Junqueira 39;s Basic Histology Pdf 15th Edition

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Osman Briseno

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Aug 3, 2024, 5:58:52 PM8/3/24

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Phosphorylation/dephosphorylation of proteins is the major post-translational mechanism involved in many cellular processes. In Rhodnius prolixus eggs from fertilized females, we detected at least two hydrolytic enzymes, a phosphatase and cathepsin D-like aspartic proteinase, both with an acid pH optimum. Acid phosphatase activity, was enhanced after second day of development and reaches a plateau around day four which is maintained up to the eclosion of the first instar larvae. This enzyme is strongly inhibited "in vitro" by 2 mM of sodium fluoride and 10 mM of tartrate Na/K but not by 1 or 100 nM of okadaic acid. Thus, this enzyme may have lisosomal origin. Aspartic proteinase activity, was measured "in vitro" using hemoglobin or purified vitellin as substrates. The activity of this enzyme also increases with embryo development. Among several proteinase inhibitors tested, pepstatin was able to abolish vitellin (VT) breakdown. When phosphatase activity was assayed in non-fertilized eggs, only a basal level was observed when compared with fertilized eggs, suggesting that this enzyme is activated in a fertilization dependent process. The increase in phosphatase activity coincides with the beginning of VT proteolysis. In addition sodium fluoride, an acid phosphatase inhibitor strongly impaired the action of cathepsin D-like aspartic proteinase suggesting a cooperative action of both enzymes and a possible relationship between protein dephosphorylation and VT degradation. This hypothesis is supported by the fact that non-fertilized eggs, which does not present phosphatase activity, does not present vitellin breakdown.

Rhodnius prolixus is a hematophagous insect which ingests large volumes of blood during a single feeding session. High concentrations of heme, iron-protoporphyrin IX, are generated as a result of hemoglobin digestion. Heme can cause damage to various biomolecules and membranes. In the insect midgut, the perimicrovillar membrane (PMVM) is the first structure to come into contact with the gut luminal contents, which contain heme at high concentrations. PMVM, in fact, can protect the microvillar membranes from direct contact with the gut luminal contents. In order to evaluate the association of heme with PMVM we used TEM to detect peroxidase activity in these membranes. We incubated the midgut in 0.1 M Cacodilate buffer pH 6.5 at 37oC with Diaminobenzidine (DAB). We detected a positive staining, which indicates the presence of heme on these membranes. We suggest that this result is probably due to a heme binding protein or lipid partition in the PMVM. In order to investigate the heme polymerization, we centrifuged the gut luminal content of R. prolixus. The heme polymerization activity was associated with the pellet. We found that the heme polymerized successfully. In order to evaluate the participation of the PMVM in the heme polymerization process, we isolated the PMVM of both R. prolixus and Dysdercus peruvianus (a phytophagous insect) in a discontinuous sucrose density gradient. These membranes were capable successfully polymerizing heme. These results suggest that the PMVM has a role in heme polymerization. The phospholipids present in the PMVM of both R. prolixus and D. peruvianus were detected. Of the phospholipids detected in R. prolixus, 52.5% consisted of Phosphatidylethanolamine (PE), 33.75% of Phosphatidylcholine (PC), and 13.78% of Phosphatidylserine (PS). In D. peruvianus the results were 60.03 % PE, 5.83 % PC, 27.29 % PS and 6.85 % a non-identified phospholipid. Ridley (1998) showed the heme polymerase activity can be obtained with PE, PS, PC and PI. Presently we are investigating the role of the PMVM protein moiety.

Study of South American triatomine bugs (Hemiptera: Reduviidae) is both of biological and medical interest, since most of them are the invertebrate hosts of Trypanosoma cruzi, causative agent of Chagas' disease, and the closely related Trypanosoma rangeli. Unlike T. cruzi, T. rangeli is pathogenic to its insect host, and colonizes and spends part of its life cycle in the salivary glands of the invertebrate vector. Scanty information is available on the histology and ultrastructure of healthy and infected glands, as well as the development of the parasites therein.

Adult Rhodnius domesticus (the main invertebrate host of T. rangeli in Santa Catarina State, Brazil) of both sexes were infected with T. rangeli, strain SC-58. Eight days post-infection the salivary glands were collected and processed for scanning electron microscopy (SEM). The glands were adhered with double face adhesive tape to SEM stubs, coated with a 20 nm thick gold layer in a sputtering device and then observed in a Zeiss DSM-940 scanning electron microscopy.

Observation of the salivary glands by scanning electron microscopy showed that they are usually elongated, unilobular structures, about 1-2 mm long, with an excretion channel arising at the medial/sub-terminal region. Parasites, both epimastigote and trypomastigote forms, were found adhered to the outer surface of the glands in high numbers, usually forming patches. Some glands were split in two pieces, in order to expose their inner surfaces. Epimastigotes and trypomastigotes could be found adhered among the microvilli. Some trypanosomes entering the glands could be also observed. Infected glands, including the microvilli, showed no visible morphological alterations due to the presence of the parasites.

Chagas'disease is an endemic protozoan disseminated in Brazil. The natural transmission occurs by excretion by the blood-feeding vector by reduviidae insect whose faeces contained the parasite Trypanosoma cruzi in their infective tripomastigote metacyclic forms. In our laboratory using Rhodnius prolixus as an insect model, we tested some lignoids (pinoresinol, burchellin, NDGA, licarin A, sesamin, podophyllotoxin) on feeding, moulting, excretion and development of T. cruzi. The oral treatment of R. prolixus with burchellin and NDGA drastically reduced the number of flagellates excreted (urine and faeces). In vitro treatments with these substances did not inhibit the number of parasites. However feeding with higher concentration of pinoresinol and NDGA had antifeedant effect and inhibited the amount blood ingested. The most important results was obtained by burchellin and pinoresinol, both extracted from brazilian plants, Aniba burchelli and Melia azedarach, respectively, by demonstration of their effect on moulting and parasites growth inhibition. in Rhodnius These findings indicate the potential use these compounds growth regulators which could interferes with Trypanosoma cruzi development in the digestive tract.

Heme (Fe-protoporphyrin IX) is a well-known generator of reactive oxygen species that cause damage to several classes of biomolecules. Some organisms, as the hematophagous insect Rhodnius prolixus, have vertebrate blood as the sole source of food. In this case, the digestion of the meal represents an oxidative challenge due to the large amount of heme release by hemoglobin degradation. One of the antioxidant mechanisms involved in the protections of Rhodnius against heme-induced oxidative injuries is a hemolymphatic heme-binding protein (RHBP). It has already been described that deleterious effects of heme are inhibited by its binding to apoRHBP. Here we propose that RHBP participates in the antioxidant defense also by transporting heme to some tissues where it is degradated by heme-oxygenase. The formation of biliverdin, a heme degradation product, in the pericardial and midgut cells is observed when hemolymphatic level of heme is increased. Injection of purified RHBP in the abdominal cavity of this insect leads to the formation of biliverdin in those tissues. This results suggest that RHBP is able to transport heme and its degradation by heme-oxygenase represents an important intracellular antioxidant mechanisms in this insect.

The "wild" eye colour observed in triatomines is black, but some authors have reported the existence of mutants with red or white eyes. The first report about red eyed mutants was that of No & Silva (1949), in which they determined that this was a recessive character linked to the X chromosome. The objective of the present work was to study the effect of the number and sequence of matings on the fecundity and fertility of Triatoma infestans females, using this recessive character as a marker. It may allow to evaluate what possibility of genetic variability would be expected, for example, in a triatomine colony that has begun from a unique female. Virgin adults were coupled in pairs and separated into five groups:

All couples were kept separated and fed once a week. Eggs were collected once a week. The mean of the eggs laid did not show statistical difference between the groups. In the fifth series, and through the expression of the eye colour genotype, we have observed a frequency of 50% for each character, suggesting that both males contributed in the same proportion to the fertilisation of the eggs. In those series in which one male was replaced by another, we observed a gradual tendency of replacement of red eyed larvae by black ones. We also observed that the dynamics of this process of replacement depends on the moment at which males were substituted. Results suggest that females may mate more than once without having a corresponding rise in their fertility or fecundity.

As those of other Hemiptera, triatomine compound eyes are focal apposition eyes with an open rhabdom. The photoreceptors (Ph) of each ommatidium are arranged in a ring of rhabdom, formed by six retinula cells, which surrounds the central double rhabdomere of the seventh cell. An eighth thinner cell does not possess a rhabdomere and is located in the peripheral ring. Densely packed pigment granules are located into the retinula, inside two primary pigment cells (PPC), which surround the soft crystalline cone formed by four cells, and inside 24 secondary pigment cells that surround the whole ommatidium. Pigments located in the distal end of the Phs and in the PPCs form an "iris" in the focal plane of the corneal lens in front of the rhabdom distal tip. These eyes would have two types of image channel, one with high sensitivity and poor resolution (the peripheral rhabdomeres) and other with low sensitivity and high resolution (the two central rhabdomeres). In contrast to neural superposition eyes, the gain in sensitivity, conveyed by the peripheral rhabdomeres, must occur at the expense of resolution. This proposed mechanism, with one photopic and one scotopic system, is supported experimentally and by the way these eyes adapt to changes in light intensity. In the dark-adapted state, the pigment cells and retinular pigments that form the "iris", withdraw to a peripheral position and the dilated cone leaves all the rhabdomeres exposed. During light adaptation, the pigment cells contract, the rhabdom is pressed down and the cone cells form a narrow thread transmitting light to the central rhabdomere. This mechanism allows a very direct control of the acceptance angle and hence, the rhabdoms light flux.