A reassessment of argasid tick salivary gland ultrastructure from an immuno-cytochemical perspective

Previous morphological and histochemical studies of argasid tick salivary glands indicated that they were less complex than ixodid salivary glands, with only three granular cell types. The present study shows that there exist at least four different granular cell types in the salivary glands of the argasid tick Ornithodoros savignyi, based on immuno-localization of the anti-hemostatic factors, apyrase and savignygrin. Both anti-hemostatic factors were localized to dense core granule type 'a' and to granule type 'b', that shares a similar homogenous morphology with non-labeled granule type 'd'. Furthermore, the major tick salivary gland proteins (TSGPs), previously implicated in granule biogenesis, were localized to all the granular cell types. This indicates that granular cell types with different morphologies can express the same proteins, while cell types that show similar morphologies may not express the same proteins. Argasid tick salivary glands seem to be more complex than previously thought and might not be amenable to morphological classification alone. Alternative classification methodologies that rely on physical expression patterns of the salivary gland proteome might be more reliable as markers for a specific granular cell type.     

Renal function in the neotropical bat, Artibeus jamaicensis

1. When feeding on figs (Ficus insipida), the bat Artibeus jamaicensis increases dietary sodium density while decreasing potassium density by primarily extracting and ingesting pulp juices rather than other parts of the fruit. 2. Based on urine osmotic pressure, these bats are uniformly dehydrated when they leave day roosts and become rapidly rehydrated (0.5-1 hr) after initiation of feeding. 3. After 2000 hr, and throughout the night there is no difference in urine concentration of free-flying bats compared with bats held in the laboratory without food or water for the same time interval. 4. Mean maximum urine concentration in this species is 972 mOsm/kg.     

The plasminogen activator family from the salivary gland of the vampire bat Desmodus rotundus: cloning and expression

Complementary DNAs coding for four Desmodus rotundus salivary plasminogen activators (DSPAs) were isolated and characterized. The predicted amino acid sequences display structural features also found in tissue-type plasminogen activator. The largest forms (DSPA alpha 1 and -alpha 2) contain a signal peptide, a finger (F), an epidermal growth factor (EGF), a kringle, and a serine protease domain, whereas DSPA beta and -gamma lack the F and F-EGF domains, respectively. Additional differences between the four forms suggest that distinct genes code for the members of the DSPA family. Transfection of DSPA-encoding cDNAs, placed under the control of the simian virus 40 late promoter, into COS-1 cells resulted in the secretion of highly fibrin-dependent PAs.     

Apoptosis: controlled demolition at the cellular level

Apoptosis is characterized by a series of dramatic perturbations to the cellular architecture that contribute not only to cell death, but also prepare cells for removal by phagocytes and prevent unwanted immune responses. Much of what happens during the demolition phase of apoptosis is orchestrated by members of the caspase family of cysteine proteases. These proteases target several hundred proteins for restricted proteolysis in a controlled manner that minimizes damage and disruption to neighbouring cells and avoids the release of immunostimulatory molecules.     

Baroreceptor mechanisms at the cellular level

Nothing is known of transduction mechanisms of baroreceptors in vivo. Not even the site of transduction is known. However, there are mechanotransducer ion channels that provide a useful model system of transduction. In these channels, transduction is accomplished by a strain-dependent increase in the probability of being open. Membrane tension is coupled to the channel by cytoskeletal strands that concentrate the strain energy from a large (approximately equal to 4000 A diameter) area of membrane and thereby provide high sensitivity. The channel is fast and does not inactivate, but viscoelastic coupling to the channel can dramatically alter the transfer function.     

Histology,ultrastructure, and seasonal variations in the bulbourethral gland of the African straw-colored fruit bat Eidolon helvum

We studied the morphological characteristics and seasonal changes of the bulbourethral gland of Eidolon helvum in a typical African tropical environment. Forty-eight bulbourethral glands were examined using gross anatomical, histological, histochemical, and ultrastructural techniques during the early rainy, late rainy, and peak dry seasons. The pear-shaped bilateral bulbourethral glands were located extra-abdominally in the inguinal region. Trabeculae from the capsule divided the parenchyma into numerous lobules of tubuloalveolar glandular acini. The mucosa was covered by a simple columnar epithelium consisting up of principal secretory cells, columnar dense cells and basal cells, which were progressively pronounced during the dry season. The principal cells contained eosinophilic granules, which were PAS positive while the dense cells did not show affinity for the stains. The mean gross weights, acini diameters, and epithelial heights were greater during the rainy season than the dry season. Ultrastructural evaluation showed that the cytoplasm of the principal cells contained well-developed Golgi complexes, rough endoplasmic reticulum, mitochondria, and secretory vesicles of varying electron densities and sizes. The secretory vesicles were numerous during the early rainy season, decreased during the late rainy season and were scanty during the peak dry season. The simple columnar epithelium observed during the rainy season was replaced by an undefined stratified epithelium during the dry season, and this was associated with cellular degenerations and regenerations. In conclusion, E. helvum has a typical mammalian bulbourethral gland, with a unique cell type, the dense cell whose functions are not well-understood. The gland exhibits cyclical seasonal variation in structure and secretory activity; being active during the early rainy season (breeding season), and showing the lowest activity during the dry season (non-breeding season). Glandular epithelial cell renewal occurs during the dry season in preparation for the next breeding season.     

Host association influences variation at salivary protein genes in the bat ectoparasite Cimex adjunctus

Parasite–host relationships create strong selection pressures that can lead to adaptation and increasing specialization of parasites to their hosts. Even in relatively loose host–parasite relationships, such as between generalist ectoparasites and their hosts, we may observe some degree of specialization of parasite populations to one of the multiple potential hosts. Salivary proteins are used by blood‐feeding ectoparasites to prevent hemostasis in the host and maximize energy intake. We investigated the influence of association with specific host species on allele frequencies of salivary protein genes in Cimex adjunctus, a generalist blood‐feeding ectoparasite of bats in North America. We analysed two salivary protein genes: an apyrase, which hydrolyses ATP at the feeding site and thus inhibits platelet aggregation, and a nitrophorin, which brings nitrous oxide to the feeding site, inhibiting platelet aggregation and vasoconstriction. We observed more variation at both salivary protein genes among parasite populations associated with different host species than among populations from different spatial locations associated with the same host species. The variation in salivary protein genes among populations on different host species was also greater than expected under a neutral scenario of genetic drift and gene flow. Finally, host species was an important predictor of allelic divergence in genotypes of individual C. adjunctus at both salivary protein genes. Our results suggest differing selection pressures on these two salivary protein genes in C. adjunctus depending on the host species.     

MHC class II DRB diversity, selection pattern and population structure in a neotropical bat species, Noctilio albiventris

Genes of the major histocompatibility complex (MHC) have a crucial role in the immune response of vertebrates, alter the individual odour and are involved in shaping mating preferences. Pathogen-mediated selection, sexual selection and maternal-fetal interactions have been proposed as the main drivers of frequently observed high levels of polymorphism in functionally important parts of the MHC. Bats constitute the second largest mammalian order and have recently emerged as important vectors of infectious diseases. In addition, Chiroptera are interesting study subjects in evolutionary ecology in the context of olfactory communication, mate choice and associated fitness benefits. Thus, it is surprising that they belong to the least studied mammalian taxa in terms of their MHC diversity. In this study, we investigated the variability in the functionally important MHC class II gene DRB, evidence for selection and population structure in the group-living lesser bulldog bat, Noctilio albiventris, in Panama. We found a single expressed, polymorphic Noal-DRB gene. The substitution pattern of the nucleotide sequences of the 18 detected alleles provided evidence for positive selection acting above the evolutionary history of the species in shaping MHC diversity. Roosting colonies were not genetically differentiated but females showed lower levels of heterozygosity than males, which might be a sign that the sexes differ in the selection pressures acting on the MHC. This study provides the prerequisites for further investigations of the role of the individual MHC constitution in parasite resistance, olfactory communication and mate choice in N. albiventris and other bats.     

Morphological diversity at different spatial scales in a Neotropical bat assemblage

The morphology of species can be used to represent their ecological position and infer potential processes determining the structure of species assemblages. This ecomorphological approach has been widely applied to the study of bat assemblages which mainly focuses on a single spatial scale and particular guilds. We extended such an ecomorphological approach to a multi-scale analysis of a Neotropical bat assemblage and its constituent guilds (aerial and gleaning insectivores, frugivores, and nectarivores) to describe their structure at different spatial scales and determine the relative importance of inter-specific competition, habitat filtering, or stochastic processes shaping such structures. We measured the occupied morphological space (size) defined by wing and skull morphology independently and the nearest-neighbour distance (structure) among species within these spaces at each spatial scale. Observed patterns were compared with random expectations derived from null models for statistical inference. When controlling for species richness and regional sampling effects in the null models, we did not find a significant effect of spatial scale in the morphological structure of the studied bat assemblage and guilds. Morphological structure followed the same patterns across scales as those expected from random drawings of sample size alone. Similar results were obtained regardless of morphological complex (wing and skull) and guilds. At both the assemblage and guild levels, bat morphological structure seems to be determined by regional, abiotic processes (e.g. habitat filtering) shaping the composition and organization of the species pool.     

Thyroid hormone action at the cellular level

Thyroid hormones influence numerous physiological and biochemical functions. The expression of the hormonal effects involves several events. The interaction of T3 with nuclear receptors, and the stimulation of mRNA production appears to be a major step. Extranuclear binding of thyroid hormones could account for early responses. Plasma membrane receptors may play a role in the cellular uptake of T3 and the stimulation of amino acids and sugar transport. A direct control of oxidative phosphorylation through binding of T3 to mitochondrial binding sites has been proposed. The role of cytosolic binding proteins remains unclear. The understanding of the mode of action of thyroid hormones requires a better knowledge of the molecular events occurring at the nuclear level, and the relation between the nuclear and extranuclear binding sites in the hormonal expression.     

Cardiac mechanics at the cellular level.

The active mechanical properties of heart muscle are load, length, and time-dependent. The capability for investigating cardiac mechanisms at the cellular level may help to distinguish between those properties of the myocardium which arise from myocardial cells and those which arise from the tissue architecture and extracellular matrix of connective fibers. We present here, for the first time, a general approach for subjecting single heart cells to isometric, isotonic, afterloaded, or physiological loading sequences, while obtaining on-line measures of cell force and length. This approach has been implemented and tested on freshly dissociated, adult frog ventricular myocytes. Examples are presented for each of the four loading sequences.     

Tissue microarrays: fast-tracking protein expression at the cellular level

Tissue microarrays maximize returns in cellular pathology whilst minimizing the use of cells and tissues. They are made by arraying cores of tissue taken from multiple donor blocks into a single recipient block. Accordingly, the histology and pathology of several hundred tissues can be represented in one tissue microarray that, when stained by immunohistochemistry, provides comprehensive topographic information on protein expression. Used with complimentary techniques, such as complementary DNA microarray analysis, tissue microarrays are providing valuable data for the identification of new markers of disease and assisting in the discovery of therapeutic targets. They are also leading a revolution in cellular pathology as high-throughput technology is introduced to maximize the information provided.     

Tissue microarrays: fast-tracking protein expression at the cellular level

Tissue microarrays maximize returns in cellular pathology whilst minimizing the use of cells and tissues. They are made by arraying cores of tissue taken from multiple donor blocks into a single recipient block. Accordingly, the histology and pathology of several hundred tissues can be represented in one tissue microarray that, when stained by immunohistochemistry, provides comprehensive topographic information on protein expression. Used with complimentary techniques, such as complementary DNA microarray analysis, tissue microarrays are providing valuable data for the identification of new markers of disease and assisting in the discovery of therapeutic targets. They are also leading a revolution in cellular pathology as high-throughput technology is introduced to maximize the information provided.     

Quantification and cellular localization of dopamine in the salivary gland of the ixodid tick Amblyomma hebraeum

Dopamine (DA) content of the salivary glands in partially fed female and fed male ticks, Amblyomma hebraeum Koch (Acari: Ixodidae), was measured by high-performance liquid chromatography with electrochemical detection or by a radioenzymatic assay for catecholamines following experimental treatment. Some glands were held in vitro for up to 3 days. Other preparations (backless explants) allowed one side to be surgically denervated, the contralateral side serving as control. Normal ticks were sampled for up to 4 days post-removal from the host (rabbits). In the backless explants, there was little if any difference in DA content between denervated and control sides, even after 4 days in vitro, indicating that unilateral denervation did not eliminate the major salivary gland pool of DA. High doses of reserpine (333 g per g body weight) and 6-hydroxydopamine (1000 g per g body weight) did not significantly reduce the DA content of the salivary gland, also suggesting that only a minor component of the DA pool is within axons innervating the salivary gland. A dispersed population of cells rich in tyrosine hydroxylase immunoreactivity (an enzyme marker for catecholamine-synthesizing cells) was found in close association with the granular acini. This further suggests that the major DA pool in the salivary gland may be in cells other than the dopaminergic nerves arising from the central nervous system. © Rapid Science Ltd. 1998