Impact of tropomyosin isoform composition on fast skeletal muscle thin filament regulation and force development.

Tropomyosin (Tm) plays a central role in the regulation of muscle contraction and is present in three main isoforms in skeletal and cardiac muscles. In the present work we studied the functional role of α- and ßTm on force development by modifying the isoform composition of rabbit psoas skeletal muscle myofibrils and of regulated thin filaments for in vitro motility measurements. Skeletal myofibril regulatory proteins were extracted (78%) and replaced (98%) with Tm isoforms as homogenous ααTm or ßßTm dimers and the functional effects were measured. Maximal Ca(2+) activated force was the same in ααTm versus ßßTm myofibrils, but ßßTm myofibrils showed a marked slowing of relaxation and an impairment of regulation under resting conditions compared to ααTm and controls. ßßTm myofibrils also showed a significantly shorter slack sarcomere length and a marked increase in resting tension. Both these mechanical features were almost completely abolished by 10 mM 2,3-butanedione 2-monoxime, suggesting the presence of a significant degree of Ca(2+)-independent cross-bridge formation in ßßTm myofibrils. Finally, in motility assay experiments in the absence of Ca(2+) (pCa 9.0), complete regulation of thin filaments required greater ßßTm versus ααTm concentrations, while at full activation (pCa 5.0) no effect was observed on maximal thin filament motility speed. We infer from these observations that high contents of ßßTm in skeletal muscle result in partial Ca(2+)-independent activation of thin filaments at rest, and longer-lasting and less complete tension relaxation following Ca(2+) removal.

Physiological function and transplantation of scaffold-free and vascularized human cardiac muscle tissue.

Success of human myocardial tissue engineering for cardiac repair has been limited by adverse effects of scaffold materials, necrosis at the tissue core, and poor survival after transplantation due to ischemic injury. Here, we report the development of scaffold-free prevascularized human heart tissue that survives in vivo transplantation and integrates with the host coronary circulation. Human embryonic stem cells (hESCs) were differentiated to cardiomyocytes by using activin A and BMP-4 and then placed into suspension on a rotating orbital shaker to create human cardiac tissue patches. Optimization of patch culture medium significantly increased cardiomyocyte viability in patch centers. These patches, composed only of enriched cardiomyocytes, did not survive to form significant grafts after implantation in vivo. To test the hypothesis that ischemic injury after transplantation would be attenuated by accelerated angiogenesis, we created "second-generation," prevascularized, and entirely human patches from cardiomyocytes, endothelial cells (both human umbilical vein and hESC-derived endothelial cells), and fibroblasts. Functionally, vascularized patches actively contracted, could be electrically paced, and exhibited passive mechanics more similar to myocardium than patches comprising only cardiomyocytes. Implantation of these patches resulted in 10-fold larger cell grafts compared with patches composed only of cardiomyocytes. Moreover, the preformed human microvessels anastomosed with the rat host coronary circulation and delivered blood to the grafts. Thus, inclusion of vascular and stromal elements enhanced the in vitro performance of engineered human myocardium and markedly improved viability after transplantation. These studies demonstrate the importance of including vascular and stromal elements when designing human tissues for regenerative therapies.

Long-term volumetric analysis of vestibular schwannomas following stereotactic radiotherapy: Practical implications for follow-up.

BACKGROUND AND PURPOSE: Transient tumor swelling is a well-known phenomenon following radiotherapy for vestibular schwannomas (VS). We analyzed the long-term volumetric changes of VS after LINAC radiosurgery, in order to determine a time interval during which a true tumor progression can be distinguished from a pseudoprogression. METHODS: Among 63 patients with VS treated by one fraction or fractionated radiotherapy, we selected 52 of them who had a minimal follow-up of 5 years. Maximal axial diameter and three-dimensional tumor volume were measured on each MRI scan. Volume changes were interpreted using different error margins ranging from 10 to 20%. Patients were categorized according to the tumor evolution pattern over time. RESULTS: Median follow-up was 83 months. One tumor (1.9%) remained stable and 26.9% had continuous shrinkage. Applying an error margin of 13%, a transient tumor enlargement was observed in 63.5% of patients, with a first peak at 6-12 months and a late peak at 3-4 years. A true progression was suspected in 4 (7.7%) patients, tumor regrowth starting after the 3rd or 4th year post-treatment. Only one patient required salvage radiotherapy. CONCLUSION: Transient swelling of VS following radiotherapy is generally an early phenomenon but may occur late. In the first 5 years, a true tumor progression cannot be differentiated from a pseudoprogression. A significant tumor expansion observed on 3 sequential MRI scans after the 3rd year may be suggestive of treatment failure. Long-term follow-up is therefore mandatory and no decision of salvage treatment should be made until the 6th year.

Regulation of hepatokine gene expression in response to fasting and feeding: Influence of PPAR-α and insulin-dependent signalling in hepatocytes.

AIM: In hepatocytes, the peroxisome proliferator-activated receptor (PPAR)-α and insulin receptor (IR) are critical for transcriptional responses to fasting and feeding, respectively. The present report analyzes the effects of nutritional status (fasting vs feeding) on the expression of a large panel of hepatokines in hepatocyte-specific PPAR-α (Pparαhep-/-) and IR (IRhep-/-) null mice. METHODS: Pparαhep-/- and IRhep-/- mice, and their wild-type littermates, were subjected to fasting or feeding metabolic challenges, then analyzed for hepatokine gene expression. Experiments were conducted in mice of both genders. RESULTS: Our data confirmed that PPAR-α is essential for regulating fasting-induced Fgf21 and Angptl4 expression. In mice lacking PPAR-α, fasting led to increased Igfbp1 and Gdf15 gene expression. In the absence of hepatic IR, feeding induced overexpression of Igfbp1, follistatin (Fst) and adropin (Enho), and reduced activin E (Inhbe) expression. Gender had only a modest influence on hepatokine gene expression in the liver. CONCLUSION: The present results highlight the potential roles of hepatokines as a class of hormones that substantially influence nutritional regulation in both female and male mice.

Cooperative cross-bridge activation of thin filaments contributes to the Frank-Starling mechanism in cardiac muscle.

Myosin cross-bridges play an important role in the regulation of thin-filament activation in cardiac muscle. To test the hypothesis that sarcomere length (SL) modulation of thin-filament activation by strong-binding cross-bridges underlies the Frank-Starling mechanism, we inhibited force and strong cross-bridge binding to intermediate levels with sodium vanadate (Vi). Force and stiffness varied proportionately with [Ca(2+)] and [Vi]. Increasing [Vi] (decreased force) reduced the pCa(50) of force-[Ca(2+)] relations at 2.3 and 2.0 microm SL, with little effect on slope (n(H)). When maximum force was inhibited to approximately 40%, the effects of SL on force were diminished at lower [Ca(2+)], whereas at higher [Ca(2+)] (pCa < 5.6) the relative influence of SL on force increased. In contrast, force inhibition to approximately 20% significantly reduced the sensitivity of force-[Ca(2+)] relations to changes in both SL and myofilament lattice spacing. Strong cross-bridge binding cooperatively induced changes in cardiac troponin C structure, as measured by dichroism of 5' iodoacetamido-tetramethylrhodamine-labeled cardiac troponin C. This apparent cooperativity was reduced at shorter SL. These data emphasize that SL and/or myofilament lattice spacing modulation of the cross-bridge component of cardiac thin-filament activation contributes to the Frank-Starling mechanism.

2-deoxy-ATP enhances contractility of rat cardiac muscle.

To investigate the kinetic parameters of the crossbridge cycle that regulate force and shortening in cardiac muscle, we compared the mechanical properties of cardiac trabeculae with either ATP or 2-deoxy-ATP (dATP) as the substrate for contraction. Comparisons were made in trabeculae from untreated rats (predominantly V1 myosin) and those treated with propylthiouracil (PTU; V3 myosin). Steady-state hydrolytic activity of cardiac heavy meromyosin (HMM) showed that PTU treatment resulted in >40% reduction of ATPase activity. dATPase activity was >50% elevated above ATPase activity in HMM from both untreated and PTU-treated rats. V(max) of actin-activated hydrolytic activity was also >50% greater with dATP, whereas the K(m) for dATP was similar to that for ATP. This indicates that dATP increased the rate of crossbridge cycling in cardiac muscle. Increases in hydrolytic activity were paralleled by increases of 30% to 80% in isometric force (F(max)), rate of tension redevelopment (k(tr)), and unloaded shortening velocity (V(u)) in trabeculae from both untreated and PTU-treated rats (at maximal Ca(2+) activation), and F-actin sliding speed in an in vitro motility assay (V(f)). These results contrast with the effect of dATP in rabbit psoas and soleus fibers, where F(max) is unchanged even though k(tr), V(u), and V(f) are increased. The substantial enhancement of mechanical performance with dATP in cardiac muscle suggests that it may be a better substrate for contractility than ATP and warrants exploration of ribonucleotide reductase as a target for therapy in heart failure.

Reactivity of Langerhans cells in human reconstructed epidermis to known allergens and UV radiation.

Epidermal Langerhans cells are the outmost guards of our immune defence system. These cells are directly involved in phenomena such as contact hypersensitivity and UV-induced immunosuppression. Some years ago we succeeded in introducing CD34(+)-derived Langerhans cells into a reconstructed human epidermis. Here we describe their reactivity after topical exposure of the reconstructed epidermis to known allergens, allergen-inducible cytokines, irritants and UV irradiation. Exposure to allergens for 24 h resulted in an activated appearance of the Langerhans cells and in some cases a decrease in their number. Concomitantly, IL-1beta and CD86 mRNA over-expressions were detected in the reconstructed epidermis. A topical treatment with TNF-alpha or IL-1beta revealed that both cytokines induced an activated appearance of the Langerhans cells as early as 4 h following application. Irritants had no effect on the integrated Langerhans cells. Exposure of the reconstructed epidermis to Solar Simulated Radiation caused a dramatic decrease in the number of Langerhans cells and a loss of dendricity in the remaining cells 24 h after irradiation. The topical application of a large spectrum UVA/B filter before irradiation prevented these UV-induced alterations. In our hands, this model provides a promising tool to evaluate the sensitization potential of new compounds and to validate the efficacy of sunscreens to prevent UV-induced immunosuppression.

The culture of skin. A review of theories and experimental methods.

Two main criticisms can be leveled against the standard methods of skin culture: they are poorly quantifiable and the cultured cell populations are heterogeneous. A new technique based mainly on enzymatic dissociation allows specific cell types to be extracted from the skin before cultivation. In this way, separate cultures of epidermal keratinocytes and dermal fibroblasts can be obtained from the same piece of skin. These purified systems have been used to study the kinetics of epidermal cell growth and to quantify the effect of various chemically defined substances on the growth and differentiation of keratinocytes. With further refinements in technique, purified populations of melanocytes can be extracted. The co-culture of pigmented melanocytes with albino keratinocytes has been proposed as a model to study pigment donation in vitro. The usual organ culture technique, including the use of large explants of skin immersed in the culture fluid, has been modified to show that adult human skin partially regenerates in vitro and that mitotic activity goes on for months in the regenerated epidermis. The use of nucleic acid hybridization techniques, combined with skin cell cultures from human tumors, opens new avenues of research on human cancer.

Methods for cultivation of keratinocytes with an air-liquid interface.

In ordinary cultures, cells are grown on artificial substrates and immersed in culture medium. In vivo, interfollicular epidermal cells grow on the basement membrane and are exposed to air. In a first effort to render the culture of these cells more physiological it seems legitimate to raise the cultured cells to the air-medium interface. Epidermal cells can be raised by the use of collagen gels maintained on a rigid support. They can also be grown on nitrocellulose filters coated with collagen or coated with a basement-membrane equivalent (BME) previously deposited by bovine corneal endothelial cells. By raising the cultures to the air-medium interface there is some evidence of a more complete differentiation, as evaluated by morphologic criteria. However, biochemically, the raising of the cultures does not seem to induce the synthesis of those keratin polypeptides which are not expressed in immersed cultures. Epidermal cells can also be raised by culturing them on dermal substrates or dermal equivalents. When they were cultured on inverted dead pig skin, epidermal cells synthesized membrane-coating granules (MCG). MCG were not found in immersed controls. By culturing epidermal-cell suspensions on dead deepidermized dermis (DED), all morphologic markers of differentiation were seen except the keratin pattern. In addition, partial reexpression of high-molecular-weight keratin polypeptides occurred. However, the complete expression of keratins by cultured cells depends on the filtering action of the dermal substrate (the cultures are fed from underneath) more than on exposure to the air-liquid interface. In summary, several methods are available to culture epidermal cells at the air-liquid interface that are of interest in an investigation of the response of these cells to epigenetic influences.

Localization of bullous pemphigoid antigen (BPA) in isolated human keratinocytes.

In early studies, the bullous pemphigoid antigen (BPA) has been localized extracellularly in the lamina lucida in the basement membrane zone. However, trypsin-dissociated basal cells can be tagged with bullous pemphigoid sera (BPS). By immunofluorescence, BPA appears located at the dermal pole of basal cells (BC). This may indicate that when BC are separated from the underlying matrix molecules, chunks of BPA remain attached to them. In the present study, fresh crude initial suspensions (CIS) of epidermal cells were prepared by trypsin-EDTA dissociation. The cells were smeared and air-dried. Polar fluorescent cells (i.e., BC) amounted to 42% +/- 7%. CIS were then passed through a fluorescence-activated cell sorter (FACS). In the fluorescent-positive fractions selected by FACS, 34% +/- 7% only of the BC were present. FACS-negative cell fractions were smeared on glass slides, air-dried, and restained with BPS + fluorescein isothiocyanate; 66% +/- 10% of BC were present in these fractions. This is evidence that trypsin-isolated BC comprise two subpopulations: one with BPA directly accessible, the other not. Viability tests and tissue culture studies indicated that the FACS-positive cell fractions were not viable. BPA was extracted from CIS, FACS-positive, and FACS-negative fractions and immunoblotted against BPS. Identical blots were found. FACS-negative cell fractions were treated with heparitinase, nitrous acid, methanol-chloroform, or EDTA without modifying the number of reacting cells. When BC were treated with Triton X-100 or permeabilized by successive freezings and thawings, the number of positive cells became comparable to those obtained by air-drying smears. Finally, BPA was localized on the intracellular part of hemidesmosomes of BC by immunoelectron microscopy. To see whether BPA was also present extracellularly, suction blisters were raised in minipigs and BPS injected into the blister cavity. BPA was found attached to all cells of the cellular roof but not to the dermal base of the blisters. When pieces of skin kept overnight in cold trypsin were reacted with BPS, BPA was found on both sides (epidermal and dermal) of the split. It is concluded that BPA has two localizations: one extracellular, essentially labile which accumulates at the dermal-epidermal junction; the other essentially stable which remains on the intracellular part of basal cell hemidesmosomes and which can be detected after permeabilization of the cells.

Onset of epidermal differentiation in rapidly proliferating basal keratinocytes.

Stratified epithelia such as epidermis are classically considered to comprise 2 cell compartments, one consisting of undifferentiated proliferative cells occupying the basal layer, and the other consisting of differentiated postmitotic cells occupying the suprabasal layers. It is also generally assumed that the 58K basic-50K acidic couple of keratins is expressed in basal cells, while the 67K basic-56K acidic couple appears in suprabasal cells. In the present work we demonstrate that the population of basal keratinocytes is heterogeneous, since 8% of them are found to express the 67-56K "suprabasal" set of keratins. The morphology of these transitional cells suggests that they are in the process of detaching from the basement membrane to move upward to the epidermis. Cytoflow-fluorometric studies showed that the fraction of cells in S plus G2/M phases is 4 times higher in transitional keratinocytes than in basal or suprabasal keratinocytes. Altogether, these results suggest that the onset of terminal differentiation occurs in human epidermis in a subpopulation of keratinocytes which are still located in the basal layer, and that a transient increase in proliferation occurs when the cells engage in terminal differentiation and are ready to move toward the suprabasal layers.

Migration of Langerhans cells into the epidermis of human skin grafted into nude mice.

In a previous study, it was demonstrated that human Langerhans cells (LC) are preserved in human skin grafted onto a nude mouse. Moreover, although it was observed that mouse LC of the host invade skin grafts from allogeneic mouse or rat, they do not penetrate in human skin grafts. In most of the human skin equivalent systems produced in vitro, LC appear to be lost. The present study was designed to investigate whether the mouse LC will repopulate a human skin equivalent. For this purpose, two different systems of skin equivalent have been grafted into the nude mouse. They were composed of human keratinocytes deposited on dead human dermis, or on lattice composed of human fibroblasts embedded in type I collagen. At different times after grafting, the presence of LC in the transplants was assayed either by indirect immunofluorescence or by electron microscopy. Indirect immunofluorescence was performed on frozen sections or on epidermal sheets with anti-Ia, anti-HLA-DR, or OKT6 antibodies. It was observed that, at 2 months after grafting, Ia(+) HLA-DR(-) OKT6(-) cells are present in grafted human epidermis. Moreover, LC with typical Birbeck granules are also detected by electron microscopy. It could be concluded, from this study, that mouse LC can repopulate human epidermis devoid of human LC.

Keratinocytes synthesize basal-lamina proteins in culture.

On histologic vertical sections of skin, the epidermis is separated from the dermis by an amorphous thin membrane, the basal lamina. Ultrastructurally, the basal lamina is composed of four areas, including the basal-cell plasma membrane and hemidesmosomes, the lamina lucida, the lamina densa, and the sub-lamina densa fibrillar region. In culture, epidermal keratinocytes are able to produce hemidesmosomes, lamina lucida, and lamina densa. There is no evidence that cultured keratinocytes can produce sub-lamina densa fibrils. Biochemically, the lamina lucida contains two major glycoproteins. One, the bullous pemphigoid antigen, is synthesized by epidermal keratinocytes in vitro. These cells also synthesize laminin, the other glycoprotein of lamina lucida. At the interface between lamina lucida and lamina densa there is probably a heparan sulfate proteoglycan. Whether this proteoglycan is produced by keratinocytes in culture is not known, but the possibility can be considered. Lamina densa contains collagen IV, and this collagen is synthesized by keratinocytes in culture. However, cultured keratinocytes may also synthesize collagen types I, III, and V. Type V is associated with the basal lamina, but its exact location is unknown. Types I and III (if they are produced in vivo) would be situated in the sub-basal lamina region. The problem of fibronectin remains unsolved. There is "some" fibronectin in the lamina lucida, but its origin is not clear.

Bullous pemphigoid antigen synthesized in vitro by human epidermal cells.

Cultured living human epidermal cells migrating on the surface of irradiated non-viable pig dermis, were found to produce bullous pemphigoid antigen at the epidermis-pig dermal junction between days 10 and 50 in culture. In certain series, the antigen was detected within the cytoplasm of the basal cells as well. These findings suggest that the bullous pemphigoid antigen is synthesized by epidermal cells.

Integration of Langerhans cells into a pigmented reconstructed human epidermis.

The majority of in vitro reconstructed human epidermis is composed of keratinocytes only. Recently, the introduction of melanocytes into epidermal reconstructs has enlarged their field of application. The completion of reconstructed epidermis by introducing Langerhans cells remained an important challenge because Langerhans cells, unlike the other epidermal cell types, cannot be subcultured and expanded. To solve this problem, we used cord blood-derived CD34+ hematopoietic progenitors. Seeding these cells, after induction of their differentiation by granulocyte macrophage-colony stimulating factor and tumor necrosis factor-alpha, onto a reconstructing epidermis, composed of keratinocytes and melanocytes, gives rise to a pigmented epidermis with melanocytes in the basal layer and resident epidermal Langerhans cells located suprabasally. Interestingly, the same result was obtained by co-seeding a mixture of keratinocytes, melanocytes, and nondifferentiated CD34+ hematopoietic progenitors on the dermal equivalent, indicating that keratinocytes provide the environmental conditions for hematopoietic progenitors to differentiate into resident epidermal Langerhans cells, expressing major histocompatibility complex class II molecules, CD1a antigen, and Birbeck granules.

Skin explant cultures: expression of cytoplasmic differentiation antigens in outgrowth cells.

In vivo, keratinocyte cytoplasmic antigens linked to keratinization have been traced with 2 distinct types of antibodies found in human sera. One type of antibody is specific for the basal cell compartment of keratinocytes while the other one is specific for upper keratinocytes. Using these markers, we followed a well-defined, in vitro human keratinocyte culture system that produces a keratinizing epithelial cell outgrowth juxtaposed to dead dermal substrate for the in vitro expression of keratinocyte cytoplasmic antigens. These antigens were found to be expressed in vitro independently from dermal influences. Their chronology, localization and topography in culture matched the in vivo situation.

Pemphigoid, pemphigus and Pr antigens in adult human keratinocytes grown on nonviable substrates.

Isolated adult human keratinocytes were grown either on plastic coverslips or a nonviable basement membrane surface containing intact laminin, type IV and V collagens, and heparan sulfate proteoglycan and examined by indirect immunofluorescence for the expression of bullous pemphigoid, pemphigus and Prlh antigens. Initial cell suspensions had a mean of 23% and 30%, respectively, of bullous pemphigoid and Prlh positive staining cells, while those stained with pemphigus serum were usually negative (19 of 22 series). Pemphigus antigen was expressed as intercellular staining between keratinocytes within 24 hr in both cultures on plastic and basement membrane. Likewise, Prlh antigen was expressed within 24 hr as a homogeneous cytoplasmic fluorescence leaving the basement membrane zone unstained. In contrast, pemphigoid antigen was expressed as a linear fluorescent band at the basement membrane zone between days 3 and 4 of culture. Systematic cell counts of bullous pemphigoid antigen positive cells from trypsin disrupted primary cultures made on plastic over time showed a nadir (8%) of positive cells in early cultures after which the percentage rapidly rose to a peak of 58% between days 14 and 21 of culture. In subcultures repeatedly disrupted at short intervals, the percentage of bullous pemphigoid positive cells remained low when compared to those interrupted and passaged over longer intervals. The percentage of bullous pemphigoid antigen bearing cells in culture over time is similar, but not identical, to the percentage of basal cells and is related to the age and known growth kinetics of the cultures system. Bullous pemphigoid, pemphigus and Prlh antigens are synthesized by the epidermal cell whether cultured on basement membrane or plastic.

The role of fibroblasts in dermal vascularization and remodeling of reconstructed human skin after transplantation onto the nude mouse.

The vascularization and the dermal remodeling of two different types of human skin reconstructed "in vitro" and grafted onto the nude mouse were studied. They were composed of human keratinocytes grown either on a human acellular deepidermized dermis (DED), or on a lattice composed of human fibroblasts embedded in bovine type I collagen, a living dermal equivalent (LDE). At different stages after grafting, the transplants were harvested and processed for an immunohistological study with species-specific and non-species-specific antibodies. At one month after grafting, the two types of grafted dermis contained blood vessels whose vascular basement membranes were labeled with a mouse-specific anti-type IV collagen antibody. With an antibody specific for human type IV collagen, a constant labeling of the vascular basement membrane was only observed in the LDE containing fibroblasts. In the DED, a constant association of the mouse endothelial cells with human type IV collagen was observed at early stages after grafting. At later stages, the human type IV collagen progressively disappeared. On the other hand, the dermal-epidermal junction underneath the human epidermis contained human type IV collagen in the two types of reconstructed skin. Labeling with the species-specific antibodies directed against human or murine type I collagen showed that the ratio murine type I collagen versus human type I collagen increased with time, suggesting that the DED is progressively invaded by mouse fibroblasts that produce the mouse collagen. On the other hand, in the LDE, the preexisting bovine type I collagen became progressively undetectable while both human type I collagen and elastic fibers were deposited by numerous human fibroblasts. Mouse type I collagen was not detected. Altogether, these observations made by grafting human skin reconstructed "in vitro" onto the nude mouse should be interesting for evaluating the usefulness of grafting a dermal substrate together with the epidermal sheet in the treatment of burns.

Invited Review: plasticity and energetic demands of contraction in skeletal and cardiac muscle.

Numerous studies have explored the energetic properties of skeletal and cardiac muscle fibers. In this mini-review, we specifically explore the interactions between actin and myosin during cross-bridge cycling and provide a conceptual framework for the chemomechanical transduction that drives muscle fiber energetic demands. Because the myosin heavy chain (MHC) is the site of ATP hydrolysis and actin binding, we focus on the mechanical and energetic properties of different MHC isoforms. Based on the conceptual framework that is provided, we discuss possible sites where muscle remodeling may impact the energetic demands of contraction in skeletal and cardiac muscle.

Gene expression profiles of three different models of reconstructed human epidermis and classical cultures of keratinocytes using cDNA arrays.

The gene expression profiles of three different models of reconstructed human epidermis were analyzed in a comparative study using cDNA array technology. The study also included normal human subconfluent keratinocytes cultured on plastic. Arrays were custom-made and comprised 504 known genes related to cutaneous biology. The gene expression profiles of the three reconstructed epidermis models shared 86% similarity; only 22 of the 504 examined genes showed a different expression level. A comparison of the 3D models with keratinocyte cultures on plastic dishes revealed a set of six genes with a considerably higher expression in the 3D models. These genes were keratin 1, corneodesmosin, filaggrin, loricrin, calmodulin-like skin protein and caspase 14, all related to keratinocyte terminal differentiation. The reported data may contribute to a better understanding and characterization of reconstructed epidermal models and may also serve as established references for investigations related to epidermal differentiation and proliferation.