Stylostome formation in trombiculid mites (Acariformes: Trombiculidae)

Stylostomes of the trombiculid mite larvae Neotrombicula pomeranzevi (Schluger), Hirsutiella zachvatkini (Schluger), Miyatrombicula esoensis (Sasa and Ogata) and Euschoengastia rotundata (Schluger) (Acariformes: Trombiculidae), formed in the host skin during feeding of the parasites on their natural hosts (voles) were studied histologically and histochemically. A stylostome is a variously shaped tube formed of solidified mite saliva that extends from the mouthparts of the parasite through the epidermis into the dermis of the host, and allows the mite to obtain its liquid food. The first step of stylostome formation is deposition of an eosinophilic cone, to which the larva’s chelicerae are glued. Organization of the stylostome depends on the mite species, and its walls may show weakly expressed longitudinal or transverse stratification. Histochemically, the stylostome is composed of complex glycoprotein with varying tinctorial properties through the width or the length of the stylostome’s walls. Beneath the distal end of the stylostome, irrespectively of its localization either in the epidermis or in the dermis of the host, a feeding cavity is formed as a result of the action of the hydrolytic components of the mite’s saliva forced through the stylostome into the wound. An inflammatory dermal reaction of moderate intensity is evolved during larval feeding and stylostome formation. It is manifested by the infiltration of the foci with neutrophiles, lymphocytes and macrophages and by dilation of capillaries of the terminal vessel bed and filling them by erythrocytes and other blood elements. Around the stylostome, necrosis of the epidermal cells occurs, leucocytes come to the damaged area and fuse with the necrotic epidermal cells, leading to the formation of the large scabs on the surface of the host’s skin. In the case of E. rotundata, single capsules having a terminal opening and containing feeding larva are formed on the abdomen of the hosts. The walls of the capsules are composed of the mite’s saliva flowing upon the surface of the host’s skin. At the bottom of the capsule, a stylostome perforating the epidermis is also present.     

Stylostome formation by Leptotrombidium mites (Acari: Trombiculidae).

The modes of stylostome formation by larvae (chiggers) of Leptotrombidium intermedium, L. fletcheri, L. arenicola, and L. deliense in parasitized mouse skin were studied histologically in relation to their capacity to transmit Rickettsia tsutsugamushi. Three types of stylostome formation were recognized among the different species: the epidermal stylostome formed by the larva of L. intermedium; the mesenchymal stylostome formed by the larva of L. fletcheri; and, the mixed stylostome formed by the larva of both L. arenicola and L. deliense. Dermal inflammations related to the three types of stylostomes were histologically defined. The possible importance of stylostome characteristics to the transmission of rickettsial organisms is discussed.     

The effects of parasitic water mite larvae (Arrenurus spp.) on zygopteran imagoes (Odonata)

Arrenurus larvae, ectoparasitic on zygopteran imagoes, attach to the host's cuticle and tear it to obtain the host's tissue fluids. Within the host's epidermis, each larval mite produces a feeding device, the stylostome, a narrow gelatinous resilient blind sac. Heavy mite infestation brings about several wounds in close proximity, accompanied by loss of more or less extensive areas of the epidermis. Despite wound repair by congregating hemocytes, local lack of epidermis seems to enfeeble the host, presumably owing to desiccation. Heavily mite-loaded zygopterans have lost the typical agility and are easily caught. A mite-induced mortality seems to exist in zygopteran populations; the infestation contributes to reduced longevity. The study of formation and decline of the arrenurid stylostome in zygopterans renders it possible to trace cellular defence reactions under natural conditions. Most stylostomes seem to thwart the ability of the host to recognize them as foreign bodies. The host's defence appears as a two-step reaction: (1) initial hemolymph clotting and deposition of melanin associated with aggregating hemocytes at the penetration site, (2) occasional subsequent melanization and cellular encapsulation of the stylostome.     

Rhipicephalus sanguineus: sequential histopathology at the host-arthropod interface

The reaction beneath the mouth parts of an adult, female Rhipicephalus sanguineus attached to a dog develops progressively over 4–5 days. The cement substance is confined to the external surface of the epidermis and does not form any organized structure in the dermis. The hypostome is imbedded in the cement substance and does not penetrate the epidermis. The cheliceral shafts are at the epidermal-dermal junction and do not extend into the dermis to any degree. Thus, it is the adhesive quality of the cement for the dog's skin that holds this tick firmly attached to its host.Edema of the epidermis appears 24 hr after attachment of the tick; the dermal infiltrate becomes prominent from 24 hr after attachment onward and initially consists of polymorphonuclear leukocytes. This cell type predominates until the tick has detached. Rupture of lymphatics occurs and infiltrated cells can be found entering these open channels. Degranulation of mast cells is associated with polymorphonuclear leukocytic infiltration. A cavity develops in the dermis progressively over the period of tick attachment and feeding. This cavity appears during the first 24 hr and its full development depends upon leukocyte infiltration and the feeding activity of the tick. During the healing phase, macrophages, lymphocytes and fibroblasts gradually replace the polymorphonuclear leukocytes. The dermis is still hypercellular in the area of former attachment 2 wk after a female tick has detached fully engorged. The dog does not appear to develop resistance to the tick's engorgment even after 2 yr of intermittent exposure, nor does the host's reaction hinder the tick's engorgment. A dog never before exposed to arthropods of any kind reacted, histologically, to tick exposure with a very similar infiltration of polymorphonuclear leukocytes as seen in dogs repeatedly exposed. It is suggested that the inflammatory response by the host to the feeding tick may play an important role in the development and spread of infectious agents transmitted by this pool feeding arthropod.     

Attachment and Feeding Devices of Water-Mite Larvae [Arrenurus spp.) Parasitic on Damselflies (Odonata, Zygoptera)

Water-mite larvae of the subgenus Arrenurus (Acari, Hydrachnellae) act as habitual ectoparasites on zygopteran imagines, mostly attached to the soft membranous cuticle. The powerful larval pedipalp claws grasp the cuticle and the distal sabre-like cheliceral segments tear it, thus obtaining the host's tissue fluids. The chelicerae and palps co-operate to anchor the larva. The attached larva soon produces—in the host's subcuticular epidermis layer, and separated from the haemocoele by the thin sheet of subepidermal connective tissue—an elongated pouch, the stylostome, consisting of an acellular gelatinous substance, apparently secreted by the larva. Presumably, interaction with components in the host's tissue fluids solidifies the stylostome, which becomes firmly fixed to the host's body wall. The stylostome is thought to lengthen by repeated alternation between the suction of tissue fluids from the host and secretion of fresh soft substance forming additional stylostome segments. The resilient stylostome develops in a cleft between the host's cuticle and the subepidermal connective tissue in connection with partial decomposition of the host's epidermis, probably caused by cytotoxins leaking from the stylostome. In attempts to wall off the wound and thus to avoid influx of foreign substances, the host lays down a melanin sleeve around the stylostome at the perforation site. Lodgement of the functional stylostome separated from the haemocoele within the host's tissues might explain why the newly-formed stylostome seems immune from cellular host reactions. However, cellular encapsulation and melanization appear to happen to outworn, non-active stylostomes.     

The histopathology of infection by Lepeophtheirus pectoralis (Müller) (Copepoda: Caligidae)

The histology of the pectoral fin of the flounder, Platichthys flesus. (L.), is described and the presence of eosinophilic granule cells in the epidermis was noted. The histopathological effects of infection by L. pectoralis result from the attachment and feeding activity of the parasite. Although the damage inflicted by L. pectoralis is usually confined to the epidermis the lesions caused by sessile life cycle stages, adult females and chalimus larvae, often extend into the dermis. In the dermis the inflammatory response comprised fibroplasia and cellular infiltration which resulted in the formation of a dense fibrous granulation tissue.     

Active muscle migration during insect metamorphosis

The R1 abdominal retractor muscles of the insect Tenebrio molitor change position during the course of metamorphosis. These muscles detach from the epidermal tendon cells at their anterior ends, and migrate in a posterior direction, parallel to the body axis, to form completely new attachments shortly before adult emergence. Movement is preceded by the loss of sarcomere structure, and the muscles migrate in a partially dedifferentiated condition, closely accompanied by satellite cells and haemocytes. Movement appears to result from the extension of muscle processes towards the epidermis posterior to the larval attachment sites, which contact reciprocal processes extended from the epidermis. Contacts at the new posterior sites are then reinforced, and relinquished at the anterior. This cycle is subsequently repeated. It is envisaged that migration ceases when the muscles encounter a contour in the epidermal gradient known to specify the position of the adult muscle attachment sites. This positional information may be encoded in the epidermal basal lamina. The muscles then redifferentiate, with concurrent differentiation of new epidermal tendon cells. Development of adult muscle attachments appears to require reciprocal morphogenetic interactions between muscle and epidermis.     

Characteristics of leaf structure and photosynthetic apparatus within the crown of systematically shadedQuercus petraea andNothofagus procera seedlings

Four-year-old seedlings ofQuercus petraea (Matt.) Liebl. andNothofagus procera (Poepp. et Endl.) Querst were grown outdoors in pots while subjected to full, medium and low irradiances. Shading and decrease in height of leaf attachment generally increased specific leaf area, the diameters of chloroplasts and of palisade and spongy mesophyll cells, but decreased leaf thickness, number of palisade cell layers, length of palisade and spongy mesophyll cells, number of chloroplasts per mesophyll cell and epidermal cell and cuticle thickness, stomata and hair densities per unit leaf area, hair length, maximum hair breath and cell wall thickness in the two species. However, inN. procera grown under full irradiance, leaves at the upper and middle positions had hairs on both upper and lower epidermes, whereas those in other treatments and all leaves in all treatments inQ. petraea, had theirs only on the upper epidermis.     

Morphological,immunohistochemical and ultrastructural characterization of the skin of turbot (Psetta maxima L.)

This study was undertaken to identify the normal morphologic, immunohistochemical and ultrastructural features of skin of the turbot (Psetta maxima L.). In the turbot skin, three morphologically distinct layers were identified: epidermis, dermis and hypodermis. The epidermis was non-keratinizing, stratified squamous epithelium that varies in thickness from 5 to 14 cells and 60 to 100 μm in size. Goblet cells were seen randomly distributed between malpighian cells in the epidermal layer. These mucous cells were mainly located in the upper third of the epidermis and displayed a spherical to elongated morphology. Dermis was divided in two well-differentiated layers, the superficial stratum laxum and the deeper stratum compactum. Hypodermis was a loose layer mainly composed by adipocytes but we could observe variable amounts of fibroblast, collagen and blood vessels. In turbot two pigmentary layers could be identified: the pigmentary layer of dermis was located between basement membrane and dermis and the pigmentary layer of hypodermis immediately above the muscular layer. Three different types of chromatophores were present: melanophores, iridophores and xanthophores. The main differences observed between groups of fish with different colouration were in the amount of melanophores and xanthophores. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous alterations and diseases in turbot.     

Progress of developmental programme during the last larval instar of Bombyx mori: Relationships with food intake,ecdysteroids and juvenile hormone

The progress of developmental programme in the epidermal cells of last instar larvae of Bombyx mori was determined by ecdysteroid injections in normal and in JH-treated larvae. To clarify the importance of food intake in the control of development, starved animals were also used.The instar begins with a period during which the larval programme is expressed: this occurs in the presence of 20-hydroxyecdysone. Epidermal cells can thereafter secrete pupal cuticle after ecdysteroid injection although the larval programme is normally still present. During the last period only pupal characters can be expressed either in normal or in 20-hydroxyecdysone-injected larvae.These different developmental phases are not correlated with obligatory and facultative feeding periods.Transition from the first to the second phases is correlated with the absence of JH effects on pupal genes. JH applications during the second period, however, prevent the expression of pupal characters after 20-hydroxyecdysone injection. Thus, during this period, the pupal programme is not stabilized. Cellular reprogramming itself occurs at the onset of the last developmental period and is probably under the control of ecdysteroids.     

FINE STRUCTURE OF THE LARVAL ANURAN EPIDERMIS,WITH SPECIAL REFERENCE TO THE FIGURES OF EBERTH

Small pieces of skin from 8 cm long Rana clamitans larvae were fixed in OsO₄, washed, dehydrated, and embedded in a methacrylate mixture. Ultrathin sections were cut on a Porter-Blum ultramicrotome and were examined in an RCA electron microscope, type EMU 2D. The sections showed that aggregates of fibrous material in the cells of the inner layer of epidermal cells are identical in disposition and size with the classical figures of Eberth. It is conclusively shown that these figures do not arise from an aggregation of mitochondrial filaments. The tendency of the fibrils to concentrate on attachment points, or thickenings of the basal plasma membrane, is noted. It is also observed that numerous mitochondria are located in the distal region of the cells of the outer layer of epidermis in association with the secretory vacuoles. Microvilli are seen occasionally on the free surface of the skin. Cisternae are found only in the cells of the outer epidermal layer, while vesicular endoplasmic reticulum is found in the cells of both epidermal layers.     

Regional specificity of anuran larval skin during metamorphosis: dermal specificity in development and histolysis of recombined skin grafts

Summary Skins from back and tail were dissected from tadpoles of Rana japonica prior to resorption of the tail and separated into epidermis and dermis by treatment with neutral protease. Homotypically and heterotypically recombined skins were constructed from the separated epidermis and dermis and transplanted into the tail of the original tadpole. Skin grafts using dermis from tail region degenerated simultaneously with resorption of the tail. However, skin grafts containing dermis from back region survived on the posterior part of the juvenile frog beyond metamorphosis. Furthermore, all epidermis underlaid with dermis from back region formed secretory glands and became flattened epithelia characteristic of adult back skin, regardless of region from which the epidermis came. Even when epidermis isolated from tail skin was cultured inside a back skin graft, the tail epidermis survived forming an epithelial cyst and developed secretory glands. These results suggest that regional specificities of anuran larval skin, i.e., development of back skin and even histolysis of tail skin, are determined by regionally specific dermis. The results also suggest that some of epidermal cells of tail skin are able to differentiate into epithelial cells similar to back skin of the adult under the influence of back dermis.     

Expression and hormonal control of a new larval cuticular multigene family at the onset of metamorphosis of the tobacco hornworm

The pattern of cuticular protein synthesis by the epidermis of the tobacco hornworm larva changes during the final day of feeding, leading to an alteration in cuticular structure and a stiffening of the cuticle. We have isolated a small multigene family which codes for at least three of the new cuticular proteins made at this time. The five genes which were isolated from this family map to two different genomic regions. Sequencing shows that one of the genes is 1.9 kb and consists of three exons coding for a 12.2-kDa acidic (pI = 5.26) protein that is predominantly hydrophilic. The deduced amino acid sequence shows regions of similarity to proteins from flexible lepidopteran cuticles and from Drosophila larval and pupal cuticles, but not to proteins found in highly sclerotized cuticles. This gene family is first expressed late on the penultimate day (Day 2) of feeding in the final larval instar and ceases expression 2 days later when metamorphosis begins. In situ hybridization shows that this gene family is expressed in all the epidermal cells of Day 3 larvae except the bristle cells and those at the muscle attachment site. Expression can be induced in Day 1 epidermis by exposure to 50 ng/ml 20-hydroxyecdysone in vitro, but only if juvenile hormone is absent. Its developmental expression, tissue specificity, and hormonal regulation strongly suggest that this multigene family is involved in the structural changes that occur in the larval cuticle just prior to the onset of metamorphosis.     

Par6b Regulates the Dynamics of Apicobasal Polarity during Development of the Stratified Xenopus Epidermis

During early vertebrate development, epithelial cells establish and maintain apicobasal polarity, failure of which can cause developmental defects or cancer metastasis. This process has been mostly studied in simple epithelia that have only one layer of cells, but is poorly understood in stratified epithelia. In this paper we address the role of the polarity protein Partitioning defective-6 homolog beta (Par6b) in the developing stratified epidermis of Xenopus laevis. At the blastula stage, animal blastomeres divide perpendicularly to the apicobasal axis to generate partially polarized superficial cells and non-polarized deep cells. Both cell populations modify their apicobasal polarity during the gastrula stage, before differentiating into the superficial and deep layers of epidermis. Early differentiation of the epidermis is normal in Par6b-depleted embryos; however, epidermal cells dissociate and detach from embryos at the tailbud stage. Par6b-depleted epidermal cells exhibit a significant reduction in basolaterally localized E-cadherin. Examination of the apical marker Crumbs homolog 3 (Crb3) and the basolateral marker Lethal giant larvae 2 (Lgl2) after Par6b depletion reveals that Par6b cell-autonomously regulates the dynamics of apicobasal polarity in both superficial and deep epidermal layers. Par6b is required to maintain the “basolateral” state in both epidermal layers, which explains the reduction of basolateral adhesion complexes and epidermal cells shedding.     

External structure of cuticle injuries and larval mouth parts of the chiggers Euschoengastia rotundata and Neotrombicula vulgaris (Trombiculidae)

When E. rotundata larvae parasitize the abdominal part of the body of their host (Clethrionomys glareolus), capsules with round terminal opening are formed from which hind part of the mite's body projects forwards. Organization of the capsules shows that their walls are formed by a substance (probably by larval saliva) which differs from host's tissues. At the bottom of the capsules there are larval adhesive sites with openings in the proximal parts of stylostomes which resemble in their structure these of N. vulgaris larvae. The latter do not form capsules when feeding on their natural hosts, Microtus arvalis. Proximal part of stylostome is formed in both cases by amorphous glutinous substance bearing imprints of mite's mobile digits of chelicerae and hypostome. Mouth parts of hungry mites and satiated larvae of both species differ only in relative sizes of constituent parts. Soft apical part of hypostome turns backwards during the feeding and forms a sucker. The feeding of larvae of trombiculids in capsules, which is formally regarded as ectoparasitism, can apparently be considered as a special type of parasitism.     

Melanin and dopa-positive cells in the skin of tropical cattle.

Various histochemical and histological techniques were used to study the melanin and dopa-positive cell distribution in the skin of some tropical and temperate breeds of cattle in Nigeria. Melanin pigments were concentrated in the basal and lower spinous layers of the epidermis and in the hair cortex, follicle sheaths and papillae of the various breeds. In the White Fulani and N'Dama breeds, melanin pigments were however found in all layers of the epidermis. Dopa-positive cells (melanocytes) were observed in the epidermis, dermis and hair follicles; the distribution pattern varied among breeds, being copiously disposed in the basal epidermis and papillary dermis in the White Fulani and Muturu and, except in areas of thick epidermal ridges, scanty in the epidermis and dermis of the Friesian and N'Dama. Mast cell distribution pattern in the various breeds was similar to that of the dopa-positive cells. Peroxidase-positive cells were present in the basal epidermis and upper dermis of the Muturu, widespread in the subepidermal layer of the N'Dama and very scanty in the dermis of the White Fulani and Friesian. Acid phosphatase activity was intense in the granular layer of the Muturu and N'Dama breeds and also in the papillary dermis and hair follicles, whereas alkaline phosphatase-positive dendritic cells, and 'clear' cells were also observed in the basal and upper epidermis.     

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。     

Xanthophore migration from the dermis to the epidermis and dermal remodeling during Salamandra salamandra salamandra (L.) larval development

During larval development of Salamandra salamandra salamandra chromatophores organize to form the definitive pigment pattern constituted by a black background with yellow patches that are characterized by epidermal xanthophores and dermal iridophores. Simultaneously the dermis undergoes remodeling from the larval stage to that typical of the adult. In the present study we ultrastucturally and immunocytochemically examined skin fragments of S. s. salamandra larvae and juveniles in order to investigate the modalities of xanthophore migration and differentiation in the context of dermal remodeling from the larval to adult stage. Semithin and thin sections showed that the dermis in newly born larvae consists of a compact connective tissue (basement lamella), to which fibroblasts and xanthophores adhere, and of a loose deep collagen layer. As larval development proceeds, fibroblasts and xanthophores invade the basement lamella, skin glands develop and the adult dermis forms. At metamorphosis, xanthophores reach the epidermis crossing through the basal lamina. We examined immunocytochemically the expression of signal molecules, such as fibronectin, vitronectin, beta1-integrin, chondroitin sulfate, E-cadherin, N-cadherin and plasminogen activator, which are known to be involved in regulating morphogenetic events. Their role in dermal remodeling and in pigment pattern formation is discussed.     

Structure of the integument of a fresh-water teleost,Bagarius bagarius (Ham.) (Sisoridae,pisces)

The skin of Bagarius bagarius (Ham.) is devoid of scales but is rough due to the presence of numerous pentagonal epidermal elevations, which are separated by deep furrows at regular intervals. These elevated pentagonal regions of the epidermis are covered by dead cornified cells in the form of caps. As the old cap goes off a new one is formed by the death of the underlying epidermal cells. The middle layer of the epidermis is mainly composed of well defined polygonal cells. Their cytoplasm is granular in nature and give reactions for protein bound sulphydryl groups. The stratum germinativum is composed of two types of basal cells, the columnar cells and the spherical cells. The flask shaped mucous glands are restricted to the epidermal furrows and secrete either neutral or acidic mucopolysaccharides. Certain large specialysed granular cells are found in the epidermis which are grouped around the taste buds. These specialysed cells may be the photocytes. Two layers of the dermis can be distinguished—the relatively thin stratum laxum and the thick stratum compactum. Dermal papillae mainly support the taste buds. The pigment cells are arranged in two layers in the dermis. The subcutis is composed of loose connective tissues, richly infiltrated with the fat cells, nerves and blood capillaries.     

Myosin Vb Mediated Plasma Membrane Homeostasis Regulates Peridermal Cell Size and Maintains Tissue Homeostasis in the Zebrafish Epidermis

The epidermis is a stratified epithelium, which forms a barrier to maintain the internal milieu in metazoans. Being the outermost tissue, growth of the epidermis has to be strictly coordinated with the growth of the embryo. The key parameters that determine tissue growth are cell number and cell size. So far, it has remained unclear how the size of epidermal cells is maintained and whether it contributes towards epidermal homeostasis. We have used genetic analysis in combination with cellular imaging to show that zebrafish goosepimples/myosin Vb regulates plasma membrane homeostasis and is involved in maintenance of cell size in the periderm, the outermost epidermal layer. The decrease in peridermal cell size in Myosin Vb deficient embryos is compensated by an increase in cell number whereas decrease in cell number results in the expansion of peridermal cells, which requires myosin Vb (myoVb) function. Inhibition of cell proliferation as well as cell size expansion results in increased lethality in larval stages suggesting that this two-way compensatory mechanism is essential for growing larvae. Our analyses unravel the importance of Myosin Vb dependent cell size regulation in epidermal homeostasis and demonstrate that the epidermis has the ability to maintain a dynamic balance between cell size and cell number.