Periderm Layer Research Articles

Isolation and Characterization of a Putative Keratin-Associated Protein Gene Expressed in Embryonic Skin of Mice

Embryonic mouse skin undergoes substantial morphologic changes from 13 days post-coitus (dpc) to 16 dpc, i.e., from simple layers of epithelial cells and periderm at 13.5 dpc to almost fully differentiated stratified epithelium with the rudiments of hair follicles at 16.5 dpc. Using RNA differential display, we isolated a gene involved in the development of mouse epidermis. This gene, tentatively designated as 4C32, encodes 197 amino acids containing six direct repeats of 10 amino acids with the CQ motif. The repetitive structure with the CQ motif is seen in most keratin-associated protein families, which are known to be specifically expressed in hair follicles. 4C32 is expressed in the outermost layer of the embryonic epidermis at 15.5 and 16.5 dpc, and abruptly disappears at 17.5 dpc, suggesting that 4C32 is expressed in the periderm. The periderm is a superficial layer of embryonic epidermis, and is known to disappear at 17 dpc in mouse embryos. The 4C32 transcripts were also detected in the developing and matured tongue tissues and in the tail scale, but not at any stage in hair follicles.

Glycogen Distribution in Relation to Epidermal Cell Differentiation During Embryonic Scale Morphogenesis in the Lizard Anolis lineatopus

AbstractThe differentiation of the epidermis during scale morphogenesis in the lizard Anolis lineatopus has been studied by autoradiographic and immunocytochemical techniques and by electron microscopy, in relation to mitotic activity and to the distribution of glycogen. The flat embryonic epidermis of the early embryo is transformed into symmetric epidermal papillae which progressively become asymmetric and eventually form scales with stratified epidermal and peridermal layers. Papilla asymmetrization and epidermal stratification derive from cell hypertrophy and multiplication in the “basal hypertrophic layer of the forming outer side of scales” (BLOS). Glycogen is scarce or absent during early stages of epidermis development. In the dermis no glycogen is found at any stage of scale morphogenesis. Glycogen particles 25–40 nm in size accumulate in hypertrophic basal cells and peridermal cells during scale development. Conversely cells in the forming inner side of scales do not accumulate glycogen, divide less frequently than in the outer side and do not form a β–keratinized layer. It is suggested that an osmotic effect related to glycogen deposition causes increased hydration of the BLOS, whose cells become swollen and contribute to the asymmetrization of the epidermal papillae. Glycogen decreases in suprabasal differentiating cells and disappears from the BLOS at the stage of complete keratinization of the scale, around the period of hatching. Terminal differentiation in the peridermis and suprabasal epidermal layers takes place by cell flattening and condensation of the nucleus and cytoplasm as typical for apoptotic cells.

Mouse insulin-like growth factor binding protein-6: expression, purification, characterization and histochemical localization

The mitogenic and metabolic activities of insulin-like growth factors (IGF) are modulated by a family of six high affinity IGF binding proteins (IGFBPs). This study describes the expression of the mouse IGFBP-6 which is unique among IGFBPs in its preferential binding of IGF II, in insect cells using the baculovirus system. The purified, O-glycosylated IGFBP-6 was functional as shown by IGF binding and by inhibition of IGF II-stimulated DNA synthesis in human fibroblasts. Specific antibodies generated in chicken against the recombinant IGFBP-6 were used for Western blotting analysis and immunohistochemistry. Strong immunoreactivity was found in ossifying bones of the cranial base, in cell clusters of the pancreas anlage, in the trigeminal ganglion, on myoblasts, on motoneurons of the spinal cord of embryonic mice. In tissues of adult mouse, strong IGFBP-6 immunostaining was present in epidermal and peridermal layers of the skin, in meningeal layers, in long-striated skeletal muscle, and in the Langerhans’ islets of the pancreas. No immunopositive staining was observed in lung and liver indicating that sites of synthesis and IGFBP action are different.

A novel extracellular matrix protein from tomato associated with lignified secondary cell walls.

A cDNA clone representing a novel cell wall protein was isolated from a tomato cDNA library. The deduced amino acid sequence shows that the encoded protein is very small (88 amino acids), contains an N-terminal hydrophobic signal peptide, and is enriched in lysine and tyrosine. We have designated this protein TLRP for tyrosine- and lysine-rich protein. RNA gel blot hybridization identified TLRP transcripts constitutively present in roots, stems, and leaves from tomato plants. The encoded protein seems to be highly insolubilized in the cell wall, and we present evidence that this protein is specifically localized in the modified secondary cell walls of the xylem and in cells of the sclerenchyma. In addition, the protein is localized in the protective periderm layer of the growing root. The highly localized deposition in cells destined to give support and protection to the plant indicates that this cell wall protein alone and/or in collaboration with other cell wall structural proteins may have a specialized structural function by mechanically strengthening the walls.

Anatomy of the Legume Nodule Cortex With Respect to Nodule Permeability

We describe the anatomy of the cortex of a range of legume nodules (43 species of 31 genera of 13 tribes, principally of the Papilionoideae). To our knowledge, the nodule anatomy of 19 of the genera examined (30 species) was previously unreported. All nodules have a layer(s) in the inner cortex with distorted radial walls ('boundary layer') and occlusions of the intercellular spaces within the middle cortex. The 'nodule endodermis' as defined by Frazer (1942) was difficult to identify unless modified by sclerification or tannin deposition. In other species, the outer cortex contains a well developed periderm, often with several layers of tannin-containing cells. When present, sclereids contain a living cytoplasm, and are interspersed with parenchyma cells to form a water-filled barrier c. 50 μm in width about the nodule. Nodule sclereids are apparent within 5 days of inoculation in Glycine max. Sclerification of the common endodermis did not significantly increase following growth at 50 or 80% rhizosphere pO2. We suggest that the intercellular space deposition, the common endodermal layer and the periderm layer will act as a fixed resistance to gas diffusion into the nodule, allowing for a fine control of a variable resistance (boundary) layer within the inner cortex.

Microstructural and Histochemical Changes in Acer platanoides Rhytidome Caused by Dendrothele acerina (Aphyllophorales) and Mycena meliigena (Agaricales)

Rhytidome blocks from Acer platanoides were incubated in vitro with Dendrothele acerina or Mycena meliigena mycelia in order to describe resultant microstructural and histochemical changes using paraffin sections and brightfield microscopy. Rhytidome consists of alternating layers of periderm and nonfunctional secondary phloem. All cells in the rhytidome, except suberized phellem cells, are lignified. Both fungi penetrated blocks, and advanced 1–2 millimeters in 20 weeks. Both species penetrated suberized phellem layers and eroded phellem cell walls from the lumen outward. In nonfunctional phloem, hyphae moved between lumina of the sieve tube elements, companion cells, and parenchyma through enlarged sieve pores, pits, and bore holes. These walls were progressively thinned from the lumen outward. Fiber and sclereid walls were penetrated through pits and bore holes, but the hyphae remained in the middle of the secondary wall, forming crescent-shaped cavities that gradually enlarged to leave a honeycomb pattern of compound middle lamellae. Both fungi displayed selective delignification and nonselective cell wall degradation patterns observed in some white rot fungi. We suggest that D. acerina and M. meliigena should be classified ecologically as saprotrophic inhabitants of the rhytidome of living trees.

Wool follicles initiate, develop and produce wool fibres in ovine fetal skin grafts

SUMMARYResearch into the mechanisms that control the initiation and development of wool follicles has been severely hampered by the inaccessibility of fetal skin in utero. The aims of this study were to determine whether ovine fetal skin, when grafted onto the athymic nude mouse (nu/nu), could be maintained outside the uterine environment and, if so, whether it would retain its ability to initiate and develop wool follicles capable of producing wool fibres.Skin was removed from the mid-side region of ovine fetuses on days 45, 55, 65, 75, 85 and 95 of gestation, and transferred to graft beds prepared on anaesthetized nude mice. After developing for 20 days on the recipients, the grafts were excised for histological examination. Control ovine fetal skin was also obtained at the above times and from fetuses on days 105 and 115, and similarly processed for histological examination.Fetal skin at all ages was successfully grafted onto nude mice; 90% of all grafts were accepted and maintained by the recipients. Follicle initiation and/or development occurred in all grafts, including those formed from day 45 fetal skin, collected and grafted prior to follicle initiation in vivo. The number of follicles in grafted skin was reduced compared to that in control fetal skin of equivalent age; however, follicle development was generally accelerated. Follicle initiation and development occurred predominantly in the peripheral zone of the grafts. Some of the follicles present in the skin at grafting were lost due to the grafting procedure, while others continued to develop and produce wool fibres. Follicle development varied considerably between grafts. All grafted skin exhibited premature loss of the periderm layer and cornification of the epidermis, probably in response to the exposure of the skin surface to the atmosphere. There was a notable absence of both arrector pili muscles and sweat glands associated with graft follicles, and a retardation of sebaceous gland development.The grafting technique developed in this study has enabled ovine fetal skin to be maintained outside the uterine environment for extended periods of time and may provide an improved means for future investigation of wool follicle initiation and development.

Distribution of acidic and basic fibroblast growth factors in ovine skin during follicle morphogenesis.

Acidic and basic fibroblast growth factors (aFGF and bFGF) have been localized by immunochemistry in ovine skin during wool follicle morphogenesis. At 40 days of gestation, prior to the appearance of follicle primordia, bFGF immunoreactivity was detected in the intermediate and periderm layers of the epidermis and at the dermal-epidermal junction. Antibodies to aFGF did not bind to skin at this age. During early follicle formation, at 76 days of gestation, both FGFs were found in the epidermis and associated with the follicle primordia. Antibodies to aFGF, in particular, bound to the basal cells of the epidermis and the follicle cell aggregations. With the development of epidermal plugs, bFGF was confined to the intermediate layers of the epidermis and the dermal-epidermal junction, whereas aFGF staining was associated with the cells of the epidermis and the plugs. At 90 days, when many different stages of follicle development were in evidence, immunoreactivity for both FGFs was associated with the cells of the elongating epidermal column, particularly those adjacent to the dermal-epidermal junction. During follicle maturation, bFGF was found in the suprabasal layer of the epidermis, in the outer root sheath of the follicle and in the basement membrane zone surrounding the bulb matrix. Conversely, strong staining for aFGF was observed in the epidermis and pilary canal contiguous with the epidermis, and in cells of the upper bulb matrix of the follicle in the region of the keratogenous zone. Western blotting of extracts of mature follicles that had been isolated from the skin showed the presence of a major aFGF immunoreactive band with an apparent molecular mass of 27 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)

Caffeic acid and glycerol are constituents of the suberin layers in green cotton fibres

The fibres of the green-lint mutant (Lg) of cotton (Gossypium hirsutum L.) are suberized and contain a large proportion of wax. The unidentified components of the wax were separated into a colourless fluorescent fraction and a yellow pigmented fraction. Using ultraviolet spectroscopy and nuclear-magneticresonance ((1)H-NMR) spectroscopy, esterified trans-caffeic acid was identified as the only phenolic component in the colourless fraction. This fraction was further purified and was shown to contain caffeic acid esterified to fatty acids (mainly ω-hydroxy fatty acids), and glycerol in molar ratios of 4∶5∶5. When 2-aminoindan-2-phosphonic acid (AIP), an inhibitor of phenylalanine ammonia-lyase (EC 4. 3. 1. 5.) was added to ovules cultured in vitro, at the beginning of secondary wall formation, the fibres remained white and the colourless caffeic-acid derivative and the yellow compounds could no longer be detected by ultraviolet spectroscopy. Fibres grown in the presence of AIP were also examined in the electron microscope. Secondary cell walls were present in the treated fibres, but the electron-opaque suberin layers were replaced by apparently empty spaces. This result indicates that cinnamic-acid derivatives are covalently linked to suberin and have a structural role within the polymer or are involved in anchoring the polymer to the cellulosic secondary wall. Purified cell walls of green cotton fibres contained about 1% (of the dry weight) of bound glycerol, 0.9% of the glycerol being extractable with the wax fraction and 0.1% remaining in the cell-wall residue. The corresponding values for white fibres were 0.03% (total), 0.02% (wax), and 0.01% (cell-wall residue). Fibres synthesizing their secondary walls in the presence of AIP contained about normal amounts of bound glycerol in the wax fraction, but glycerol accumulation in the cell-wall residue was inhibited by about 95%. These observations indicate that glycerol is an important constituent of cotton-fibre suberin. Considerable amounts of bound glycerol could also be determined in exhaustively extracted cell walls of the cork layer of potato periderm (1.2%) and smaller amounts in the outer epidermal cell wall of Agave americana L. leaf (0.1%) indicating that the presence of glycerol in suberins and possibly also in cutins may be more widespread than previously thought.

Assessment of Larval Feeding Damage of the Cabbage Maggot (Diptera: Anthomyiidae) in Relation to Oviposition Preference on Canola

A choice bioassay was used in the laboratory to investigate oviposition preference of the cabbage957g962, Delia radicum (L.), for canola, Brassica campestris L. cv. Tobin, in different developmental stages. Given a choice of two different ages of canola plants, females invariably preferred to oviposit in sand around the oldest plants. Greatest preference was shown for 5-wk-old plants in the stem elongation stage. The effect of oviposition on plants in the five-leaf (3-wk-old), stem elongation (5-wk-old), and initial flowering (7-wk-old) stages was also examined by artificial infestation with 10 eggs per plant and assessment of root damage and numbers of puparia recovered. Root damage or survival from eggs to pupation did not differ significantly with stage of plant development. In a separate experiment, root damage was related (r2 = 0.76) to introduction of 10, 25, or 50 eggs per plant in the stem elongation stage. However, percentage survival from eggs to pupation and pupal weight did not differ significantly among treatments. Microscopic examination of root damage revealed that larvae consumed a narrow band of tissue bordered on the outside of the taproot by a thin layer of periderm and phloem tissue and on the inside by the parenchyma cells of secondary xylem. Independent of larval density, wounds never penetrated to the center of the root. Consequently, no plants in any of the development stages examined were killed by larval feeding. Plants appeared to compensate for damage by a significant increase in root weight with increasing level of infestation.

Drought‐induced changes in hydraulic conductivity and structure in roots of Ferocactus acanthodes and Opuntia ficus‐indica

summaryDrought‐induced changes in hydraulic conductivity (Lp) and anatomy were investigated for 1‐, 3‐ and 12‐month‐old roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus‐indica (L.) Miller. Responses were similar for the two species but varied for the three root ages. Drying in soil for 30 d caused little change in Lp or internal structure for 1‐month‐old roots, primarily due to the formation of soil sheaths in the root hair zone. For 3‐month‐old roots, Lp declined three‐ to five‐told after 30 d of drying, partly because of lacunae caused by rupture of cortical cells. For 12‐month‐old roots after 30 d of drying, the dehydration of suberized peridermal layers led to a two‐ to three‐fold decline in Lp. Measurements of axial hydraulic conductance per unit pressure gradient (Kh) before and after pressurization indicated that air embolism, caused by 30 d of drying, decreased Khby 53, 97, and 98% for 1‐ 3‐ and 12‐month‐old roots, respectively. Rewetting after 30 d of drying restored Kh to initial values within 7 d for all three root ages. Lpafter rewetting attained 100 % of its initial value for 1‐month‐old roots arid about 60% for 3‐ and 12‐month‐old roots. The formation of soil sheaths around young roots, the reduction in radial conductivity for older roots by cortical lacunae and peridermal dehydration, and the reduction in Kh by embolism thus caused a moderate, partly reversible decline in Lp that can help limit water loss from roots to the soil during drought.

Discolourations of carrot ( Daucus carota L.) during wet chilling storage

The outer layers (‘skin’) of the storage organ of five carrot cultivars were investigated anatomically. Changes in this skin during storage conditions in a chilling room and in the open field were examined. Factors responsible for the reduction of skin brightness during wet chilling storage were determined and suggestions were made to prevent down-grading of the vegetable. During wet chilling storage, apparently drier conditions are present in comparison with field preservation. This causes the death of especially thin-walled cells, like those of the phellogen and secretory cells of the oil ducts. A fatty layer is formed, composed of dead, crushed cells, which is responsible for the decreasing brightness of the skin. This phenomenon is intensified by the production of a new periderm layer in deeper areas of the storage organ, to prevent a further loss of moisture. Cultivars ‘Nangano’ and ‘Tamino’ are especially susceptible in this respect. Raising the storage temperature in the chilling room by ∼4° C to speed up the production of the new periderm layer, and/or an application of a thin layer of vegetable oil on the carrots are suggestions to reduce the evaporation.

Onset of expression of peanut lectin-binding glycoproteins is correlated with stratification of keratinocytes during human epidermal development in vivo and in vitro.

During gestation the epidermis develops from a single layer of ectoderm into a layer of keratinocytes overlaid by a layer of periderm; this is followed by a progressive increase in the number of layers of keratinocytes, until finally the distinct granular and cornified layers characteristic of mature epidermis are formed. As part of our investigation into the function of the peanut lectin-binding glycoproteins of cultured human keratinocytes, we have examined their expression at different stages of human epidermal development. We found that the onset of expression of the glycoproteins coincided with the transition from a two- to a three-layered epidermis, both in vivo and in organ culture. In adult epidermis, the patterns of binding of peanut lectin and Limax flavus lectin are complementary, with peanut binding more strongly to suprabasal keratinocytes and Limax flavus lectin binding more strongly to cells in the basal layer. We found that the complementary pattern of binding of the two lectins was established at, or shortly after, the onset of stratification and retained throughout development. In contrast, expression by keratinocytes of involucrin, a protein precursor of the cornified envelope, occurred after stratification had begun. Finally, we identified the peanut lectin-binding glycoproteins of adult epidermis by immunoblotting with an antiserum raised against the glycoproteins of cultured neonatal keratinocytes. In conclusion, expression of the peanut lectin-binding glycoproteins is an early event in epidermal development, and this would be consistent with a role for the glycoproteins in stratification.

Determination of optimum conditions for suberization, wound periderm formation, cellular desiccation and pathogen resistance in wounded Solanum tuberosum tubers

To determine the optimal environment for wound healing, potatoes ( Solanum tuberosum) were wounded and then cured for 7 days at a range of temperatures (10–30 °C) and relative humidities (50–98% RH). An accurate mixing system was used to provide continuous ventilation with air streams of different temperatures and humidities, instead of the closed system used by most previous workers. Histochemical staining was employed to determine the extent and deposition of lipid and lignin (the major components of suberin) and wound periderm formation. Weight loss and the thickness of the desiccated cell layers were also measured, as was the resistance of the cured surface to infection by pathogens. The optimum conditions for formation of suberin, periderm, minimum water loss and resistance to pathogens were found to be at 25 °C and 98% RH. Temperature was the most important factor affecting deposition of lipid, lignin and periderm formation. Humidity had a relatively larger effect on weight loss, thickness of the desiccated cell layers and resistance to infection by Fusarium oxysporum and Erwinia carotovora pv. carotovora. The thickness of the desiccated cell layers was highly correlated with resistance to pathogens. Least infection was most highly correlated with curing conditions that minimized desiccation. Resistance to infection was also significantly correlated with the thickness of the lipid, lignin and periderm layers.

Canker formation and decay in sugar maple and paper birch infected by Cerrenaunicolor

Cerrenaunicolor (Bull.: Fr.) Murr. (= Daedaleaunicolor) (Aphyllophorales, Polyporaceae) was found to cause a canker rot on two northern hardwood tree species, sugar maple (Acersaccharum Marsh.) and paper birch (Betulapapyrifera Marsh.). Pathogenicity of the fungus was determined by inoculation and examination of cankers 6 months, 1.5 years, and 2.5 years later. The two isolates used were found to differ in pathogenicity. Chemical and morphological barriers formed to compartmentalize the fungus. A zone of enhanced cell wall lignification and the formation of suberized impervious cells which composed the necrophylactic periderm in the host were observed. Xylem discoloration, callus formation, and periderm layers were more pronounced in maple than in birch. Cerrenaunicolor moved past host barriers via a mass of hyphae which annually penetrated weak points in the necrophylactic periderm and subsequently killed the adjacent cambium. Once past the necrophylactic periderm and into the xylem, C. unicolor was an aggressive decay organism which caused an extensive white rot. In naturally infected trees, columns of decay were two or three times longer than the cankers. Multiple zones of decayed and discolored wood were present in the xylem as a result of repeated attacks by the fungus.

Wound Healing and Weight Loss of Sweet Potatoes Harvested at Several Soil Temperatures

Abstract Roots of three sweet potato [Ipomoea batatas (L.) Lam] cultivars, Centennial, Jewel, and Pope, were harvested at three soil temperature ranges, cured for 1 to 7 days at 30°C and 90% to 95% RH, and stored at 13° to 13.5° and 90% and 95% RH. Wound healing during curing was evaluated using a rapid color test and histochemical methods. The color test was a good indicator of the lignification phase of wound healing for ‘Centennial’ and ‘Jewel’, and a fair indicator for ‘Pope’. Wound healing rates for the cultivars were similar. Roots harvested from the warmest soils (22° to 25°) had higher color scores (most wound lignification) up to 3 days of curing. After 5 days, there were ≈2.7 layers of lignified cells and one layer of wound periderm. After 16 weeks of storage, roots harvested at soil temperatures of 10° to 12° and 22° to 25° had lost more weight and developed more rots than did roots harvested at 15° to 17°, despite the fact that wound healing progress was similar. Thus, factors other than wound healing strongly influence storage stability.

Genetics and Histology of a Corky-Stem Mutant in Pigeonpea

A mutant pigeonpea (Cajanus cajan (L) Millsp.) characterized by cork formation on its stems and branches was identified and designated as “corky-stem.” The inheritance of this trait was studied in the F1, F2, and BC1F1 (mutant × F1) generations of two crosses. The results suggest that the corky-stem character is governed by one recessive allele and one dominant allele, designated sm and Ck, respectively. The dominant form of the sm allele completely masked the expression of the Ck allele, resulting in a smooth stem surface. Cork formation was attributed to the development of a periderm layer which is normally absent in the pigeonpea stem.

Immunocytochemical Localization and Time Course of Appearance of an Anionic Peroxidase Associated with Suberization in Wound-Healing Potato Tuber Tissue

Thin sections of wound-healing potato tuber tissue were stained with rabbit antibody prepared against a suberization-associated anionic peroxidase and then stained with a goat anti-rabbit antibody-fluorescein conjugate. When these sections were examined with an epiilluminating fluorescence microscope, bright green fluorescent linear deposits were observed on the inner side of cell walls in the periderm layer. Initial deposits which were often not contiguous throughout the wall were first observed in some cells after 3 days of wound-healing and subsequently these layers became more pronounced so that all 6 day old periderm cells had green fluorescent layers on their inner walls. This fluorescence was not present in the walls of parenchyma cells or in the walls of periderm cells treated with preimmune serum and anti-rabbit IgG-FITC conjugate. Thin sections of wound-healing potato tissue which were stained with anti-peroxidase antibody and a goat anti-rabbit antibody-rhodamine conjugate exhibited a similar time course of development with a bright reddish-orange fluorescent layer observed on the inside wall of periderm cells. The production of this suberization-associated anionic peroxidase in wound-healing tissue was also demonstrated by an immunobinding dot blot assay which showed that the largest increase in the enzyme level occurred between 4 and 6 days of wound-healing. The present results support the hypothesis that this anionic peroxidase is involved in the deposition of the aromatic polymeric domain of suberin.

Identification and characterization of glycoproteins secreted by the skin of the day 16 fetal mouse.

The secretion of tissue-specific proteins during mouse skin development, was investigated by incubating day 16 fetal skin explants in the presence of [35S]methionine and analyzing the medium electrophoretically. The medium was found to contain five proteins, which could be classified into two groups according to molecular weight. The kinetics of release of these proteins indicated that they were specifically secreted and not released by cytolysis. Mapping of the proteins by partial proteolytic digestion revealed that although the digestion patterns between the two molecular weight groups were different, within each group similar patterns were seen, suggesting that they were structurally related. Incubation in the presence of tunicamycin resulted in the decrease in molecular weight of the secreted proteins, indicating that the proteins were glycosylated. The results suggest that the two groups of structurally related glycoproteins were secreted by the peridermal layer of the fetal skin.

Autoradiographic study of glycoprotein synthesis during embryonic epidermogenesis of the mouse in vitro.

Forelimb buds of mouse embryos (day 11 + 3 h of development) were cultured for 6 days. During this period, the epidermis developed from a two-layered stage (basal and periderm cell layer) to a multilayered squamous epithelium wih stratum granulosum and stratum corneum. To investigate the glycoprotein synthesis during epidermogenesis in vitro, the limb buds were labeled for 30 min or 4 h with 3H-fucose at successive stages of development. Until the development of the stratum intermedium, no different labeling of the individual layers of the epidermis and the periderm was observed. Shortly before the beginning of the stratum granulosum, a strong labeling of the outer region of the intermediate layer, where the shape of the cells had changed from cuboid to flat, was visible. When the stratum granulosum developed, even in this layer and in the upper stratum spinosum, strong glycoprotein synthesis was observed, indicated by strong labeling with 3H-fucose. In the developing stratum corneum, no labeling of this layer was detectable 30 min or 4 h after 3H-fucose application. Labeling of peridermal cells was weak in the early stages of development and ceased in the period of stratum granulosum formation, indicating a stop of glycoprotein synthesis in this embryonal cell layer before its disappearance.