidermis (49-65 d estimated gestational age), immunoreactivities of involucrin, small proline-rich proteins, all the transglutaminases, and lamellar granule-associated protein were present only in the periderm. In the three-layered epidermis and thereafter (66-160 d estimated gestational age), loricrin became positive in the periderm cells, transglutaminases extended to the entire epidermis, and lamellar granule-associated protein was detected in intermediate cells as well as periderm cells. Immunoelectron microscopy demonstrated that both major cornified cell envelope precursor proteins, involucrin and loricrin, were restricted to the cornified cell envelope in periderm cells at this stage of development. After 160 d estimated gestational age, the periderm had disappeared and cornified cell envelope proteins and lamellar granule-associated proteins were expressed in the spinous, granular, and cornified cells and transglutaminases were detected in the entire epidermis. These findings indicate that cornified cell envelope precursor proteins, transglutaminases, and lamellar granule-associated proteins are expressed in coordination in periderm cells during human epidermal development and suggest that periderm cells form cornified cell envelope in the process of regression.

Expression of differentiation markers during fetal skin development in humans: immunohistochemical studies on the precursor proteins forming the cornified cell envelope

The cornified cell envelope is formed during the terminal differentiation of epidermis through cross-linking of specific proteins by transglutaminases. The specific arrangement of individual protein in the cornified cell envelope and participation of individual protein in the cornified cell envelope at different regions of skin, i.e., palm, foreskin, lips, etc. are not clearly understood. In order to understand the pattern and expression schedule of each individual precursor protein during the differentiation and formation of cornified cell envelope, the expression of precursor proteins in developing human fetal skins from the first to the third trimester were examined by immunohistochemical studies. Involucrin was found in the periderm and intermediate layer from 14 wk estimated gestational age, while loricrin and small proline-rich protein 1 were found in the periderm from 16 wk estimated gestational age. Filaggrin and trichohyalin that are absent in the adult cornified cell envelope were found in the granular and horny layers from 24 wk estimated gestational age. The precursor proteins except trichohyalin did not change their patterns after the onset of initial expression during development. Trichohyalin was transiently expressed in the granular and horny layers of the epidermis from 24 wk estimated gestational age with peak expression at 27 wk estimated gestational age, but was not detected in adult skin. In hair follicles, trichohyalin expression was stable without change from 20 wk estimated gestational age. These findings suggest that fetal skin may have different sets of barriers from the second trimester; the immature cornified cell envelope is formed in the early second trimester and the mature cornified cell envelope is formed in the late second or early third trimester when filaggrin and trichohyalin appear.

Development of skin barrier function in premature infants

Histologic analysis suggests that epidermal development is complete in utero at approximately 34 wk gestational age. Infants born more prematurely have elevated rates of both transepidermal water loss and transcutaneous heat loss, and have difficulty maintaining homeostasis. The underdeveloped integument is also a portal of entry for infection and the percutaneous uptake of toxins. Previous measurements of transepidermal water loss have suggested that, regardless of gestational age, competent barrier function is attained within 2-4 wk postnatal age. In this study we have utilized another noninvasive biophysical technique, low frequency impedance spectroscopy, to complement transepidermal water loss measurements. We present longitudinal data from infants ranging from 23 to 32 wk gestational age. The results suggest that, for ultra-low birth weight infants (23-25 wk gestational age), the complete development of a fully functional stratum corneum can require significantly longer than 4 wk. In contrast, the data from the older infants suggest that a postnatal existence period of 2-4 wk may not be necessary to attain functional maturity, because infants born at 30 and 32 wk gestational age were found to have barrier function comparable with that of adults.

Monoclonal antibody against adult marrow-derived mesenchymal stem cells recognizes developing vasculature in embryonic human skin

We have described previously a monoclonal antibody (SH2) that specifically recognizes undifferentiated mesenchymal progenitor cells isolated from adult human bone marrow. These cells, which we operationally refer to as mesenchymal stem cells, have the capacity to differentiate and form distinct mesenchymal tissues such as bone and cartilage when the isolated cells are placed in the appropriate in vivo or in vitro environment. We report here the partial biochemical characterization of the antigen recognized by the SH2 antibody. Metabolically radiolabelled adult marrow-derived mesenchymal stem cells in culture were extracted and immunoprecipitated with the SH2 antibody. The purified antigen migrated as a single band of 90 kDa after sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed under reducing conditions. The SH2-immunoprecipitated protein exhibited a molecular weight band shift after removal of N-linked oligosaccharides. We investigated the expression of the SH2 antigen, along with the endothelial markers factor VIII-related antigen and Ulex europaeus I (UEA-I) lectin during specific developmental periods in human dermal embryogenesis and in the postnatal period through aged adults. Frozen sections of human embryonic, fetal, or postnatal skin ranging from 8 weeks estimated gestational age (EGA) through 84 years of age were immunostained or double immunolabelled with antibodies SH2, UEA-I, or factor VIII-related antigen followed by second antibodies with fluorescent markers. Positive cell surface reactivity with the SH2 antibody was seen in cells in the vascular plane in the earliest specimens (day 55 EGA) corresponding to the late cellular dermis period. During the period of the cellular to fibrous transition, in which the initiation of appendage development occurs, most SH2-reactive cells colocalized with vasculature markers UEA-I and factor VIII-related antigen, although there was a subset of cells recognized by SH2 antibody that did not colocalize with the endothelial markers. In contrast to the endothelial markers UEA-I and factor VIII-related antigen, in which the number of immunopositive cells became more prominent with age and maturation of the dermis, the frequency of cells that contained the SH2-reactive antigen diminished with age. The SH2 reactivity evident in embryonic, fetal, and early postnatal periods was not observed in human skin specimens taken from adults greater than 30 years old. These observations support the hypothesis that the SH2 antigen is a cell surface marker of developing microvasculature and may play a role in dermal embryogenesis and angiogenesis.

Transdermal drug delivery. Clinical aspects

The delivery of drugs into and through the skin is a recognized and effective means of therapy for dermatologic, regional, and systemic disease. The selection of drug candidates and the rational design of suitable formulations depends upon the biological make-up of the skin's barrier, and the physiochemical interactions between the membrane, the delivery system technology, and the active agent. This article summarizes the state of the art and examines more recent developments that are the subject of considerable research at this time. In addition, the potential to use the skin as a portal for noninvasive clinical chemistry (e.g., for glucose monitoring in diabetics) is discussed.

Elevated levels of the endogenous retrovirus ERV3 in human sebaceous glands

ERV3 (HERV-R) is a complete human endogenous retrovirus located on the long arm of chromosome 7. Long terminal repeat-envelope (env) gene spliced mRNAs of 9 and 3.5 kb are widely expressed in human tissues and cells, but gag-pol mRNAs have not been found. Furthermore, the env gp70 gene contains an open reading frame throughout its length. The highest expression of ERV3 mRNA detected so far is in placenta and the lowest in choriocarcinoma cell lines. We have previously shown that the human monoblastic cell line U-937 and some normal and neoplastic tissues also express high levels of ERV3 env message by Northern blot analysis; however, this method does not distinguish between mRNA expression in different cell types in tissues. In this report, we have studied the ERV3 mRNA expression in specific cell types of human skin by in situ hybridization. We found high levels expression of ERV3 env mRNA in human sebaceous glands in normal skin and dermoid cysts of the ovary. In all glands, the expression is maximal in the periphery of the lobule and ceases towards the center in the region of characteristic holocrine secretion. Since it is known that the regulation of sebaceous glands is primarily via steroid hormones, particularly androgens, it is possible that expression of ERV3 is hormone dependent.

The expression and localization of bcl-2 protein in normal skin and in non-melanoma skin cancers

Non-melanoma skin cancers are the most commonly diagnosed malignancies and are typically indolent in their clinical behavior. Although predisposing factors leading to the development of these cancers, such as ultraviolet irradiation, are well described, the molecular events involved in their pathogenesis are incompletely understood. The localization of bcl-2 expression within the skin was determined using immunohistochemical methodologies and an anti-bcl-2 monoclonal antibody. The cytoarchitectural distribution of bcl-2 protein in normal skin included basal keratinocytes, the dermal papillae of the hair follicle, the keratinized Huxley's and Henle's layers, and the keratinized outer root sheath cells of the isthmus and infundibulum of the hair follicle. In addition, intense immunoreactivity was noted in the secretory coil of eccrine sweat glands. The distribution of bcl-2 protein within normal skin did not correlate with the known histologic localization of stem cell compartments. Basal cell carcinomas expressed high levels of bcl-2 protein. In contrast, squamous cell carcinomas typically exhibited no immunohistochemically detectable bcl-2 protein. The findings suggest a potential contribution of bcl-2 gene deregulation to the pathogenesis of some types of non-melanoma skin cancer.

Prenatal development of the integument in Delphinidae (Cetacea: Odontoceti)

The prenatal development of epidermis, dermis, and hypodermis was studied in embryos of different age of two delphinid species (Stenella attenuata, Delphinus delphis), using light and transmission electron microscopical methods. The delphinid embryo is covered by a multilayered tissue formed by four different epidermal generations (periderm, stratum intermedium-I, str. intermedium-II, str. spinosum) produced by the str. basale. The first layer appears at about 40-50 mm of body length, the second type (s.i.-I) about 60-160 mm, and the third type (s.i.-II) is present at 160-500 mm. The first spinosal cells are produced at 225-260 mm body length; thenceforth, the epidermis increases continuously in thickness. Epidermal ridge formation begins about 400-mm body length. The development of the dermis is characterized by the early production of thin connective tissue fibers (40-70-mm body length) and simultaneously the cutaneous muscle matures in structure. Vascular development intensifies between embryos of 150-225 mm, and collagen production increases markedly in fetuses of 225-260-mm length. These events are paralleled by an increase in dermal thickness. The first elastic fibers can be recognized in the skin from the abdomen at about 600-mm body length. The development of the hypodermis is marked by very rapid and constantly progressing growth, beginning about 60-mm body length. The first typical fat cells appear in animals of 360-400 mm. Regional differences are obvious for all skin layers with regard to the flippers, where structural maturation proceeds more rapidly than in dorsal or abdominal regions.

Prenatal diagnosis of Sjögren-Larsson syndrome using enzymatic methods

Sjögren-Larsson syndrome (SLS) is an autosomal recessive disorder characterized by the presence of congenital ichthyosis, mental retardation, and spasticity. The primary biochemical defect in SLS has recently been identified to be a deficiency of fatty aldehyde dehydrogenase (FALDH), which is a component of fatty alcohol:NAD+ oxidoreductase (FAO). We monitored four pregnancies at risk for SLS by measuring FAO and FALDH in cultured amniocytes or cultured chorionic villus cells. The enzymatic results in one case using amniocytes obtained during the second trimester predicted an affected SLS fetus, which was confirmed at termination of the pregnancy. Another at-risk fetus was predicted to be affected with SLS using cultured chorionic villus cells obtained in the first trimester, and fetal skin fibroblasts confirmed a profound deficiency of FAO and FALDH. Two other fetuses were correctly predicted to be unaffected. These results demonstrate that SLS can be diagnosed prenatally using enzymatic methods.

Location of stem cells of human hair follicles by clonal analysis

We have examined the growth capacity of keratinocytes isolated from human scalp hair follicles. Like the keratinocytes of glabrous epidermis, most of the colony-forming cells are classified as holoclones or meroclones when analyzed in a clonal assay. Some of them have extensive growth potential, as they are able to undergo at least 130 doublings. Therefore, the hair follicle, like the epidermis, contains keratinocytes with the expected property of stem cells: an extensive proliferative capacity permitting the generation of a large amount of epithelium. We have also examined the distribution of clonogenic keratinocytes within the hair follicle. Several hundred colony-forming cells are concentrated at a region below the midpoint of the follicle and outside the hair bulb. This region lies deeper than the site of insertion of the arrector pili muscle, which corresponds with the position of the bulge when the latter can be identified. In contrast, few colony-forming cells are present in the hair bulb, where most of the mitotic activity is observed during the active growth phase of the follicle. Paraclones, which are present both in the midregion and in the bulb of hair follicles, are unlikely to be the transient amplifying cells expected from kinetic studies.

Dynamic expression patterns of tenascin, proteoglycans, and cell adhesion molecules during human hair follicle morphogenesis

The development of skin appendages such as hair, feathers, and teeth is brought about by reciprocal interactions between epidermal and mesenchymal tissues and is thought to be influenced in part by cell adhesion molecules and components of the extracellular matrix. The developmental distributions of tenascin, neural cell adhesion molecule (NCAM), E-cadherin, intercellular adhesion molecule 1 (ICAM-1), chondroitin sulfate proteoglycan (CSPG), and the heparan sulfate proteoglycan perlecan were studied in relation to hair follicle morphogenesis in fetal human skin. Tenascin first appeared in developing skin in focal concentrations at the epidermal-mesenchymal interface, just prior to, and presumably correlated with, hair follicle initiation. Tenascin immunostaining remained prominent in the basement membrane zone and extracellular matrix of the follicle sheath during subsequent morphogenetic stages. Two forms of tenascin (M(r) 250 x 10(3) and 280-300 x 10(3)), were revealed by Western blots of skin extracts. NCAM immunolabeling was initially present throughout the dermis, and became progressively restricted to the dermal condensation and the follicle sheath. Western blot analysis revealed an isoform of NCAM (M(r) 160 x 10(3)) which lacked polysialic acid. At all stages, E-cadherin staining was diminished on follicle cells situated adjacent to the basement membrane, relative to cells in the follicle interior. Follicle-specific immunostaining for ICAM-1 was transient, appearing only at the pre-germ and hair germ stages of development. Antibodies to three distinct CSPG determinants revealed unique immunolabeling patterns following follicle initiation: One CSPG epitope co-distributed with tenascin in the follicle basement membrane and follicle sheath extracellular matrix; one CSPG epitope was similarly expressed, and was also found on follicle epithelial cells; and the third CSPG determinant was noticeably absent from the follicle sheath during elongation of the developing appendage. Perlecan was concentrated in the dermal papilla, in addition to its distribution in all skin basement membranes. A model for how these diverse molecules may interact to influence human hair follicle morphogenesis is presented.

Segregation of keratinocyte colony-forming cells in the bulge of the rat vibrissa

The epidermis and its related appendages such as the hair follicle constitute the epithelial compartment of the skin. The exact location and distribution of the keratinocyte colony-forming cells within the epidermis or its appendages are unknown. We report that in the rat vibrissa, keratinocyte colony-forming cells are highly clustered in the bulge-containing region. Approximately 95% of the total colonies formed in culture from fractionated vibrissae were in this location and fewer than 4% were located in the matrix area of the follicle. Finer dissection of the bulge-containing region located the colony-forming cells in the small part containing the bulge itself. The segregation of keratinocyte colony-forming cells in the bulge confirms the hypothesis that the bulge is the reservoir of the stem cells responsible for the long-term growth of the hair follicle and perhaps of the epidermis as well.

Fatty acid and lipid composition in vitro and in vivo of rat epidermis

1. Fatty acid and lipid compositions of cultured rat keratinocytes were compared with those of intact epidermis prepared from newborn and adult rats. 2. The uniqueness of the lipid profile of cultured cell manifested itself in the accumulation of a novel lipid which co-migrated with monoalkyldiacylglyceride on thin-layer chromatography. 3. Concentration of the branched-chain fatty acid was specifically high in the cholesterol ester fraction of the intact cell, and was decreased by cultivation under submerged conditions.

[Differentiation of the ruminal epithelium of cattle during intrauterine development]

The prenatal development of the bovine ruminal epithelium was studied with light- and electronmicroscopical techniques. During the period of the nonstratified epithelium a pseudostratified epithelium is found in the dorso-cranial part, whereas the other areas possess a one-layered epithelium, which is, like the pseudostratified epithelium, transformed to a multilayered epithelium from the 7th week onwards. From the 9th week the period of the stratified epithelium starts with the formation of the stratum profundum and stratum superficiale. First signs of keratinization are seen in the superficial cells from 2.3 months onwards. With 4 months fetal cornified cells can be identified, with 5.5 months a single-layered stratum basale is seen on the differentiating papillar connective tissue, and the superficial cells are transformed to balloon-cells. In suprapapillar areas, a stratum spinosum is formed at the prenatal age of 7.5 months. During epitheliogenesis a horizontal and vertical differentiation of the cells can be observed. The first one includes the differentiation of undifferentiated, embryonal cells to the basal cells of the stratum profundum, the latter the development of the basal cells to spinous cells and then to fetal cornified and balloon-cells. The ultrastructural changes during the process of keratinization were especially considered.

Epidermal ridge formation in the human fetus: a correlation to the appearance of basal cell heterogeneity and the expression of epidermal growth factor receptor and cytokeratin polypeptides in the epidermis

This paper aims to clarify an expression of epidermal growth factor receptor (EGFR) and cytokeratin 10 and/or 11 in relation to primary and secondary epidermal ridge formation of the human fetus. Firstly, scanning electron microscopy revealed heterogeneity in basal cell morphology during epidermal ridge formation. Basal cells had a uniform, smooth, and polygonal dermal surface until formation of the primary epidermal ridges. Thereafter, the dermal surface became ruffled and elliptic except at the primary epidermal ridges. Secondly, EGFR was detected by monoclonal antibody and autoradiography using 125I-EGF. The antibody reacted with primary epidermal ridge, stratum basale, stratum intermedium, and outer layer of sweat duct. The reactivity became stronger at the primary epidermal ridge than at the secondary one. The binding of 125I-EGF was concentrated in the primary epidermal ridge and sweat duct. Thirdly, cytokeratin 10 and/or 11, a maturation marker of keratinocytes, was detected by monoclonal antibody. The antibody reacted only with the stratum intermedium before secondary epidermal ridge formation. Afterward, it also reacted with the stratum basale of the secondary epidermal ridge but never reacted with that of primary epidermal ridge. The results indicate that basal cells of the secondary epidermal ridge enter the maturation process and suggest a localization of epidermal stem cells on the primary epidermal ridges. Concerning epidermal ridge formation, we suppose that the formation of the primary epidermal ridge causes the segregation of the epidermal stem cells, and that the increased density of the basal cells between the two primary epidermal ridges brings about the change in their dermal surface shape and the formation of the secondary epidermal ridge.

Development of the hair in the rat: in vivo and in transplanted tissue

Differentiation of the hair was examined in the head skin of rat embryos aged from days 12.5 to 18.5 of gestation. In 12.5-day-old embryos, the skin consisted of single layered epidermis and underlying loose connective tissue. On day 17.5 of gestation, the epidermis appeared to have a two or three layered epithelium, and the subepidermal connective tissue gave rise to an overlying dense tissue, into which blood capillaries arose from the deeper layer. The epidermis showed partial thickenings, where basal cells were arranged perpendicular to the surface of the epidermis. Beneath the epidermal thickenings, a number of connective tissue cells appeared to have accumulated and occasionally were accompanied by blood capillaries. In sequential development of the skin, the thickenings protruded as cords to the underlying dermal tissue and formed hair follicles covered with a connective tissue sheath. Skin obtained from 12.5-day-old embryos was transplanted singly or with cerebral cortex into the third ventricle of adult male rats. Thirty days after the transplantation, hairs and sebaceous glands had developed from the grafted skin. Hair growth tended to be more prominent in the cotransplanted skin grafts. However, no nerve fibers immunoreactive for substance P or calcitonin gene-related peptide (CGRP) were found in the grafted skin, although these fibers appeared in the dermis at the end of gestation in vivo. These results showed that the skin of 12.5-day-old embryos was able to induce hair growth in the third ventricle without accompanying peripheral neuronal fibers or blood capillaries, although the effects of connective tissue cells could not be ruled out.

Dopa reaction test in hair bulbs of fetuses and its application to the prenatal diagnosis of albinism

No information is available on the amount of tyrosinase normally present in fetuses. A dopa reaction test in hair bulbs from the scalp of normal fetuses obtained after abortion showed that tyrosinase is present in fetuses as early as 17 weeks. Only faint activity was detected in skin specimens other than from the scalp. This assay can serve as a quick and reliable method for the prenatal diagnosis of tyrosinase-negative albinism.

Common antigen expression between human periderm and other tissues identified by GB1-monoclonal antibody

From 4 weeks estimated gestational age (EGA) until the end of the second trimester (24 weeks EGA) the fetal epidermis is covered by a specialised epithelium, the periderm. The origin and function of periderm remain speculative. We have demonstrated, using indirect immunofluorescence and immunoperoxidase staining, that periderm is recognised by a mouse IgM monoclonal antibody (Mab) GB1, which has been raised against a simple extract of human amnion. Immunoelectron microscopy localises GB1 to the amniotic surface of periderm, particularly in association with the microvilli, and also bordering cellular identations of the periderm cells. GB1 antigen (ag) is also expressed by the epithelium of fetal oesophagus, fetal and adult conjunctiva and cornea but is absent in a variety of other fetal and adult tissues including bladder, oral mucosa and thymus. The similar distribution of GB1 ag in both periderm and membranes possibly suggests a common origin and the shared expression with fetal oesophagus and fetal and adult eye may indicate a function related to the fluid environment. We therefore feel that GB1 Mab may be of use in further investigations into the origin, structure and function of human periderm.

Prenatal diagnosis of X-linked hypohidrotic ectodermal dysplasia by linkage analysis

Prenatal diagnosis of X-linked hypohidrotic ectodermal dysplasia was previously performed by the direct histological analysis of fetal skin obtained by late second trimester fetoscopy. The recent gene mapping of the locus for the disorder to the region of Xq11-21.1 now permits the indirect prenatal diagnosis of the disorder by the method of linkage analysis, based on closely linked marker loci, during the first trimester of pregnancy. We report the prenatal diagnosis of a male fetus with a high probability of the disorder by a linkage analysis utilizing restriction fragment length polymorphisms at the DXS159, PGK1, and DXS72 loci, from a DNA sample obtained by a chorionic villus biopsy at 9 weeks gestation. After further counseling, the pregnancy was terminated but the diagnosis could not be confirmed by histological analysis, even though analysis of skin samples by light and electron microscopy showed lack of hair germs, primary dermal ridges, and sweat gland primordia, due to the early developmental stage of the fetus. The use of DNA-based linkage analysis now offers the opportunity for an earlier diagnosis of X-linked hypohidrotic ectodermal dysplasia by a method other than fetal skin sampling. However, families must also fully understand the present limitations of the method prior to undertaking the procedure.

Fetal skin biopsy in prenatal diagnosis of some genodermatoses

Various methods of obtaining fetal skin for prenatal diagnosis of certain autosomal-recessive congenital genodermatoses have been assessed. An attempt was made to obtain fetal skin by fetoscopy in 15 patients prior to pregnancy termination for a variety of medical reasons at 18-26 weeks. Specimens were obtained only in five cases (8 successful attempts out of 48). In twelve cases, of which five had a history of a child with junctional (Herlitz type) or dystrophic (Hallopeau-Siemens type) epidermolysis bullosa or non-bullous congenital ichthyosiform erythroderma at 16-25 weeks of pregnancy, fetal skin was obtained without fetoscopy under direct ultrasonic control. Specimens were obtained in all cases (33 successful attempts out of 39). In three cases, fetal pathology was diagnosed by the method of semi-thin and ultra-thin skin sections, and the respective pregnancies were terminated.

Harlequin fetus and micromelia

A fetus was born prematurely after a 34-week pregnancy whose evolution was marked by the ultrasonic finding at 23 weeks of a considerable shortening of the long bones. At birth, the newborn infant bore the appearance of a harlequin fetus. There was no dwarfism, but the micromelia discovered in utero was confirmed both clinically and radiologically. Such global micromelia associated with this kind of pathology has never been described, not to mention witnessed, in utero and may be part of the fetal akinesia sequence phenotype.

Development of dermal ridges in the volar skin of fetal pigtailed macaques (Macaca nemestrina)

Development of the dermal ridges in volar skin was investigated in 28 pigtailed macaque (Macaca nemestrina) fetuses of known gestational age, ranging from 51 days postconception to newborn. Histology, scanning electron microscopy, and staining of the abraded dermal surface were used in the study. Morphological features of the dermal-epidermal system and their changes with advancing age are described. Chronology was established for stages in the development of the volar skin, i.e., the differentiation of the primary and secondary epidermal ridges (PER and SER) at the undersurface of the epidermis corresponding to the formation of primary and secondary dermal ridges (PDR and SDR) and the development of the dermal papillae. PDRs were first seen at 55 gestational days and SDRs at 93 days. Differentiation of sweat ducts occurred over the period between 60 and 119 gestational days. A regional sequence of differentiation starting with the digital apices of the hand and ending in the calcar area and the phalanges of the foot was documented. Generally, morphogenesis in the macaque was accelerated relative to that in the human fetus by approximately 3 weeks.

The expression of congenital ichthyosiform erythroderma in second trimester fetuses of the same family: morphologic and biochemical studies

The first born offspring of first-cousin parents was affected with a keratinization disorder thought to be nonbullous congenital ichthyosiform erythroderma (CIE). In each of three subsequent pregnancies, the parents elected to have prenatal diagnosis based on evaluation of fetal skin biopsies. The epidermis of fetus 1 was identical to normal 21-wk estimated gestation age (EGA) fetal epidermis, but because keratinization begins normally around 24 wk EGA, the procedure was repeated 4 wk later. A thin epidermis with a few layers of stratum corneum indicated a normal fetus and a healthy infant was born at term. Skin biopsy samples from fetus 2 gave conflicting results; the epidermis of one sample appeared normal but the second had 5-15 layers of incompletely keratinized cells superficial to basal and intermediate layers. The hair canals of both samples were hyperkeratotic. Pelleted amniotic fluid cells contained aggregates of incompletely keratinized epidermal cells and concentric rings of keratinized cells. The fetus was thought to be affected and the pregnancy terminated. Regional variation in epidermal thickness and keratinization was noted upon gross examination of the fetus and by histology of the skin. Marked hyperkeratinization of follicles was evident in all regions. No abnormal keratins were expressed in the affected epidermis but epidermal lipids analyzed from two body regions had a lower triglyceride content and a higher content of free sterols compared with age-matched, normal fetal epidermis. Immunolabeling for markers of differentiation revealed variable stages of epidermal differentiation according to region. Four structurally identical biopsy samples were obtained from a third fetus. The epidermis appeared normal for age and hair canals were keratinized to various extents. The pregnancy was continued and at 33 wk a male infant was born with a severe ichthyosis of the face and scalp and fine, white scaling on the body. The epidermis of both the severely and mildly affected regions of the newborn had a thick, compact stratum corneum and other features of CIE. Scars from all four fetal biopsies were identified on the trunk, in areas which appeared less affected clinically. This study reports, for the first time, the criteria for prenatal diagnosis of CIE and the variable expression of this disorder in the midtrimester fetus. More importantly, it demonstrates the risks and pitfalls of this in utero diagnosis based on epidermal morphology.

Morphometric and statistical analyses describing the in utero growth of human epidermis

Epidermal development of human embryonic and fetal skin from the lower limb was studied using morphometric and statistical methods. Epidermal growth, as defined by an increase in epidermal thickness and the number of cell layers, occurred in three distinct stages during the first and second trimesters. The first growth spurt occurred between 5 and 13 weeks estimated gestational age (EGA) and was followed by a plateau phase with little change in epidermal thickness from 14 to 21 weeks, after which the epidermis began to increase in height again. The periderm reached its maximal height by approximately 13 weeks EGA, and by 25 weeks was shed into the amniotic fluid. Thus, within a five-month period (5 to 25 weeks EGA) the epidermis changed from a single cell layer less than 10 micron thick to a 10 to 12-cell layer, keratinized epithelium greater than 60 micron thick. In contrast, epidermis from adult lower limb consisted of about 25 cell layers and was almost 75 micron in thickness. The age-related differences in epidermal thickness probably reflect changes in cell size and shape more than changes in the directional movement (apically vs. laterally) of proliferating keratinocytes, because the addition of cell layers throughout development was relatively constant. During the plateau phase, when there is a rapid increase in fetal growth rate, the suprabasal keratinocytes become more flattened, thereby allowing for the addition of new cell layers while maintaining a relatively constant epidermal thickness.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural observations on the development of the human conjunctival epithelium

In human embryos with a gestation age of 8.6-22 weeks, the palpebral conjunctival epithelium was examined by transmission electron microscopy (TEM). During the gestation period studied, the structural integrity of the tissue is established by an increase in the quantity of tonofilaments, desmosomes, and hemidesmosomes as well as by the undulating appearance of the cell membranes, the widening of the intercellular space, and the development of cytoplasmic protrusions into it. The superficial cells display a chronological sequence in the elaboration of transport mechanisms. A precursor stage is described for hemidesmosome formation at the interface between the basal cell membrane and the conjunctival stroma.

Ultrastructure of first trimester chorionic villi with regard to the prenatal diagnosis of genodermatoses

Hopes are held out for chorion villus sampling, a technique which is gaining more and more importance for the first trimester prenatal diagnosis of chromosomal aberrations and metabolic abnormalities. A variety of inherited skin diseases can be diagnosed postnatally and prenatally (in the second trimester) by ultrastructural diagnostic markers. For evaluation of prenatal diagnosis in the first trimester, we investigated chorionic villi derived from the trophoblast layer of the early pregnancy by light microscopy and conventional electron microscopy. The ultrastructure of the cellular layers covering the villi, i.e., the inner cytotrophoblast and the outer syncytiotrophoblast, as well as that of the connective tissue of the inner extraembryonic mesoderm, are thoroughly described in relation to the ultrastructural changes in certain genodermatoses including epidermolyses and keratinization disorders. We found that chorionic villi have only a few of the characteristics differentiated in skin, and none of the structures which are relevant to the diagnosis of genodermatoses. In our view, the ultrastructural approach is not suitable for first trimester prenatal diagnosis of genodermatoses in chorionic villi.

Lamellar granule extrusion and stratum corneum intercellular lamellae in murine keratinocyte cultures

Lamellar granules are specialized epidermal organelles containing stacks of membranous disks that are extruded into the intercellular spaces in the upper portion of the granular layer. The extruded disks are believed to undergo biochemical and biophysical changes to form the stratum corneum intercellular lipid sheets that constitute the epidermal permeability barrier. Little is known about this important component of epidermal differentiation, in part due to lack of a suitable in vitro model. We have demonstrated microscopically the presence of characteristic lipid membrane structures in a primary keratinocyte culture system which shows morphologic differentiation comparable to that seen in vivo. A basal cell-enriched fraction of isolated neonatal mouse keratinocytes was plated into Vitrogen-coated 30 mm Millicell (Millipore, Bedford, Massachusetts) wells, fed daily with Medium 199 containing 10% fetal bovine serum, 10 micrograms/ml each of insulin and hydrocortisone, and kept at 32 degrees C in a 5% CO2/95% air atmosphere in a humidified incubator. Three days after plating, cultures were placed on living, epidermis-free mouse dermis at the air/liquid interface. At 2 wk, histologic examination showed multiple well-organized cell layers, including a distinct granular layer and a well-developed stratum corneum. Transmission electron microscopy demonstrated numerous lamellar granules and extrusion of their contents into the intercellular space. After fixation with ruthenium tetroxide, stacked intercellular lamellae in the stratum corneum were seen. Both the presence of dermis and growth at the air/liquid interface were necessary to achieve complete differentiation. This system conclusively demonstrates the formation of complex epidermal lipid structures in vitro and should allow the mechanisms and regulation of their synthesis to be elucidated.

Epidermal Langerhans' cells and dermal dendritic cells in human fetal and neonatal skin: an immunohistochemical study

The dendritic cells in skin biopsies from 36 fetuses (from 16 weeks' gestational age on) and neonatal infants of different ages were investigated using a number of markers for various cells of the immune system and immunohistochemistry. Epidermal Langerhans' cells were found in all cases in a predominantly basal localization. The number of OKT6-positive Langerhans' cells and the development of their dendritic processes gradually increased with age. Dermal dendritic cells were present as well. Both HLA-DR-positive and Leu-10-positive dermal dendritic cells were found in the superficial and deep dermis, often in a perivascular distribution. The OKT6-positive dermal dendritic cells were few in number and occurred only in the upper dermis.

Arrested epidermal morphogenesis in three newborn infants with a fatal genetic disorder (restrictive dermopathy)

Two sibs and one unrelated infant were born prematurely with taut, shiny, restrictive skin that was abnormal in structure, organization, biochemistry, and state of differentiation. Prominent abnormalities in all regions of the skin were recognized by light and electron microscopy, immunohistochemistry, and biochemistry. The epidermis was hyperplastic, hyperkeratotic, and parakeratotic. Keratohyaline granules were abnormal in structure, but the keratohyalin-derived protein filaggrin was apparently normal in quantity and biochemistry. The epidermal cells contained less than the expected quantity of high-molecular-weight, differentiation-specific keratins and the tissue stained with antikeratin antibodies in an aberrant pattern. Additional 48 and 56 kD keratin polypeptides, indicative of a hyperproliferative state, were expressed. The dermal-epidermal junction was remarkably flat and the dermis was thinner than normal. The connective tissue appeared stretched and was oriented like tendon rather than dermis. Collagen fiber bundles and fibrils were smaller in diameter than normal. The nails were normal but other epidermal appendages such as the pilosebaceous structures and the eccrine sweat glands were underdeveloped, suggesting that morphogenesis of these structures was arrested at an early stage in utero. The subcutaneous fat was at least twice the thickness of the dermis. The skin abnormalities appeared to be the cause of the flexion contractions, characteristic facies, and inability to survive because of restricted respiratory movements. The structural and biochemical abnormalities in the skin of affected infants may serve as markers for prenatal and postnatal diagnosis of the disorder, and may provide insight into the basic mechanism of the disease.

Proliferation of human embryonic and fetal epidermal cells in organ culture

The morphology of human embryonic and fetal skin growth in organ culture at the air-medium interface was examined, and the labeling indices of the epidermal cells in such cultures were determined. The two-layered epidermis of embryonic specimens increased to five or six cell layers after 21 days in culture, and the periderm in such cultures changed from a flat cell type to one with many blebs. The organelles in the epidermal cells remained unchanged. Fetal epidermis, however, differentiated when grown in this organ culture system from three layers (basal, intermediate, and periderm) to an adult-type epidermis with basal, spinous, granular, and cornified cell layers. Keratohyalin granules, lamellar granules, and bundles of keratin filaments, organelles associated with epidermal cell differentiation, were observed in the suprabasal cells of such cultures. The periderm in these fetal cultures formed blebs early but was sloughed with the stratum corneum in older cultures. The rate of differentiation of the fetal epidermis in organ culture was related to the initial age of the specimen cultured, with the older specimens differentiating at a faster rate than the younger specimens. Labeling indices (LIs) of embryonic and fetal epidermis and periderm were determined. The LI for embryonic basal cells was 8.5% and for periderm was 8%. The fetal LIs were 7% for basal cells, 1% for intermediate cells, and 3% for periderm. The ability to maintain viable pieces of skin in organ culture affords a model for studying normal and abnormal human epidermal differentiation from fetal biopsies and for investigating proliferative diseases.

Structural and histochemical aspects of epidermis development of fetal porcine skin

Epidermal development of fetal porcine skin was studied in fetuses from 41 days of gestation until birth with scanning and electron microscopy techniques as well as histochemical methods, including immunohistochemistry. The porcine fetus develops a relatively thick and solid multilayered cover of epidermal cells, which is not lost before birth. It consists of tightly packed cells of the periderm and the stratum intermedium. The periderm cells are totally filled with filamentous proteins; in the intermediate cells, the filamentous proteins are concentrated in the cell periphery, forming a thick marginal zone. Immunohistochemically, the cytofilaments could be identified as cytokeratins of lower and higher molecular weights. The first thin stratum corneum lamellae are formed below the stratum intermedium at about 80-85 days of gestation.

Histochemical and morphological studies on mammalian epidermal peridermal granules

We performed morphological studies on the epidermal peridermal granules (PG) of newborn mice using histological, fluorescent and electron microscopic methods. PG appeared during the 17th to 18th day of foetal life, and remained in the outermost epidermal layers until 5 days after birth. PG were evenly distributed over the entire cutaneous surface of the mouse, except the tail. PG were found to contain protein and corresponded to sites of transglutaminase activity, but they were devoid of lipids and nucleic acids. They could be differentiated clearly from keratohyalin granules. Together, these studies suggest that PG represent a unique epidermal protein product that serves as a marker of late foetal development.