CYTOPLASMIC MICROTUBULES : I. Hydra

Small cytoplasmic tubules are present in the interstitial cells and cnidoblasts of hydra. They are referred to here as "microtubules." These tubular elements have an outside diameter of 180 A and an inside diameter of 80 A. By difference, the membranous wall is estimated to be 50 A thick. The maximum length of the microtubules cannot be determined from thin sections but is known to exceed 1.5 µ. In the interstitial cells the microtubules are found in the intercellular bridges, free in the cytoplasm and in association with the centrioles. In the cnidoblast they form a framework around the developing nematocyst and in late stages are related to the cnidocil forming a tight skein in the basal part of the cell. Especially in this cell, confluence of microtubules with small spherical vesicles of the Golgi complex has been observed. It is proposed that these tubules function in the transport of water, ions, or small molecules.     

Further observations on dividing and non-dividing cnidoblasts in the regenerating isolated gastrodermis of Hydra

Summary Cnidoblasts derived from the dedifferentiation of gland cells in the regenerating isolated gastrodermis of Hydra are capable of nuclear and cytoplasmic division. The daughter cell containing the nematocyst apparently develops normally. The fate of the other daughter cell remains obscure, but it is believed that it is also capable of developing a nematocyst. Only a single bi-nucleated cnidoblast was observed and it was in the process of degeneration. It is suggested that at least in the present system, cnidoblasts are derived not only from interstitial cells but also from pre-existing cnidoblasts.This investigation was supported by the National Science Foundation Grant No. GB 8384.With the technical assistance of Linda Bookman.     

The fine structure of differentiating interstitial cells in Hydra

Summary Interstitial cells of hydra are small undifferentiated cells containing an abundance of free ribosomes and few other cytoplasmic organelles. They are capable of differentiating into epitheliomuscular, digestive, glandular, nerve cells, and cnidoblasts. Developing epitheliomuscular and digestive cells acquire bundles of filaments, 50 Å in diameter, which later are incorporated into the muscular processes. Early gland cells develop an elaborate rough-surfaced endoplasmic reticulum and one or more Golgi apparatus. Secretory granules originate in the Golgi region eventually filling the apex of the cell. Neurons are recognized first by the presence of an elaborate Golgi apparatus, absence of a well-developed endoplasmic reticulum, and later the appearance of cytoplasmic processes. The most striking feature of nematocyst formation by cnidoblasts is the presence of a complex distribution system between protein synthesizing rough-surfaced endoplasmic reticulum and the nematocyst. This system consists of connections between cisternae of the endoplasmic reticulum with smooth Golgi vesicles which in turn are connected to minute tubules, 200 Å in diameter. The tubules extend from the Golgi region around the nematocyst finally entering the limiting membrane of the nematocyst. It is suggested that the interstitial cells of hydra represent a model system for the investigation of many aspects of cell differentiation.This work was supported by grants from the National Cancer Institute (TlCA-5055) and from the National Institute of Arthritis and Metabolic Diseases (AM-03688), National Institutes of Health, Department of Health, Education and Welfare.The author is indebted to Dr. Russell J. Barrnett for his guidance and interest throughout this investigation.     

FINE STRUCTURE OF THE NERVOUS SYSTEM OF HYDRA

Fine structural details of the cells and processes of the hydranenous system are reported in this paper. Ganglion cells aresmall bipolar or multipolar cells situated above the muscularprocesses of epitheliomusiular cells. An elaborate Colgi apparatusconsisting of parallel lamellae and small and large vesiclesis present in these cells. Some cells are poor in ribosomeswhile others contain numerous free ribosomes. In the ribosome-richcells, small membranous microtubules originating from the nuclearenvelope extend into the cytoplasm and neurites. The neuritesalso contain vesicles and mitochondria and terminate at thebases of cnidoblasts and on the muscular processes of epitheliomuscularcells. Specialized synapses were not observed. A second cell type contains many membrane-bounded dense granules,1000 A in diameter, and these are considered to be neurosecretorycells. Neurosecretory granules on cnidoblasts and epitheliomuscularcells. Sensory cells are small elongated cells originate inthe Golgi apparatus and are abundant in neurites which alsoterminate situated between the apical surfaces of epithelialand digestive cells. These cells are characterized by an apicalspecialization which appears to be a modified cilium. Neurosensorycells were also observed. The intimate connection of the nervoussystem with cnidoblasts suggests a role in nematocyst discharge.The finding of neurosecretory material supports the hypothesisthat the neural control of regeneration in hydra is regulatedby material released at nerve endings.     

The Development of the Cnidoblasts of Hydra : An Electron Microscope Study of Cell Differentiation

The general histological organization of Hydra is reviewed and electron microscopic observations are presented which bear upon the nature of the mesoglea, the mode of attachment of the contractile processes of the musculo-epithelial cells, and the cytomorphosis of the cnidoblasts. Particular attention is devoted to the changes in form and distribution of the cytoplasmic organelles in the course of nematocyst formation. The undifferentiated interstitial cell is characterized by a small Golgi complex, few mitochondria, virtual absence of the endoplasmic reticulum, and a cytoplasmic matrix crowded with fine granules presumed to be ribonucleoprotein. These cytological characteristics persist through the early part of the period of interstitial cell proliferation which leads to formation of clusters of cnidoblasts. With the initiation of nematocyst formation in the cnidoblasts, numerous membrane-bounded vesicles appear in their cytoplasm. These later coalesce to form a typical endoplasmic reticulum with associated ribonucleoprotein granules. During the ensuing period of rapid growth of the nematocyst the reticulum becomes very extensive and highly organized. Finally, when the nematocyst has attained its full size, the reticulum breaks up again into isolated vesicles. The Golgi complex remains closely applied to the apical pole of the nematocyst throughout its development and apparently contributes to its enlargement by segregating formative material in vacuoles whose contents are subsequently incorporated in the nematocyst. The elaboration of this complex cell product appears to require the cooperative participation of the endoplasmic reticulum and the Golgi complex. Their respective roles in the formative process are discussed.     

Cytophotometric studies of nucleic acids and basic proteins during somatic and germinal differentiation of the interstitial cells of Hydra cauliculata (Hyman 1938)

Cytophotometric studies were made of the interstitial cells of Hydra during their differentiation into cnidoblasts and spermatozoa. DNA, RNA and basic proteins were measured by ultraviolet, Feulgen and alkaline Fast Green methods. Interstitial cells were found to contain approximately twice as much Feulgen-stained DNA as spermatozoa but an amount equal to that of the cnidoblast. DNA values for spermatogenic cells obtained by UV measurements were comparatively greater than those obtained using the Feulgen reaction, but were approximately equivalent after treatment of the cells with RNase. The Fast Green-histone/Feulgen-DNA ratio increased during the differentiation of both the cnidoblast and the spermatozoon. A relative increase in the lysine-rich histone fractions appeared to be largely responsible for these changes. During the terminal stages of spermatogenesis, however, the lysine-rich histones were replaced by more arginine-rich varieties.     

The development of the cnidoblasts of Hydra; an electron microscope study of cell differentiation

The general histological organization of Hydra is reviewed and electron microscopic observations are presented which bear upon the nature of the mesoglea, the mode of attachment of the contractile processes of the musculo-epithelial cells, and the cytomorphosis of the cnidoblasts. Particular attention is devoted to the changes in form and distribution of the cytoplasmic organelles in the course of nematocyst formation. The undifferentiated interstitial cell is characterized by a small Golgi complex, few mitochondria, virtual absence of the endoplasmic reticulum, and a cytoplasmic matrix crowded with fine granules presumed to be ribonucleoprotein. These cytological characteristics persist through the early part of the period of interstitial cell proliferation which leads to formation of clusters of cnidoblasts. With the initiation of nematocyst formation in the cnidoblasts, numerous membrane-bounded vesicles appear in their cytoplasm. These later coalesce to form a typical endoplasmic reticulum with associated ribonucleoprotein granules. During the ensuing period of rapid growth of the nematocyst the reticulum becomes very extensive and highly organized. Finally, when the nematocyst has attained its full size, the reticulum breaks up again into isolated vesicles. The Golgi complex remains closely applied to the apical pole of the nematocyst throughout its development and apparently contributes to its enlargement by segregating formative material in vacuoles whose contents are subsequently incorporated in the nematocyst. The elaboration of this complex cell product appears to require the cooperative participation of the endoplasmic reticulum and the Golgi complex. Their respective roles in the formative process are discussed.     

Die Klebstoffhaare an den Antheren vonCyclanthera pedata (Cucurbitaceae)

The highly specialized, two-celled hairs fringing the anthers ofCyclanthera pedata (L.)Schrad. and its relatives aid in pollination by producing a glue which sticks the coarse pollen grains onto insect visitors. This was proven by direct observations, confirming older assumptions. The adhesive is extruded from the big basal cell which bursts upon the slightest touch to the small top cell.—Turgor and, possibly, swelling pressure of the sticky material, are responsible for plasmoptysis and ejaculation. Cell contraction is due to tension of cuticular clips and, to a minor degree, to elasticity of the pectinic wall. A preformed apical dehiscence line disrupts when the top cell is bent aside.—The anthers hairs of a flower develop synchronously. From light and electron microscopic observations, the adhesive appears not to be a product of internal secretion. It originates from the endopolyploid giant nucleus of the basal cell, which finally degenerates by liquefying and swelling. The numerous peculiar elaioplasts apparently do not contribute to the hair's function.—The anther hairs are homologous to, and possibly have evolved from the so-called explosion hairs occurring on the green parts of manyCucurbitaceae.

Herrn Professor Dr.Walter Leinfellner zum 70. Geburtstag gewidmet.     

The Wheel Organ and Hatschek's Groove in the Lancelet,Branchiostoma lanceolatum (Cephalochordata)

The wheel organ is a specialized epithelium in the roof and sides of the adult lancelet oral cavity. It borders the oral epithelium proper, separated by a thin strip of margin cells which are not ciliated but contain a few large dense-cored vesicles apically. The wheel organ cells are tall and strongly ciliated and have dark, heterochromatin-rich nuclei. Dorsally, and slightly paramedially, the organ is further specialized, forming the so-called Hatschek's groove (pit), which consists of two ciliated cell types. The first type synthesizes a dense granular material, the granules being approximately 95 nm in diameter. This is stored basally and apparently it is also released through the basal cell membrane into the blood cavities. The cells at the bottom of Hatschek's groove have peculiar rod-shaped apical cellular regions. Each cell bears one tall cilium surrounded by microvilli and it is apparently involved in the production of secretory material into the groove. It is evident that the histology, and probably also the function, of the wheel organ and its groove is much more complex than hitherto believed.     

Glucose uptake by symbiotic Chlorella in the green-hydra symbiosis

There is a correlation between the ability of symbiotic Chlorella algae to take up glucose and their survival in green hydra grown in continuous darkness. Although normal symbionts of European green hydra, which persist at a stable level in dark-grown animals, possessed no detectable constitutive ability to take up glucose when grown in light, uptake was induced after incubation in a medium containing glucose. Further, symbionts isolated from hydra grown in darkness for two weeks had acquired a constitutive uptake ability. Neither NC64A nor 3N813A strains of algae, in artificial symbiosis with hydra, persisted in dark-grown animals, and they showed little or no uptake ability, although in culture NC64A possessed both constitutive and inducible glucose-uptake mechanisms. In contrast, mitotic indices in all three types of algae in symbiosis with hydra increased after host feeding, indicating that the factor which stimulates algal cell division is not identical to the substrate utilised during heterotrophic growth.Abbreviations E/E normal Hydra-Chlorella symbiosis - E/NC, E/3N artificial symbioses between Hydra and Chlorella strains NC64A and 3N813A, respectively - 3-OMG 3-O-methyl-D-glucose - SDS sodium dodecyl sulfate     

Effects of dactinomycine (actinomycine D) on budless hydra and during its budding process.

The effect of dactinomycine (actinomycine D) is manifested in various ways, which depends upon its concentration and animal condition at the time of treatment. Dactinomycine is citotoxic in stronger concentations so hydra dies quickly. In thinner concentrations it stops the mitotic activity of the cell, but the basic metabolic processes continue as before. Interstitial cells differenciate into cnidoblasts for some time, the cnid production is not halted, but all of these cells disappear as well as zimogen cells which dedifferentiate into gastrodermal interstitial and into mucous cells. Such animals live longer but die eventually. The effect of dactinomycine is generally milder on animals with a larger cell mass, in hydras with the budding tendency where exist such reserves and in those hydras in which the budding process has begun. In these a part of mobile undamaged zimogen cells can remain. They keep their reproduction ability. These animals can survive and keep on growing normally.     

Identification and characterization of the epithelial polarity receptor ”Frizzled” in Hydra vulgaris

The Wnt signaling pathway plays an important role in the specification of cell patterning during development in many species. Here we report the isolation and characterization of a putative Wnt receptor, Frizzled, in Hydra vulgaris. Analysis of the amino acid sequence of Frizzled in hydra reveals that this receptor contains many strong sequence similarities to other known Frizzled receptors. Hydra divergence is estimated to have occurred about one billion years ago; thus comparison of the Frizzled sequence of hydra with that of other species is likely to provide important information on the structure and function of those highly conserved regions. Northern and Southern blotting reveal that the Frizzled receptor in hydra has a 2.34-kb message size, and that it is encoded by a single gene. In situ hybridization using hydra frizzled as a probe reveals that the receptor message is restricted to the endoderm in adult hydra. This distribution supports the hypothesis that the Frizzled receptor is functioning in a pathway that controls cell differentiation in hydra. Received: 24 September 1999 / Accepted: 7 December 1999     

Different nematocytes have different synapses in the sea anemone Aiptasia pallida (Cnidaria,Anthozoa)

Sea anemones feed by discharging nematocysts into their prey, but the pathway for control of nematocyst discharge is unknown. The purpose of this study was to investigate the ultrastructural evidence of neuro-nematocyte synapses and to determine the types of synaptic vesicles present at different kinds of nematocyst-containing cells. The tip and middle of tentacles from small specimens of Aiptasia pallida were prepared for electron microscopy and serial micrographs were examined. We found clear vesicles in synapses on mastigophore-containing nematocytes and dense-cored vesicles in synapses on basitrich-containing nematocytes and on one cnidoblast with a developing nematocyst. In addition, we found reciprocal neuro-neuronal and sequential neuro-neuro-nematocyte synapses in which dense-cored vesicles were present. It was concluded that : (1) neuro-nematocyte synapses are present in sea anemones, (2) different kinds of synaptic vesicles are present at cells containing different types of nematocysts, (3) synapses are present on cnidoblasts before the developing nematocyst can be identified and these synapses may have a trophic influence on nematocyst differentiation, and (4) both reciprocal and sequential synapses are present at the nematocyte, suggesting a complex pathway for neural control of nematocyst discharge. J. Morphol. 238:53–62, 1998. © 1998 Wiley-Liss, Inc.     

Ultrastructure of the supporting cells in the paratympanic organ of chicken,Gallus gallus domesticus

The paratympanic organ is a specialized sensory organ of birds located in the medial wall of the tympanic cavity. It possesses a sensory epithelium formed by type II hair cells and supporting cells. The supporting cells are tall, narrow units that extend from the basement membrane to the free epithelial surface. They show a fine structure characterized by numerous mitochondria, a conspicuous Golgi complex and a well-developed RER. Moreover, some uncommon structures, probably formed by heaped RER cisternae, are frequently present in the cytoplasm. Adjacent supporting cells are connected by numerous and extensive gap junctions; moreover, small gap junctions between hair cell and supporting cells are to be found. The possible mechanical and metabolical functions of the paratympanic organ supporting cells are discussed. J. Morphol. 236:65–73, 1998. © 1998 Wiley-Liss, Inc.     

Ultrastructure and serotonin immunocytochemistry of the parietal-pineal complex in the Japanese grass lizard, Takydromus tachydromoides.

The fine structure and immunocytochemical localization of serotonin in the cells of the receptor line were studied in the parietal eye and pineal organ proper of the Japanese grass lizard, Takydromus tachydromoides. Typical photoreceptor cells (PC) were the predominant cell type in the receptor line of the parietal eye, the outer segments of which had regular stacks of numerous disks similar to those of cones. The pineal organ contained relatively few PCs, which showed less well-developed outer segments than those of the parietal eye. In contrast, secretory rudimentary photoreceptor cells (SRPC) accounted for the majority of receptor cells in the pineal organ. These cells were structurally characterized by whorl-like lamellar outer segments and numerous dense-cored vesicles (80-280 nm in diameter). A small number of SRPC were also found in the parietal retina, which were similar to those in the pineal organ. In the parietal-pineal complex, numerous mitochondria located in the PC were larger and rounder than those in the SRPC. In the PC, basal processes prossessed only synaptic ribbons, whereas in the SRPC some of these processes contained synaptic ribbons and others contained dense-cored vesicles, rarely having both. Serotonin-immunoreactive cells were found not only in the pineal organ but also in the parietal eye, which closely resembled the cells of the receptor line in their size and shape. Furthermore, on immunoelectron microscopy for serotonin using the protein A-gold technique, gold particles indicating serotonin-immunoreactive sites were restricted in the core of dense-cored vesicles in the SRPC of the pineal organ. Regional differences in the distributions of the PC, SRPC and serotonin-immunoreactivity were found in the parietal-pineal complex.     

The adoral sense organ in protobranch bivalves (Mollusca): comparative fine structure with special reference to Nucula nucleus

Abstract. The adoral sense organ in bivalve molluscs is a paired ridge of specialized epithelium positioned laterally at the base of the labial palps near the mouth opening, clearly distinguishable from the surrounding epithelia. Six species of the protobranch order Nuculoida, and one species of Solemyoida, were investigated by light microscopy concerning presence, gross anatomy, and innervation of the adoral sense organ. The organ was described in detail for Nucula nucleus and N. nitidosa by transmission electron microscopy; in these two species, the organ was characterized as a pseudostratified epithelial thickening with specialized cells bearing a specialized microvillar border and a basal matrix with a lamellar layer. Three types of bipolar primary receptor cells were recognized and these were reconstructed for N. nucleus. Most of the receptor cells had 2 cilia orientated parallel to the cell surface; in addition, there were 2 types of supporting cells and 1 type of basal cell. The surrounding epithelial cells were narrow with short microvilli and lacked cilia. The homology of the organ within protobranch bivalves was suggested by a character-complex of (1) position, (2) dimension of the epithelium, (3) innervation, (4) pseudostratified construction, (5) dimension of the specialized microvillar border, (6) thickening of the basal matrix, and (7) presence of specialized cell types such as receptor cells. Despite the estimated high number of protobranch species there is only scant information available on the adoral sense organ from 24 species of 8 genera. Structures and receptor types that are similar to those found in the adoral sense organ are widespread in molluscs and other invertebrate groups; this may indicate a plesiomorphy of these characters rather than an apomorphy for the protobranch clade. Therefore, the adoral sense organ may be of minor phylogenetic value above the level of protobranch orders.     

Jaws that snap: control of mandible movements in the ant Mystrium

Ants of the genus Mystrium employ a peculiar snap-jaw mechanism in which the closed mandibles cross over to deliver a stunning blow to an adversary within about 0.5 ms. The mandible snapping is preceded by antennation and antennal withdrawal. The strike is initiated by contact of the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is stored by a catapult mechanism. Recording of closer muscle activity indicates that the mandibles are not triggered by any fast muscle. Instead, we suppose that activity differences between the left and right mandible muscles imbalance a pivot at the mandible tip and release the strike. The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and of a complex muscle receptor organ shows that the mandibles are also adapted to functions other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks.     

Die Cnidogenese der Octocorallia (Anthozoa,Cnidaria): II. Reifung,Wanderung und Zerfall von Cnidoblast und Nesselkapsel

Migration of cnidoblasts has never been observed in Anthozoa. In contrast to hydrozoans, anthozoans are repeatedly reported to develop nematocysts locally without migration in the entoderm as well as in the ectoderm. The majority of the nematocysts studied in different Octocorallia species (Alcyonaria:Alcyonarium digitatum, Parerythropodium coralloides; Gorgonaria:Pseudopterogorgia aerosa; Pennatularia:Veretillum cynomorium) originate from the ectoderm of the scapus, where, however, no mature nematocysts occur. Cnidoblasts containing immature nematocysts accumulate in the distal scapus, from where they migrate singly like amoebae into the pinnulae of the tentacles. The nematocysts mature during migration, during which the capsular matrix becomes completely electron-translucent. Only in the oral disc, where few nematocysts occur, do they mature locally without migration. In the Octocorallia, nematocyst development and maturation takes places only in the ectoderm. Development of nematocysts has never been observed in the entoderm, nor in the pharynx; this demonstrates its entodermal origin. The entoderm contains only degenerated or phagocytized nematocysts. Contrary to hydrozoans, the mature anthozoan cnidocyte is rounded and has no processes to the mesogloea. Instead of a cnidocil it has a ciliary cone consisting of a normal flagellum, stereocilia and macrovilli. The cnidocyte is characterised by abundant electron-translucent cytoplasm and nematocyst-anchoring structures made up of cross-striated, collagen-like fibrillae and a fibrous basal ring. The position of the cross-striated fibrillae is distally similar to that of the supportive rods in hydrozoan cnidoblasts. The present study clearly demonstrates that structure and, possibly, function of an octocorallian cnidocyte is much simpler than that of a hydrozoan cnidocyte. On the other hand, cnidoblast migration, occurring in Hydrozoa as well in Octocorallia, turned out to be a much older phylogenetic character than was formerly believed.     

A SEM analysis of DMSO treated hydra polyps

Summary— Scanning electron microscopy revealed that exposure of hydra polyps to DMSO at concentrations used for permeabilizing tissue results in striking changes in epithelial cell morphology. Epithelial cells from treated polyps rounded up in shape and formed numerous large blebs at the cell surface. Along the borders of epithelial cells numerous small projections became detectable. The DMSO-induced changes at the cell surface corresponded to drastic changes in the intracellular organization. No evidence could be found for DMSO induced opening of cell junctions and/or opening of the interstitial space. The results demonstrate that DMSO affects the morphology and intracellular organization of hydra epithelial cells. Thus, caution is necessary in interpreting cell behavior in DMSO treated tissue.     

Characterization of the VPS10 domain of SorLA/LR11 as binding site for the neuropeptide HA

The single transmembrane receptor sorLA/LR11 contains binding domains typical for the low-density lipoprotein receptors and a VPS10 domain which, in the related receptor sortilin, binds the neuropeptide neurotensin. SorLA is synthesized as a proreceptor which is processed to the mature form by a furin-like propeptidase. Endogenous sorLA and its hydra homologue HAB bind the neuropeptide head activator (HA). Transiently expressed partial sorLA constructs were investigated for ligand binding. We found that HA binds with nanomolar affinity to the VPS10 domain. The sorLA propeptide also bound to the VPS10 domain, whereas the receptor-associated protein RAP interacted both with the class A repeats and the VPS10 domain. The sorLA propeptide inhibited binding of HA to full-length sorLA and to the VPS10 domain. It also interfered with binding of HA to hydra HAB, which is taken as evidence for a highly conserved tertiary structure of the VPS10 domains of this receptor in hydra and mammals. The propeptide inhibited HA-stimulated mitosis and proliferation in the human neuroendocrine cell line BON and the neuronal precursor cell line NT2. We conclude that sorLA is necessary for HA signaling and function.