The salivary gland secretions of a neotropical bumblebee

Summary The larval salivary gland secretions ofBombus atratus were studied with cytochemical and cytophysical methods. In the young feeding larvae a proteic filamentous secretion depicting striations perpendicular to the long axis of its fibrillary threads and exhibiting a wellordered macromolecular array was found. It appears not to differ from the silk secretion described for the fully grown larvae of an europeanBombus species. However, in the fully grown larvae ofB. atratus changes which have not yet been reported for other bees occur involving the salivary gland secretion. Two secretion types are then distinguishable. One is composed of carboxylated and sulfated acid glycosaminoglycans and glycoprotein(s) (mucous secretion), and the other has the same composition as that of the filamentous secretion of the young larvae, although differing morphologically and in terms of macromolecular alignment (flocculent secretion). The filamentous secretion is assumed to be involved inB. atratus with the spinning of the silken partitions which at a relatively early stage separate the larvae reared within a common cell from one another. The mucous and flocculent secretions will participate in the cocoons which will cover the pupating larvae. The filamentous and flocculent secretions appear to contain an -helical fibroin, glycoprotein(s) and lipoprotein(s), but not collagen-type proteins.     

The innervation of the salivary gland of the moth,Manduca sexta

Summary The salivary glands of the moth, Manduca sexta (Insecta: Sphingidae), are unlike most other salivary glands in that they are innervated from one source only. Vital staining of nerves with methylene-blue reveals numerous fine nerves extending to the glands from the oesophageal nerve, a part of the stomatogastric or visceral nervous system. Light and electron microscopy confirm that only the fluid-secreting cells, confined to a discrete region in these glands, are innervated. Axons with or without glial wrappings are found in intercellular spaces between fluid-secreting cells. Axons lacking a glial sheath contain, after glutaraldehyde-osmium tetroxide fixation, large granular and small agranular vesicles. In nerve endings in glands fixed with permanganate these smaller vesicles are granular, having the electron-dense cores characteristic of monoamine-containing neurons. These nerve endings with synaptoid areas are in close (direct) contact with the fluid-secreting cells.I am grateful to Professor T. Weis-Fogh for accommodation in the department of Zoology and to Dr. Nancy Lane for use of A.R.C. facilities and advice. Thanks are also due to Drs. M. J. Berridge, S.H.P. Maddrell, and W. T. Prince and Mr. R. A. Leslie for helpful discussion. Financial assistance from Clare College, Cambridge is gratefully acknowledged.     

The structure of the salivary gland of the moth (Manduca sexta)

Summary The salivary glands of the moth,Manduca sexta, are described, emphasizing correlations between structure and function in an attempt to explain the production of a dilute saliva. Each of the paired glands consists of five distinct regions: protein secreting, fluid secreting, thin duct, bulbous duct, and common duct. Each region constists of a single, ultrastructurally distinct, cell type. It is proposed that the protein and fluid secreting regions produce an enzyme-containing primary saliva isosmotic with the haemolymph; this saliva is modified in the remaining regions of the gland to yield a dilute saliva. Acknowledgements. We thank Professor T. Weis-Fogh for accommodation in the Department of Zoology and Dr. J. E. Treherne for use of A.R.C. facilities. We are especially grateful to Dr. Nancy Lane for encouragement, advice and critical comments and to Drs. M. J. Berridge and S.H.P. Maddrell for helpful discussion. H.A.R. is grateful to Clare College, Cambridge for financial aid.     

An electron microscopic study of Babesia microti invading erythrocytes

Summary Intracellular sporozoan parasites invade the host cell through the invagination of the plasma membrane of the host and a vacuole is formed which accommodates the entering parasite. The vacuole may disappear and the invaginated membrane of the host then becomes closely apposed to that of the parasite's own membrane. As a result the parasite is covered by two membranes. Members of the class Piroplasmea differ from other Sporozoa in that their trophozoites are covered by a single membrane. By screening numerous sections of intraerythrocytic Babesia microti belonging to the class Piroplasmea, it was found that merozoites of Babesia enter the erythrocytes of hamsters in the same way as those of other Sporozoa. When a merozoite touches the red blood cell with its anterior end it becomes attached to the membrane of the host, which starts to invaginate and a parasitophorous vacuole is formed. The vacuolar space disappears rapidly and the membrane of the vacuole and that of the parasite become closely adjacent. At this stage the parasite is surrounded by two plasma membranes. The outer membrane derived from the invaginated host membrane disintegrates quickly and the parasite is left with a single membrane throughout its life span.Supported by Grant AI 08989 from the U.S. Public Health Service. The excellent technical assistance of Ms. Renata Klatt is gratefully acknowledged     

Embryonic expression of the engrailed homologue of Rhynchosciara americana

The segment polarity gene engrailed is involved in the determination of segment posterior identity in Drosophila. engrailed has been largely used for comparative developmental studies due to its evolutionary conservation from nematodes to humans. By in situ hybridization of an engrailed cDNA probe from Drosophila to polytene chromosomes of fourth instar larvae of Rhynchosciara americana we have shown that engrailed-like sequences must be localized in band 6 of chromosome A in this species. The pattern of engrailed protein expression during R. americana embryo development is diffuse at first evolving into a nuclear striped pattern after quite a length of time. In addition, our results suggest a possible developmentally regulated molecular modification of engrailed protein in R. americana embryos.     

Uptake of ferritin by the cephalopod optic gland

Summary Horse spleen ferritin, injected into the blood of the octopus, leaves the capillaries via pericyte junctions and windows. One hour after the administration, ferritin has entered the optic gland main cells; three hours later, it is accumulated in dense-bodies. The evidence for resorption supports earlier papers reporting that the ultrastructure of the organ is unusual for an endocrine gland.We thank Professor R. Martin for his help and for permission to work in his laboratory at the Ulm University (Germany) and the Swiss Government for financial support     

Virus assembly inHincksia hincksiae (Ectocarpales, Phaeophyceae) An electron and fluorescence microscopic study

Summary The filamentous brown algaHincksia hincksiae can be infected by a large icosahedral double-stranded DNA virus (HincV-1). The virus shows extended latency and is replicated only in cells homologous to sporangia. Virus formation was studied by transmission electron microscopy, DAPI staining, and -tubulin immunofluorescence. Inhibition of cytokineses results in multinucleate cells, which are the first indication of virus replication in productive cells; the microtubular cytoskeleton does not seem to be affected by the virus. Replication of viral DNA begins in the nuclei, which increase in size and eventually disintegrate. Virus assembly takes place in a mixed nucleo-/cytoplasm. Capsids bud from cisternae, which are interpreted as modified endoplasmic reticulum aggregated to virus assembly centres. The internal membranous component of the virus is thus derived from the endoplasmic reticulum. The particles are empty (electron translucent) when assembled, and the nucleoprotein core seems to be packaged subsequently through an opening in the capsid. A number of fine structural features not previously reported from brown algae and related to virus formation are described. Our results on Hincksia hincksiae virus are compared with observations made on various other icosahedral DNA viruses infecting eukaryotic algae and animals.Abbreviations ASFV African swine fever virus - BSA bovine serum albumin - DAPI 4,6-diamidino-phenylindole - dsDNA double-stranded DNA - EGTA ethyleneglycol-bis-(b-amino-ethyl ether)-N,N-tetraacetic acid - ER endoplasmic reticulum - FV-3 frog virus 3 - HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid - HincV-1 Hincksia hincksiae virus type 1 - PBCV-1 Paramecium bursaria Chlorella virus 1 - PBS phosphate-buffered saline - rER rough endoplasmic reticulum - TBS Tris-buffered saline Tris tris-(hydroxymethyl)-aminomethane - VAC virus assembly centre - VLP virus-like particle - VPC virus-producing cell     

Intracellular polymerized haemocyanin in the branchial gland of a cephalopod

Summary Polymerized haemocyanin molecules have been identified as rings, about 25 nm in diameter, forming linear arrays within cytoplasmic vesicles, close to the nucleus. They were observed by transmission electron microscopy in the polygonal cells of the branchial gland of Eledone moschata Lamarck. These observations confirm previous data suggesting that haemocyanin is synthetized in the branchial gland cells of Octopoda.     

Morphological and functional study of the effect of isoproterenol on salivary gland cells

Summary The cellular mechanisms responsible for the structural and functional alterations produced in salivary glands by isoproterenol (ISP) were investigated. Postnatal rats were injected with ISP, and alterations in the structure and protein components of the submandibular glands were determined. Normal age-dependent protein patterns detected by electrophoresis are attributed to the biochemical and functional differentiation of proacinar and acinar secretory cells and correlate with structural changes in these cells. Structural changes induced by ISP involve the acinar cells without detectably altering terminal tubule cells. In addition, synthesis of a specific protein by the glands is enhanced by ISP treatment. By comparing protein patterns in the submandibular glands of control and treated rats, it was concluded that ISP increases synthesis of a specific salivary protein normally produced by proacinar cells during a limited period of glandular development. These results suggest that a neurally mediated regulatory mechanism that becomes altered by ISP plays a role in normal salivary gland development.Supported in part by NIDR grant DE-02670.The authors wish to thank Dr. C.A. Schneyer for her comments in the preparation of this paper     

Three muscle fibre types in the axial muscle of axolotl (Ambystoma mexicanum Shaw) A quantitative lightand electron microscopic study

Morphometric analysis by light microscopy of p-phenylene-diamine stained semithin sections of axolotl tail muscle revealed differences in the cross-sectional area of the fibres and in the number of mitochondria and of lipid inclusions per fibre, and indicated the presence of three distinct types of fibres. The tripartition was found to be statistically highly significant. Representative fibres from each group established by light microscopic morphometry were subjected to an ultrastructural morphometric analysis. The volume content of mitochondria amounted to 9.8% of the fibre volume for red, 4.0% for intermediate and 0.8% for white fibres. The myofibrils composed 60%, 70% and 83% in the same fibres. The volume of the sarcotubular system (t-tubuli and sarcoplasmic reticulum) was 2.5% in red, 4.5% in intermediate and 11.7% in white fibres. The three fibre types also demonstrated differences in myofibrillar cross-striation pattern and number of triads. The reliability of the light microscopic morphometry was tested by correlation with EM montages of the representative fibres.     

Electron microscopic study on the early histogenesis of thymus in the toad,Xenopus laevis

Summary Sequential electron microscopic observations of thymic histogenesis in the toad, Xenopus laevis, reveal that the thymus arises as epithelial buddings of the visceral pouches at Nieuwkoop-Faber stage 40, and acquires its basic histological features at stages 48–49. In the rudiments and the surrounding mesenchyme at stages 43–45, there are non-epithelial cells with pseudopodia, abundant ribosomes, and marginated heterochromatin. These cells, possible precursor cells of thymic lymphocytes, are frequently observed to attach and pass through the basal lamina which coats the thymic rudiment. The proliferation and differentiation of large lymphocytes are evident at stage 47. During stages 48–49 the small lymphocytes, lymphoid cortex and epithelial medulla including the thymic cysts, differentiate, and vascularization occurs.The results provide an ultrastructural basis for recent experimental evidence that the thymus exerts its essential function at stages 47–48. The possibility of non-epithelial derivation of thymic lymphocytes is discussed.The author wishes to express his thanks to Asst. Prof. Ch. Katagiri for his helpful advice during the course of this study     

Electron microscopic study on the thyroid gland of the salamander Hynobius nebulosus in the breeding season

Summary The thyroid gland of adult salamanders, Hynobius nebulosus, in the breeding season was studied by electron microscopy. The follicular cells are different in cell height and fine structures; the taller cells with many cell organelles and granules and the lower cells with a few cell organelles and granules are both present in the same follicle. In the cytoplasm, three types of membrane-bounded granules, namely, cytosomes, colloid droplets, and vacuolar bodies and circular membrane complexes occur. The vacuolar bodies are subdivided into two types; the ordinary type having loosely distributed particles and the specific type containing tubules and/or closely packed filaments, crystalloid structures, except for the particles. The chromophobe colloids within the Bensley-cells correspond to extremely large, ordinary type vacuolar bodies, while the Langendorff-colloid cells possess increased numbers of granular cisternae of endoplasmic reticulum and a ribosome-rich, dense cytoplasmic matrix but not extremely large colloid. The intracytoplasmic circular membrane complexes appear in the Golgi area of cytosome-rich cells. It is suggested that they originate from the Golgi apparatus which was activated to produce many cytosomes. Intranuclear inclusions consisting of microtubules and filaments and tight junctions between two adjacent lateral plasma membranes are occasionally encountered.     

Substrate-histochemical investigations and ultrahistochemical demonstrations of acid phosphatase in larval and prepupal salivary glands of Drosophila melanogaster

Summary A major function of the larval salivary glands of Drosophila melanogaster is known to be the production of a mucopolysaccharide that serves as an adhesive during puparium formation. In order to localize the mucosubstances during development substrate histochemical methods were used, and the site of acid phosphatase was demonstrated by the ultrahistochemical lead-salt method. It could be shown that the glue-granules in the corpus cells of larval salivary glands as well as the large secretion vacuoles in the prepupal corpus cells give a positive -amylase-resistent PAS-reaction, which indicates neutral mucosubstances. Granular PAS-positive deposits in the larval and prepupal collum cells were reduced after preincubation with -amylase and may represent glycogen, which has also been seen in electron micrographs of these cells. The Hale-reaction gave a weak indication that acid mucosubstances are present in the larval glue granules and in the large prepupal secretory vacuoles. After digestion of sialic acid with -neuraminidase the weak indication was absent showing that the acid mucosubstances had been sialomucines. Ultrahistochemical demonstration of acid phosphatase indicated the presence of this enzyme in Golgi fields and lysosomal structures. Acid phosphatase seems to be missing in the large secretion vacuoles of the prepupal salivary gland.It is concluded, that the large vacuoles in the corpus cells of prepupal salivary glands represent a secretion product, obviously a mucosubstance. The lysosomal structures, containing acid phosphatase, may be accumulated in preparation for the autolysis of the gland which begins about two hours after the pupal moult, i.e. 15 hours after puparium formation.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft (Ga 97/6).     

The innervation of the salivary gland of the tick,Boophilus microplus

Summary Salivary of the ixodid tick Boophilus microplus Canestrini are at least partially innervated by a branch of the pedipalpal nerve. Axons containing both large granular and smaller agranular vesicles were observed within the acini associated with all types of secretory cells. A modification of the Falk-Hillarp histochemical technique was used to demonstrate discrete areas of fluorescence within the salivary acini. It is suggested that the transmitter involved with the control of salivary activities is a catecholamine and may even be dopamine.This work formed part of a thesis submitted to the University of Cambridge for the degree of Ph.D. and was supported by a studentship from the Science Research Council. I would like to thank Drs. D.J. Beadle, M.J. Berridge and H.A. Robertson for their encouragement and advice     

An electron microscopic study of non-fixed and non-dehydrated normal human stratum corneum

Summary This is an electron microscopic study of non-fixed and non-dehydrated normal human stratum corneum from the lumbar region.Non-stained sections have a low contrast. In sections examined 3 days after skin biopsy the cytoplasm of the cells shows a uniform contrast or exhibits dark and light areas. A single layer delimits the cytoplasm from the intercellular space. The latter is partly filled out with substance.In sections stained 2 to 4 days after skin biopsy the fibrils are distinct. On the basis of the variations in their opacity and ultrastructure three types of horny cells are clearly distinguishable. In cells of type 1 intensely stained keratohyalin and less opaque fibrillar substance occur. A distinct keratin pattern is not found. In cells of type 2 the fibrils show areas with distinct kerytohyalin and keratin pattern and transitional phases between these two stages of fibrillar differentiation. The keratin pattern representing the final stage of the fibrillar differentiation process is visualized through a successive discoloration of the filaments, whereas the interfilamentous substance retains the opacity of the keratohyalin. In cells of type 3 the entire fibrillar substance exhibits a keratin pattern. This consists of less opaque filaments with a diameter of 74 Å. The septa representing the interfilamentous substance are estimated as 30 Å at their thinnest points. These observations of the fibrils are completely comparable to the findings in fixed and dehydrated normal human stratum corneum.In sections stained particularly more than 18 days after skin biopsy the fibrils exhibit pronounced changes in their staining properties with concomitant decrease in distinctness or a complete extinction of the keratin pattern.The observations of the modified plasma membrane and the intercellular space in stained sections correspond to the findings in fixed and dehydrated normal human stratum corneum. The modified plasma membrane and the structures in the intercellular space appear with equal distinctness, whether the sections are stained 2 to 4, 6 to 12 or 14 to 21 days after skin biopsy.This investigation was supported by grants from the Edvard Welander Foundation and from the Swedish Medical Research Council (B71-12X-2708-03).