Dermal extracellular lipid in birds

A light and electron microscopic study of the skin of domestic chickens, seagulls, and antarctic penguins revealed abundant extracellular dermal lipid and intracellular epidermal lipid. Dermal lipid appeared ultrastructurally as extracellular droplets varying from less than 1 micron to more than 25 microns in diameter. The droplets were often irregularly contoured, sometimes round, and of relatively low electron density. Processes of fibrocytes were often seen in contact with extracellular lipid droplets. Sometimes a portion of such a droplet was missing, and this missing part appeared to have been "digested away" by the cell process. In places where cells or cell processes are in contact with fact droplets, there are sometimes extracellular membranous whorls or fragments which have been associated with the presence of fatty acids. Occasionally (in the comb) free fat particles were seen in intimate contact with extravasated erythrocytes. Fat droplets were seen in the lumen of small dermal blood and lymph vessels. We suggest that the dermal extracellular lipid originates in the adipocyte layer and following hydrolysis the free fatty acids diffuse into the epidermis. Here they become the raw material for forming the abundant neutral lipid contained in many of the epidermal cells of both birds and dolphins. The heretofore unreported presence and apparently normal utilization of abundant extracellular lipid in birds, as well as the presence of relatively large droplets of neutral lipid in dermal vessels, pose questions which require a thorough reappraisal of present concepts of the ways in which fat is distributed and utilized in the body.     

Collagen degradation in the rabbit skin during short-term tissue culture

Full thickness rabbit skin explants were cultured on plastic dish for 1 week and the sequential morphological changes were examined daily by light and electron microscopy. During the cultured period, bundles of dermal collagen fibres gradually loosened and were removed from the upper dermis and from the cut margin of the explant, which was covered by a sheet of migrating epidermal cells. In these areas, cells containing phagocytosed collagen fibrils were observed from the 3rd day to the end of the culture period. These cells containing phagocytosed collagen fibrils included dermal fibroblasts and macrophages, epidermal keratinocytes and endothelial cells lining blood vessels. The presence of acid phosphatase activity in vacuoles containing the collagen fibrils suggested that intracellular degradation of collagen was occurring. In addition, extracellular collagen degradation was recognized around fibroblasts and beneath the migrating epidermis by the high collagenolytic activity at these sites. These findings suggest that both intra- and extracellular collagen degradation may participate in collagen removal from dermal connective tissue in cultured skin explants.     

Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians

Alibardi, L. 2011. Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians. —Acta Zoologica (Stockholm) 00 :1–11. The cytology and distribution of chromatophores responsible for skin pigmentation in chelonians is analyzed. Epidermal melanocytes are involved in the formation of dark spots or stripes in growing shelled and non‐shelled skin. Melanocytes rest in the basal layer of the epidermis and transfer melanosomes into keratinocytes during epidermal growth. Dermal melanophores and other chromatophores instead remain in the dermis and form the gray background of the skin. When dermal melanophores condense, they give origin to the dense spots or stripes in areas where no epidermal melanocytes are present. In the latter case, the epidermis and the corneous layer are transparent and reveal the dermal distribution of melanophores and other chromatophores underneath. As a result of this basic process of distribution of pigment cells, the dark areas visible in scales can have a double origin (epidermal and dermal) or a single origin (epidermal or dermal). Xanthophores, lipophores, and a cell containing both pterinosomes and lipid droplets are sparse in the loose dermis while iridophores are rarely seen in the skin of chelonians analyzed in the present study. Xanthophores and lipophores contribute to form the pale, yellow or oranges hues present among the dark areas of the skin in turtles.     

Protein gene product 9.5-immunoreactive nerve fibres and cells in human skin

Summary Sections of human skin were processed according to the indirect immunofluorescence technique with a rabbit antiserum against human protein gene product 9.5 (PGP 9.5). Immunoreactivity was detected in intraepidermal and dermal nerve fibres and cells. The intraepidermal nerves were varicose or smooth with different diameters, running as single processes or branched, straight or bent, projecting in various directions and terminating in the stratum basale, spinosum or granulosum. The density of the intraepidermal nerves varied between the different skin areas investigated. PGP 9.5-containing axons of the lower dermis were found in large bundles. They separated into smaller axon bundles within the upper dermis, entering this portion of the skin perpendicular to the surface. Then they branched into fibres mainly arranged parallel to the epidermal-dermal junctional zone. However, the fibres en route to the epidermis traversed the upper dermis more or less perpendicularly. Furthermore, immunoreactive dermal nerve fibres were found in the Meissner corpuscles, the arrector pili muscles, hair follicles, around the eccrine and apocrine sweat glands and around certain blood vessels. Such fibres were also observed around most subcutaneous blood vessels, sometimes heavily innervating these structures. Numerous weakly-to-strongly PGP 9.5-immunoreactive cells were found both in the epidermis and in the dermis.     

Ultrastructural and immunocytochemical detection of keratins and extracellular matrix proteins in lizard skin cultured in vitro

The present study shows the localization of epidermal and dermal proteins produced in lizard skin cultivated in vitro. Cells from the skin have been cultured for up to one month to detect the expression of keratins, actin, vimentin and extracellular matrix proteins (fibronectin, chondroitin sulphate proteoglycan, elastin and collagen I). Keratinocytes and dermal cells weakly immunoreact for Pan-Cytokeratin but not with the K17-antibody at the beginning of the cell culture when numerous keratin bundles are present in keratinocyte cytoplasm. The dense keratin network disappears after 7-12 days in culture, and K17 becomes detectable in both keratinocytes and mesenchymal cells isolated from the dermis. While most epidermal cells are lost after 2 weeks of in vitro cultivation dermal cells proliferate and form a pellicle of variable thickness made of 3-8 cell layers. The fibroblasts of this dermal equivalent produces an extracellular matrix containing chondroitin sulphate proteoglycan, collagen I, elastic fibers and fibronectin, explaining the attachment of the pellicle to the substratum. The study indicates that after improving keratinocyte survival a skin equivalent for lizard epidermis would be feasible as a useful tool to analyze the influence of the dermis on the process of epidermal differentiation and the control of the shedding cycle in squamates.     

Beneath the minerals, a layer of round lipid particles was identified to mediate collagen calcification in compact bone formation

Astronauts lose 1-2% of their bone minerals per month during space flights. A systematic search for a countermeasure relies on a good understanding of the mechanism of bone formation at the molecular level. How collagen fibers, the dominant matrix protein in bones, are mineralized remains mysterious. Atomic force microscopy was carried out, in combination with immunostaining and Western blotting, on bovine tibia to identify unrecognized building blocks involved in bone formation and for an elucidation of the process of collagen calcification in bone formation. Before demineralization, tiles of hydroxyapatite crystals were found stacked along bundles of collagen fibers. These tiles were homogeneous in size and shape with dimensions 0.69 x 0.77 x 0.2 micro m(3). Demineralization dissolved these tiles and revealed small spheres with an apparent diameter around 145 nm. These spheres appeared to be lipid particles since organic solvents dissolved them. The parallel collagen bundles had widths mostly <2 micro m. Composition analysis of compact bones indicated a high content of apolar lipids, including triglycerides and cholesterol esters. Apolar lipids are known to form lipid droplets or lipoproteins, and these spheres are unlikely to be matrix vesicles as reported for collagen calcification in epiphyseal cartilages. Results from this study suggest that the layer of round lipid particles on collagen fibers mediates the mineral deposition onto the fibers. The homogeneous size of these lipid particles and the presence of apolipoprotein in demineralized bone tissue suggest the possibility that these particles might be of lipoprotein origin. More studies are needed to verify the last claim and to exclude the possibility that they are secreted lipid droplets.     

Reconstitution of human epidermis in vitro is accompanied by transient activation of basal keratinocyte spreading

Frozen human cadaver skin obtained from the skin bank was thawed and incubated in serum-free medium for 1–2 days, after which the original epidermis could be removed mechanically. Transmission electron microscopic observations showed that the dermal matrix remaining behind contained intact bundles of collagen fibrils but no live cells and that a continuous lamina densa persisted in the basement membrane region. Indirect immunofluorescence analyses demonstrated linear staining of the basement membrane region by antibodies against laminin and type IV collagen and discontinuous staining with antibodies against fibronectin. Scanning electron microscopic observations revealed a normal topographical arrangement of dermal matrix papilla and interspersed crypts on the surface of the matrix. Epidermal cells placed on the dermal matrix attached in 1–2 h and spread by 24 h. After 1 week of culture the epidermis was reconstituted, at which time approximately 30% of the epidermal cells were basal keratinocytes and the remainder were more differentiated keratinocytes. A high degree of differentiation of the reconstituted epidermis was shown by the formation of hemidesmosomes along the basement membrane, the formation of desmosomes characterized by intercellular dense lines, and the presence of a cell layer containing keratohyalin granules. At various times during epidermal reconstitution, cells were harvested and tested in short-term assays for adhesion to fibronectin substrata. During the first several days there was a transient activation of basal keratinocyte spreading analogous to the modulation of keratinocyte spreading that we have observed during epidermal reconstitution in vivo.     

On the vascularization and structure of the skin of a Korean bullhead Pseudobagrus brevicorpus (Bagridae, Teleostei) based on its entire body and appendages

To investigate the vascularization and structure of the skin and its relationship to cutaneous respiration in Pseudobagrus brevicorpus , a histological study by light microscopy was carried out on 15 regions of the skin, including eight body regions, six fins and the barbel. The skin consisted of the epidermis, dermis and subcutis in all regions, except for the barbel that had a relatively thin dermis and subcutis. The epidermis was composed of the outermost layer, the middle layer and the stratum germinativum. There were two kinds of gland cells: the unicellular mucus cells and large club cells. The middle layer had a small number of fine blood capillaries accompanied by dermal collagen in all regions; the mean number of blood capillaries ranged from 0.9 to 5.9. The mean diffusion distance between the capillary endothelial cells and the surface of the epidermis ranged from 50.6 to 126.8 μm. Based on these intra-epithelial blood capillaries, the relative surface area of the respiratory epithelium ranged from 0.1 to a maximum value of 1.2%. The dermis lacking scales had collagen bundles arranged parallel to each other, but vertical fiber bundles around the dorso-lateral regions were seen at intervals. Sensory organs such as taste buds, pit organs and lateral canals were found whereby the taste buds in particular were more abundant in the epidermis of the barbel. The vascularization of the skin may be closely related to an additional respiratory system used to deal with an extreme hypoxic condition during dry seasons.     

Distribution of extracellular matrix components in nuchal skin from fetuses carrying trisomy 18 and trisomy 21

We have investigated histologically the elevations of the skin in dorsal and lateral neck (nuchal) regions of human fetuses carrying karyotypes of trisomy 18 (Edwards' syndrome) and trisomy 21 (Down's syndrome). Cavities filled with interstitial fluid were found in the dermis, epidermal basement membrane and occasionally in the epidermis of trisomy-18 fetuses, but were not delineated by an epithelium or basement membrane as judged by the absence of immunostaining for laminin, collagen IV and collagen VII. Dilated vessels were also found at the interface between dermis and subcutis. Neither normal fetal skin nor that of trisomy-21 fetuses contained cavities or dilated vessels. In order to detect possible alterations of the extracellular matrix in trisomy-18 and trisomy-21 skin, the distribution of glycoproteins, glycosaminoglycans and proteoglycans was studied immunohistochemically. In trisomy-21 and control skin, the dermis stained intensely for fibronectin, whereas the subcutis reacted only weakly. In trisomy-18 skin, the stronger staining for fibronectin appeared in the subcutis, and the prevailing collagen type was collagen III, collagen type I being absent. In the skin of trisomy-21 fetuses, collagen VI was more irregularly arranged and densely packed, whereas collagen I was more widely spaced than in normal fetuses. More hyaluronan was present in the dermis and subcutis of trisomy-21 fetuses than in that of trisomy-18 and control fetuses. A correlation seems to exist between undelimited cavities and collagen III in trisomy-18 skin, and between hyaluronan and the specific arrangement of collagen in trisomy-21 skin.Abbreviations bm Basement membrane - ep epidermis - d dermis - sc subcutis - hf hair follicle - c capillary This article is dedicated to Professor Dr. Konrad Märkel on the occasion of his 70^th birthday     

Barnacle bonding: Morphology of attachment of Xenobalanus globicipitis to its host Tursiops truncatus

Xenobalanus globicipitis, a unique type of small pseudo‐stalked barnacle occurs on the appendages of cetaceans, including the common bottlenose dolphin Tursiops truncatus. In this study, we examined attachment structures of X. globicipitis and modifications to the skin of T. truncatus in areas of attachment compared to skin nearby an attachment site. Barnacles and their six calcareous footplates were measured for their length and width. There was a positive correlation of barnacle width and length to footplate width and length. The thickness of the stratum corneum increased significantly in areas of attachment compared to skin nearby a footplate. The mitotic stratum germinativum at the base of the dermal papillae did not change significantly in areas of attachment compared to skin nearby a footplate. The stratum germinativum lining the lateral walls of the dermal papillae was significantly thicker in areas of skin nearby a footplate compared to in areas of attachment. Skin of T. truncatus nearby a footplate, displayed dermal papillae extending from the dermis and pointing roughly perpendicular to the epidermal stratum corneum. At sites of X. globicipitis attachment, the dermal papillae were forced to extend laterally, parallel to the stratum corneum, and the dermal papillae length to width ratio at an attachment site was significantly higher than on skin near an attachment site. Our results show that attachment of X. globicipitis through production of footplates organized into calcareous rings, leads to a thickened stratum corneum of the epidermis, a thinner lateral mitotic stratum germinativum and displaced structures of the upper dermis. These resulting modifications to the epidermis and dermis of the host may add to securing barnacle attachment to its host. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Lipid of normal and regenerating limb tissues of the adult newt, Diemictylus viridescens: acidic and non-acidic lipids, phospholipids, and cholesterol

Cryostat-cut sections of unamputated and amputated-regenerating limbs of the adult newt were examined following the Nile blue test for acidic and non-acidic lipids, the acid hematein and plasmal tests for phospholipids, and a Schultz test for cholesterol. Triglycerides (Nile blue test) are prominent in dermis and macrophages: triglyceride droplets are scattered in epidermis, wound epithelium, and regeneration blastema. Fatty acids (Nile blue test) are present in all tissues of the normal and regenerating limb: nerve myelin contains relatively little free fatty acid, while macrophages appear to contain the least amount of this lipidic substance. Plasmalogens (plasmal test) are prominent in the myelin of nerves, and macrophages: a weak cytoplasmic reaction obtains in the epidermis, subcutaneous glands, striated muscle, tunics of blood vessels, wound epithelium, blastema cells, chondrocytes, perichondrium and periosteum. Mitochondria responding for cephalin, lecithin, and sphingomyelin (acid hematein test) are ubiquitously distributed among the cells and tissues of the normal and regenerating limb. These phosphatides are prominent in nerve myelin, macrophages, and in dermal droplets: a variable response obtains from the myofibrils of striated muscle. Cholesterol (Schultz test) was demonstrated only in nerve myelin and in macrophages associated with injured nerves. Particular attention was paid to the lipid responses of the regeneration blastema, and the conclusion was reached that not all of the lipid previously demonstrated with sudan dyes was characterized by the current series of lipid tests. A modified Nile blue sulfate test that promises greater specificity in distinguishing between acidic and non-acidic lipids is introduced.     

A histochemical study of ultraviolet B irradiation and Origanum hypericifolium oil applied to the skin of mice

Abstract

Ultraviolet (UV) rays cause skin damage. Chronic exposure to UV irradiation causes decreased collagen synthesis, degenerative changes in collagen bundles, accumulation of elastotic material and increased epidermal thickness. Origanum hypericifolium, an endemic Turkish plant, belongs to Lamiaceae family. The main constituents of its oil are monoterpenes including cymene, carvacrol, thymol and γ-terpinene. The effects of undiluted O. hypericifolium oil on UVB irradiated skin of mice were investigated histochemically. Four groups of female BALB/c mice, whose dorsal hair was shaved, were allocated as follows: non-UVB irradiated (Group 1), UVB-irradiated (Group 2), O. hypericifolium oil treated (Group 3), and O. hypericifolium oil treated and UVB irradiated (Group 4). Sections of dorsal skin samples were stained with Mallory's phosphotungstic acid hematoxylin for collagen fibers and Taenzer-Unna orcein for elastic fibers. Sections also were stained with hematoxylin and eosin to measure epidermal thickness. We observed intense staining of collagen and homogeneous, scattered thin elastic fibers in Group 1; scattered and weakly stained collagen and curled, amorphous, accumulate elastic fibers in Group 2; and intense staining of collagen in Groups 3 and 4. Accumulation of elastic fibers in the dermis was unremarkable in Groups 3 and 4. In Groups 3 and 4, O. hypericifolium oil treatment thickened the epidermis. Epidermal thickness was greatest in Group 4. We suggest that O. hypericifolium oil may block UVB induced alterations of collagen and elastic fibers, and increase epidermal thickness.     

Reconstitution of the epidermal basement membrane after enzymatic dermal-epidermal separation of embryonic mouse skin

Pieces of trypsin-isolated 14-day embryonic mouse epidermis were recombined with various living or non-living dermal or non-dermal substrates, in order to analyse the reconstruction of the dermal-epidermal junction. The constitution and ultrastructure of the epidermal basement membrane were characterized by immunolabelling of laminin, type IV collagen and bullous pemphigoid antigen, and by transmission electron microscopy. Trypsin treatment of dorsal skin followed by dermal-epidermal separation does not visibly damage the epidermal basement membrane, which remains attached to the lower face of epidermis. When freshly isolated epidermis is reassociated with dermis, the basement membrane is first degraded during the first 4 h of culture, then reconstituted within 24 h. When epidermis is cultured in isolation the basement membrane disappears within 4 h and is not reconstructed. Epidermis, precultured for 4 h and thus deprived of its basement membrane prior to reassociation, is able to reconstruct an antigenically and ultrastructurally normal basement membrane, when recombined with living or frozen-killed (-20 degrees C) dermis, with muscle tissue, or with a film of fibrous type I collagen. No basement membrane is reconstituted when the epidermis is recombined with heat (100 degrees C) killed dermis. It is concluded that, in the reconstituted epidermal basement membrane, laminin, type IV collagen, bullous pemphigoid antigen, and lamina densa are of exclusive epidermal origin.     

The tentacles of Ichthyophis (Amphibia: Caecilia) with special reference to the skin

The skin of the paired tentacles of Ichthyophis consists of a cornified epidermis of 5–7 layers of epidermal cells, and a glandular dermis of ducted mucous glands, in association with collagen, blood vessels, fibroblasts, granulocytes, sparse melanophores and characteristic laminophores of unknown function. The epidermis is highly innervated at all levels below the stratum corneum by naked neurites, which originate as branches from large unmyelinated nerve bundles (and associated Schwann cells), located sub-epidermally, and which are part of the trigeminal cranial nerve. Myelinated nerves are also present below the epidermis, spatially associated with capillaries and glands. The study of the ultrastructure of the tentacle supports a concept of a sensory function, possibly tactile, though until further information from experimentation is available, any ideas on the specific nature of these sensory activities must remain speculative.     

Quantitative studies on the skin of the paired species of lampreys,Lampetra fluviatilis (L.) and Lampetra planeri (BLOCH)

The number of mucous, club, and granular cells in the epidermis, and the number of rows of subcutaneous adipose cells, as well as the thickness of the epidermis and the dermal collagen layer, have been recorded for the larval and metamorphosing stages of the anadromous parasitic lamprey, Lampetra fluviatilis, and for the larval, metamorphosing, and adult stages of the nonparasitic lamprey, Lampetra planeri. In L. fluviatilis, the mucous cells predominated in all stages but were more abundant in fully metamorphosed individuals than in larvae. During metamorphosis, the number of granular cells increased continuously, whereas the club cells showed little change. Although lampreys do not feed during metamorphosis, there was an increase in the thickness of the epidermis and in the dermal collagen sheath; the latter increase probably foreshadows the increase in activity by the adults. Simultaneously, there is a reduction in the subcutaneous fat layer, which can be attributed to mobilization of lipid as an energy source. Changes similar to those just described for L. fluviatilis were also found in metamorphosing L. planeri. However, the pattern altered markedly during adult stages in this nonparasitic species. There were marked declines in the number of cells, in the thickness of the epidermis, in the width of the collagen sheath, and in the quantity of subcutaneous fat.     

Quantitation of adipose conversion and triglycerides by staining intracytoplasmic lipids with Oil red O.

Cultured 3T3-F442A cells differentiate into adipocytes and accumulate lipid droplets in the cytoplasm. When fat cells are stained with Oil red O, the degree of staining seems to be proportional to the extent of cell differentiation. We report here a fast and simple method to quantitate the extent of adipose conversion by staining the accumulated lipid with Oil red O and determining the amount of extracted dye at 510 nm. The results show that Oil red O specifically stains triglycerides and cholesteryl oleate but no other lipids. This technique is a valuable tool for processing large numbers of cell cultures or samples in which adipose differentiation and/or accumulated triglycerides is to be quantitated.     

Cell culture from lizard skin: a tool for the study of epidermal differentiation

An in vitro system of isolated skin cells has been developed in order to address the understanding on the factors that control the shedding cycle and differentiation of lizard epidermis. The skin from the regenerating lizard tail has been separated in epidermis and dermis, cells have been dissociated, cultivated in vitro, and studied ultrastructurally after 1–30 days of culture condition. Dissociated keratinocytes after 12 days in culture show numerous cell elongations and contain bundles of keratin or sparse keratin filaments. These cells often contain one to three 0.5–3 μm large and dense “keratinaceous bodies”, an organelle representing tonofilament disassembling. Most keratinocytes have sparse tonofilaments in the cytoplasm and form shorter bundles of keratin in the cell periphery. The dissociated dermis mainly consists of mesenchymal cells containing sparse bundles of intermediate filaments. These cells proliferate and form multi-stratified layers and a dermal pellicle in about 2–3 weeks in vitro in our basic medium. Conversely, cultures of keratinocytes do not expand but eventually reduce to few viable cells within 2–3 weeks of in vitro condition. It is suggested that dermal cells sustain themselves through the production of growth factors but that epidermal cells requires specific growth factors still to be identified before setting-up an in vitro system that allows analyzing the control of the shedding cycle in lizards.     

Dermal breaks: migratory cell pathways opened in anuran tadpole skin at climactic metamorphosis

In this report, we studied the formation of breaks in the frog dermis during its remodelling at climactic metamorphosis. This remodelling consisted of detachment of the basement lamella collagen from the epidermis. The detached part, called derived collagen, was progressively fractured by breaks. We focused our attention on dermal cell localization during break formation. Firstly, at early climax, dermal cells were localized inside fractures opened in the derived collagen. Secondly, at the later climax, the fractures became breaks, making room for the dermal cells themselves. Thirdly, in derived collagen of the froglet, the well-opened breaks contained elongated dermal cells. At climax, DAB immunoperoxidase staining of fibronectin revealed a granular pattern at the surface of epidermal and dermal cells. Unexpected staining revealed that the dermal breaks contained fibronectin in the form of vertical lines. The foregoing results suggest that the dermal breaks are migratory pathways for dermal cells in derived collagen remodelled at climax.     

Dorsal skin responses to subchronic ultraviolet B (UVB)-irradiation in Wistar-derived hypotrichotic WBN/ILA-Ht rats

Dorsal skin responses to a subchronic UVB-irradiation (10kJ/m2/rat /day), were examined in Wistar-derived hypotrichotic WBN/ILA-Ht rats for up to 3 months. Hyperplasia of epidermal cells and hair follicle epithelial cells as well as parakeratosis developed at 1 month and progressed thereafter, resulting in a prominent epidermis thickening and formation of epidermal ingrowths projecting into the dermis. At the same time, the percentage of proliferating cell nuclear antigen (PCNA)-positive epidermal cells significantly increased after I month. In some portions of the hyperplastic epidermis, especially of the epidermal ingrowths, keratinocytes were somewhat pleomorphic and migrated into the dermis. In the upper dermis, edema with capillary congestion, mast cell infiltration and fibroblast proliferation developed at I month, and the intensity of edema and the number of dermal mast cells was most prominent at 3 months. Edema spread to the epidermis, resulting in intercellular edema and subsequent dissociation of epidermal cells. Degeneration of collagen fibers was also detected in the upper dermis, especially beneath the epidermis. In addition, although not significant because of a large individual difference, the serum IgE concentration, showed a tendency to increase after 2 months. The present study clarified the characteristics of the dorsal skin responses to a subchronic UVB-irradiation in rats.     

FORMATION AND ORIGIN OF BASAL LAMINA AND ANCHORING FIBRILS IN ADULT HUMAN SKIN

The purpose of this investigation was to study the formation and origin of basal lamina and anchoring fibrils in adult human skin. Epidermis and dermis were separated by "cold trypsinization." Viable epidermis and viable, inverted dermis were recombined and grafted to the chorioallantoic membrane of embryonated chicken eggs for varying periods up to 10 days. Basal lamina and anchoring fibrils were absent from the freshly trypsinized epidermis before grafting although hemidesmosomes and tonofilaments of the basal cells remained intact. Basal lamina and anchoring fibrils were absent from freshly cut, inverted surface of the dermis. Beginning 3 days after grafting, basal lamina was noted to form immediately subjacent to hemidesmosomes of epidermal basal cells at the epidermal-dermal interface. From the fifth to the seventh day after grafting, basal lamina became progressively more dense and extended to become continuous in many areas at the epidermal-dermal interface. Anchoring fibrils appeared first in grafts consisting of epidermis and viable dermis at five day cultivation and became progressively more numerous thereafter. In order to determine the epidermal versus dermal origin of basal lamina and anchoring fibrils, dermis was rendered nonviable by repeated freezing and thawing 10 times followed by recombination with viable epidermis. Formation of basal lamina occurred as readily in these recombinants of epidermis with freeze-thawed, nonviable dermis as with viable dermis, indicating that dermal viability was not essential for synthesis of basal lamina. This observation supports the concept of epidermal origin for basal lamina. Anchoring fibrils did not form in recombinants containing freeze-thawed dermis, indicating that dermal viability was required for anchoring fibrils formation. This observation supports the concept of dermal origin of anchoring fibrils.