Case Report: COVID-19 Patient With Chief Complaint of Anosmia and Ageusia; a Unique Perspective on Atypical Symptomatology and Management in the Military.

A novel corona virus, severe acute respiratory syndrome coronavirus-2, found in Wuhan, China in December 2019 has since spread to multiple continents and has been implicated in thousands of deaths. This pandemic-causing virus has been initially described (corona virus disease 2019 [COVID-19]) with the presentation of fever, cough, and shortness of breath. The majority of studies published have been conducted on inpatient cases and a shortage of tests has encouraged screening only of patients with classic presentation. A positive COVID-19 case of a healthy military male, with the chief complaint of anosmia and ageusia, instigated local re-evaluation of the screening protocol for possible COVID-19 patients. Multiple studies in Europe have implicated anosmia and ageusia as symptoms associated with COVID-19, and subsequently, anosmia and ageusia have been added to Centers for Disease Control and Prevention screening guidelines as well. There should be a higher index of suspicion when evaluating a patient with high-risk activities, travel, and atypical symptoms. More studies need to be conducted with a healthy outpatient population to further understand this disease and decrease its impact.

Mice that lack thrombospondin 2 display connective tissue abnormalities that are associated with disordered collagen fibrillogenesis, an increased vascular density, and a bleeding diathesis.

Thrombospondin (TSP) 2, and its close relative TSP1, are extracellular proteins whose functions are complex, poorly understood, and controversial. In an attempt to determine the function of TSP2, we disrupted the Thbs2 gene by homologous recombination in embryonic stem cells, and generated TSP2-null mice by blastocyst injection and appropriate breeding of mutant animals. Thbs2-/- mice were produced with the expected Mendelian frequency, appeared overtly normal, and were fertile. However, on closer examination, these mice displayed a wide variety of abnormalities. Collagen fiber patterns in skin were disordered, and abnormally large fibrils with irregular contours were observed by electron microscopy in both skin and tendon. As a functional correlate of these findings, the skin was fragile and had reduced tensile strength, and the tail was unusually flexible. Mutant skin fibroblasts were defective in attachment to a substratum. An increase in total density and in cortical thickness of long bones was documented by histology and quantitative computer tomography. Mutant mice also manifested an abnormal bleeding time, and histologic surveys of mouse tissues, stained with an antibody to von Willebrand factor, showed a significant increase in blood vessels. The basis for the unusual phenotype of the TSP2-null mouse could derive from the structural role that TSP2 might play in collagen fibrillogenesis in skin and tendon. However, it seems likely that some of the diverse manifestations of this genetic disorder result from the ability of TSP2 to modulate the cell surface properties of mesenchymal cells, and thus, to affect cell functions such as adhesion and migration.

Molecular biology of osmoregulation.

The drought of 1983 resulted in some 10 billion dollars in agricultural losses and has focused attention on the vulnerability of our major crops to this devastating form of environmental stress. This article is concerned with the molecular biology of a new class of genes, called osm (osmotic tolerance) genes, that protect bacteria like Escherichia coli against osmotic stress and may work in a similar manner in plants and animals. Osm genes govern the production of a class of molecules, such as betaine and proline, that protect the cell and its constituents against dehydration. These osmoprotectant molecules have been known for many years to accumulate in plants but have only recently been shown to have potent antistress activity for bacteria.

DNA copy number gains in head and neck squamous cell carcinoma.

Gene amplification, a common mechanism for oncogene activation in cancer, has been used as a tag for the identification of novel oncogenes. DNA amplification is frequently observed in head and neck squamous cell carcinoma (HNSCC) and potential oncogenes have already been reported. We applied restriction landmark genome scanning (RLGS) to study gene amplifications and low-level copy number changes in HNSCC in order to locate previously uncharacterized regions with copy number gains in primary tumor samples. A total of 63 enhanced RLGS fragments, indicative of DNA copy number changes, including gains of single alleles, were scored. Enhanced sequences were identified from 33 different chromosomal regions including those previously reported (e.g. 3q26.3 and 11q13.3) as well as novel regions (e.g. 3q29, 8q13.1, 8q22.3, 9q32, 10q24.32, 14q32.32, 17q25.1 and 20q13.33). Furthermore, our data suggest that amplicons 11q13.3 and 3q26.3-q29 may be divided into possibly two and three independent amplicons, respectively, an observation supported by published microarray expression data.

A common uptake system for serotonin and dopamine in human platelets.

Kinetic and pharmacologic properties of uptake of serotonin and dopamine by normal human platelets have been investigated to test whether platelets can be employed as a model system for the reuptake of serotonin and dopamine in brain. Uptake of serotonin into platelets closely resembles reuptake of serotonin into serotonergic neurons. In contrast, uptake of dopamine into platelets appears to be mediated inefficiently via the specific serotonin uptake mechanism, based upon several lines of evidence. Serotonin and dopamine compete with each other, Antidepressant drugs, which are competitive inhibitors of uptake of both of these neurotransmitters, act at the same concentration of drug despite large differences in the Km values. Serotonin antagonists inhibit both serotonin and dopamine uptake. Finally, a serotonin-specific uptake inhibitor (fluoxetine) blocks dopamine, as well as serotonin, uptake.

Basic fibroblast growth factor enhances the coupling of intimal hyperplasia and proliferation of vasa vasorum in injured rat arteries.

Basic fibroblast growth factor (bFGF) is mitogenic for smooth muscle cells (SMC) and angiogenic. We examined the in vivo effects of bFGF in balloon denuded carotid arteries of laboratory rats. bFGF was administered continuously from polymer-based devices at 34 ng/d into the periadventitial space of rat carotid arteries for 2 wk. Intimal hyperplasia was not observed in the absence of injury or with lipopolysaccharide induced endothelial dysfunction. Different degrees of vascular injury produced proportionally more intimal hyperplasia. bFGF increased the intimal hyperplastic response 1.3-fold with severe vascular injury, and 2.4-fold with more mild injury. Increased cell proliferation, not extracellular matrix production, accounted for these effects. Cell density was unchanged for the control and bFGF-treated groups, and the number of proliferating intimal cells at 2 wk rose to an amount equivalent to the increase in mass; 1.9- and 4.0-fold for severe and lesser injury, respectively. The relative ability of heparin to reduce SMC proliferation was not altered by the presence of bFGF.bFGF also induced profound angiogenesis within and surrounding the polymeric releasing device, and in the vasa vasorum immediately around the injured arteries. bFGF's effect on vasa was linearly related to the amount of SMC proliferation within the blood vessel. Thus, the in vivo mitogenic and angiogenic potential of bFGF are coupled, and may be similarly modulated by the products of local injury and/or factors in the vessel wall.

Liver unit admission following paracetamol overdose with concentrations below current UK treatment thresholds.

BACKGROUND: It has been suggested that current UK thresholds for treating paracetamol overdose should be reduced, following case reports of patients developing fatal liver failure after presenting with paracetamol concentrations below these thresholds. AIM: To determine the frequency of severe liver dysfunction following paracetamol overdose when paracetamol concentrations are below current UK antidote thresholds. DESIGN: Retrospective case note review. METHODS: Details were collected from all patients admitted to liver transplant units in Newcastle and Edinburgh with paracetamol-induced hepatotoxicity. RESULTS: Of 696 patients admitted to the two liver units following paracetamol overdose, 14 presented between 4 and 15 h after overdose with paracetamol concentrations below current UK treatment thresholds (estimated annual population rate 0.15/million person-years). Over the period of study, >100 000 presentations with paracetamol overdose would be expected in the catchment populations for these liver units. DISCUSSION: In view of the rarity of this event, this research does not suggest a need to lower the current thresholds for antidotal treatment.

Function of PU.1 (Spi-1), C/EBP, and AML1 in early myelopoiesis: regulation of multiple myeloid CSF receptor promoters.

Our studies of the promoters of the myeloid CSF receptors (M, GM, and G) in cell lines have led to the findings that the promoters are small, and are all activated by the PU.1 and C/EBP proteins. To date, we have only found evidence for involvement of C/EBP alpha, although further experiments will be needed to exclude the role of C/EBP beta and C/EBP delta in receptor gene expression. These studies suggest a model of hematopoiesis (Fig. 2) in which the lineage commitment decisions of multipotential cells are made by the alternative patterns of expression of certain transcription factors, which then activate growth factor receptors which allow those cells to respond to the appropriate growth factor to proliferate and survive. For example, expression of GATA-1 activates its own expression, as well as that of the erythropoietin receptor, inducing these cells to be capable of responding to erythropoietin. Similarly, expression of PU.1 activates its own promoter, and turns on the three myeloid CSF receptors (M, GM, and G), pushing these cells along the pathway of myeloid differentiation. C/EBP proteins, particularly C/EBP alpha, are also critical for myeloid receptor promoter function, and may also act via autoregulatory mechanisms. Murine C/EBP alpha has a C/EBP binding site in its own promoter. Human C/EBP alpha autoregulates its own expression in adipocytes by activating the USF transcription factor. Myeloid genes expressed later during differentiation, such as CD11b, are also activated by PU.1, which is expressed at highest levels in mature myeloid cells, but not by C/EBP alpha, which is downregulated in a differentiated murine myeloid cell line. Consistent with this model are the findings that overexpression of PU.1 in erythroid cells blocks erythroid differentiation, leading to erythroleukemia, and overexpression of GATA-1 in a myeloid line blocks myeloid differentiation. While these findings have provided some framework for understanding myeloid gene regulation, there are a number of critical questions to be addressed in the near future: What is the pattern of expression of the C/EBP proteins during the course of myeloid differentiation and activation of human CD34+ cells? What is the effect of targeted disruption and other mutations of the C/EBP and AML1 proteins on myeloid development and receptor expression? What are the interactions among these three different types of factors (ets, basic region-zipper, and Runt domain proteins) to activate the promoters? What is the effect of translocations, mutations, and alterations in expression of these factors, particularly in different forms of AML?

Differential targets of CpG island hypermethylation in primary and metastatic head and neck squamous cell carcinoma (HNSCC).

Head and neck squamous cell carcinomas (HNSCC) often metastasise to the cervical lymph nodes. It is known for HNSCC as well as other cancers that progression from normal tissue to primary tumour and finally to metastatic tumour is characterised by an accumulation of genetic mutations. DNA methylation, an epigenetic modification, can result in loss of gene function in cancer, similar to genetic mutations such as deletions and point mutations. We have investigated the DNA methylation phenotypes of both primary HNSCC and metastatic tumours from 13 patients using restriction landmark genomic scanning (RLGS). With this technique, we were able to assess the methylation status of an average of nearly 1300 CpG islands for each tumour. We observed that the number of CpG islands hypermethylated in metastatic tumours is significantly greater than what is found in the primary tumours overall, but not in every patient. Interestingly, the data also clearly show that many loci methylated in a patient's primary tumour are no longer methylated in the metastatic tumour of the same patient. Thus, even though metastatic HNSCC methylate a greater proportion of CpG islands than do the primary tumours, they do so at different subsets of loci. These data show an unanticipated variability in the methylation state of loci in primary and metastatic HNSCCs within the same patient. We discuss two possible explanations for how different epigenetic events might arise between the primary tumour and the metastatic tumour of a person.

Intra-epidermal retention of type VII collagen in a patient with recessive dystrophic epidermolysis bullosa.

An infant born with severe blisters on the limbs, face, trunk, and oral mucosa was diagnosed by light and electron microscopy to have recessive dystrophic epidermolysis bullosa. Transmission electron microscopy showed that the basal lamina remained with the epidermis and that the floor of the blister was exposed collagen of the papillary dermis. No banded anchoring fibrils were observed along either the roof or the floor of the blister; however, small filamentous structures, possibly immature anchoring fibrils, extended down from the lamina densa along the blister roof. Some basal and suprabasal keratinocytes contained large vesicles filled with filamentous matrix of variable electron density. Immunofluorescent staining of skin for type VII collagen showed sparse and irregular staining of type VII collagen along the blister roof, and intense intracellular labeling for type VII collagen in clusters of epidermal cells in basal and suprabasal layers. Type VII collagen appeared to be synthesized by keratinocytes but not secreted.

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.

Growth factor and growth factor receptor localization in the hair follicle bulge and associated tissue in human fetus.

The bulge region of the hair follicle has been thought to contain follicular stem cells. The bulge in the human follicle is a collection of undifferentiated cells that is prominent only in the fetal period. Antibodies that recognize epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), EGF receptor, platelet-derived growth factor (PDGF) A and B chains, PDGF alpha and beta receptors, and the low-affinity nerve growth factor receptor (p75) were used to study the bulge and associated mesenchymal cells in this fetal period. Weak EGF and TGF-alpha immunoreactivities were seen in the bulge. Confocal laser scanning microscopic images revealed intracytoplasmic and intranuclear punctate patterns of immunoreactivities in the bulge cells labeled by anti-EGF and anti-TGF-alpha antibodies. All the bulge cells stained strongly for EGF receptor. Cells within the bulge were labeled both with PDGF A chain and with PDGF B chain, although the immunoreactivities were weak in the outermost layer of cells. The follicular sheath was strongly immunoreactive with antibodies against both PDGF alpha and beta receptors. p75 was expressed in mesenchymal cells around the hair follicle and in the lower portion of the bulge. These differential labeling patterns suggested that EGF, TGF-alpha, and nerve growth factor may be involved in regulation of the growth and differentiation of bulge cells and that PDGFs may have related functions in the interaction arising between the bulge and associated tissue during follicle morphogenesis.

Localization of type I human skin collagenase in developing embryonic and fetal skin.

Type I human skin collagenase (HSC-1) was localized in developing embryonic and fetal skin ranging from 6 to 20 weeks estimated gestational age using an antigen-specific, affinity-purified, polyclonal antiserum to HSC-1 and an avidin-biotin alkaline phosphatase procedure. Double immunolabeling with monoclonal antibodies for Factor VIII-related antigen, type IV collagen, and the 68-kilodalton neurofilament subunit was performed using a direct peroxidase procedure. By 8 weeks estimated gestational age, HSC-1 localized to the periderm, the basal cell epidermal keratinocytes, dermal fibroblasts, and surrounding extracellular matrix. At 12 weeks estimated gestational age, HSC-1 immunolabeling showed a continued association with the epidermis and dermis. Dermal and subcutaneous blood vessels and the surrounding extracellular matrix were positive for HSC-1 labeling. HSC-1 staining was also found around developing nerves and in association with dermal fibroblasts. In the developing hair follicle, HSC-1 was present in keratinocytes of the pre-germ, germ, hair peg, and bulbous hair peg. HSC-1 immunoreactivity was also found in association with the hair canal, the bulge, and the dermal papillae, but was absent from the fetal sebaceous gland. These data demonstrate the association of HSC-1 with the development of interfollicular epidermis, the dermal collagenous matrix, the process of angiogenesis, the development of nerves, and hair follicle morphogenesis.

Mutations in the COL3A1 gene result in the Ehlers-Danlos syndrome type IV and alterations in the size and distribution of the major collagen fibrils of the dermis.

Ehlers-Danlos syndrome type IV (EDS type IV) results from heterozygosity for mutations in the COL3A1 gene that encodes the chains of type III procollagen. By using light, transmission, and scanning electron microscopy, we examined skin biopsies from 22 individuals with EDS type IV in whom the COL3A1 mutations had been identified. The most striking changes in EDS type IV were correlated with point mutations that substituted a residue for a glycine near the carboxyl-terminal end of the triple-helical domain of pro alpha1(III). In three cases with the mutation G1012R, G1018V, or G1021E, cells in the dermis had extremely dilated rough endoplasmic reticulum (RER), the dermis was thin, and there was a reduced proportion of collagen although the proportion of elastic fibers appeared increased. In these tissues, collagen fibrils were small (65-80 nm) compared to normal (95-110 nm). Fibrils 80-90 nm in diameter and moderately dilated RER were found with mutations G769R, G373R, and G061E and with exon-skipping mutations of exons 34 and 45. With mutations G034R and G016C and exon-skipping mutations that deleted the sequences of exons 7, 8, 14, 18, 24, and 27, fibrils were more variable in size (85-120 nm). The composite collagen fibrils characteristic of EDS types I and II were not found in EDS type IV. These findings indicate that mutations in the COL3A1 gene have effects on secretion, fibrillogenesis, and skin architecture that reflect the position and nature of the mutation.

Expression of amphiregulin is regulated in cultured human keratinocytes and in developing fetal skin.

Previous studies have indicated that amphiregulin is a major autocrine factor for human keratinocytes. To evaluate the possibilities that amphiregulin could function in fetal skin morphogenesis and contribute to the growth regulation of epidermis, immunostaining with a specific anti-amphiregulin monoclonal antibody was observed at different stages of fetal skin development, and the results were compared with neonatal and adult skin specimens and cultured neonatal keratinocytes. Immunoreactive amphiregulin was readily detected in the periderm and basal epidermal layers of embryonic epidermis but became gradually less detectable in the periderm concurrent with an increase in staining of the spinous layer as it developed during the fetal period. Basal and spinous keratinocyte expression of amphiregulin was predominantly cytoplasmic, but with punctate nuclear foci, and this pattern persisted into the neonatal period. At all developmental stages, epithelial and mesenchymal cells of the follicle were reactive, often in a nuclear pattern. Dermal mesenchymal cells were increasingly reactive in late fetal skin, but the staining decreased postnatally. In adult skin only randomly scattered nuclei of spinous keratinocytes and follicular structures such as the inner root sheath were stained. Examination by scanning laser confocal microscopy of cultured neonatal keratinocytes showed a nonrandom distribution of amphiregulin to the peripheral cytoplasm and plasma membranes at the outer perimeter of cell colonies, with much less reactivity of apposed keratinocyte membranes at interior sites. Nuclei were heterogeneously stained. Amphiregulin reactivity declined at higher cell densities. These data indicate that expression of amphiregulin is regulated in vitro and developmentally during cutaneous morphogenesis.

Structure of the dermal matrix during development and in the adult.

To describe a normal adult dermis is a seemingly simple task considering the diverse microscopic methods available for examination of the tissue, staining procedures to delineate the fibrous and cellular components, and immunolabeling techniques to identify precisely the various fibrous elements. Yet it is not simple because the range of normal in any of the dermal components has never been surveyed. There are well recognized age-related changes in the dermis; the tissue can be modified by environmental insults (e.g., actinic damage) and alterations can occur in tissue of individuals with inherited disorders of connective tissue metabolism, other metabolic diseases (e.g., diabetes) and in those receiving topically applied or systemic medication. From our own experience there is also marked individual variability (at any age) in the connective tissue architecture and its fibrous components. Thus, we are describing the structure of a normal dermis without demonstrating the range of normal in any one of its elements. Reference will occasionally be made to abnormal conditions of the matrix since through these deviations it is possible to understand more about the normal. Structural and biochemical properties of the dermal connective tissue in human embryos and fetuses have been described in a number of studies, but in only a few instances was the goal of the research focused on this problem; instead, fetal tissue was used for comparative purposes in aging studies, or a certain characteristic of the fetal dermis was pointed out along with the description of another structure (e.g., hair follicle). In the few instances where a sequential study was carried out on one matrix component during development, an animal (pig, chick) was selected for the work.

Ontogeny of structural components at the dermal-epidermal junction in human embryonic and fetal skin: the appearance of anchoring fibrils and type VII collagen.

The ontogeny and composition of the dermal-epidermal junction (DEJ) in developing human embryonic and fetal skin was studied at progressive stages of gestation by immunofluorescence microscopy and immunocytochemistry using transmission electron microscopy (TEM). The DEJ of embryonic skin at 5 weeks estimated gestational age (EGA) was a simple basement membrane zone limited to the basal cell plasma membrane, lamina lucida, and lamina densa. A network of reticular collagen fibrils (reticular lamina) was deposited beneath the lamina densa by 6 weeks. Coincident with the onset of increased complexity in epidermal and dermal structure, at the time of the embryonic to fetal transition, the DEJ displayed additional components that were markers of maturation. At 7-8 weeks EGA, fine filamentous structures extended from the DEJ into the reticular lamina. By 9 weeks EGA hemidesmosomes and banded anchoring fibrils were recognizable, although distributed sparsely at the DEJ. With increasing gestational age, these structures displayed greater electron density and structural completeness. By the end of the first trimester, the DEJ appeared ultrastructurally similar to that of mature skin. Weak immunofluorescent labeling demonstrated the presence of type VII collagen at the DEJ by 8 weeks EGA. From 10-12 weeks EGA immunofluorescent labeling of the DEJ for type VII collagen was distinctly punctate, while immunoperoxidase labeling observed by TEM was linear, continuous, and sublamina densa in position. With ongoing gestation the immunofluorescent labeling became increasingly stronger at the DEJ. Thus, type VII collagen was present at the DEJ in the zone immediately beneath the lamina densa, before the appearance of mature anchoring fibrils but coordinate with the appearance of fine filamentous, unbanded structures, and appeared to increase with the development and accumulation of anchoring fibrils.

The appearance of four basement membrane zone antigens in developing human fetal skin.

In order to study the ontogeny of various structural and antigenic components of the basement membrane zone of human skin, we have examined skin specimens from 20 aborted fetuses ranging in gestational ages from 6 to 25 weeks, utilizing light microscopy, transmission electron microscopy, and indirect immunofluorescence with antibodies to bullous pemphigoid antigen, laminin, type IV collagen, and to the antigen defined by KF-1 monoclonal antibody. Both laminin and type IV collagen were detectable as early as 6 weeks of gestational age. In contrast, bullous pemphigoid antigen and the antigen defined by KF-1 antibody were not detectable before 10 weeks and 16 weeks, respectively. The appearance of bullous pemphigoid antigen correlated with stratification of the epidermis and the formation of hemidesmosomes and anchoring fibrils at the basement membrane zone. KF-1 antigen is first expressed when the epidermis is further stratified, hemidesmosomes and anchoring fibrils are present in greater numbers and with increased frequency at the dermal-epidermal junction, and hair follicles have begun to bud downward from the basal layer of the epidermis. Our findings suggest an orderly sequence to the appearance of these basement membrane zone components within human skin.

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.