Unusual cholesterol esters in the sebum of young children

Cholesterol esters (CE) having fatty acids of more than 18 carbons are a prominent feature of fetal skin surface lipid (vernix caseosa), but are a minor component of adult lipid. The difference may be related to the fact that fetal sebaceous glands generally synthesize little lipid. If so, it would be expected that prepuberal children, who also have very inactive glands, would secrete CE with a large proportion of very-long-chain fatty acids. To test this conjecture, skin surface CE from young children were isolated and analyzed. Sebum was extracted from the hair of 38 children, aged six to nine. To obtain a measure of sebaceous lipogenesis, the class composition of the lipid was determined by quantitative thin-layer chromatography and the ratio of wax esters/[cholesterol + cholesterol esters] (WE/[CH + CE]) was calculated. CE were then isolated from the lipid and hydrolyzed. The freed fatty acids were converted to fatty acid methyl esters (FAME) and analyzed by capillary gas chromatography to determine the proportion with more than 18 carbons. FAME from five of the subjects were then separated into saturated and monounsaturated fractions and analyzed again by gas chromatography to identify chain types. Ratios of WE/[CH + CE] ranged from 0.08 to 2.8 in the subjects. The proportion of CE FAME with more than 18 carbons ranged from 15 to 72%, with the highest proportion being found in the children with the lowest WE/[CH + CE]. The saturated FAME were mostly iso- or anteiso-branched, whereas the monounsaturated FAME were mostly straight-chain extension products of 16: 1 delta 9 or 18: 1 delta 9.     

Dilutional effect of increased sebaceous gland activity on the proportion of linoleic acid in sebaceous wax esters and in epidermal acylceramides

Sebaceous wax esters and epidermal acylceramides were isolated from skin surface lipid obtained from children and from young adults. Fatty acid methyl esters (FAME) were prepared from the esterified fatty acids of these lipid classes and analyzed to ascertain the proportions of methyl linoleate (18:2 delta 9,12), methyl sebaleate (18:2 delta 5,8), and methyl sapienate (16:1 delta 6). On the same subjects, 2 measures of sebum secretion rate were obtained, namely the sustainable wax ester secretion rate (WESR) on the forehead and the ratio of wax esters/(cholesterol + cholesterol esters) [WE/(CH + CE)] in the surface lipid. The proportions of methyl linoleate in FAME from the wax esters decreased, and the proportions of methyl sebaleate increased, with increased rates of sebum secretion. For both methyl linoleate and methyl sebaleate, a better correlation was obtained when the ratio of WE/(CH + CE) was used as a measure of sebum secretion rather than the WESR. The proportions of methyl linoleate in the FAME from the acylceramides were also inversely related to ratios of WE/(CH + CE). In acylceramides, linoleate was replaced by sapienate, a major fatty acid of human sebum. It appears, therefore, that sebum fatty acid composition may change with changes in sebaceous gland activity, and that sebum fatty acids can enter the epidermis and be incorporated into epidermal lipids.     

Characterization of angiotensin-converting enzyme expression during epidermis morphogenesis in humans: a potential marker for epidermal stem cells

Background  Recent evidence has revealed that angiotensin-converting enzyme (ACE) participates in cutaneous wound healing and contributes to the pathophysiological process of some skin diseases. However, little is known about the role of ACE in epidermis morphogenesis during development.
Objective  To clarify the expression pattern of ACE during embryonic development of human skin.
Methods  Skin samples were obtained from aborted fetuses at different gestational ages and from healthy individuals. Localization of ACE, together with β₁-integrin, keratin 19 (K19) and p63 was examined by immunofluorescence and immunohistochemical staining.
Results  In human fetal skin, at 11–13 weeks of gestation, ACE-positive cells were observed in the primitive epidermis. As the fetuses developed, ACE-positive cells appeared in all the epidermal layers. From 21 weeks of gestation, ACE expression was largely restricted to the basal layer of the fetal epidermis. In contrast, ACE-positive cells were found only in the adult skin basal layer which harbours epidermal stem cells. To explore the possible link between ACE and epidermal stem cells, we further examined the expression of β₁-integrin, K19 and p63, the putative markers for epidermal stem cells. Consistent with the results of ACE expression, from 21 weeks of gestation, the expression of β₁-integrin, K19 and p63 was mainly confined to the basal layer. Immunofluorescent double labelling revealed that ACE-positive cells substantially overlapped with β₁-integrin-, K19- and p63-positive cells.
Conclusions  Our results suggest that ACE may play a role in human epidermis morphogenesis during fetal life and serve as an unrecognized marker for keratinocyte progenitor cells.     

Changes in the relative amounts of endogenous and exogenous fatty acids in sebaceous lipids during early adolescence

Skin surface lipid samples were collected from the scalps of 40 males, aged 9-15, and the lipid class composition of each was analyzed by quantitative thin layer chromatography. The ratio of wax esters/[cholesterol + cholesterol esters] (WE/[CH + CE]) increased with age. The wax ester, cholesterol ester, triglyceride, and free fatty acid classes were isolated from each sample and the fatty acid compositions were determined by capillary gas chromatography of fatty acid methyl esters (FAME) prepared from each lipid class. The concentrations of most of the different types of fatty acids were found to be correlated with the WE/[CH + CE] ratio. Those straight chain fatty acids that are thought to be synthesized mainly within the sebaceous glands, such as 14:0, 14:1, 16:1, and 18:2 delta 5, 8 tended to increase with increasing WE/[CH + CE], while fatty acids which circulate in the blood, such as 18:0, 18:1, and 18:2 delta 9, 12, tended to decrease with increasing WE/[CH + CE]. For the majority of straight chain fatty acid types, the data could be fitted to the equation y = a + b/[x + 1], which can be derived from simple assumptions concerning the origins of the various sebum components. The FAME from the wax esters were separated into saturated and monounsaturated fractions and analyzed by capillary gas chromatography to determine the concentrations of the different types of branched chain FAME present. In the wax esters, straight chain fatty acids tended to increase with increasing WE/[CH + CE], while terminally branched (iso and anteiso) fatty acids tended to decrease. Other branched chain fatty acids increased up to a WE/[CH + CE] ratio of about 2 and then decreased at higher ratios.     

Effect of aging on sebaceous gland activity and on the fatty acid composition of wax esters

Using fused-silica capillary gas chromatography, we investigated sebum samples from 55 healthy individuals to discover the effects of aging on the sebaceous gland activity and on the fatty acid composition of wax exters. The sebaceous gland activity, which was expressed by the ratio of wax esters/[cholesterol + cholesterol esters] (WE/[C + CE]), showed a distinct change from infancy through maturity to senescence; the curve of the ratio made a peak in our subjects's 20s. Using the fatty acid analyses, we found an interesting relationship between C16:1 straight and C16:1 iso-branched chains, each of which occupied a large proportion in the fatty acids of wax esters; the former increased in proportion from infancy toward the 20s, with a correlation with aging (r = 0.788, p less than 0.01), and decreased thereafter until our subject's 50s (r = -0.611, p less than 0.01). In contrast, the proportion of the latter followed an entirely reversed course with advancing age. The percentages of C16:1 straight chain components were correlated positively with the WE/[C + CE] ratio (r = 0.642, p less than 0.01), while there was found to be a negative correlation between the proportion of C16:1 iso-branched chain components and the WE/[C + CE] ratio (r = -0.556, p less than 0.01). The results suggest that more active sebaceous glands in lipid production excrete lipids with a higher proportion of C16:1 straight chain fatty acid and a lower proportion of C16:1 iso-branched chain fatty acid. As well as the sebaceous gland activity, the fatty acid composition in sebum wax esters is affected by advancing age in Japanese.     

Topical beta-carotene is converted to retinyl esters in human skin ex vivo and mouse skin in vivo

Human epidermis contains endogenous retinoids (retinol and retinyl esters) and carotenoids (mostly beta-carotene). Previous studies have shown that the enzymes involved in retinoid metabolism are present in human epidermis. There is still a controversy about the presence in the skin of the enzymes able to convert beta-carotene into vitamin A (retinol), although a recent study demonstrated the conversion of beta-carotene into retinol in human cultured epidermal cells. In this study, we addressed the question of the possible bioconversion of topical beta-carotene into vitamin A or derivatives by human and mouse skin. Surgically excised human abdominal skin was mounted on Franz perfusion chambers to assess the cutaneous penetration of topical beta-carotene as well as its metabolism, after a 24-h incubation period, whereas hairless mice received topical beta-carotene 24 h before assaying epidermal beta-carotene and retinoid concentrations. Epidermal retinoid and beta-carotene concentrations were determined by high-pressure liquid chromatography. Topical beta-carotene penetrated well into human and mouse epidermis and induced a 10-fold (human) and a threefold (mouse) increase of epidermal retinyl esters, which demonstrates that topical beta-carotene is converted into retinyl esters by human and mouse epidermis and thus appears as a precursor of epidermal vitamin A.     

Cutaneous lipid synthesis during late fetal development in the rat

Lipid synthesis in fetal skin may be important both for the development of a mature epidermal permeability barrier and for growth. In these studies, we measured cutaneous cholesterol, sphingolipid and fatty acid synthesis during the critical period of epidermal barrier development in fetal rats to determine whether barrier function influences synthetic rates. In addition, the activities of HMG CoA reductase, serine palmitoyl transferase and acetyl coenzyme A carboxylase were evaluated. In whole skin, synthesis of cholesterol, ceramide, sphingomyelin and fatty acid decreased from day 17 to day 21 of gestation, as did the activity of HMG CoA reductase, serine palmitoyl transferase and acetyl coenzyme A carboxylase. In both the epidermis and dermis, a decrease in cholesterol, ceramide, sphingomyelin and fatty acid synthesis was measured over days 19–21 of gestation. Epidermal HMG CoA reductase activity also decreased over this same time period. In summary, epidermal and dermal synthetic rates and enzyme activity were highest early in gestation when the barrier was least competent and decreased as competence was achieved. Since other studies with mature animals have revealed that epidermal synthetic rates and enzyme activity are highest when barrier disruption is maximal, enhanced epidermal lipid synthesis precedes the estabilishment of a competent barrier in both fetal and mature rodents.     

Suppression of sebum secretion with 13-cis-retinoic acid: effect on individual skin surface lipids and implications for their anatomic origin

The contribution of the keratinizing epidermis to the human skin surface lipid film has been difficult to ascertain because, after its release from the epidermal cells, epidermally derived lipid inevitably becomes mixed with sebum. In the present study, the sustainable rates of production of the 5 neutral lipid classes found on the skin surface (triglycerides + free fatty acids, wax esters, cholesterol, cholesterol esters, and squalene) were measured on the foreheads of acne patients before, during, and following treatment with 13-cis-retinoic acid, a drug which suppresses sebum production profoundly. Since sebum production was high in the patients before treatment and was suppressed to a few percent of the pretreatment level in some of the patients during treatment, data covering a wide range of sebum production rates were obtained. By using squalene as a measure of sebum production and plotting the rates of production of the other lipid classes vs the rate of production of squalene, it was possible through extrapolation to estimate the residual (i.e., epidermal) rate of production of each lipid class at zero sebum production. The results indicated that epidermis releases triglycerides + free fatty acids and cholesterol to the skin surface. The cholesterol esters in freshly secreted skin surface lipids appeared to be almost entirely sebaceous in origin. Measurements were also made of the percentages of cholesterol esters in lipid collected from the scalp after several days' accumulation and were compared to corresponding values for the forehead lipid. The percentages of cholesterol esters in scalp lipid tended to rise when sebum production was suppressed by the drug, rather than remaining relatively constant as occurred in the freshly secreted forehead lipid. This result indicated that epidermis may contribute to skin surface cholesterol esters, probably through skin surface esterification of epidermal cholesterol.     

Expression of caspase-14 and keratin-19 in the human epidermis and appendages during fetal skin development

Caspase-14 is a seemingly non-apoptotic caspase involved in keratinocyte differentiation and cornification of the skin. Keratin-19 is an epithelial marker and a potential marker of epidermal stem cells that is expressed during human fetal skin development. We examined the immunohistochemical expression of caspase-14 in relation to CK-19 in the human fetal skin during development and perinatally, to assess their role in human skin maturation. Skin samples were received at autopsy. In the fetal epidermis, caspase-14 was predominantly expressed in the more differentiated layers, gradually disappearing from the basal layer toward term. By contrast, keratin-19 expression gradually decreased with epidermal maturation through gestation (rho = ?0.949; p = 0.0001) and was a marker of the germinative layers. Keratin-19 was preserved in scarce basal cell nests at term and postnatally. Caspase-14 and keratin-19 were inversely expressed in the differentiating epidermal layers through gestation (p < 0.0001). Concerning the appendages, in hair follicles and sebaceous glands, caspase-14 located preferentially in the more differentiated layers of the inner root sheath, whereas keratin-19 was expressed in the outer sheath. Eccrine sweat glands showed a variable pattern of caspase-14 and keratin-19 expression. In conclusion, caspase-14 emerged as a marker of human skin differentiation during development, while keratin-19 marked the germinative epithelial layers in the fetal epidermis and appendages and possibly the nests of epidermal stem cells.     

Relationship of protoporphyrin IX synthesis to photodynamic effects by 5-aminolaevulinic acid and its esters on various cell lines derived from the skin

Background  5-Aminolaevulinic acid (ALA) and its esters act as precursors to the fluorescent photosensitizer protoporphyrin IX (PpIX) in photodynamic therapy (PDT). There is little information about how ALA and its esters induce PpIX synthesis and photodynamic effects in cell lines derived from the skin.
Objectives  We compared the amount of PpIX synthesis induced by ALA and its esters in skin cell lines, and evaluated the relationship of PpIX synthesis to photodynamic effects by ALA and its esters in vitro .
Methods  Four cell lines, including human epidermal keratinocytes (HEK), human dermal fibroblast (hF), A431, and TXM13 were used. Cell survival was evaluated by the MTT assay. Fluorescence spectroscopy was used to measure the amount of PpIX synthesis induced by ALA and its esters. Flow cytometry measured cell death induced by ALA- and its esters-mediated PDT.
Results  ALA and its esters were not toxic at concentrations lower than 2 mmol L⁻¹ in all cell lines. PpIX synthesis was dose-dependent at low doses (0·01–0·1 mmol L⁻¹), and ALA esters were more effective than ALA. Cell death occurred from necrosis rather than apoptosis just after light irradiation illumination on both ALA and its esters-treated cells. Cell death related more to PpIX synthesis than the irradiation light dose.
Conclusions  PpIX production by ALA and its esters was induced on both normal and malignant cell lines derived from the skin, and cell death of PDT responses is closely related to the amount of PpIX synthesis rather than to the irradiation dose.     

Topical Spironolactone Reduces Sebum Secretion Rates in Young Adults

The effects of topically applied spironolactone on the sebum secretion rates (SSR) of young adults were investigated. SSR was expressed as the ratio of wax esters/[cholesterol + cholesterol esters] (WE/[C + CE]) and the amount of sebaceous lipids (squalene, triacylglycerol and wax esters). Topical spironolactone 5% gel applied to the right cheeks of the subjects produced a significant reduction in the SSR at 12 weeks (4 weeks after termination of application), but not at 8 weeks (the end of treatment). Untreated “control” areas (the left cheeks of the subjects) showed no significant change during the study. None of the subjects experienced skin rash or signs of local irritation. This results suggests that topical spironolactone may be effective in the treatment of acne patients with high SSR     

Comparison between human fetal and adult skin

Healing of early-gestation fetal wounds results in scarless healing. Since the capacity for regeneration is probably inherent to the fetal skin itself, knowledge of the fetal skin composition may contribute to the understanding of fetal wound healing. The aim of this study was to analyze the expression profiles of different epidermal and dermal components in the human fetal and adult skin. In the human fetal skin (ranging from 13 to 22 weeks’ gestation) and adult skin biopsies, the expression patterns of several epidermal proteins (K10, K14, K16, K17, SKALP, involucrin), basement membrane proteins, Ki-67, blood vessels and extracellular matrix proteins (fibronectin, chondroitin sulfate, elastin) were determined using immunohistochemistry. The expression profiles of K17, involucrin, dermal Ki-67, fibronectin and chondroitin sulfate were higher in the fetal skin than in adult skin. In the fetal skin, elastin was not present in the dermis, but it was found in the adult skin. The expression patterns of basement membrane proteins, blood vessels, K10, K14, K16 and epidermal Ki-67 were similar in human fetal skin and adult skin. In this systematic overview, most of the differences between fetal and adult skin were found at the level of dermal extracellular matrix molecules expression. This study suggests that, especially, dermal components are important in fetal scarless healing.     

Epidermal barrier lipids in human vernix caseosa: corresponding ceramide pattern in vernix and fetal skin

BACKGROUND: Vernix caseosa is a protective biofilm covering the fetus during the last trimester. Vernix and epidermal barrier lipids (i.e. cholesterol, free fatty acids and ceramides) appear to share protective functions for fetal and neonatal skin. OBJECTIVES: To analyse vernix samples for epidermal barrier lipid content, and to compare lipid profiles of vernix with those of fetal and postnatal epidermis. METHODS: Vernix samples were collected from 21 healthy term neonates. Skin samples were collected from 10 fetuses aborted between gestational week (GW) 16 and 25, nine infants and 11 older children. Lipids were extracted according to standard protocols and analysed by high-performance thin-layer chromatography. RESULTS: Vernix contained 196.5 +/- 70.1 microg barrier lipids mg-1 protein (mean +/- SD). Cholesterol formed the major barrier lipid fraction (52.8%), followed by free fatty acids (27.7%) and ceramides (20.1%). The ceramide composition of vernix resembled that of mid-gestational (GW 23-25) fetal epidermis both qualitatively and quantitatively, while there were major differences from postnatal epidermis. The total epidermal ceramide concentration increased significantly between prenatal and postnatal samples. CONCLUSIONS: The composition pattern of ceramides mirrors that of mid-gestational fetal epidermis. Vernix thus represents a 'homologous' substitute for the immature epidermal barrier in fetal skin. The differential role of individual ceramides in this process remains to be established.     

Skin lipid content during early fetal development

Although little is known about changes in the lipid composition of the skin during fetal development, information regarding the developmental sequence of fetal skin lipid content could be important for understanding the emergence of epidermal barrier function, as well as providing baseline criteria for prenatal diagnosis of certain inherited disorders of cornification. In these studies, epidermis was separated from dermis in fetal skin samples ranging from 50 to 140 d, estimated gestational ages (EGA), and its lipid composition was analyzed by quartz rod microchromatography/flame-ionization and thin layer chromatography. Lipid biochemical data were correlated with developmental milestones observed by electron microscopy (morphologic studies). The lipid composition of epidermal and dermal fractions from skin samples between 50 and 110 d EGA was similar, with both tissues exhibiting a predominance of free sterols and phospholipids. After 110 d EGA dermis became enriched in triglycerides, corresponding to the progressive development of adipocytes after this time. EGA epidermis after 110 d was enriched not only in triglycerides, but also sterol esters. Moreover, ceramides and glycosphingolipids also became increasingly prominent, changes that were greatest in epidermis from older fetuses and from cephalad regions. These changes in epidermal lipid composition corresponded morphologically to the progressive emergence of both folliculocentric epidermal cornification and sebaceous gland development.     

An immunohistochemical and immunoelectron microscopic study of the ontogeny of rat Langerhans cell lineage with anti-macrophage and anti-Ia monoclonal antibodies

An immunohistochemical study with anti-macrophage and anti-Ia monoclonal antibodies was performed to clarify the relationship between Langerhans cells (LC) and indeterminate cells (IC) in rat epidermis both in adulthood and in the fetal stage. On immunoelectron microscopy, a mouse anti-rat macrophage monoclonal antibody, TRPM-1, recently produced by us, reacted with IC and some LC in adult rat skin. Ontogenic study revealed that TRPM-1-positive cells first appeared in the epidermis of fetal rat heads on Day 17 of gestation and then spread caudally along the anterior-posterior axis. On Day 20 of gestation, when the distribution of the TRPM-1-positive cells over body surface became even, Ia-positive cells appeared in the epidermis and began to increase in number. Ia-positive cells with Birbeck granules were found on Day 21 of gestation. These results indicate that. TRPM-1-positive IC matured into Ia-expressing LC after being exposed to microenvironmental change during the perinatal period. The number of Ia-positive cells exceeded that of TRPM-1-positive cells at around 5 d after birth. Afterwards, there were more dendritic Ia-positive cells found in the interfollicular areas than TRPM-1-positive ones. However, local concentrations of the TRPM-1-positive IC in the follicular infundibula were frequently found in the fetal stage and occasionally in adulthood. These TRPM-1-positive cells in the follicular infundibula were thought to be a precursor pool in the epidermis for LC.     

Differentiation markers in fetal epidermis: transglutaminase and transpeptidase.

Two members of the transpeptidase family of enzymes, transglutaminase and gamma glutamyl transpeptidase, were assayed histochemically and biochemically in developing rat epidermis from day 15 of gestation through postnatal day 5. Electron microscopic examination of serial skin biopsies enabled precise dating of fetal epidermis and periderm and correlation of ultrastructural details of the cells with marker enzyme activities. Transglutaminase activity appeared histochemically in surface epidermis and in hair follicle inner root sheath on day 18 and day 21 of gestation, respectively, concomitant with the onset of terminal keratinization in these tissues. Enzyme activity was biochemically detectable 2 days before the histochemical stain became positive. Transpeptidase was active in fetal epidermis prior to keratinization but was only detectable in basal cells thereafter. Subsequent to birth, enzyme activity rose geometrically in hair follicles undergoing initial differentiation, and was thereafter found in all anagen hairs. Transglutaminase is active only in cells approaching terminal keratinization, while transpeptidase is associated with early phases of epidermal proliferation and differentiation.     

Expression of macrophage migration inhibitory factor in rat skin during embryonic development

Abstract:  We have previously shown that human epidermal keratinocytes express macrophage migration inhibitory factor (MIF) mRNA, and immunohistochemical studies showed that MIF is expressed in human epidermis. To explore the possible pathophysiological roles of MIF in skin during rat fetal development, we examined the expression patterns of MIF during rat epidermal development using Northern blot analysis and in situ hybridization. Expression of MIF mRNA was first detected by in situ hybridization in the developing epidermis and hair germ cells from embryonic day (ED) 16. From ED 19, moderate levels of MIF expression were detected in the epidermis and epithelial sheath cells of growing hair follicles. In postnatal rat skin, higher MIF expression was detected in the epidermis and hair follicles on postnatal day 3. These observations were also confirmed by Northern blot analysis. Immunohistochemical analysis with an anti-MIF antibody showed a similar distribution to that of the mRNA. Our results suggest that MIF is associated with epidermal and hair follicle development.     

Label-retaining cells in human embryonic and fetal epidermis

Human embryonic and fetal epidermis was examined and labeling indices (LIs) for basal, intermediate, and periderm cells were determined. The LI for fetal basal cells was 8-11% and the LI for fetal intermediate cells was 7.5-9%. The total fetal epidermal LI was 16-20%, which equaled the basal LI for embryonic epidermis. After 21 days in organ culture, only basal cells in the fetal epidermis labeled with tritiated thymidine, while both basal and intermediate cells in the embryonic epidermis labeled and the total LI for fetal and embryonic epidermal cells was the same as the adult epidermal LI (7%). The LI for periderm decreased with increasing estimated gestational age (EGA) from 9.5% at 49 days EGA to 0.4% at 85 days EGA. A subpopulation of epithelial cells that retained tritiated thymidine label and that have some of the attributes associated with stem cells has been previously demonstrated in rodents. In order to examine human embryonic and fetal epidermis for the presence of such cells, epidermis from various gestational ages were labeled and grown in organ culture for 21 days. The mean percent label-retaining cells (LRCs) for embryonic and fetal epidermis was determined. Approximately 4% of the embryonic and 2% of the fetal epidermal cells retained label for 21 days in organ culture. Embryonic LRCs were found in the basal and suprabasal layers, but fetal LRCs were found only in the basal layer. The presence of LRCs in human embryonic and fetal epidermis suggests that epithelial cell proliferation in these tissues may be regulated via a stem cell pattern of proliferation.     

正常胎儿及成人皮肤凝集素亲和组织化学研究

用１７种生物素化凝集素研究了２９例胎儿和２３例成人皮肤细胞表面复合糖的糖基的变化。结果表明：在胎儿、成人表皮细胞之间ＢＳＬ－Ｉ、 ＤＢＡ、 ＵＥＡ－Ｉ、 ＳＴＬ、 ＳＪＡ、 ＷＧＡ、 ＤＳＬ，在皮脂腺之间ＲＣＡ－Ｉ、 ＲＣＡ－ 、ＥＣＬ，在汗腺之间 ＷＧＡ、 ＤＳＬ、 ＰＨＡ－Ｅ、 ＣｏｎＡ的凝集素受体阳性率差异有显著性（Ｐ＜０．０５或０．０１）。提示在皮肤分化发育过程中，其细胞表面复合糖的糖基发生了有意义的变化。     

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.