Concentric Cell Layers Research Articles

Anguilla anguilla vs Contracaecum rudolphii: Granuloma allows host tolerance and parasite survival

High survival of the nematode Contracaecum rudolphii in European eel, Anguilla anguilla L. despite an extensive recruitment of immune cells in granulomas is described. A total of 39 eel specimens captured in Canneviè lagoon (Northern Adriatic Sea, Italy) was obtained from local fishermen. The fish were examined for the presence of endoparasitic helminths. Twenty-six eels (67%) harbored third-stage larvae (L3) of Contracaecum rudolphii A and the intensity of infection ranged from 1 to 100 parasites per fish (mean 11.4). A total of 296 larvae were counted and 293 were alive and encysted in the serosa (primarily on external surface of the rectum) as conspicuous granulomas, appearing as white nodules. Histological sections showed a granuloma formed around an individual larva and consisted of three concentric cell layers, containing numerous mast cells (MCs), fibroblasts, macrophages, and epithelioid cells. Encysted larvae were also present in other layers of the intestinal wall, including the mucosa, where recruitment of macrophage aggregates in lamina propria was documented. Immunohistochemical investigations, applying eight antibodies raised against immune cell markers, revealed histamine and serotonin in MCs and inducible-nitric oxide synthase and toll-like receptor-2 in macrophages surrounding the parasite larvae. The study indicates that this innate cellular response in the eel has a chronic inflammatory character and keeps the nematode larvae arrested in a state allowing both host tolerance and parasite survival. The European eel serves as prey for birds and the high survival of C. rudolphii A larvae in the eel indicates that this fish species is a good paratenic host for the parasite allowing completion of its life cycle in birds.

In preprints: new insights into root stem cells and their diversity.

In preprints: new insights into root stem cells and their diversity.

Plant roots employ cell-layer-specific programs to respond to pathogenic and beneficial microbes

Plant roots are built of concentric cell layers that are thought to respond to microbial infections by employing specific, genetically defined programs. Yet, the functional impact of this radial organization remains elusive, particularly due to the lack of genome-wide techniques for monitoring expression at a cell-layer resolution. Here, cell-type-specific expression of tagged ribosomes enabled the isolation of ribosome-bound mRNA to obtain cell-layer translatomes (TRAP-seq, translating ribosome affinity purification and RNA sequencing). After inoculation with the vascular pathogen Verticillium longisporum, pathogenic oomycete Phytophthora parasitica, or mutualistic endophyte Serendipita indica, root cell-layer responses reflected the fundamentally different colonization strategies of these microbes. Notably, V.longisporum specifically suppressed the endodermal barrier, which restricts fungal progression, allowing microbial access to the root central cylinder. Moreover, localized biosynthesis of antimicrobial compounds and ethylene differed in response to pathogens and mutualists. These examples highlight the power of this resource to gain insights into root-microbe interactions and to develop strategies in crop improvement.

Cytological characterization of anther development in Panax ginseng Meyer.

Ginseng (Panax ginseng), a valued medicinal herb, is a slow-growing plant that flowers after 3years of growth with the formation of a solitary terminal umbel inflorescence. However, little is known about cytological events during ginseng reproduction, such as the development of the male organ, the stamen. To better understand the mechanism controlling ginseng male reproductive development, here, we investigated the inflorescence and flower structure of ginseng. Moreover, we performed cytological analysis of anther morphogenesis and showed the common and specialized cytological events including the formation of four concentric cell layers surrounding male reproductive cells followed by subsequent cell differentiation and degeneration of tapetal cells, as well as the formation of mature pollen grains via meiosis and mitosis during ginseng anther development. Particularly, our transverse section and microscopic observations showed that the ginseng tapetal layer exhibits obvious nonsynchronous cell division evidenced by the observation of one or two tapetal layers frequently observed in one anther lobe, suggesting the unique control of cell division. To facilitate the future study on ginseng male reproduction, we grouped the anther development into 10 developmental stages according to the characterized cytological events.

Reconstruction of Vascular Structure with Multicellular Components using Cell Transfer Printing Methods

Natural vessel has three types of concentric cell layers that perform their specific functions. Here, the fabrication of vascular structure is reported by transfer printing of three different cell layers using thermosensitive hydrogels. Tetronic-tyramine and RGD peptide are co-crosslinked to prepare cell adhesive and thermosensitive hydrogels. The hydrogel increases its diameter by 1.26 times when the temperature reduces from 37 °C to 4 °C. At optimized seeding density, three types of cells form monolayers on the hydrogel, which is then transferred to the target surface within 3 min. Three monolayers are simultaneously transferred on one substrate with controlled shape and arrangement. The same approach is applied onto nanofiber scaffolds that are cultured for more than 5 d. Every type of monolayer shows proliferation and migration on nanofiber scaffolds, and the formation of robust cell-cell contact is revealed by CD31 staining in endothelial cell layer. A vascular structure with multicellular components is fabricated by transfer of three monolayers on nanofibers that are manually rolled with the diameter and length of the tube being approximately 3 mm and 12 mm, respectively. Collectively, it is concluded that the tissue transfer printing is a useful tool for constructing a vascular structure and mimicking natural structure of different types of tissues.

Perspectives on Hair Evolution Based on Some Comparative Studies on Vertebrate Cornification

Hair evolution contributed to the biological success of mammals. Hair origin from synapsid scales is speculative and requires extensive modifications of the morphogenetic process transforming lens-shaped dermis of scales into small dermal papillae in hair. Hair evolution from glands is hypothetical but is supported from studies on the signaling control of hair vs. glandular morphogenesis. Based on immunocytochemical and comparative studies, it is hypothesized that the onion-like organization of hair derived from glandular pegs which central part produced lipids and some keratin. In a following stage, involucrin, trichohyalin, and keratins were produced in the central cells of the gland and formed a solid medulla surrounded by keratinocytes of the inner root sheath. The origin of this protohair was possibly related to increased concentration of beta-catenin and other signaling molecules in epithelial cells following the evolution of a dermal papilla. The latter activated the keratogenic genes, already utilized in cells of the claws, in concentric layers of cells of the glandular peg. Lipidogenic genes were depressed. As new genes evolved in the genome of synapsids, new circular layers of keratinocytes containing specialized hard keratins and keratin-associated proteins were formed around medullary cells. The new keratinocytes probably originated the cortex separating medulla from the external cells that became the inner root sheath. The hypothesis indicates that in a following stage, the medulla was obliterated or replaced by cortical cells while the external part of the cortex formed a cuticular surface due to the different growth rate with inner root sheath cells.

Cytological analysis and genetic control of rice anther development

Microsporogenesis and male gametogenesis are essential for the alternating life cycle of flowering plants between diploid sporophyte and haploid gametophyte generations. Rice (Oryza sativa) is the world's major staple food, and manipulation of pollen fertility is particularly important for the demands to increase rice grain yield. Towards a better understanding of the mechanisms controlling rice male reproductive development, we describe here the cytological changes of anther development through 14 stages, including cell division, differentiation and degeneration of somatic tissues consisting of four concentric cell layers surrounding and supporting reproductive cells as they form mature pollen grains through meiosis and mitosis. Furthermore, we compare the morphological difference of anthers and pollen grains in both monocot rice and eudicot Arabidopsis thaliana. Additionally, we describe the key genes identified to date critical for rice anther development and pollen formation.

Emergence and patterning of the five cell types of the Zea mays anther locule

One fundamental difference between plants and animals is the existence of a germ-line in animals and its absence in plants. In flowering plants, the sexual organs (stamens and carpels) are composed almost entirely of somatic cells, a small subset of which switch to meiosis; however, the mechanism of meiotic cell fate acquisition is a long-standing botanical mystery. In the maize ( Zea mays) anther microsporangium, the somatic tissues consist of four concentric cell layers that surround and support reproductive cells as they progress through meiosis and pollen maturation. Male sterility, defined as the absence of viable pollen, is a common phenotype in flowering plants, and many male sterile mutants have defects in somatic and reproductive cell fate acquisition. However, without a robust model of anther cell fate acquisition based on careful observation of wild-type anther ontogeny, interpretation of cell fate mutants is limited. To address this, the pattern of cell proliferation, expansion, and differentiation was tracked in three dimensions over 30 days of wild-type (W23) anther development, using anthers stained with propidium iodide (PI) and/or 5-ethynyl-2′-deoxyuridine (EdU) (S-phase label) and imaged by confocal microscopy. The pervading lineage model of anther development claims that new cell layers are generated by coordinated, oriented cell divisions in transient precursor cell types. In reconstructing anther cell division patterns, however, we can only confirm this for the origin of the middle layer (ml) and tapetum, while young anther development appears more complex. We find that each anther cell type undergoes a burst of cell division after specification with a characteristic pattern of both cell expansion and division. Comparisons between two inbreds lines and between ab- and adaxial anther florets indicated near identity: anther development is highly canalized and synchronized. Three classical models of plant organ development are tested and ruled out; however, local clustering of developmental events was identified for several processes, including the first evidence for a direct relationship between the development of ml and tapetal cells. We speculate that small groups of ml and tapetum cells function as a developmental unit dedicated to the development of a single pollen grain.

Reparative Perineural Hyperplasia and Dermatofibroma

To the Editor: In the February 2009 issue of this journal, Dr Beer published the original study titled “Reparative perineural hyperplasia: a series of 10 cases.”1 In that study, the author nicely described a series of 10 cutaneous reexcision specimens containing concentric proliferation of perineural cells around nerves in the mid or deep dermis. Such histological alteration occurred in intimate association to fibrosis and/or chronic inflammatory infiltrate. Immunohistochemistry confirmed the perineural differentiation and helped to exclude other processes such as neoplastic perineural invasion and reexcision perineural invasion. The author proposed the term “reparative perineural hyperplasia” (RPH) as a descriptor for this phenomenon. Recently, we had the opportunity to observe similar findings in association to a dermatofibroma (DF) without history of previous local surgery. A 25-year-old woman sought medical attention for a lump on her right leg of 3-month duration. She denied previous local trauma and was otherwise in a perfect health condition. The attending dermatologist described the lesion as a 0.8-cm nodule over the anterior aspect of the right leg and performed a 4-mm punch biopsy. The microscopic low-power magnification revealed an unencapsulated and well-delimited deep dermal lesion, which spared the superficial dermis (Fig. 1A). Higher power examination showed classic features of DF, including spindle cells with inconspicuous nucleoli, homogeneous chromatin, and barely evident cytoplasm disposed in a slightly storiform collagenous stroma, as well as collagen entrapment in the outer portions of the lesion (Fig. 1B). No necrosis, mitosis, or nuclear atypia were observed. The deepest portion of the DF extended into the subcutaneous fat through the interlobular fibrous septa, toward the deepest margin of the specimen (Figs. 1A, C). At the dermo-hypodermic junction, close to an interlobular fibrous septum, one could observe a nerve entrapped by the main lesion (Fig. 1C). Interestingly, the perineurium of this nerve showed hyperplastic features including ring-like layers of spindle cells harboring plump and hyperchromatic nuclei and with immunoprofile confirmatory of perineurium (EMA+, AE1/AE3−, and S100 protein−) (Figs. 2A, B). A slight chronic inflammatory infiltrate composed of lymphocytes and plasmocytes was found in adjacent areas to this nerve.FIGURE 1: A, Low-power magnification revealed a deep dermal unencapsulated and well-delimited lesion. B, Classic features of DF: spindle cells with inconspicuous nucleoli, homogeneous chromatin, and barely evident cytoplasm disposed in a slightly storiform collagenous stroma and collagen entrapment. C, DF extension into the subcutaneous fat through the interlobular fibrous septa. Near to an interlobular fibrous septum, a nerve entrapped by the main lesion is seen.FIGURE 2: A, This nerve's perineurium showed hyperplastic features including 3-4 cell thick, ring-like layers of spindle cells harboring plump and hyperchromatic nuclei. B, Immunohistochemistry shows cytoplasmatic expression of EMA in the perineural cells.Normal perineurium may present up to 12 concentric cell layers depending on the location and nerve size, and the cells are invariably flattened.2 In nerves of the deep dermis or of the transition between the dermis and the subcutaneous tissue, the perineurium usually has 1-3 concentric layers of thin cells. Although in Dr. Beer's series, the illustrations depict 4-6 cells thick perineurium with slight hyperchromatic nuclei, the present case harbors a 3-4 cells thick perineurium with prominent nuclear enlargement and hyperchromasia. Except for this detail and for the association to DF, these nerve alterations were indistinguishable from the ones described by Dr. Beer in his article. Despite the fact that the current patient denied previous local trauma, the role of trauma in the pathogenesis of perineural hyperplasia in this case cannot be ruled out for the following reasons: (1) unnoticed minor injuries are likely to occur in the lower leg of any healthy and active person; (2) it occurred in association to a DF, an entity that is widely known (at least a subset of cases) to be related to trauma; and (3) in Dr Beer's series (the only series so far on RPH), all patients had been submitted to cutaneous surgery. This case illustrates that RPH is not restricted to the context of prior surgical procedure. Indeed, perineural hyperplasia such as the one described here may occur in other fibrosis-associated or trauma-elicited conditions, including cutaneous involvement by systemic sclerosis3 and Morton's neuroma.4 However, to our knowledge its association to a DF has not been noticed in the past. The importance of recognizing RPH in the current case is to avoid potential misinterpretation of a DF as a peripheral nerve sheath tumor or desmoplastic melanoma. Perhaps, RPH is a phenomenon more common than one would expect, and we believe that from Dr. Beer's study on RPH will be observed more frequently, including in association to other cutaneous conditions related to local trauma or fibrosis. Alessandra C. Macarenco, MD Dermis-Clinica Dermatologica, Sao Jose dos Campos, SP, Brazil Ricardo S. Macarenco, MD CIPAX-Medicina Diagnostica, Sao Jose dos Campos, SP, Brazil

New tools for visualization and analysis of morphogenesis in spherical embryos

Many classical models of development, including amphibians, fish, and echinoderms, have embryos that are approximately spherical and contain concentric cell layers during early development. Neighbor relationships in such curved cell layers are not conveniently assayed or measured by conventional physical or optical sectioning techniques. To answer these challenges, we have constructed computational methods that correct for spherical distortion in 2D images and that allow extraction of concentric cell layers from 3D digital images. These methods for quantitative analysis and visualization of early development in spherical embryos are introduced by using them for the quantitative analysis of 2D and 3D images of gastrula stage Xenopus laevis.

Ultrastructural study of the precursor to fungiform papillae prior to the arrival of sensory nerves in the fetal rat

The structure of precursors to fungiform papillae without taste buds, prior to the arrival of sensory nerve fibers at the papillae, was examined in the fetal rat on embryonic day 13 (E13) and 16 (E16) by light and transmission electron microscopy in an attempt to clarify the mechanism of morphogenesis of these papillae. At E13, a row of rudiments of fungiform papillae was arranged along both sides of the median sulcus of the lingual dorsal surface, and each row consisted of about 10 rudiments. There was no apparent direct contact between papillae rudiments and sensory nerves at this time. Bilaterally towards the lateral side of the tongue, adjacent to these first rudiments of fungiform papillae, a series of cord-like invaginations of the dorsal epithelium of the tongue into the underlying connective tissue, representing additional papillary primordia parallel to the first row, was observed. The basal end of each invagination was enlarged as a round bulge, indented at its tip by a mound of fibroblasts protruding into the bulge. At E16 there was still no apparent direct contact between rudiments of fungiform papillae and sensory nerves. Each rudiment apically contained a spherical core of aggregating cells, which consisted of a dense assembly of large, oval cells unlike those in other areas of the lingual dorsal epithelium. The differentiation of these aggregated cells was unclear. The basal lamina was clearly recognizable between the epithelium of the rudiment of fungiform papillae and the underlying connective tissue. Spherical structures, which appeared to be sections of the cord-like invaginations of the lingual epithelium that appeared on E13, were observed within the connective tissue separated from the dorsal lingual epithelium. Transverse sections of such structures revealed four concentric layers of cells: a central core, an inner shell, an outer shell, and a layer of large cells. Bundles of fibers were arranged in the central core, and the diameters of bundles varied somewhat depending on the depth of the primordia within the connective tissue and their distance from the median sulcus. Ultrastructural features of cells in the outer shell differed significantly in rudiments close to the lingual epithelium as compared to those in deeper areas of connective tissue. Around the outer shell there was a large-cell layer consisting of one to three layers of radially elongated, oval cells that contained many variously sized, electron-dense, round granules. Large numbers of fibroblasts formed dense aggregates around each spherical rudiment, and were separated by the basal lamina from the large-cell epithelial layer. Progressing from deep-lying levels of the rudiments of the papillae to levels close to the lingual surface epithelium, the central core, inner shell, and outer shell gradually disappeared from the invaginated papillary cords.

Schwann Cell-Derived Desert Hedgehog Signals Nerve Sheath Formation.

Reciprocal signaling between axons and Schwann cells during development is well established. The contribution of Schwann cells to the formation and maintenance of the protective nerve sheaths (endo-, peri-, and epineurium) has been less studied. Although mesenchymal cells contribute to all these structures, only perineurial cells contribute to the diffusion barrier between nerves and surrounding tissues. During development, prospective perineurial cells shift from a mesenchymal to epithelial phenotype, forming concentric layers of cells around the nerve fascicles that collectively form a barrier against unwanted molecules and cellular infiltration. We have studied the role of Schwann cells in the formation and maintenance of this barrier. The signaling molecule Desert hedgehog is expressed in Schwann cell precursors, and in Schwann cells until at least postnatal day 10, while its receptor patched is seen in mesenchymal cells surrounding the developing nerve at embryo day 15. In Desert hedgehog knockout mice, the connective tissue sheaths in adult nerves appear highly abnormal by electron microscopy. There is almost no epineurium, and the perineurium is thin and highly abnormal. In addition, perineurial-like cells invade the endoneurial space, forming mini-fascicles around small bundles of nerve fibers similar to those seen in regenerating nerves. Functional tests reveal that the diffusion and cellular infiltration barrier is compromised, demonstrating that Desert hedgehog signaling from Schwann cells to the mesenchyme is involved in the formation of a morphologically and functionally normal perineurium.

Bridging defects in nerve continuity: influence of variations in synthetic fiber composition.

Synthetic filaments introduced into a silicone tube may help to enhance axonal growth over extended defects in nerve continuity [1]. Here we test the influence of number (0, 3, 7 or 15), size (diameter 150 or 250 microm) and material of filaments (polyamide or catgut) enclosed in such tubes (inner diameter 1.98 mm) on axonal growth across a 10 mm defect in rat sciatic nerve. The morphology of the tube content was analyzed four weeks post-surgery. The area of the formed tissue matrix inside the tube showed no difference between the groups. Myelinated axons were observed in the formed tissue matrix inbetween and peripheral to the filaments, however, separated from the filaments by concentric cell layers. The number of myelinated axons was less in the tubes with 15 filaments, most pronounced when catgut filaments were used. In most cases, except in tubes with 15 catgut filaments, fibers had grown into the distal nerve segment (pinch reflex test/light microscopy). We conclude that an intrinsic framework consisting of a limited number of synthetic filaments inside an extrinsic framework (silicone tube) does not disturb nerve regeneration. The formed tissue matrix was neither influenced by the presence or the numbers (if less than or equal to seven filaments), type of filaments nor the size of the filaments indicating the importance of the inserted nerve segments.

Characteristics of multicellular spheroids formed by primary cultures of human thyroid tumor cells.

Features of multicellular tumor spheroids (MCTS) differed depending on their types of cells. MCTS formed by 4000 human thyroid primary culture epithelial tumor cells displayed diameters between 0.31 and 0.33 mm within 2 days regardless of the stage of malignancy of the originating tumors. Their cellular composition reflected that of the originating tumor in regard to DNA content and the expression of cytokeratin, vimentin, as well as thyroglobulin. During the following 3 weeks, their sizes increased up to diameters of 0.42 mm when their cells had been derived from carcinomas, and MCTS originating from adenomas stopped growing within the next 2 days. After 8 days of incubation, proliferating cells were only found in carcinoma MCTS. The cells were randomly distributed over the total volume of the spheroids, which displayed irregular cell arrangements but not concentric cell layers and did not form necrotic centers.

TOPOLOGICAL MAPS AND MODELS OF SHAPES

We study the topological properties of physical froths. They are cellular networks with minimum incidence numbers (D+1 edges incident on a vertex in D-dimensions), and with cells with homogeneous shapes and sizes. We present a method where the structure of froths is analyzed as organized in concentric layers of cells around a given, arbitrary, central cell. A map gives, by recursion, the number of cells in successive layer. In 2 and 3 dimensions this map (logistic map) has one parameter, given as a function of the average topological properties of the cells in the layers. From the behaviour of the number of cells per layer with the topological distance, one obtains the curvature of the space tiled by the froth. By using the map it is therefore possible to characterize the shape of the manifold tiled by the froth in term of the topological arrangements of its tiles. We propose a topological method to compute the Gaussian curvature of a surface from a sample of points.

Statistical properties and shell analysis in random cellular structures.

We investigate the statistical properties of two-dimensional random cellular systems (froths) in terms of their shell structure. The froth is analyzed as a system of concentric layers of cells around a given central cell. We derive exact analytical relations for the topological properties of the sets of cells belonging to these layers. Experimental observations of the shell structure of two-dimensional soap froth are made and compared with the results on two kinds of Voronoi constructions. It is found that there are specific differences between soap froths and purely geometrical constructions. In particular these systems differ in the topological charge of clusters as a function of shell number, in the asymptotic values of defect concentrations, and in the number of cells in a given layer. We derive approximate expressions with no free parameters which correctly explain these different behaviors. \textcopyright{} 1996 The American Physical Society.

La théorie des feuillets: implications embryologiques et évolutives.

The germ-layer theory states that all Metazoa develop from embryos composed of two or three concentric cell layers. The embryos of the diploblastic animals comprise two germ layers (ectoderm and endoderm). Those of the triploblastic animals have an additional germ layer (mesoderm). The germ-layer theory is useful for interpreting embryonic development. But it also has evolutionary implications. According to the promoters of the theory, the corresponding germ layers of all Metazoa must be considered homologous. In evolutionary terms, this means that the diploblastic animals have a common ancestor whose soma comprised two cell layers. Similarly, all triploblastic animals are supposed to derive from a three-layer organism. Thus, the germ-layer theory is recapitulative in nature. It implies that early embryos of living animals are similar to their two- or three-layer ancestors. The embryological aspect of the germ-layer theory incites little controversy. its evolutionary aspect is much more difficult to evaluate. If the germ layers are homologous, this could mean that homologous genes direct the formation of each germ layer in all animals, and are active in all cells of a given layer. These genes presumably derive from those that were active in the corresponding germ layers of archaic Metazoa. This conjecture proves to be at least partially true, since homologous genes are expressed in mesodermal cells of early insect and vertebrate embryos.

Embryology and taxonomical position of Retzia capensis (Retziaceae)

The ovules of Retzia capensis are anatropous, unitegmic and tenuinucellate. A well‐developed hypostase of concentric layers of cells is present. Embryo sac formation follows Polygonum type. The central part of the mature embryo sac contains rich amounts of starch grains, which disappear at the beginning of the endosperm development. The endosperm formation results in a chalazal haustorium of a great number of long, narrow, densely plasmatic cells, a micropylar haustorium of loosely plasmatic cells, and a middle region which in the beginning is only partly cellular, but later the whole endosperm consists of long, narrow cells. The hypostase prevents the chalazal endosperm haustorium from penetrating to the lower part of the ovule, while the micropylar haustorium is able to grow upwards into the long micropyle. The cellular endosperm formation, the formation of endosperm haustoria, of which the micropylar is most distinctive, and formation of a well‐developed hypostase all indicate a close relationship to Buddleiaceae and part of Scrophulariaceae. Therefore, both Retziaceae and Buddleiaceae should be placed in the order Scrophulariales.

Morphological correlates of permeability in the frog perineurium: vesicles and "transcellular channels".

Lanthanum, applied to the outside of the fixed sciatic nerve of Rana pipiens, did not enter the endoneurium, but was halted by functionally tight junctions at the inner layers of the perineurium. This component of the blood-nerve barrier consists of several concentric layers of cells interspersed with an extracellular matrix of amorphous ground substance, collagen fibrils, and fine filaments. Numerous vesicular profiles are closely associated with the surface membranes of all the cells. The application of lanthanum to fixed tissue revealed that these profiles are attached to the cell surface by narrow necks, and open to the extracellular space. The attenuated cells are filled by the vesicular structures, which often appear to overlap. Stereoscopic electron microscopy showed that these vesicles did not fuse with each other or with the apposing cell surface to form transcellular channels. Channel formation does not appear to contribute significantly to the permeability of any of the perineurial layers.

Apocrine Acrosyringeal Complex in the Human Skin

The acrosyringium of human apocrine sweat apparatus has been studied by light and electron microscopy using horizontal continuous serial sections. The apocrine acrosyringium is composed of 3 structurally different portions, a highly keratinizing upper portion, an incompletely keratinizing midportion, and a least keratinizing lower portion. Throughout these 3 portions, there are 2 distinctly different but closely inter-related cellular units, namely (I) a keratinization process lacking membrane-coating granules but containing keratohyalin droplets occurring in its inner cell layer, and (II) a keratinization process rich in membrane-coating granules and containing keratohyalin granules occurring in its outer surrounding concentric cell layers. In contrast to the inner cell layer, the outer cell layer does not belong to the duct proper but rather should be considered as the periacrosyringeal complex layer which is specially differentiated to envelop the intra-epithelial duct. This apocrine acrosyringeal complex in the hair follicle seems to be essentially similar to that of the eccrine apparatus in the epidermis.