A light and electron microscopic investigation of the digestive system of the Ophiuroid ophiuroiderma panamensis (Brittle Star)

The Brittle Star digestive system is composed of buccal, pharyngeal, esophageal and stomach cavities. The buccal and pharyngeal cavities are lined by columnar cells covered by a cuticle, and are apparently concerned with mucous production. Coelomocytes and tall columnar cells are described in the esophagus and stomach epithelia. The columnar cells are adapted for nutrient absorption, enzyme synthesis, and lipid storage. Nerves are found beneath the epithelia within a connective tissue layer. Smooth muscle and coelomic layers lie external to the connective tissue layer. The coelomic layer lines a perivisceral space and has diverse modifications of its perivisceral surface; a pedicle-cuticle modification perhaps having general significance in echinoderms.     

Fine Structure of the ‘Slit Organs’ of the Pycnogonid Anoplodactylus petiolatus (Anoplodactylidae)

Abstract The ‘slit organs’ of Anoplodactylus petiolatus are found all over the body cuticle. They are composed of a cuticular pore apparatus, an inner and an outer canal cell, and of four large and one to three small compartment cells. Plasma of the latter seven cells is almost completely filled with large membrane-enclosed compartments that contain either numerous small vesicles (one of the large cells) or homogeneous material of varying electron density (three large and all the small cells). Microvilli are found in the apical region of the compartment cells. The nucleus is situated basally where Golgi-cisternae, coated vesicles and free ribosomes are frequently found. Apical microvilli and vesicles are also formed by the inner canal cell indicating that it might directly be involved in transport. Anatomically the ‘slit organs’ are similar to class III glands described for many arthropods. In addition, discharge of secretion via large intracellular compartments is also a feature found in arthropod glands. Although pycnogonids appear to take up substances across the cuticle, a genuine secretion rather than a more generalized transport function is suggested for the ‘slit organs’.     

Fine structure and probable function of ring organs in the mite Histiostoma feroniarum (Acari: Actinotrichida: Acaridida: Histiostomatidae)

Histiostoma feroniarum, like other histiostomatid mites, possesses peculiar ring organs that are visible under the light microscope as ventrally located, characteristic rings of sclerotized cuticle. The ring organ is composed of three elements: a disc of modified cuticle, ring organ cells located underneath the disc, and an "empty" chamber frequently visible between the cuticular disc and the cells. The cuticle of the disc is not perforated and differs from the surrounding unmodified cuticle as revealed by special staining developed for light microscopy and by electron microscopy. The ring organ cells show a polarity, with a practically smooth apical surface and an extremely folded basal membrane. The basal invaginations reach the apical cell portion, where they form tubular canaliculi distributed beneath the apical cell membrane. The cytoplasm contains many mitochondria, which are usually in contact with the cell membrane invaginations. Structurally, the ring organ cells closely resemble the transport cells described in osmoregulatory organs both in water-inhabiting and terrestrial arthropods. Thus, our results support earlier suggestions of an osmoregulatory function performed by sclerotized rings (=ring organs), as an adaptation to aqueous environments. A possible homology with similar organs of other mites is discussed.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Study of nsLTPs in Lotus japonicus genome reveal a specific epidermal cell member (LjLTP10) regulated by drought stress in aerial organs with a putative role in cutin formation

The cuticle is the first defense against pathogens and the second way water is lost in plants. Hydrophobic layers covering aerial plant organs from primary stages of development form cuticle, including major classes of aliphatic wax components and cutin. Extensive research has been conducted to understand cuticle formation mechanisms in plants. However, many questions remain unresolved in the transport of lipid components to form cuticle. Database studies of the Lotus japonicus genome have revealed the presence of 24 sequences classified as putative non-specific lipid transfer proteins (nsLTPs), which were classified in seven groups; four groups were selected because of their expression in aerial organs. LjLTP8 forms a cluster with DIR1 in Arabidopsis thaliana while LjLTP6, LjLTP9, and LjLTP10 were grouped as type I LTPs. In silico studies showed a high level of structural conservation, and substrate affinity studies revealed palmitoyl-CoA as the most likely ligand for these LTPs, although the Lyso-Myristoyl Phosphatidyl Choline, Lyso-myristoyl phosphatidyl glycerol, and Lyso-stearyl phosphatidyl choline ligands also showed a high affinity with the proteins. The LjLTP6 and LjLTP10 genes were expressed in both the stems and the leaves under normal conditions and were highly induced during drought stress. LjLTP10 was the most induced gene in shoots during drought. The gene was only expressed in the epidermal cells of stems, primordial leaves, and young leaflets. LjLTP10 was positively regulated by MeJA but repressed by abscisic acid (ABA), ethylene, and H₂O₂, while LjLTP6 was weakly induced by MeJA, repressed by H₂O₂, and not affected by ABA and ethylene. We suggest that LjLTP10 is involved in plant development of stem and leaf cuticle, but also in acclimation to tolerate drought stress in L. japonicus.     

A role for BMP heterodimers in roof plate-mediated repulsion of commissural axons

During spinal cord development, commissural neurons extend their axons ventrally, away from the roof plate. The roof plate is the source of a diffusible repellent that orients commissural axons in vitro and, thus, may regulate the trajectory of commissural axons in vivo. Of three Bmps expressed in the roof plate, BMP7, but not BMP6 or GDF7, mimics the roof plate activity in vitro. We show here that expression of both Bmp7 and Gdf7 by roof plate cells is required for the fidelity of commissural axon growth in vivo. We also demonstrate that BMP7 and GDF7 heterodimerize in vitro and that, under these conditions, GDF7 enhances the axon-orienting activity of BMP7. Our findings suggest that a GDF7:BMP7 heterodimer functions as a roof plate-derived repellent that establishes the initial ventral trajectory of commissural axons.     

胸窗萤的防卫行为：反射性出血及翻缩腺反应

为了探讨胸窗萤Pyrocoelia pectoralis Oliver, 1883的防卫行为, 对成虫的反射性出血行为及幼虫的翻缩腺体形态进行了研究。结果表明： 胸窗萤具有复杂的多重防卫行为策略。成虫利用闪烁、 假死、 反射性流血进行防卫, 幼虫则利用闪烁、 假死和微小的翻缩腺体进行防卫。反射性流血发生在雄成虫的前胸背板和鞘翅边缘, 而雌成虫仅在前胸背板边缘观察到有反射性流血行为。扫描电镜观察到直径大约32 μm的圆坑状结构环绕前胸背板或鞘翅边缘一圈。雌虫鞘翅牙也具有相似的圆坑状结构。幼虫具有9对乳头状的翻缩腺体, 位于中胸、 后胸和第1～7节侧板上。超薄切片发现, 腺体表面的棒状结构内部中空, 棒状结构连接一个发达的分泌细胞。细胞内连接棒状结构的部位着生致密的管状内质网。行为学实验发现, 胸窗萤血液对蚂蚁具有非常有效的拒避作用。     

Special cutaneous receptor organs of fish. IV. Ampullary organs of the nonelectric catfish, Kryptopterus

Ampullary organs of the transparent catfish, Kryptopterus bicirrhus, are present in large numbers on the head and in a regular pattern of lines on the body and fins. The organs lie in the epidermis, and have a pore that opens to the surface. Flattened cells form a roof and walls. On the floor of the organ there are a “sensory hillock,” composed of spherical receptor cells and columnar supporting cells, and a “secretory hillock” composed of columnar secretory cells. The receptor cells are nonciliated and have only afferent innervation. The organ cavity is filled with jelly. The organs are compared with ampullary organs of the weakly electric fish Eigenmannia, ampullae of Lorenzini of Raja, and small pit organs of Amiurus. Structural characteristics of the ampullary organs of Kryptopterus make them especially suitable for electrophysiological studies.     

Ultrastructural investigation of the vesicular glands in Scutigera coleoptrata (Chilopoda,Notostigmophora)

In the notostigmophoran centipedes, two pairs of vesicular glands have evolved. These paired glands are situated in the first and second trunk segment and open via cuticular ducts in the upper part of the particular pleura. The vesicular glands of Scutigera coleoptrata were investigated using light and, for the first time, electron microscopical methods. The glands consist of wide sac‐like cavities that often appear vesicular. The epithelia of both glands are identically structured and consist of numerous glandular units. Each of these units consists of four different cells: a single secretory cell, a small intermediary cell, and one proximal and one distal canal cell. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cells. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the ultrastructure of glandular units of the vesicular glands is comparable to that of the glandular units of other epidermal glands in Chilopoda and Diplopoda, although the glands look completely different in the light microscope. Thus, it is likely that the vesicular glands and epidermal glands share the same ground pattern. With regard to specific differences in the cuticular lining of the intermediary cells, a common origin of epidermal glands in Myriapoda and Hexapoda is not supported. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

An ultrastructural analysis of the cuticle,epidermis and esophageal epithelium of Eisenia foetida (Oligochaeta)

The epidermis of Eisenia is covered by a cuticle and rests on a basement lamella. The cuticle, which is resistant to a variety of enzymes, is composed of non-striated, bundles of probable collagen fibers that are orthogonally oriented and are embedded in a proteoglycan matrix. The basement lamella consists of striated collagen fibers with a 560 Å major periodicity. Proximity and morphology suggest that the epidermis may contribute to both the cuticle and the basement lamella — that is, the single tissue may synthesize at least two types of collagen. The epidermis is a pseudostratified epithelium containing three major cell types (columnar, basal and gland) and a rare fourth type with apical cilia. The esophagus is lined by a simple cuticulated epithelium composed predominantly of a single cell type, which resembles the epidermal columnar cell. Rare gland cells occur in the esophageal epithelium, but basal cells are lacking.     

Ultrastructural investigations on the nuchal organ of the protandric polychaete,Ophryotrocha puerilis (Polychaeta,Dorvilleidae)

Summary The nuchal organs of the protandric hermaphrodite Ophryotrocha puerilis were studied by electron microscopy. Ophryotrocha puerilis is the first species hitherto described which possesses four instead of two nuchal organs. These sensory structures are located as ciliary pits at the posterior margin of the prostomium. Histologically, the nuchal organs are composed of supporting cells with long motile cilia and bipolar sensory cells, the perikarya of which form four distinct nuchal ganglia adjoining the brain. These structural components are concentrically arranged around the central sensory area. This area is covered by a modified cuticle, whereas the cuticle above the peripheral region of the sense organ exhibits the appearance typical for polychaetes. Two types of vesicular material are produced in the basal supporting cells, a dense-cored one within the central supporting cells only and a clear irregular-shaped one in all of these cells. The first type is considered to be responsible for the formation of the modified cuticle. The significance of these most probably long-distance chemoreceptory organs and their possible role in reproductive behaviour is discussed.     

Renal Lipotoxicity-Associated Inflammation and Insulin Resistance Affects Actin Cytoskeleton Organization in Podocytes

In the last few decades a change in lifestyle has led to an alarming increase in the prevalence of obesity and obesity-associated complications. Obese patients are at increased risk of developing hypertension, heart disease, insulin resistance (IR), dyslipidemia, type 2 diabetes and renal disease. The excess calories are stored as triglycerides in adipose tissue, but also may accumulate ectopically in other organs, including the kidney, which contributes to the damage through a toxic process named lipotoxicity. Recently, the evidence suggests that renal lipid accumulation leads to glomerular damage and, more specifically, produces dysfunction in podocytes, key cells that compose and maintain the glomerular filtration barrier. Our aim was to analyze the early mechanisms underlying the development of renal disease associated with the process of lipotoxicity in podocytes. Our results show that treatment of podocytes with palmitic acid produced intracellular accumulation of lipid droplets and abnormal glucose and lipid metabolism. This was accompanied by the development of inflammation, oxidative stress and endoplasmic reticulum stress and insulin resistance. We found specific rearrangements of the actin cytoskeleton and slit diaphragm proteins (Nephrin, P-Cadherin, Vimentin) associated with this insulin resistance in palmitic-treated podocytes. We conclude that lipotoxicity accelerates glomerular disease through lipid accumulation and inflammation. Moreover, saturated fatty acids specifically promote insulin resistance by disturbing the cytoarchitecture of podocytes. These data suggest that renal lipid metabolism and cytoskeleton rearrangements may serve as a target for specific therapies aimed at slowing the progression of podocyte failure during metabolic syndrome.     

Early posterior/ventral fate specification in the vertebrate embryo

Slit is expressed in the midline of the central nervous system both in vertebrates and invertebrates. In Drosophila, it is the midline repellent acting as a ligand for the Roundabout (Robo) protein, the repulsive receptor which is expressed on the growth cones of the commissural neurons. We have isolated cDNA fragments of the zebrafish slit2 and slit3 homologues and found that both genes start to be expressed by the midgastrula stage well before the axonogenesis begins in the nervous system, both in the axial mesoderm, and slit2 in the anterior margin of the neural plate and slit3 in the polster at the anterior end of the prechordal mesoderm. Later, expression of slit2 mRNA is detected mainly in midline structures such as the floor plate cells and the hypochord, and in the anterior margins of the neural plates in the zebrafish embryo, while slit3 expression is observed in the anterior margin of the prechordal plate, the floorplate cells in the hindbrain, and the motor neurons both in the hindbrain and the spinal cord. To study the role of Slit in early embryos, we overexpressed Slit2 in the whole embryos either by injection of its mRNA into one-cell stage embryos or by heat-shock treatment of the transgenic embryos which carries the slit2 gene under control of the heat-shock promoter. Overexpression of Slit2 in such ways impaired the convergent extension movement of the mesoderm and the rostral migration of the cells in the dorsal diencephalon and resulted in cyclopia. Our results shed light on a novel aspect of Slit function as a regulatory factor of mesodermal cell movement during gastrulation.     

Morphology of defense glands of the opilionids (daddy longlegs) Leiobunum vittatum and L. flavum (Arachnida: Opiliones: Palpatores: Phalangiidae)

Opilionid defense glands consist of 0.5 × 0.9-mm sacs attached to the underside of low tubercles located on the dorsal side of the cephalothorax, posterior to the first pair of legs. Each gland opens via an elongated slit, located in the posterior floor of a crater that is situated at the summit of the tubercle. The center of the sac, called the reservoir, is lined by a cuticle consisting of epicuticle and endocuticle which is continuous through the slit with the exoskeleton. The layers of cuticle vary in thickness with different locations in the gland. A hemocoelomic (basement) membrane, 0.5–1, μ thick, forms the boundary between glandular cells and hemocoel. The gland has a nonsecretory portion consisting only of cuticle-supporting cells and a secretory portion consisting of secretory and cuticle-supporting cells. The cuticle lining the reservoir in the secretory area is broached by many cuticle-lined ductules, each of which drains an isolated intercellular space called the intercalated cistern. This in turn drains microvilli-lined canaliculi located between and extending into secretory cells. The cisterns are devoid of microvilli. Secretory cell cytoplasm contains a Golgi apparatus, many free ribosomes, rough endoplasmic reticulum (RER), two types of granules (speckled and dense), and mitochondria. Speckled granules are partially filled with fairly large particles and are found in association with the Golgi apparatus. They also surround canaliculi into which they empty. Dense granules are packed with very small particles, have a gray homogeneous appearance, and are scattered throughout the cytoplasm. Mitochondria containing matrix granules tend to scatter throughout the cytoplasm but are concentrated around canaliculi.     

Arabidopsis LTPG Is a Glycosylphosphatidylinositol-Anchored Lipid Transfer Protein Required for Export of Lipids to the Plant Surface

Plant epidermal cells dedicate more than half of their lipid metabolism to the synthesis of cuticular lipids, which seal and protect the plant shoot. The cuticle is made up of a cutin polymer and waxes, diverse hydrophobic compounds including very-long-chain fatty acids and their derivatives. How such hydrophobic compounds are exported to the cuticle, especially through the hydrophilic plant cell wall, is not known. By performing a reverse genetic screen, we have identified LTPG, a glycosylphosphatidylinositol-anchored lipid transfer protein that is highly expressed in the epidermis during cuticle biosynthesis in Arabidopsis thaliana inflorescence stems. Mutant plant lines with decreased LTPG expression had reduced wax load on the stem surface, showing that LTPG is involved either directly or indirectly in cuticular lipid deposition. In vitro 2-p-toluidinonaphthalene-6-sulfonate assays showed that recombinant LTPG has the capacity to bind to this lipid probe. LTPG was primarily localized to the plasma membrane on all faces of stem epidermal cells in the growing regions of inflorescence stems where wax is actively secreted. These data suggest that LTPG may function as a component of the cuticular lipid export machinery.     

Slit sense organs on the scorpion leg (Androctonus australis L., Buthidae)

As in other arthropods the exoskeleton of arachnids is subjected to loads generated by external stimuli and behavioral activities. Far from being mere by-products of various activities such loads act as signals for mechanoreceptors capable of detecting minute displacements caused by them in the cuticle. In arachnids the slit sense organs serve in this capacity. Spiders have the most elaborate system of slit sense organs. Our previous studies clearly pointed to a functional significance of their specific location and orientation, as well as degree and type of aggregation (isolated, grouped, compound or lyriform) on respective body parts. The present study extends our work to the slit sense organs of scorpions. It gives a detailed account of the topography of the organs on the walking legs. In general slits are less orderly arranged on the legs of scorpions than on those of spiders. In the scorpion they never aggregate to form lyriform organs. Instead there are groups at comparable locations forming much more irregular, but still specific patterns. Isolated slits are more numerous on the scorpion leg, but are also less regularly distrubuted there. A common feature of the majority of slits on both the spider and the scorpion leg is their position on the lateral surfaces and their orientation roughly parallel to the long axis of the leg.     

The conserved transmembrane protein TMEM-39 coordinates with COPII to promote collagen secretion and regulate ER stress response

Dysregulation of collagen production and secretion contributes to aging and tissue fibrosis of major organs. How procollagen proteins in the endoplasmic reticulum (ER) route as specialized cargos for secretion remains to be fully elucidated. Here, we report that TMEM39, an ER-localized transmembrane protein, regulates production and secretory cargo trafficking of procollagen. We identify the C. elegans ortholog TMEM-39 from an unbiased RNAi screen and show that deficiency of tmem-39 leads to striking defects in cuticle collagen production and constitutively high ER stress response. RNAi knockdown of the tmem-39 ortholog in Drosophila causes similar defects in collagen secretion from fat body cells. The cytosolic domain of human TMEM39A binds to Sec23A, a vesicle coat protein that drives collagen secretion and vesicular trafficking. TMEM-39 regulation of collagen secretion is independent of ER stress response and autophagy. We propose that the roles of TMEM-39 in collagen secretion and ER homeostasis are likely evolutionarily conserved.     

ABC-type transporters and cuticle assembly: Linking function to polarity in epidermis cells

The aerial organs of plants are covered with a cuticle, a continuous layer overlaying the outermost cell walls of the epidermis. The cuticle is composed of two major classes of the lipid biopolymers: cutin and waxes, collectively termed cuticular lipids. Biosynthesis and transport of cuticular lipids occur predominantly in the epidermis cells. In the transport pathway, cuticular lipids are exported from their site of biosynthesis in the ER/plastid to the extracellular space through the plasma membrane and cell wall. Growing evidence suggests that ATP-binding cassette (ABC) transporters are implicated in transport of cuticular lipids across the plasma membrane of epidermal cells. The Arabidopsis ABC-type transporter protein CER5 (WBC12) was reported to act as a wax monomers transporter. In recent works, our group and others showed that a CER5-related protein, DESPERADO (DSO/WBC11), is required for cutin and wax monomers transport through the plasma membrane of Arabidopsis epidermis cells. Unlike the cer5 mutant, DSO loss-of-function had a profound effect on plant growth and development, particularly dwarfism, postgenital organ fusions, and altered epidermal cell differentiation. The partially overlapping function of CER5 and DSO and the fact that these proteins are half-size ABC transporters suggest that they might form a hetero-dimeric complex while transporting wax components. An intriguing observation was the polar localization of DSO in the distal part of epidermis cells. This polar expression might be explained by DSO localization within lipid rafts, specific plasma membrane microdomains which are associated with polar protein expression. In this review we suggest possible mechanisms for cuticular lipids transport and a link between DSO function and polar expression. Furthermore, we also discuss the subsequent transport of cuticular constituents through the hydrophobic cell wall and the possible involvement of lipid transfer proteins in this process.Key words: ABC transporter, cuticular lipids, polar expression, plasma membrane, epidermis     

MORPHOLOGICAL AND FUNCTIONAL ASPECTS OF AN INSECT EPIDERMAL GLAND

The sternal gland of primitive termites of the genus Zootermopsis (Z. nevadensis or Z. angusticollus) (Hagen) seems more organized than that of higher termites, in being comprised of three cell layers. It is also studded with about 200 campaniform sensilla. Below the meshwork cuticle of the gland lies a layer of columnar epithelial cells whose apical surfaces form a brush border, and whose basal surfaces are sculptured into a basketwork into which the second layer fits. Below the brush border are small microtubule-associated pits and coated vesicles. No channels can be seen either within or, except for the sensilla, between the cells. The second cell layer probably secretes the trail-following pheromone. Numerous electron-lucent droplets and large channels containing lipid micelles are found in the cytoplasm here, but the channels cannot be traced out of the secretory layer. The third layer consists of large pyriform cells. The campaniform sensilla are composed of three cells: the sensory cell proper whose dendrite carries a modified 9 + 0 sensory process, an accessory supporting cell that secretes an electron-opaque sheath, and an enveloping cell. At the cell borders of the sensillum, regions of septate and tight junction appear. There are also septate junctions between columnar cells and possibly tight junctions between columnar and secretory cells that would open an intracellular and molecular pathway to the endocuticle. The campaniform sensilla may be part of a feedback control system that determines the amount of pheromone deposited during trail laying.     

Clearing pigmented insect cuticle to investigate small insects' organs in situ using confocal laser-scanning microscopy (CLSM)

Various microscopic techniques allow investigating structures from submicron to millimeter range, however, this is only possible if the structures of interest are not covered by pigmented cuticle. Here, we present a protocol that combines clearing of pigmented cuticle while preserving both, hard and soft tissues. The resulting transparent cuticle allows confocal laser-scanning microscopy (CLSM), which yields high-resolution images of e.g. the brain, glands, muscles and fine cuticular structures. Using a fluorescent dye, even single labeled neurons can be visualized and resolved up to an imaging depth of 150 μm through the cleared cuticle. Hydrogen-peroxide, which was used to clear the cuticle, does not preclude immunocytochemical techniques, shown by successful labeling of serotonin-immunoreactive neurons (5HT-ir) in the ants' brain. The ‘transparent insect protocol’ presented here is especially suited for small arthropods where dissection of organs is very demanding and difficult to achieve. Furthermore, the insect organs are preserved in situ thus allowing a more precise three-dimensional reconstruction of the structures of interest compared to, e.g., dissected or sectioned tissue.