The fine structure of micrococcus radiodurans

Summary The fine structure of the radiation-resistant bacterium, Micrococcus radiodurans, isolated by Anderson, was studied by electron microscopy of intact and disrupted cells using thin sectioning and negative staining techniques. The cytoplasm and nuclear structures are normal, but the cell wall and sheath are more complex than any so far described for a bacterium. The surface consists of four distinct layers, each having a characteristic fine structure, one of which has been tentatively identified as that responsible for maintaining the rigidity of the cells. Striations with a periodicity of 175 to 200 Å are visible in thin sections of this layer, and a pseudo-hexagonal array of dark holes is seen in surface view of negatively-stained fragments. It is concluded that this layer is the main structural element of the cell wall of M. radiodurans. The other three layers of the surface have not been clearly located in thin sections; one of these layers has a well-defined pattern of hexagonally arranged units similar to that observed in Spirillum serpens by Murray but with different dimensions.Sir Halley Stewart Research Fellow.     

Ein direkter Beweis für die Fähigkeit einzelner Sehzellen des Insektenauges,die Schwingungsrichtung polarisierten Lichtes zu analysieren

Summary Action potentials from single visual cells of the compound eye are lead off during illumination of the retina of Calliphora erythrocephala by means of intracellular capillary microelectrodes. The size of the monophasic and depolarizing action-potentials depends on light-intensity and on plane of polarized light. Turning the plane of polarization from maximum to minimum efficacy equals a decrease of intensity of about 50%. As the dioptric apparatus is optically isotropic, the experiments described here prove the hypothesis of Autrum and Stumpf, namely that the single visual cell responds to different planes of polarization with different states of excitation.

---

---

Die Untersuchungen wurden von der Deutschen Forschungsgemeinschaft unterstützt.     

FINE STRUCTURE OF THE OCTOPUS RETINA

The fine structure of the visual and the supporting cells and of the blood capillaries in the octopus retina is described. Lamellated structures contained in the proximal segment of the visual cell consist of compact arrays of dense membranes each of which is quintuple-layered and divides at its margins into two thinner sheets or membranes which are connected directly with the agranular or granular endoplasmic reticulum. Proximal to the deeper extremities of the rhabdomeres, the lateral plasma membranes of two adjoining visual cells contact each other forming a quintuple-layered compound membrane, which results in occlusion of the intercellular space. The central layer of the compound membrane is of high density, so that the membrane, as a whole, appears to be a single thick layer at low magnifications. The supporting cells are connected with the neighboring visual cells by two types of junctions. Long slender processes extend from the supporting cells to the surface of the retina through narrow spaces among the distal segments of the visual cells. The capillary endothelial cells are characterized by luminal surfaces irregularly contoured and by lateral surfaces elaborately interdigitated. The functional significance of the close contact between adjoining visual cells is discussed.     

Die Feinstruktur der Cerebraldrüse von Planorbarius corneus L. (Basommatophora)

Summary The fine structure of the cerebral gland of the fresh water snail Planorbarius corneus has been described. The apical cell surfaces of the epithelium bordering the lumen are covered with short microvilli and in some parts with cilia. There is a remarkable enlargement of the basal surface of those cells underlying the perineurium by long branched cell processes. The fine structure and density of the substances in the lumen differ; inclusions of paracrystallin structure are found. The possible functional significance of these organs in Pulmonates is discussed.

---

---

Frau Prof. Dr. B. Scharrer zum 60. Geburtstag gewidmet.

---

Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.     

The fine structure and cytology of the association between the parasitic red algaHolmsella australis and its red algal hostGracilaria furcellata

Summary Holmsella australis Noble andKraft ms. is a colourless red algal parasite, forming whitish pustules on its photosynthetic red algal host,Gracilaria furcellata Harvey. In the infected region, host cortical tissue continues to grow and enclose the expanding pustule. Filaments of both host and parasite grow apically, the cells being connected by primary pit connections (PCs). Secondary PCs form between cells of the same species, and in addition,H. australis initiates the formation of secondary PCs with cells ofG. furcellata. All three types of secondary PC are morphologically distinct. In hostparasite PCs the surface adjoining the host cell is similar in structure to a host-host PC, while that adjoining the parasite cell has the structure of a parasite-parasite PC. The plasma membrane is continuous between the cells of the unrelated host and parasite. In addition, a cap membrane is typically produced only on the host surface, though occasionally the parasite side is enclosed by a cap membrane as well. Cap membranes are absent from parasite-parasite PCs (making them intracellular), while host-host PCs are typically extracellular, both cells producing cap membranes. The presence or absence of a cap membrane in certain positions appears to vary, and suggests that cells may be able to regulate its presence. Since transport of nutrients would be expected to occur from host to parasite cells, and between parasite cells, the morphological evidence presented here suggests the PCs may be the pathway.     

The intracytoplasmic channel in pigment epithelial cells of the chick retina

Summary The fine structure of pigment epithelial cells in the chick retina was studied by electron microscopy with a special attention to the intracytoplasmic channel which is considered to be an important passage of metabolites from the choroidal side to the vitreal side. The chick retina was fixed either by perfusion with glutaraldehyde followed by osmium tetroxide or by immersion in situ with osmium tetroxide before removal of the eyeball. The infoldings appearing in the basal zone of the retinal pigment epithelial cell were provided with the gear-like projection which was encountered as their bottom in many cases, suggesting selective absorption of proteins. It was noticed that certain interspaces of the infoldings were continuous to tubular elements of the agranular endoplasmic reticulum. Moreover, the tubular elements were found in association with such other cellular components as nuclear envelope, mitochondria, fuscin granules and plasma membrane surrounding the outer segment of photoreceptor. The pigment epithelial cell appeared to be continuous with the photoreceptor through the pores of their plasma membranes. The presence of a certain intracytoplasmic channel from the choroid to the photoreceptor is considered to facilitate the transport of metabolites in the pigment epithelial cell.Part of these observations was presented at the Sixth International Congress for Electron Microscopy, Kyoto in 1966.I wish to thank Prof. Gonpachiro Yasuzumi for his valuable advices and discussions through this study.     

Observations on the micro-anatomy of crystallolithus hyalinus gaarder and markali

Summary The fine structure of Crystallolithus hyalinus (Gaarder and Markali), known to be the motile stage of Coccolithus pelagicus (Wallich) Schiller (Parke and Adams 1960), has been investigated for purposes of comparison with Chrysochromulina and Prymnesium, recently recognised as probably related to it. Anoptral contrast light microscopy of living cells and electron microscopy of thin sections and shadow-cast whole mounts show that there is a close resemblance to species of Chrysochromulina not only in cell structure but also in the details of haptonema structure and scale structure. The origin of the scales from internal vesicles has been traced as in other genera but the holococcoliths (crystalloliths) do not appear to arise in this way. The mode of origin of the crystalloliths is thus unknown, but it is suggested that they may be developed outside the cell from calcite secreted in solution into the appropriate cavity. Their constant position between a layer of scales and an outer enveloping skin is consistent with this and one unfamiliar cytoplasmic organelle, composed of peculiar thick-walled tubes within some large superficial vesicles, is described as perhaps involved in this process. Apart from these special features the resemblance to both Chrysochromulina and Prymnesium is sufficient to add considerable weight to Christensen's suggestion (Christensen 1962) that a new group should be defined to accommodate these genera.     

The fine structure of the compound sense organs on the cirri of Nereis diversicolor

Summary A study of the fine structure of the sense organs on the prostomial cirri and palps of Nereis diversicolor shows them to consist of two types of cell. There are between 7 and 15 sensory cells and a similar number of associated cells which contain many osmiophilic granules. The cell bodies of both are sub-epidermal, having a long distal process which reaches the surface in a raised sensory hillock. The sensory cells carry a cilium, which passes through the cuticle and emerges surrounded by a sheath formed from the outer layers of the epicuticle. Scanning electron micrographs show the surface of the cirrus to be covered by hair-like epicuticular microvilli, through which the sheathed cilia protrude. There is also a second type of sensory cell which occurs singly between the epithelial cells. The distal membrane of this cell is formed into a tuft of approximately 55 large microvilli which open through a pore in the epicuticle. It is suggested by their position and structure, that both these receptors resemble chemoreceptors.We should like to acknowledge the advice and technical help of Dr. J. A. Nott of the N.E.R.C. unit of Electron Microscopy, Menai Bridge, and Dr. P. E. Secker of the School of Electronic Engineering for use of the Cambridge Stereoscan. The work is supported by a grant from the Science Research Council to D.A.D.     

Histochemical studies on catecholaminergic cells in the carp retina

Histochemical studies on catecholaminergic cells were conducted with the carp (Cyprinus carpio) retina. Catecholamine (CA)-containing cell bodies appear sparsely distributed among amacrine cells in the innermost cellular row of the inner nuclear layer (INL) and occasionally in the outer half part of the inner plexiform layer (IPL); only exceptionally are they found among ganglion cells. The fluorescent cells interspersed with the amacrine cells and in the IPL send their fiber processes toward both the outer plexiform layer (OPL) and the IPL; the fine fibers form dense networks in the INL and IPL. Pretreatment of the fish with intramuscular injection of reserpine (20 hr prior to enucleation) completely depleted CA from the retina. The fluorescence of catecholaminergic cells was enhanced, and the number of fluorescent cells visible was increased, by intravitreous injection ofl-DOPA, DA, and NA (3 hr prior to enucleation). A combination of pretreatment with intramuscular reserpine and intravitreous NA was particularly effective. These results indicate that catecholamines may play an important role in the modulation of the membrane potential of horizontal cells.     

The fine structure of the endocardial endothelium

Summary The fine structure of the endocardium of the rat was studied at the level of the papillary muscles. In accordance with what is already known about endothelial cells of blood vessels, the occurrence of numerous vesicles underlying the plasma membrane was observed, indicating the pinocytotic activity of the endocardial endothelial cells.The plasma membrane, as in all other cells, consists of two electron-dense layers separated by a light interspace. However, after phosphotungstic acid staining, it appears as a thickened single band at the free cell surface. This characteristic feature decreases towards the lateral cell boundaries. Intensely stained are also clumps of material pinched off from the plasma membrane and released into the cavity.Assistant at the Department of Anatomy of the University, Torino, Italy (Dir.: Prof. F. Loretti). The author was awarded a grant from the Italian Consiglio Nazionale delle Ricerche for the present investigation.The author wishes to thank Mrs. Behrens and Miss Anhut for excellent technical assistance.     

The fine structure of cephalopod blood vessels

Summary The fine structure of blood vessels of the retina and arms of Octopus and the lip of Sepia is described.There are two main types of vessels. The first type (type 1) has a complete basement membrane, an incomplete lining of endothelial cells formed into finger—like processes, and a complete investment of pericytes surrounding the vessel. These latter cells contain myofilaments. The second type (type 2) is smaller and contains few if any myofilaments, and has a less complexly folded endothelium. This type is subdivided into three forms depending on the number of pericytes and the form of the endothelial lining.Amoebocytes are described and these form a distinct group of cells.The fine structure of hemocyanin is observed in normally fixed material and is correlated with its previously described structure.These observations are related to their possible functional importance.

---

Zusammenfassung Die Ultrastruktur von Blutgefäßen der Retina und der Arme von Octopus und der Lippe von Sepia wird beschrieben.Es bestehen vorwiegend zwei Gefäßtypen. Der erste Typ (Typ 1) zeigt eine geschlossene Basalmembran, eine unvollständige Begrenzung durch Endothelzellen, die fingerförmige Fortsätze bilden und eine vollständige Pericytenhülle um das Gefäß. Die letztere enthält Myofilamente. Der zweite Typ (Typ 2) ist kleiner und enthält wenig oder keine Myofilamente. Er besitzt ein weniger komplex gefaltetes Endothel. Dieser Typ wird gemäß der Zahl der Pericyten und der Form der endothelialen Begrenzung in drei Gruppen unterteilt.Deutlich verschiedene Amoebozyten werden beschrieben.Die Ultrastruktur von Haemocyanin ist an normal fixiertem Material zu beobachten. Sie wird zu ihrer in früheren Arbeiten beschriebenen Struktur in Beziehung gebracht.Die Beobachtungen werden in Hinblick auf ihre mögliche funktionelle Bedeutung diskutiert.

---

---

Acknowledgements. We would like to acknowledge the encouragement and advice of Professor J. Z. Young and Dr. E. G. Gray. Mrs. J. I. Astafiev did the drawings and Mr. A. Aldrich and Mr. S. Waterman helped with the photography.     

Fine structure of argyrophil and argentaffin cells in the gastro-intestinal tract of the fowl

Summary The fine structure of granular cells in the proventriculus gizzard and intestine of the fowl has been described. The proventriculus and gizzard have only one type of granular cell, the pure argyrophil cell. In the intestine two cell types are shown. One corresponds to the argyrophil cell seen in the proventriculus and gizzard. The other, more common, is considered to be the argentaffin cell of the intestine. Structural differences between these two cell types confirm the known differences in histochemical reaction. Acknowledgement. I wish to thank Mr. R. N. C. Aitken, Department of Veterinary Histology and Embryology for supplying the birds used in this study.     

N-Methyl-d-aspartate receptors in the retina

The vertebrate retina is a “genuine neural center” (Ramón y Cajal), in which glutamate is a major excitatory neurotransmitter. Both N-methyl-d-aspartate (NMDA) and non-NMDA receptors are expressed in the retina. Although non-NMDA receptors and/or metabotropic glutamate receptors are generally thought to be responsible for mediating the transfer of visual signals in the outer retina, there is recent evidence suggesting that NMDA receptors are also expressed in photoreceptors, as well as horizontal and bipolar cells. In the inner retina, NMDA receptors, in addition to other glutamate receptor subtypes, are abundantly expressed to mediate visual signal transmission from bipolar cells to amacrine and ganglion cells, and could be involved in modulation of inhibitory feedback from amacrine cells to bipolar cells. NMDA receptors are extrasynaptically expressed in ganglion cells (and probably amacrine cells) and may play physiological roles in a special mode. Activity of NMDA receptors may be modulated by neuromodulators, such as d-serine and others. This article discusses retinal excitotoxicity mediated by NMDA receptors.     

Retinal mosaics of a primitive jumping spider,Spartaeus (Salticidae: Araneae): A transition between principal retinae serving low and high spatial acuities

Summary Previous papers (Blest andPrice 1984,Blest andSigmund 1984) have described the receptor mosaics in the tiered principal retinae of jumping spiders with high and low visual acuities, respectively. The latter paper offers a phylogenetic model for the later stages in the evolution of high acuity retinae in which layer I, farthest from the dioptrics, is alone required to sustain fine visual discriminations. Nevertheless, current evidence does not establish that the low acuity principal retinae of primitive jumping spiders were modified to yield the high acuity retinae of advanced forms: each might have evolved independently from a common precursor.We now show that the principal retina ofSpartaeus (the type genus of a primitive subfamily, theSpartaeinae) is a true intermediate between the low acuity retina ofYaginumanis and the high acuity retina ofPortia (also in theSpartaeinae).InSpartaeus, foveal layer I receptors at the anatomical outer side of the retina each bear a single rhabdomere designed as a light guide. Inner layer I receptors each have two rhabdomeres, and rhabdomeres of horizontally adjacent receptors are contiguous, so that optical pooling limits their acuity. Horizontal staircasing of the tips of layer I receptors was shown byBlest et al. (1981) to cause outer receptors to receive focused images from remote planes in object space, and inner receptors from nearer planes. In the high-acuity retina ofPortia all foveal layer I receptors are light-guides, and in the low-acuity retina ofYaginumanis none are. Layer I inSpartaeus, therefore, is a true intermediate step in the evolution of a high-acuity retina, and the local region of the foveal layer I mosaic modified to that end is concerned, appropriately, with the resolution of distant objects.The layer II mosaic is degraded, although less so than inPortia. Layer III is conservative throughout theSalticidae. Foveal layer IV exhibits greater homogeneity inSpartaeus than in other forms.     

A specialized trophospongium in large neurons of Leptodora (Crustacea)

Summary A specialized type of trophospongium has been described in large nerve cells of the cerebral ganglion of the planktonic crustacean Leptodora kindtii. It consists of three parts (Fig. 6). The first is, as a rule, long; it is composed of an infolding of the plasma membrane of the neuron, an intercellular space and a slender process of a glial cell. The second segment from the end of the glial process to the beginning of the X-body is always short; it is characterized by the presence of a desmosome-like junction. The third part consists of a labyrinth of cisternal spaces lined by membranes which are continuous with the infoldings of the surface membrane of the nerve cell.This investigation was supported by U.S.P.H.S. Grant NB 02145-04. The skillful assistance of Mrs. Cynthia Jones, Mr. Stanley Brown and Mr. Douglas Gasner in different phases of this work is gratefully acknowledged.     

Über den Bau und die Hell-Dunkel-Adaptation der Augen des Polychäten Platynereis dumerilii

Summary The eye of Platynereis dumerilii consists of three components: a short optic nerve, a cup-shaped retina, and a vitreous body within the cup. The opening of the retinal cup is called pupil. The retina is composed of supporting cells and visual cells. The supporting cells are stuffed with dark blue violet pigment granules. The visual cells have orange pigment granules which are only found in the narrow middle piece of the cells. The supporting cell pigment may be lacking in abnormally pigmented eyes. The jellylike matter of the vitreous body apparently is produced by the supporting cells. It is of high protein contents and does not seem to be derived from the cuticle which consists of polysaccharides.The ultrastructure of the photoreceptor region shows club-shaped processes of visual cells. Each club is of low electron density and contains elongate membranous structures. It is surrounded by many microvilli. The clubs correspond to the rods in light microscopy.The eye of Platynereis dumerilii adapts to changes in light intensity by movements of the retina and the rods. The cup-shaped retina spreads towards its pupillar opening thus adapting the pupil area to light intensity. The length of the rods in darkfixed immature specimens is about 20, in light-fixed ones about 7 . In mature specimens (Heteronereis) the length is 46 or 19 respectively.During metamorphosis the eyes enlarge to about three times their original volume. This enlargement is due to an increase in volume of the retina and the vitreous body, not to cell divisions.

---

---

Durchgeführt mit Unterstützung durch ein Stipendium aus Mitteln der Fritz-Thyssen-Stiftung, ferner mit Hilfe der Deutschen Forschungsgemeinschaft.

---

Die Anregung zu dieser Arbeit und das Platynereis-Zuchtmaterial verdanke ich Herrn Prof. Dr. C. Hauenschild. Für Hilfe bei der Herstellung des Bildmaterials danke ich Frl. U. Poltz (Freiburg).     

Ultrastructure of transitional epithelium of man

Summary Blocks of human normal renal pelvis and ureter obtained at the time of surgery were fixed in glutaraldehyde and osmium with or without ruthenium red, for electron microscopic observations. The transitional epithelium is arranged in three cell layers: basal, intermediate and superficial. All epithelial cells show numerous microvilli and contain the characteristic vesicles of transitional epithelium, bundles of cytoplasmic filaments, microtubules and numerous free ribosomes. The epithelial extracellular compartment is notably large and appears as an intricate, tridimensional network of canaliculi and cisternae which are wider in the intermediate and superficial layers and in which microvilli and cytoplasmic folds of vicinal cells are often attached or interdigitated. At these sites there are desmosomes.The surface of all transitional epithelial cells is covered by a fibrillar mucous coat which is more developed at the plasmalemma of the free border of luminal cells in which microvilli are also seen. Ruthenium red stains selectively the plasmalemma and the mucous coat of the free surface of the epithelium, indicating the presence of an acid polysaccharide. With this technic (Luft, 1965), it is observed, radiating from the plasmalemma, branching filaments which measure 100 Å in diameter forming a zone of varying density which is about 400 m wide and which corresponds, at the light microscopic level, to the luminal border of the transitional epithelial cells in which a sialomucin has been identified. The slender filaments have a beaded appearance. At the free border, superficial cells are attached by functional complexes in which tight junctions seal the epithelial intercellular space, which is opened at the level of the basement membrane where only desmosomes are observed.The ultrastructure of human transitional epithelium of urinary tract resembles the duct cells of the salt gland of certain marine birds (Fawcett, 1962) and the amphibian epidermis (Farquhar and Palade, 1965) in which there are active processes of transport. The mucous surface coat, selectively stained by the ruthenium red, contains a sialomucin (Monis and Dorfman, 1965, 1967).The ultrastructure and histochemistry of the mucous fluffy coat of man transitional epithelium and the observations of Porter and Tamm (1955), on the ultrastructure of preparations of the Tamm and Horsfall mucoprotein (1952) are bases for suggesting that transitional epithelium of urinary tract of man is the site of biosynthesis of certain urinary mucoids. Present investigations are directed to obtain evidence to substantiate this hypothesis.General Abbreviations B basal cell - E exfoliating cell - I intermediate cell - L lumen - S superficial cell - SC surface coat - bm basement membrane - ci cell infolding - d desmosome (macula adhaerens) - f fibroblast - fi cytoplasmic filaments - is intercellular space - jc junctional complex - ly lysosome - lym lymphocyte - mt microtubules - m mitochondria - mv microvilli - n nucleus - r ribosomes - rv round vesicle - zo zonula occludens - za zonula adherens Dr. Monis wishes to thank Dr. E. De Robertis for the use of the electron microscope facilities of the Instituto de Anatomía General y Embriologia, Facultad de Medicina, Universidad de Buenos Aires. — Prof. E. Trabucco and Dr. R. J. Borzone (Cátedra de Clinica Genitourinaria de la Facultad de Medicina, Universidad de Buenos Aires) generously supplied the specimens which were the bases of this study. — Thanks are due to Mrs. A. M. Novara and Mrs. Defilippi-Novoa for efficient technical help and to Miss Rosa Gentile for secretarial assistance. Photomicrography by Mr. M. A. Saenz.Dr. Zambrano is investigator (CNICT).     

The Subchordal Cells of Oikopleura dioica and O. albicans (Appendicularia,Chordata)

Abstract Oikopleura dioica has two large subchordal cells which were studied in vivo and with light and electron microscopy. They have fixed positions within the haemocoel of the tail but change their morphology continually by protruding and withdrawing processes in an amoeboid manner. Also the fine structure varies considerably from one animal to the next. The cell surface sometimes indicates a strong pinocytotic activity with many coated pits and vesicles. In other cases there are many small vesicles which are interpreted as exocytotic. They are found both in the cytoplasm close to the plasma membrane and in the haemocoelic fluid. Subchordal cells with no pronounced surface activity have a large amount of rough endoplasmic reticulum, which suggests that they synthesize proteins. The presence of subchordal cells in the tail is correlated with the presence of the ontogenetically related bioluminescent oral gland cells in the pharynx; either both types exist simultaneously or both are lacking. It is speculated that the two cell types are also functionally co-ordinated. Oikopleura albicans has a multitude of tiny subchordal cells which have essentially the same fine structure as the two large Oikopleura dioica cells.     

Ultrastructure of the developing gizzard epithelium in the chick embryo

Summary The fine structure of the gizzard epithelium is described at different stages in the development of the chick embryo. The elaborate apical processes, a characteristic feature, take part in secretion at thirteen days, but do not seem to have this function at nine and ten days. The formation of glands begins at thirteen days but the adult fine structure of the gland cells is not attained until hatching. The distinct surface layer present between thirteen and seventeen days may have a protective function. Acknowledgement. The author is grateful for research facilities provided by Professor G. M. Wyburn, Anatomy Department, The University of Glasgow.     

FGF /FGFR Signal Induces Trachea Extension in the Drosophila Visual System

The Drosophila compound eye is a large sensory organ that places a high demand on oxygen supplied by the tracheal system. Although the development and function of the Drosophila visual system has been extensively studied, the development and contribution of its tracheal system has not been systematically examined. To address this issue, we studied the tracheal patterns and developmental process in the Drosophila visual system. We found that the retinal tracheae are derived from air sacs in the head, and the ingrowth of retinal trachea begin at mid-pupal stage. The tracheal development has three stages. First, the air sacs form near the optic lobe in 42-47% of pupal development (pd). Second, in 47-52% pd, air sacs extend branches along the base of the retina following a posterior-to-anterior direction and further form the tracheal network under the fenestrated membrane (TNUFM). Third, the TNUFM extend fine branches into the retina following a proximal-to-distal direction after 60% pd. Furthermore, we found that the trachea extension in both retina and TNUFM are dependent on the FGF(Bnl)/FGFR(Btl) signaling. Our results also provided strong evidence that the photoreceptors are the source of the Bnl ligand to guide the trachea ingrowth. Our work is the first systematic study of the tracheal development in the visual system, and also the first study demonstrating the interactions of two well-studied systems: the eye and trachea.