Larval Digestive System Research Articles

Larval digestive system ontogeny and early weaning in neon tetra Paracheirodon innesi.

The intensive culture of characid teleosts for ornamental trade is highly dependent on live feed organisms, particularly Artemia nauplii, to provide nutrition through the larval stage. Live feeds have inherent disadvantages relative to prepared microparticulate diets (MDs), specifically availability, labor and cost. In this research, the dependence of larval Paracheirodon innesi on live Artemia was confirmed via a nutritional trial. Next, digestive system ontogeny was characterized from the onset of exogenous feeding through metamorphosis. P. innesi exhibited an agastric larval stage, as well as low digestive enzyme activity at the onset of exogenous feeding followed by abrupt increases in trypsin, lipase and pepsin activity. Differentiation of the stomach, including gastric gland formation and production of neutral mucopolysaccharides, as well as the onset of pepsin activity, did not occur until 20days post hatch (dph; 5.24 ± 0.20mm). This shift from agastric to gastric digestive modes is indicative of a proliferation of digestive capacity and subsequent prey diversity in other fish species exhibiting similar altricial larval stages.Based on this information, different schedules for weaning from Artemia to a MD were evaluated. For P. innesi fed until 32 dph, weaning beginning at 12 dph and 17 dph resulted in similar survival to live Artemia (mean: 22.0 ± 1.7%), and the MD resulted in the lowest survival (0.8 ± 0.3%). These results indicate that weaning is possible prior to gastric differentiation, potentially resulting in the reduction of Artemia use in the larval culture P. innesi.

The Use of Probiotics during Rearing of Hermetia illucens: Potential, Caveats, and Knowledge Gaps.

Given the novelty of the industrial production of the edible insects sector, research has primarily focused on the zootechnical performances of black soldier fly larvae (BSFL) in response to different substrates and rearing conditions as a basis to optimize yield and quality. However recently, research has started to focus more on the associated microbes in the larval digestive system and their substrates and the effect of manipulating the composition of these communities on insect performance as a form of microbiome engineering. Here we present an overview of the existing literature on the use of microorganisms during rearing of the BSFL to optimize the productivity of this insect. These studies have had variable outcomes and potential explanations for this variation are offered to inspire future research that might lead to a better success rate for microbiome engineering in BSFL.

Identification and characterization of key genes in insulin signaling pathway as molecular targets for controlling the fall webworm, Hyphantria cunea.

The insulin signaling pathway is closely related to metabolism, growth, reproductive capacity and lifespan of insects. However, the physiological function of the insulin signaling pathway is little known in Hyphantria cunea. Five insulin signaling pathway genes (HcInR, HcPI3K, HcAKT, HcFOXO and HcTOR) in H.cunea were identified and characterized in this study. The spatiotemporal expression profiles of the genes showed that HcInR, HcAKT, HcPI3K and HcTOR expressions were higher at the egg stage than those in other development stages, whereas HcFOXO was highly expressed in the adult stage; all of these genes were highly expressed in the larval digestive system, especially in the midgut and hindgut. After RNA interference (RNAi) of the five genes in 5th instar H.cunea larvae, weight gain and survival rate (except in the siHcAKT-injected group) were significantly decreased, and the developmental duration of larval and pupal stages were prolonged. In addition, knockdown of five genes in 7th instar larvae decreased the pupation rate, survival rate and oviposition capacity, and resulted in abnormal development during larval-pupal transition. Our findings indicate that the insulin signaling pathway plays essential roles in growth and development and the molting process in H.cunea, providing an important basis for developing new potentially molecular targets for RNAi-based pest control and understanding the mechanism of H.cunea outbreak. © 2022 Society of Chemical Industry.

Structural basis of lignocellulose deconstruction by the wood-feeding anobiid beetle Nicobium hirtum

The details of the lignocellulose deconstruction processes in the digestive systems of wood-feeding insects remain elusive. This study aimed to examine the biochemical conversion of lignocellulose in the digestive system of a wood-feeding anobiid beetle, Nicobium hirtum, one of the most important pests of wooden products in Japan. To this end, N. hirtum larvae were fed with Japanese red pine (softwood) and Japanese beech (hardwood) sapwood diets, as well as an artificial diet containing Shorea wood (hardwood) sapwood sawdust. The structural differences between the original and digested (feces) lignocellulose samples were examined using wet-chemical and two-dimensional (2D) nuclear magnetic resonance (NMR) methods. Cellulose and hemicelluloses, especially mannan in the softwood diet, were preferentially degraded over lignin in the larval digestive system. As a result, lignin was enriched in the digested lignocellulose residues. Lignin compositional analyses based on thioacidolysis and 2D NMR determined that the proportions of oxidized lignin aromatic units were notably increased after digestion. Further, the 2D NMR analyses revealed the accumulation of aldehyde and hydroxypropiovanillone/syringone end-unit structures in lignin, indicating that oxidative and/or reductive modifications of lignin polymers occur in the larval digestive system. Such structural alterations of lignin may facilitate the dissociation of the lignin barrier, thereby liberating polysaccharides for subsequent enzymatic conversion for assimilation and energy.

Facultative planktotrophy in larvae of the purple mussel Perumytilus purpuratus

ABSTRACT The developmental pattern in the mid-intertidal mussel Perumytilus purpuratus was investigated through laboratory cultures. Larval development, growth, survival rate, and time to reach the post-larval stage were determined using triplicated feeding/non-feeding treatments in artificial seawater at 18.2 ± 0.5°C. Development of the larval digestive system was examined histologically. We found that P. purpuratus have ova (121.1 ± 2.7 μm diameter) with a jelly coating, the digestive system develops in the trochophore, the veliger shell has a large prodissoconch-1 and a small prodissoconch-2, the larval period lasted between 10 and 14 days, and larvae could reach metamorphosis without the presence of particulate food. Unlike most of the mytilid species with pelagic larvae, a facultative planktotrophic development is evident in this species. This developmental pattern could be favourable in unstable and changing environments such as rocky shores.

Dynamic Immune Response to Vibriosis in Pacific Oyster Crassostrea gigas Larvae during the Infection Process as Supported by Accurate Positioning of GFP-Tagged Vibrio Strains.

As the immune system is not fully developed during the larval stage, hatchery culture of bivalve larvae is characterized by frequent mass mortality caused by bacterial pathogens, especially Vibrio spp. However, the knowledge is limited to the pathogenesis of vibriosis in oyster larvae, while the immune response to pathogenic microorganisms in this early life stage is still far from being fully elucidated. In this study, we combined green fluorescent protein (GFP)-tagging, histological and transcriptomic analyses to clarify the pathogenesis of experimental vibriosis and the mechanisms used by the host Pacific oyster Crassostrea gigas larvae to resist infection. The Vibrio strains first colonized the digestive system and rapidly proliferated, while only the transcription level of IκB kinase (IKK) and nuclear factor κB (NF-κB) associated with signaling transduction were up-regulated in oyster at 18 h post challenge (hpc). The mRNA levels for integrin β-1, peroxinectin, and heat shock protein 70 (HSP70), which are associated with phagocytosis, cell adhesion, and cytoprotection, were not upregulated until 30 hpc when the necrosis already happened in the larval digestive system. This suggested that the immunity in the early stages of C. gigas is not strong enough to prevent vibriosis and future research may focus on the strengthening of the gastrointestinal immune ability to defend vibriosis in bivalve larvae.

Embryonic and larval development of the caridean shrimp Palaemon argentinus (Decapoda, Caridea): effects of salinity and diet

Abstract The caridean shrimp Palaemon argentinus is a species of commercial and ecological interest. Its numerous larval stages, the lack of knowledge on their nutritional requirements, and their ability to survive in a wide range of salinities raise questions on the optimum conditions for larval rearing in captivity. The present study was aimed at evaluating embryonic development under different salinities and larval development under different combinations of salinities and diet regimes, in order to define alternative, cheaper culture conditions. We tested salinities usually encountered by the species in natural habitats (0.1, 1 and 5 ppt) and a highly protein-inert diet (Tetracolor®) as a potential replacement for live food (nauplii of Artemia salina). The incubation period and fecundity were similar among salinity treatments. Overall, the number of survival days and percentage of zoeae that moulted two, three and four times were higher when embryogenesis occurred at 5 ppt and when larvae were exposed to 5 ppt. These results suggest that the conditions experienced by embryos affect the performance of the first larval stages, and probably reflect the lower energetic requirements of zoeae to osmoregulate as water and haemolymph osmolarity become closer. On the other hand, larval performance was better when fed A. salina nauplii than Tetracolor®. The latter may not cover the nutritional requirements of zoeae or may have low digestibility due to insufficient enzymes in the undeveloped larval digestive system. Based on the present results, we conclude that a salinity of 5 ppt combined with a diet consisting of Artemia sp. nauplii is optimal for larval culture at early stages.

Ontogenetic development of the gastrointestinal tract of African lungfish larvaeProtopterus aethiopicus(Heckel 1851): A light microscopy study

The organogenesis of the digestive system was described in the African lungfish (Protopterus aethiopicus) from 6 days post-hatching (6 DPH) to 17 days post-hatching (17 DPH) reared at 27 degrees C. To elucidate the position of the gastrointestinal tract in relation to the neural tube, notochord and yolk sac at 6 DPH, and to the vertebral column, lungs and kidneys at 17 DPH, larvae were mapped by means of computer-assisted 3D reconstructions starting from histological serial sections. The larvae showed a simple digestive tract, which appeared as a straight undifferentiated and closed tube at 6 DPH. Microscopical observation showed that yolk reserves were not completely depleted by 17 DPH. During the endogenous feeding period at least up to 17 DPH, the larval digestive system experienced a fast transformation with almost complete development of most digestive organs (pharyngeal teeth, intestinal vestibule, intestine and liver). Our findings suggest that, by 17 DPH, African lungfish larvae are ready to start exogenous feeding.

Identification and expression characterization of a novel carboxypeptidase A-like gene (RvCPA) during early developmental stages in the gastropod Rapana venosa (Muricidae)

Rapana venosa is an economically important aquaculture species in China. Carboxypeptidases (CPs) A and B (CPA and CPB, respectively) hydrolyze peptides and proteins and play critical roles in the development of the digestive system in animals. In this study, a full-length CPA-like cDNA sequence from R. venosa (RvCPA) was isolated using RACE, and RvCPA mRNA expression levels were analyzed in different tissues and developmental stages by quantitative real-time PCR. Additionally, the expression patterns of RvCPA under different diets were investigated in competent larvae of R. venosa. The full-length cDNA of the RvCPA gene was 1,810 bp and consisted of a 1,296-bp open reading frame (ORF) encoding 431 aa. Phylogenetic analysis revealed high homology of RvCPA with CPs from Biomphalaria glabrata, Pomacea canaliculata, and Ampullaria crossean. Our results showed that RvCPA had higher expression in the salivary gland than in other tissues and that the expression of RvCPA was dramatically increased in the juvenile (postlarval) stage compared with other stages, indicating that functional changes occur in the larval digestive system during the food habit transition. Furthermore, we found that an animal diet could significantly increase the expression of RvCPA, which may suggest that animal diets can promote the development of the digestive system. This information on a novel CP in R. venosa that participates in digestion and is related to the food habit transition may broaden our understanding of digestive system development during metamorphosis in carnivorous gastropods.

Histological, histochemical and biochemical characterization of larval digestive system ontogeny in black tetra Gymnocorymbus ternetzi to inform aquaculture weaning protocols

Identifying an appropriate larval diet is a significant challenge in aquaculture. To overcome this bottleneck, characterization of larval fish digestive system ontogeny is critical for optimizing nutritional protocols. Intensive culture of characids for ornamental trade is highly dependent on live Artemia nauplii through the larval stage. Live feeds have unique challenges relative to prepared microparticulate diets (MDs), specifically pertaining to availability, labor, and cost. In this study, a feeding trial was conducted to compare three commercially available MDs in larval Black Tetra Gymnocorymbus ternetzi. Larvae exhibited poor survival and growth for MDs relative to Artemia. Digestive system ontogeny was characterized using histology, histochemistry, and digestive enzyme activity assays from the onset of exogenous feeding through the larval stage. G. terntzi exhibited an agastric larval stage, as well as low digestive enzyme activity at the onset of exogenous feeding, followed by increases in trypsin, lipase, and pepsin activity. Histological differentiation of the stomach, including gastric gland formation and production of periodic acid Schiff positive neutral mucopolysaccharides, as well as the onset of pepsin activity, occurred at 22 days post hatch (dph). This shift from agastric to gastric digestion indicated elevated digestive capacity and increased ability to consume a diversity of prey.Based on these data, experiments were conducted to evaluate different weaning times from Artemia to a MD. Larvae were fed Artemia exclusively from hatch through the end of the trial, a MD exclusively, or were transitioned from Artemia to a MD at three different time points. For G. ternetzi fed until 33 dph, weaning beginning at 13 dph exhibited higher survival (20.6 ± 1.8%) than live Artemia and weaning beginning at 18 dph and 23 dph (mean: 13.6 ± 1.5%), while the MD resulted in the lowest survival (0.8 ± 0.2%). These results indicate that weaning is possible prior to gastric differentiation, suggesting that it is possible to rely less on Artemia as a larval feed in this characid species.

Colorado potato beetle chymotrypsin genes are differentially regulated in larval midgut in response to the plant defense inducer hexanoic acid or the Bacillus thuringiensis Cry3Aa toxin

When Colorado potato beetle larvae ingested potato plants treated with the plant defense inducer compound hexanoic acid, midgut chymotrypsin enzyme activity increased, and the corresponding chymotrypsin genes were differentially expressed, evidence of the larval digestive proteolytic system’s plasticity. We previously reported increased susceptibility to Cry3Aa toxin in larvae fed hexanoic acid treated plants. Here we show that the most expressed chymotrypsin gene in larvae fed hexanoic acid treated plants, CTR6, was dramatically downregulated in Cry3Aa intoxicated larvae. lde-miR-965-5p and lde-miR-9a-5p microRNAs, predicted to target CTR6, might be involved in regulating the response to hexanoic acid but not to Cry3Aa toxin.

Plant cell wall degrading enzymes, pectinase and cellulase, in the digestive system of the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

In digestion, the red palm weevil, Rhynchophorus ferrugineus, has been adapted to overcome the plant cell wall barrier, specially lignocellulosic and pectic compounds, by producing cellulase and pectinase enzymes. Partial biochemical characterisations of cellulase and pectinase were determined in the larval digestive system of the pest. Larval midgut extract showed an optimum activity for cellulase and pectinase against carboxyl methyl cellulose and pectin at pH 6.0 and 7.0, respectively. Larval midgut cellulase and pectinase were more stable at pH 4.0–8.0 and pH 6.0–8.0 than in highly acidic and alkaline condition, respectively. However, cellulase and pectinase showed to be more stable at pH 6.0 and 7.0, respectively, when the incubation time increased. Maximum activity for cellulase and pectinase incubated at different temperatures was observed at 50°C. Cellulase and pectinase activity significantly decreased in the presence of EDTA and SDS. On the contrary, Ca<sup>2+</sup>, Mg<sup>2+</sup>,and Na<sup>+</sup> significantly affect pectinase activity and K<sup>+</sup> did not affect the enzyme activities. Ca<sup>2+</sup> and Mg<sup>2+</sup> increased cellulase activity as well. K<sub>M </sub>and V<sub>max</sub> for pectinase activity were 0.92 mg/ml and 290 units/mg. Zymogram analyses revealed the presence of one form of pectin methyl esterase and one form of cellulase in the larval digestive system.  

Characterization and ontogenetic development of digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae.

The major digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae were characterized, and the physiological characteristics of the enzymes during early ontogeny were clarified using biochemical and molecular approaches. The maximum activity of trypsin (Try), chymotrypsin (Ct) and amylase (Amy) was observed at pH 6-11, 8-11 and 6-9, respectively. Maximum activity of Try, Ct and Amy occurred at 50 °C, that of lipase (Lip) was at 60 °C and that of pepsin (Pep) was at 40-50 °C. These pH and thermal profiles were similar to those for other fish species but differed from those previously reported for adult bluefin tuna. Enzyme activity for all enzymes assayed was found to decrease at high temperatures (Try, Ct, Amy and Pep: 50 °C; Lip: 40 °C), which is similar to findings for other fish species with one marked exception-increased Try activity was observed at 40 °C. Lip activity appeared to be dependent on bile salts under our assay conditions, resulting in a significant increase in activity in the presence of bile salts. Ontogenetic changes in pancreatic digestive enzymes showed similar gene expression patterns to those of other fish species, whereas marked temporal increases in enzyme activities were observed at 10-12 days post hatching (dph), coinciding with previously reported timing of the development of the pyloric caeca in bluefin tuna larvae. However, complete development of digestive function was indicated by the high pep gene expression from 19 dph, which contradicts the profile of Pep activity and previously reported development timing of the gastric gland. These findings contribute to the general knowledge of bluefin tuna larval digestive system development.

Histological development of the digestive system of the Amazonian pimelodid catfish Pseudoplatystoma punctifer

The organogenesis of the digestive system was described in the Amazonian pimelodid catfish species Pseudoplatystoma punctifer from hatching (3.5 mm total length, TL) to 41 days post-fertilization (dpf) (58.1 mm TL) reared at 28°C. Newly hatched larvae showed a simple digestive tract, which appeared as a straight undifferentiated and unfolded tube lined by a single layer of columnar epithelial cells (future enterocytes). During the endogenous feeding period, comprised between 20 and 96 h post-fertilization (3.5 to 6.1 mm TL), the larval digestive system experienced a fast transformation with the almost complete development and differentiation of most of digestive organs (buccopahrynx, oesophagus, intestine, liver and exocrine pancreas). Yolk reserves were not completely depleted at the onset of exogenous feeding (4 dpf, 6.1 mm TL), and a period of mixed nutrition was observed up to 6 to 7 dpf (6.8 to 7.3 mm TL) when yolk was definitively exhausted. The stomach was the organ that latest achieved its complete differentiation, characterized by the development of abundant gastric glands in the fundic stomach between 10 and 15 dpf (10.9 to 15.8 mm TL) and the formation of the pyloric sphincter at the junction of the pyloric stomach and the anterior intestine at 15 dpf (15.8 mm TL). The above-mentioned morphological and histological features observed suggested the achievement of a digestive system characteristic of P. punctifer juveniles and adults. The ontogeny of the digestive system in P. punctifer followed the same general pattern as in most Siluriform species so far, although some species-specific differences in the timing of differentiation of several digestive structures were noted, which might be related to different reproductive guilds, egg and larval size or even different larval rearing practices. According to present findings on the histological development of the digestive system in P. punctifer, some recommendations regarding the rearing practices of this species are also provided in order to improve the actual larval rearing techniques of this fast-growing Neotropical catfish species.

Development of the digestive system in dusky kob, Argyrosomus japonicus, larvae

In order to contribute to the development of larval rearing technologies of dusky kob, Argyrosomus japonicus, we studied the morphology and histology of the larval digestive system from hatching to 30 days after hatch. At hatch, the digestive tract appeared as a simple tube. The mouth was closed (endogenous feeding) and it opened by 65 degree days (DD). Supranuclear vacuoles appeared by 88 DD, initiating exogenous feeding. By 145 DD, the oil globule had disappeared. The stomach, intestine, rectum and gastric glands were visible by 224 DD. Number and size of supranuclear vacuoles began to decrease with progressive vacuolisation of the enterocytes and intestinal folds became obvious. The rectum was well differentiated at 338 DD but lacked supranuclear vacuoles in the enterocytes, suggesting limited nutrient absorption. At this stage, lipid absorption shifted to the hindgut, which now contained many lipid vacuoles. Goblet cells were visible in the midgut as gastric glands appeared, and their number increased from 292 DD. At the start of the third developmental phase, the larvae had a fully functional digestive system.

Histological and histochemical study of the digestive system of the Argentine anchovy larvae (Engraulis anchoita) at different developmental stages of their ontogenetic development

AbstractIn this work, histological and histochemical features of the larval digestive system of Argentine anchovy Engraulis anchoita were described. Structural changes during ontogenetic development were also characterized, and comparisons between the beginning and the end of larval development were made. Histological sections of larvae were subjected to histochemical and routine histological techniques to localize and differentiate glycoproteins (GPs). Both at an early and a late larval stage, the oesophageal goblet cells reacted more intensely than those of the rest of the digestive tract, and only the oesophagus exhibited metachromasia with toluidine blue techniques at different pHs, thus revealing diverse GPs at different concentrations. The GPs histochemical composition in the intestine varied with the developmental stage and the intestinal zone. The absence of goblet cells characterized the foregut; however, they started differentiation at an advanced stage in the midgut. These cells could be detected in the hindgut both at the beginning and at the end of development. The attached glands showed a varied glycoprotein composition. The digestive tract of E. anchoita presented a high level of complexity, related to the multiple functions of mucus in the digestive tract, such as lubrication, protection, antimicrobial function and ionic and osmotic regulation.

Rearing and Injection of <em>Manduca sexta</em> Larvae to Assess Bacterial Virulence

Manduca sexta, commonly known as the tobacco hornworm, is considered a significant agricultural pest, feeding on solanaceous plants including tobacco and tomato. The susceptibility of M. sexta larvae to a variety of entomopathogenic bacterial species(1-5), as well as the wealth of information available regarding the insect's immune system(6-8), and the pending genome sequence(9) make it a good model organism for use in studying host-microbe interactions during pathogenesis. In addition, M. sexta larvae are relatively large and easy to manipulate and maintain in the laboratory relative to other susceptible insect species. Their large size also facilitates efficient tissue/hemolymph extraction for analysis of the host response to infection. The method presented here describes the direct injection of bacteria into the hemocoel (blood cavity) of M. sexta larvae. This approach can be used to analyze and compare the virulence characteristics of various bacterial species, strains, or mutants by simply monitoring the time to insect death after injection. This method was developed to study the pathogenicity of Xenorhabdus and Photorhabdus species, which typically associate with nematode vectors as a means to gain entry into the insect. Entomopathogenic nematodes typically infect larvae via natural digestive or respiratory openings, and release their symbiotic bacterial contents into the insect hemolymph (blood) shortly thereafter(10). The injection method described here bypasses the need for a nematode vector, thus uncoupling the effects of bacteria and nematode on the insect. This method allows for accurate enumeration of infectious material (cells or protein) within the inoculum, which is not possible using other existing methods for analyzing entomopathogenesis, including nicking(11) and oral toxicity assays(12). Also, oral toxicity assays address the virulence of secreted toxins introduced into the digestive system of larvae, whereas the direct injection method addresses the virulence of whole-cell inocula. The utility of the direct injection method as described here is to analyze bacterial pathogenesis by monitoring insect mortality. However, this method can easily be expanded for use in studying the effects of infection on the M. sexta immune system. The insect responds to infection via both humoral and cellular responses. The humoral response includes recognition of bacterial-associated patterns and subsequent production of various antimicrobial peptides(7); the expression of genes encoding these peptides can be monitored subsequent to direct infection via RNA extraction and quantitative PCR(13). The cellular response to infection involves nodulation, encapsulation, and phagocytosis of infectious agents by hemocytes(6). To analyze these responses, injected insects can be dissected and visualized by microscopy(13, 14).

Pectinase and cellulase activity in the digestive system of the elm leaf beetle, Xanthogaleruca luteola Muller (Coleoptera: Chrysomelidae)

The elm leaf beetle, Xanthogaleruca luteola, is a serious pest of elm trees in urban areas. Partial biochemical characterization of pectinases and cellulases was conducted using the larval digestive system of the pest. Midgut extracts from larvae showed optimum activity for pectinase and cellulase against pectin and carboxymethyl cellulose, respectively, under acidic conditions (pH 6). Pectinases and cellulases were respectively more stable under acidic conditions (pH 4–7) and slightly acidic conditions (pH 5–7) than under highly acidic and alkaline conditions. However, the enzymes were more stable in slightly acidic conditions (pH 6) when incubation time was increased. Maximum activity for the pectinases and cellulases incubated at different temperatures was observed at 45 and 50°C, respectively. Mg2+ remarkably increased pectinase activity, and cellulase activity increased significantly in the presence of Ca2+ and Mg2+. Sodium dodecyl sulfate significantly decreased pectinase and cellulase activity. The Michaelis–Menten constant (KM) and the maximal reaction velocity (Vmax) values for pectinase were 2mg·mL−1 and 0.017mmol·min−1·mg−1 protein toward pectin, respectively. Zymogram analyses revealed the presence of one and five bands of pectinase and cellulase activity, respectively, in the larval midgut extract.

Biochemical characterisation of α- and β-glucosidases and α- and β-galactosidases from red palm weevil, Rhynchophorus ferrugineus (Olivier) (Col.: Curculionide)

The red palm weevil, Rhynchophorus ferrugineus (Olivier), is one of the most destructive pests of palm trees in the southeast of Iran. Digestion in the alimentary canal of the red palm weevil is facilitated by some carbohydrases. Results of the in vitro studies indicated the presence of α- and β-glucosidases and α- and β-galactosidases in the digestive system and haemolymph of this pest. In the digestive system of females, the activities of α-glucosidase and β-galactosidase were higher than those of β-glucosidase and α-galactosidase. Also, the specific activity of  α- and β-glucosidases and α- and β-galactosidases in the female digestive system was much higher than that in larvae. Results showed that the highest activities of α- and β-glucosidases were at pH 5 and of α- and β-galactosidases at pH 4. The R. ferrugineus α- and β-glucosidases and α- and β-galactosidases have an optimum temperature activity at 50, 50–60, 40–60, and 40°C, respectively. A zymogram pattern in the native gel revealed that R. ferrugineus α- and β-glucosidases and α- and β-galactosidases in the digestive system showed 2, 3, 1 and 1 major bands, respectively. The activity of α-glucosidase in the digestive system of larvae and female adults was higher than that of the other carbohydrases. Therefore, it is the most important subject for further study and design of a new approach to the control of this pest using carbohydrase inhibitors.  

Visualizing digestive organ morphology and function using differential fatty acid metabolism in live zebrafish

Lipids are essential for cellular function as sources of fuel, critical signaling molecules and membrane components. Deficiencies in lipid processing and transport underlie many metabolic diseases. To better understand metabolic function as it relates to disease etiology, a whole animal approach is advantageous, one in which multiple organs and cell types can be assessed simultaneously in vivo. Towards this end, we have developed an assay to visualize fatty acid (FA) metabolism in larval zebrafish (Danio rerio). The method utilizes egg yolk liposomes to deliver different chain length FA analogs (BODIPY-FL) to six day-old larvae. Following liposome incubation, larvae accumulate the analogs throughout their digestive organs, providing a comprehensive readout of organ structure and physiology. Using this assay we have observed that different chain length FAs are differentially transported and metabolized by the larval digestive system. We show that this assay can also reveal structural and metabolic defects in digestive mutants. Because this labeling technique can be used to investigate digestive organ morphology and function, we foresee its application in diverse studies of organ development and physiology.