Cytokeratin localization in toe pads of the anuran amphibian Philautus annandalii (Boulenger, 1906)

We have examined cytokeratin distribution and their nature in toe pads of the Himalayan tree-frog Philautus annandalii. Toe pads are expanded tips of digits and show modifications of their ventral epidermis for adhesion. The toe pad epidermal cells, being organized into 3–4 rows, possess keratin bundles, especially in surface nanostructures that are involved in adhesion. Immunohistochemical localization using a pan-cytokeratin antibody revealed that cytokeratin immunoreactivity is the strongest in the mid- to basal cell rows of the epidermis, which parallels our previous ultrastructural observation of dense keratin bundles present in this part of the epidermis. The remainder of the epidermis (i.e., the superficial cell layer) showed little immunoreactivity. Immunoblot analysis revealed that toe-pads possessed keratins prominently in the molecular mass of 50 kDa. Possible presence of keratin 5 in toe pad epidermis has been correlated with its usual distribution pattern in mammalian epidermis.     

Structure of adhesive organ of the mountain-stream catfish, Pseudocheneis sulcatus (Teleostei: Sisoridae)

The structure and ultrastructure of the adhesive organ (AO) in the catfish, Pseudocheneis sulcatus (Sisoridae), an inhabitant of the sub‐Himalayan streams of India, is described. The surface of the AO is thrown into folds, the ridges of which bear curved spines. The AO epidermis consists of 10–12 tiers of filament‐rich cells, of which the outer tier cells project spines lined with a thick plasma membrane and bear bundles of tonofilaments (TF). Their cytoplasm contains TF and large mucus‐like granules, but no obvious organelles. A second tier of living cells with spines is present beneath the outer tier and seems to replace the latter when its spines are damaged or shed. The outer tier cells react positively with antibody to cytokeratin. Actin labelling is clearly absent from the outer tier, indicating that keratinization of the outer tier occurs in the absence of actin filaments. In the cells of the third to fifth tiers, the cytoplasm possesses abundant small mucous granules (0.1–0.3 µm), and fewer TF compared to the cytoplasm in the spines. The cells of the innermost tiers and the basal layer possess few TF bundles, but no mucous granules. The potential of AO filament cells to produce both mucous granules and keratin filaments is noteworthy. The observations provide evidence that specific regions of fish epidermis can actually undergo a true process of keratinization.     

Ultrastructure of the epidermis of the lizard (Lacerta vivipara) at the resting stage of the sloughing cycle

The ultrastructure of the epidermis of the lizard ( Lacerta vivipara ) one day after sloughing is described. The non-keratinized layers of the epidermis are essentially similar in structure to those of amphibians and mammals. The cells of the basal layer are not however separated from each other by the large spaces described in the amphibian (Farquhar & Palade, 1965). The middle layers of the epidermis at this stage of the sloughing cycle produce neither the characteristic mucous granules found in amphibians nor the keratohyalin granules of mammals. A small number of granules corresponding in size and location to the "Odland bodies" of both mammalian and amphibian epidermis are, however, present. The intermediate layer cells also contain a number of bodies similar in appearance to those described by Farquhar & Palade as lysosomes in amphibian skin. These structures are both osmium iodide and acid phosphatase positive. Unlike the condition in amphibians and mammals, the cytoplasm of cells in the layer immediately beneath the keratinized strata is honeycombed with small vesicles, and contains large irregular vacuoles of uncertain content. Certain nonkeratinizing elements within the epidermis are tentatively interpreted as nerve terminations. Two morphologically distinct keratinized strata can be distinguished, the inner stratum consisting of flattened cells similar to those of the stratum corneum of mammalian epidermis; individual cell outlines cannot be distinguished in the outer stratum, which has a structure similar to that of avian feather keratin. A shallow surface zone of the outer keratinized stratum has been identified as the Oberhautchen. This consists of longitudinally disposed leaflets or laminae which are responsible for the sculptured pattern of the epidermal surface. The observations reported here provide a basis for analysis of changes occurring at other stages of the sloughing cycle.     

Keratinization of the outer surface of the avian scutate scale: Interrelationship of alpha and beta keratin filaments in a cornifying tissue

Summary The outer surface of adult Gallus domesticus scutate scale was studied as a model for epidermal cornification involving accumulation of both alpha and beta keratins. Electron-microscopic analysis demonstrated that the basal cells of the adult epidermis contained abundant lipid droplets and that filament bundles and desmosomes were distributed throughout the cell layers. Indirect immunofluorescence microscopy and double-labeling immunogold-electron microscopy confirmed that the stratum germinativum contained alpha keratin but not beta keratin. Beta keratins were first detected in the stratum intermedium and were always found intermingled with filament bundles of alpha keratin. As the differentiating cells moved into the outer regions of the stratum intermedium and the stratum corneum, the large mixed keratin filament bundles labeled increasingly more with beta keratin antiserum and relatively less so with alpha keratin antiserum. Sodium dodecyl sulfate-polyacrylamide gel analysis of vertical layers of the outer surface of the scutate scale confirmed that cells having reached the outermost layers of stratum corneum had preferentially lost alpha keratin. The mixed bundles of alpha and beta keratin filaments were closely associated with desmosomes in the lower stratum intermedium and with electron-dense aggregates in the cytoplasm of cells in the outer stratum intermedium. Using anti-desmosomal serum it was shown that these cytoplasmic plaques were desmosomes.     

Histochemical and ultrastructural analyses of adhesive setae of lizards indicate that they contain lipids in addition to keratins

We studied the distribution of lipid material and organelles in the epidermal layers of toe pads from two species of lizards representing the two main lizard families in which adhesive scansors are found (gekkonids and polychrotids), the dull day gecko, Phelsuma dubia and the green anole, Anolis carolinensis. Although lipids are a conspicuous component of the mesos layer of squamate reptiles and function in reducing cutaneous water loss, their distribution has not been specifically studied in the highly elaborated epidermal surface of adhesive toe pads. We found that, in addition to the typical cutaneous water loss‐resistant mesos and alpha‐layer lipids, the Oberhäutchen (including the setae) on the most exterior layers of the epidermis in P. dubia and A. carolinensis also contain lipid material. We also present detailed histochemical and ultrastructural analyses of the toe pads of P. dubia, which indicate that lipid material is closely associated spatially with maturing setae as they branch during the renewal phase of epidermal regeneration. This lipid material appears associated with the packing of keratin within setae, possibly affecting permeability to water loss in the pad lamella, where the surface area is from 4–60‐fold greater compared with normal scales. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Differentiation of the epidermis of scutes in embryos and juveniles of the tortoise Testudo hermanni with emphasis on beta-keratinization

The sequence of differentiation of the epidermis of scutes during embryogenesis in the tortoise Testudo hermanni was studied using autoradiography, electron microscopy and immunocytochemistry. The study was mainly conducted on the epidermis of the carapace, plastron and nail. Epidermal differentiation resembles that described for other reptiles, and the embryonic epidermis is composed of numerous cell layers. In the early stages of differentiation of the carapacial ridge, cytoplasmic blebs of epidermal cells are in direct contact with the extracellular matrix and mesenchymal cells. The influence of the dermis on the formation of the beta‐layer is discussed. The dermis becomes rich in collagen bundles at later stages of development. The embryonic epidermis is formed by a flat periderm and four to six layers of subperidermal cells, storing 40–70‐nm‐thick coarse filaments that may represent interkeratin or matrix material. Beta‐keratin is associated with the coarse filaments, suggesting that the protein may be polymerized on their surface. The presence of beta‐keratin in embryonic epidermis suggests that this keratin might have been produced at the beginning of chelonian evolution. The embryonic epidermis of the scutes is lost around hatching and leaves underneath the definitive corneous beta‐layer. Beneath the embryonic epidermis, cells that accumulate typical large bundles of beta‐keratin appear at stage 23 and at hatching a compact beta‐layer is present. The differentiation of these cells shows the progressive replacement of alpha‐keratin bundles with bundles immunolabelled for beta‐keratin. The nucleus is degraded and electron‐dense nuclear material mixes with beta‐keratin. In general, changes in tortoise skin when approaching terrestrial life resemble those of other reptiles. Lepidosaurian reptiles form an embryonic shedding layer and crocodilians have a thin embryonic epidermis that is rapidly lost near hacthing. Chelonians have a thicker embryonic epidermis that accumulates beta‐keratin, a protein later used to make a thick corneous layer.     

Light and electron microscopic analyses of the high deformability of adhesive toe pads in White's tree frog,Litoria caerulea

White's tree frog (Litoria caerulea) has large, adhesive toe pads that are among the softest of all known biological structures. To explore the morphological basis for the physical properties of the toe pads, the internal microstructure of the toe pads in L. caerulea was examined using both light and transmission electron microscopy. Three design elements that are distinct from other areas of skin were observed. First, the keratinocytes comprising the adhesive surface of the toe pad all contained keratin filament bundles (tonofibrils) exhibiting structural anisotropy. Specifically, the curved conformation of the hierarchical (branching) tonofibrils was characterized by the formation of anastomoses consisting of tonofibrils beneath the adhesive cell surface and stem keratin filament bundles concentrated in the lower‐middle part of the dorsal‐side of adhesive cells. Second, the cytoplasm of keratinocytes in the most superficial cell layer contained glycoproteins (stained by periodic acid/Schiff reagent) that are considered to confer high viscoelasticity. Third, the dermis contained large lymph spaces interspersed with elastic fibers and collagen fibers, which were relatively sparsely distributed compared to the dorsal skin of the toe pads. The profiles of these structures were easily deformed by the slight application of pressure. These findings reaffirmed that the unique internal architecture of the toe pads in L. caerulea contributed to their remarkable softness and high deformability, which in turn increased the contact area and provided improved adaptability to the local topography of natural surfaces. J. Morphol. 277:1509–1516, 2016. © 2016 Wiley Periodicals, Inc.     

Protein and carbohydrate histochemistry in relation to the keratinization in the epidermis of Barbus sophor (Cyprinidae, Pisces)

The distribution of protein and carbohydrate constituents in the epidermis of Barbus sophor is described in order to give a better understanding of its cellular organization and physiology.
Various cytochemical techniques show the keratinized nature of the outer free margins of the polygonal cells in the most-superficial layer. These contain appreciable amounts of cysteine bound sulphydryl groups, basic proteins, protein bound NH₂ groups, ribonucleic acid and calcium and give a strong Papanicolaou's reaction. Absence of cystine bound disulphide groups suggests that the cornified layer in B. sophor is probably mechanically weak as adjacent keratin chains remain unbonded. The polygonal cells showing keratinization at the outer free margins remain metabolically active and are not sloughed off at the surface. This is in contrast to the keratinized epidermis of other teleosts so far reported in which the keratinized cells are dead and are sloughed off at the surface.
In addition to keratinization the polygonal cells undergo mucogenesis synthesizing sulphated acid mucopolysaccharides.
The presence of eosinophilic granular cells in the epidermis is interesting. The possible role of these cells in the protection of the epidermis has been discussed. The epidermis on the inner surface of the scale is very thin so it may not have much protective significance in these areas.     

The structure and development of the digital lamellae of lizards

The epidermal setae and the spinules of the digital lamellae of anoline and gekkonid lizards are shed periodically along with the rest of the outer layer of the skin. These structures are developed within the lamellae prior to ecdysis. The setae are larger and more complicated than the spinules and begin their development first. The setae of Anolis start as aggregations of tonofibrils beneath the plasma membrane of the presumptive Oberhautchen cells. These cells are arranged in rows parallel to the surface, several cell layers beneath the alpha layer of the skin. The developing setae protrude into the clear layer cells as finger-like projections, with the tonofibrils longitudinally oriented in the direction of growth. About 100 setae are formed by each Oberhautchen cells in Anolis. In late development, the clear layer cells lose their cellular contents and when shed along with all distal cells, retain a template of the new setae or spinules. The spinules and setae are formed before the fibrous and alpha layers of the new skin. The fibrous layer, which occurs only on the ventral (outer) layer of the lamellae, and the Oberhautchen with its setae and spinules, is considered the beta layer. The alpha layer, which occurs adjacent to the fibrous layer on the ventral surface and adjacent to the Oberhautchen on the dorsal (inner) surface, is morphologically identical to that of mammalian α keratin. The shed lizard skin consists of the alpha and beta layers as well as the degenerating cells of the outer epidermal generation, and the clear layer. The clear layer that is shed shows the template of the new setae and spinules developed in the new skin layer. The separation of the new from the old skin occurs along the intercellular space between the clear layer cells and the new Oberhautchen. The alpha layer of the skin is not fully keratinized at shedding. The setae of the digital lamellae of lizards represent unique epidermal structures — intracellular keratinized microstructures.     

Fine structure of the organ of attachment of the teleost, Garra gotyla gotyla (Ham)

We describe the morphology of the attachment organ (AO) of the teleost, Garra gotyla gotyla (Cyprinidae). It is located ventrally around the mouth opening and used by the species for attachment to submerged rocks in sub-Himalayan streams and rivers where it lives. The AO consists of three crescentic parts and a central callus part. Scanning electron microscopy (SEM) shows the former to possess numerous tubercles, each of which bears about 23–27 curved spines. Light microscopy shows the epidermis of the tuberculated parts to possess one type of cell arranged into 7–8 rows. Transmission electron microscopy (TEM) reveals these cells to contain abundant tonofilaments (hence called the filament cells). The epidermis of the callus part possesses the filament cells and additionally mucous cells, which are absent in the tuberculated parts. The superficial epidermis is apparently keratinized (thickness: 5–8 μm), and a part of the cells of the outer row is modified into spines. These cells show a thick plasma membrane envelope and possess mucous granules (diameter: 0.1–0.3 μm) and bundles of tonofilaments. The cells of the inner two to four rows possess similar organelles and additionally, prominent Golgi bodies and rough endoplasmic reticulum. Immunohistochemically, the cells of the outer row and the spines stain positively for cytokeratin. The cells of the innermost rows (five to eight) possess few tonofilaments and no mucous granules. It is evident that the filament cells of the mid- to upper epidermis are specialized for the production of mucous granules and tonofilaments, which is unique for the teleost epidermis concerned. It appears that the tuberculated parts with spines assist in anchorage and interlocking with the substratum, while the central callus part probably utilizes both suction and frictional mechanisms, and mucous secretion protects the spines from damage during anchorage and abrasion.     

Observations on the histochemistry and ultrastructure of regenerating caudal epidermis of the tuatara Sphenodon punctatus (Sphenodontida,Lepidosauria, Reptilia)

Study of the histology, histochemistry, and fine structure of caudal epidermal regeneration in Sphenodon punctatus through restoration of a scaled form reveals that the processes involved resemble those known in lizards. Following establishment of a wound epithelium (WE), subjacent scale neogenesis involves epidermal downgrowths into the dermis. Although the process is extremely slow, and most new scales do not overlap, their epidermal coverings reestablish epidermal generation (EG) formation. As in lizards, the flat, alpha-keratogenic, WE cells contain lipids as revealed by their affinity for Sudan III. A few mucous cells that store large PAS-positive mucus-like granules also occur in WE. During differentiation of WE cells, among the bundles of 70-nm tonofilaments are many lamellar bodies (LBs) and mucous granules (MGs) that discharge their contents into the cytoplasm and extracellular spaces producing a strongly PAS-positive keratinized tissue. Richness of epidermal lipids coexistent with mucus is a primitive characteristic for amniote vertebrates, probably related to functions as a barrier to cutaneous water loss (CWL). As scale neogenesis begins, beneath the superficial WE appear 3-5 layers of irregularly shaped cells. These contain tonofilament bundles surrounded by small, round keratohyalin-like granules (KHLGs) and a keratinized matrix with beta-keratin packets and a 3-5-nm thick keratin granulation. This mixture of alpha- and beta-keratogenic capacities resembles that seen in the innermost cells of a normal tuatara epidermal generation. As in the latter, but in contrast to both normal and regenerating lizard epidermis, no definable shedding complex with interdigitating clear layer and oberhautchen cells occurs (Alibardi and Maderson, 2003). The tortuous boundaries, and merging beta-keratin packets, identify subjacent keratinizing cells as precursors of the typical stratified, squamous beta-layer seen in long-term regenerated caudal skin wherein the entire vertical sequence of epidermal layers resembles that of normal scales. The sequence of events in caudal epidermal regeneration in S. punctatus resembles that documented for lizards. Observed differences between posttrauma scale neogenesis and scale embryogenesis are responses to functional problems involved in, respectively, restoring, or forming, a barrier to CWL while accommodating rapid somatic growth.     

A putative new hydrostatic skeletal function for the epidermis in Monhysterids (Nematoda)

The ultrastructure of the epidermis of two Monhysterid nematodes (Geomonhystera disjuncta and Diplolaimella dievengatensis) is studied in detail. The epidermis is composed of discrete uninucleated cells. The cytoplasmic layer of the epidermis between the cuticle and the somatic muscles is very thin and contains bundles of filaments that attach the muscles to the cuticle. The epidermal chords are voluminous and contain the nuclei and most of the cell organelles. In the chords many large electron-transparent vacuoles are found. It is hypothesized that these vacuoles fulfill a function as a compartmentalised hydrostatic skeleton.     

Comparative Cryo‐SEM and AFM studies of hylid and rhacophorid tree frog toe pads

Cryo‐scanning electron microscopy (cryo‐SEM) and atomic force microscopy (AFM) offer new avenues for the study of the morphology of tree frog adhesive toe pads. Using these techniques, we compare toe pad microstructure in two distantly related species of tree frog, Litoria caerulea, White (Hylidae) and Rhacophorus prominanus, Smith (Rhacophoridae), in which the toe pads are considered to be convergent. AFM demonstrates the extraordinary similarity of both surface microstructures (largely hexagonal epithelial cells surrounded by deep channels) and nanostructures (an array of nanopillars, ca. 350 nm in diameter, all with a small dimple at the apex). The cryo‐SEM studies examined the distribution of the fibrillar cytoskeleton within the different layers of the stratified toe pad epithelium, demonstrating that the cytoskeletal elements (keratin tonofilaments) that lie at an angle to the surface are relatively poorly developed in L. caerulea, clearly so in comparison to R. prominanus. Cryo‐SEM also enabled the visualization of the fluid layer that is critical to a toe pad's adhesive function. This was achieved by examination of the frozen fluid residues left behind after removal of a toe within the cryo‐SEM's experimental chamber. Such ‘toeprints’ demonstrated the presence of a wedge of fluid surrounding each toe pad, as well as fluid filling the channels that surround each epithelial cell. Cryo‐SEM was used to examine epithelial cell shape. In a sample of 582 cells, 59.5% were hexagonal, the remainder being mainly pentagonal (23.1%) or heptagonal (16.1%). The distribution of differently‐shaped cells was not random, but was not associated with either pad curvature or the distribution of mucous pores that provide fluid for the frogs' wet adhesion mechanism. Our main finding, the great similarity of toe pad structure in these two species, has important implications for biomimetics, for such convergent evolution suggests a good starting point for attempts to develop adhesives that will function in wet conditions. J. Morphol. 274:1384–1396, 2013. © 2013 Wiley Periodicals, Inc.     

松江鲈鱼皮肤的显微和亚显微结构

采用光学显微镜、扫描电镜和透射电镜,对松江鲈鱼(Trachidermus fasciatus)成体皮肤的显微和亚显微结构进行了观察。结果表明,松江鲈鱼体表不同部位皮肤的厚薄不一,但基本结构相似。皮肤由表皮和真皮层构成。松江鲈鱼的皮肤裸露无鳞,表皮层较薄,由约4～8层细胞构成,主要由复层上皮细胞和黏液细胞及基底细胞组成。表层细胞呈扁平、多边形,细胞之间主要靠桥粒紧密连接,连接处形成增厚的边缘嵴状突起。表皮细胞游离面向内凹陷,表面形成指纹状微嵴。黏液细胞呈圆形或卵圆形,散布在上皮细胞之间。黏液细胞内的黏原颗粒具有椭圆颗粒状、均匀致密的块状和疏松丝状3种不同形态。真皮通过基膜与表皮相连,由稀疏层和致密层构成。真皮结缔组织在腹部较厚而在其他部位较薄。表皮与真皮连接处有色素层,头部、背部、尾柄和体侧皮肤色素细胞分布多,色素层明显,而腹部和颏部皮肤缺少色素。松江鲈鱼黄河群体真皮层中有角质棘状突起,而滦河群体则无。头部、体侧和尾柄处皮肤上还分布有侧线孔和表面神经丘等感觉器官。     

Formation of large micro‐ornamentations in developing scales of agamine lizards

The embryonic scales of two Australian agamine lizards (Hypsilurus spinipes and Physignatus lesueuerii) derive from the undulation of the epidermis to form dome‐shaped scale anlage that later become asymmetric and produce keratinized layers. Glycogen is contained in basal and suprabasal cells of the forming outer scale surface that are destined to differentiate into β‐keratin cells. The outer peridermis is very flat, but the second epidermal layer, provisionally identified as an inner peridermis, is composed of large cells that accumulate vesicular bodies and a network of coarse filaments. The sequence of epidermal layers produced beneath the inner peridermis in these agamine lizards corresponds to that of previously studied lizards, but the first subperidermal layer has characteristics of both clear (keratohyalin‐like granules) and oberhautchen (dark β‐keratin packets) cells. This layer is here identified as an oberhautchen since it fuses with the underlying β‐keratinizing cells forming large spinulae as the entire tissue becomes syncytial so that the units appear to increase in size. These spinulae very likely represent sections of honeycomb‐shaped micro‐ornamentations. A mesos layer appears underneath the β‐layer before hatching. J. Morphol. 240:251–266, 1999. © 1999 Wiley‐Liss, Inc.     

The developmental cytology of the nuptial pad in the red-spotted newt.

The ultrastructure of developing, mature and regressing nuptial pads has been examined and interpreted in the red-spotted newt. The development of the pad begins with a thickening of the dermis. Mitotic activity then increases the cell layers of the epidermis from about four to approximately eight. Simultaneously, keratinocytic synthetic activity shifts to produce more tonofilaments and fewer mucous granules. In the upper cell layers, the shift is followed by an increase in cytoplasmic volume with bundles of tonofilaments accumulating on the anterior side of each cell, displacing the nucleus posteriorly. After this rearrangement, the enlarged cells become grouped into ascending columns that tilt posteriorly from the basal epidermal layer at an angle of about 45°. Also the flattened cells of the monolayered stratum corneum become superficially roughened and with successive molts are replaced by orderly rows of cornified conical structures possessing cusps that are directed posteriorly. Each cone then lies at the top of one of the germinative columns. In rudimentary pads induced on female newts, the epidermis attains a height of only five or six layers and columns are not evident, but other developmental features of the male are present. During regression, mitosis is slowed and the developmental sequence is reversed.     

A STUDY OF THE FINE STRUCTURE OF THE EPIDERMIS OF RANA PIPIENS

The epidermis of adult Rana pipiens has been studied by electron microscopy and histological and histochemical methods. It was found that the epidermis is engaged in the production of both keratin and mucus. The basal cells are mainly filled with tonofilaments, whereas the cells located in the mid-portion of the epidermis contain both tonofilaments and mucous granules. Golgi vesicles and endoplasmic reticulum are found in relative abundance in the mucus-producing cells and seem to be involved in the production of mucous granules. The mucus seen was partly retained within the cells and partly secreted into the intercellular spaces. The outermost keratinized cells contain mainly filaments and a few remnants of cell constituents.     

Epidermal differentiation in the developing scales of embryos of the Australian scincid lizard Lampropholis guichenoti

Formation of the first epidermal layers in the embryonic scales of the lizard Lampropholis guichenoti was studied by optical and electron microscopy. Morphogenesis of embryonic scales is similar to the general process in lizards, with well‐developed overlapping scales being differentiated before hatching. The narrow outer peridermis is torn and partially lost during scale morphogenesis. A second layer, probably homologous to the inner peridermis of other lizard species, but specialized to produce lipid‐like material, develops beneath the outer peridermis. Two or three lipogenic layers of this type develop in the forming outer surface of scales near to the hinge region. These layers form a structure here termed “sebaceous‐like secretory cells.” These cells secrete lipid‐like material into the interscale space so that the whole epidermis is eventually coated with it. This lipid‐like material may help to reduce friction and to reduce accumulation of dirt between adjacent extremely overlapping scales. At the end of their differentiation, the modified inner periderm turns into extremely thin cornified cells. The layer beneath the inner peridermis is granulated due to the accumulation of keratohyalin‐like granules, and forms a shedding complex with the oberhautchen, which develops beneath. Typically tilted spinulae of the oberhautchen are formed by the aggregation of tonofilaments into characteristically pointed cytoplasmic outgrowths. Initially, there is little accumulation of β‐keratin packets in these cells. During differentiation, the oberhautchen layer merges with cells of the β‐keratin layer produced underneath, so that a typical syncytial β‐keratin layer is eventually formed before hatching. Between one‐fourth distal and the scale tip, the dermis under epidermal cells is scarce or absent so that the mature scale tip is made of a solid rod of β‐keratinized cells. At the time of hatching, differentiation of a mesos layer is well advanced, and the epidermal histology of scales corresponds to Stage 5 of an adult shedding cycle. The present study confirms that the embryonic sequence of epidermal stratification observed in other species is basically maintained in L. guichenoti. J. Morphol. 241:139–152, 1999. © 1999 Wiley‐Liss, Inc.     

闽楠营养器官的解剖结构及其生态适应性

采用石蜡切片和光学显微技术对闽楠(Phoebe bournei(Hemsl.)Yang)营养器官的解剖结构及其生态适应性进行了研究。结果显示,闽楠为典型异面叶,叶片中脉发达,维管束呈扇形,导管径向排列,韧皮部外侧有大量韧皮纤维分布。上表皮外侧具角质层,下表皮外侧无角质层,下表皮细胞呈犬牙状向外凸起,有表皮毛和气孔分布,气孔为双环型、外凸;栅栏组织由1层细胞组成,海绵组织由3~4层细胞组成。茎的初生结构中,表皮轻微角质化,厚角细胞5~6层,薄壁细胞5~7层,维管束为外韧型;茎的次生结构中,表皮外部角质层加厚,木栓层细胞3~4层,木栓形成层细胞1层,栓内层细胞2~3层,维管束紧密排列连成环状,次生韧皮部和次生木质部发达,形成层细胞2~3层。根的次生结构中木栓层细胞5~6层,木栓层内侧具1层木栓形成层,栓内层细胞2层。闽楠营养器官的解剖结构特征一方面呈现出阴生植物的特点,另一方面也对阳生和旱生环境具有一定的适应性。     

A histochemical study of keratinization in the domestic fowl (Gallus gallus)

The microanatomy of the epidermis of the domestic fowl is described and related to the distribution of various histochemical constituents involved in keratinization.
The avian horny layer over the back is composed of a loose network of structurally solid horny cells. This is in contrast to most mammalian epidermal horny cells in which structural keratin is found only in the peripheral cytoplasm, and the interior of the keratinocyte contains soluble products of cytolysis with possibly some free keratin filaments dispersed in the fluid material.
The avian tarsal epidermal horny scales show similarities to both the scales of lizards and snakes and to mammalian tail scales which appear to be homologous structures.
It is suggested that a thin layer of cells containing no detectable disulphide bonds, found in the tarsal scale region of the young chick, is probably mechanically weak and may function as a fission plane for sloughing of the horny layer. A specialized epidermis and thickened horny layer is developed in the fowl on the plantar underside of the toes, but this is quite different in structure from the mammalian plantar epidermis.
The overlapping of zones rich in ribonucleic acid (RNA) and bound cysteine (SH) in the growing feather suggests that protein synthesis and the preparatory stages to keratin disulphide bonding normally occur concurrently in feather formation. This is in contrast to the growing hair which has a region rich in RNA followed immediately before it becomes keratinized by a discrete keratogenous zone weak in RNA but rich in bound cysteine.