Genes controlling posterior gut development in theDrosophila embryo

Our present detailed understanding of the genetic mechanisms controlling segmentation has been made possible, in large part, by comprehensive screens of cuticular morphology that identified genes involved in epidermal patterning. To systematically identify genes involved in internal morphogenesis, specifically development of the gut, we have screened mutant embryos produced by a collection of 53 embryonic lethal mutations affecting embryonic pattern formation or differentiation, and a collection of 161 deficiencies covering, in aggregate, approximately 70% of the genome. Staining with the anti-crumbs antibody was used to characterize the Malpighian tubules and hindgut, as well as other internal organs. The geneshuckebein, tailless andwingless, and two previously undescribed loci at 24C/D and 68D/E, are required to establish the primordia for the posterior midgut and hindgut/Malpighian tubules. A locus in region 30A/C is required for extension of the midgut epithelium to surround the yolk, and region 36E/37F is required for outbudding of the Malpighian tubule primordia. Several deficiencies were identified that uncover loci with specific effects on the morphogenesis (elongation, lumen formation) of the hindgut and Malpighian tubules and on the formation of constrictions in the midgut.     

Development of the Malpighian tubules in Cloeon dipterum (Ephemeroptera)

The development of the Malpighian tubules is studied in Cloeon dipterum through all stages from the youngest larva to the adult. The Malpighian tubules are found to be outgrowths of the posterior part of the endodermal midgut and not of the ectodermal hindgut. In the adult the part of the intestine with the tubule openings becomes separated by an ingrowing fold of the epithelium from the anterior main part of the midgut that forms a large thin-walled and air-filled bladder. The characteristics of the developmental stages, which served to determine the age of the animals, are given.     

Change with age of feulgen-DNA values in the blood-sucking insect,Triatoma infestans klug

Summary Feulgen-DNA values were evaluated cytophotometrically in the Malpighian tubes of T. infestans at the nymphal, adult and ageing life periods. In all cases the total nuclear Feulgen-DNA contents were found to be distributed within the 32C and 64C classes. However, part of the Feulgen-DNA values is shifted to lower intervals in ageing insects, as compared with nymphal and adult individuals, promoted by decrease in Feulgen-DNA values of the euchromatins. Changed response to Feulgen reaction due to some aging-induced alteration in DNP complexes, and/or breaks and loss of DNA in the euchromatins, as part of the senescence process, are ascribed to be responsible for such phenomenon.     

Complexity in evolved regulatory variation for alcohol dehydrogenase genes in HawaiianDrosophila

Summary The alcohol dehydrogenase gene (Adh gene) ofDrosophila affinidisjuncta is expressed at a higher level in the larval midgut and Malpighian tubules than the homologous gene fromDrosophila hawaiiensis. This study analyzed thecis-acting sequences responsible for these regulatory differences in larval tissues ofDrosophila melanogaster transformants. A series of 10 chimeric and deletedAdh genes was introduced into the germ line ofD. melanogaster, and tissue-specific expression levels were quantified by gel electrophoresis of tissue extracts. Sequences in the upstream region of the two genes had the strongest influence on enzyme production in the midgut and Malpighian tubules. Other sequence elements also showed effects, some of which were tissue specific. Most gene fragments displayed context-dependent effects, thus supporting the proposed model of polygenic regulation ofAdh gene expression.     

Ultrastructural changes in the gut and the Malpighian tubules of Epilachna varivestis after application of the new antibiotic Nikkomycin involve an osmoregulatory defect

The effect of the antibiotic Nikkomycin was investigated on the Malpighian tubules and the gut of fourth-instar larvae of the Mexican bean beetle, Epilachna varivestis. Within the Malpighian tubules, three different stages in cell alterations can be recognized. A stage of increased activity (Stage A), and two stages of dedifferentiation (Stages B and C) which are distinguishible by characteristic mitochondrial morphology. In Stage C individuals, when Malpighian tubule function stops entirely, alterations in the midgut take place, that are signs of increased activity. Measurements of hemolymph osmotic pressure showed that there is a considerable increase to a higher level which is maintained. Compared with the ultrastructural data, the regulation of osmotic pressure on a higher level may, in part, be the result of compensation for the failure of Malpighian tubule function by the midgut.     

Ultrastructural changes in the muscles,midgut, hemopoietic organ,imaginal discs and Malpighian tubules of the mosquito Aedes aegypti larvae infected by the fungus Coelomomyces stegomyiae

Fungi belonging to the genus Coelomomyces can infect mosquito larvae and develop within the larval hemocoel. To examine fungal development, Aedesaegypti larvae infected with Coelomomyces stegomyiae Keilin were fixed, embedded and sectioned for both light and electron microscopy. While fungal hyphae of C. stegomyiae did not invade cells other than the cuticular epithelial cells, they did penetrate a number of tissues including muscles, midgut, hemopoietic organ, imaginal discs, and Malpighian tubules. This revised version was published online in July 2006 with corrections to the Cover Date.     

DNA-RNA bodies in midgut cells of the stick insect, Bacillus rossius.

In the anterior part of the midgut and in the Malpighian tubules of the stick insect Bacillus rossius, about 10% of the epithelial cells develop endonuclear bodies which appear as DNA-RNA masses; in these cells the usual nucleoli are no longer evident. The DNA-RNA bodies are first formed in third instar larvae, become numerous in the fourth instar and persist in adults. In all larval instars and adults a different kind of DNA-body has been noticed in the epithelial cells of the posterior midgut. The DNA-RNA bodies of the anterior midgut and of the Malpighian tubules have been interpreted as the result of somatic gene amplification, whereas the DNA masses of the posterior midgut are likely due to a virus infection.     

The influence of ouabain on the elimination of injected and orally applied dyes in Drosophila hydei

The sour dyes azocarmine and indigocarmine are excreted through the Malpighian tubules and the midgut after injection into the body cavity of third instar Drosophila hydei larvae. After injection, the other organs are free of dyes. The epithelium of the midgut does not allow orally applied dyes to pass into the haemolymph. Ouabain diminishes significantly the content of dyes in the cavity of the Malpighian tubules and of the midgut. The maximal concentration of azocarmine decreases in the Malpighian tubules to about 65 per cent and in the midgut to about 70 per cent. Indigocarmine decreases in the Malpighian tubules to about 55 per cent. The content of indigocarmine of the midgut does not change significantly after ouabain injections. As ouabain inhibits active ion transport, the decrease of the concentration of dyes is seen as proof of the coupling of active ion transport processes and of excretion of the dyes. Moreover, this decrease points to an ouabain-sensitive transport mechanism, which is localized in the epithelia of the Malpighian tubules and midgut.     

Immunocytochemical localization of a vacuolar-type ATPase in Malpighian tubules of the ant Formica polyctena

The presence of a vacuolar-type ATPase in Malpighian tubules of the ant Formica polyctena was investigated immunocytochemically, using antibodies to vacuolar ATPases of Manduca sexta midgut and bovine kidney. Specific labelling was observed at the brush border of the epithelium extending along the entire length of the tubules. These findings agree with the current view that a vacuolar ATPase is situated at the apical membrane of Malpighian tubule cells and other insect epithelial cells, being the energizing element of an electrogenic potassium pump. When antibodies were tested on tubules in different secretion conditions prior to fixation, no differences were observed in the distribution of the vacuolar ATPase.This work was supported by grants from the European Community (SCI-CT90-0480), from the Ministerio de Educación y Ciencia DGICYT, Spain (CE 91-0002), and from the Deutsche Forschungsgemeinschaft (Wi 698-3).     

Tissue-specific schedule of selective replication in Drosophila nasutoides

Summary Dramatic changes in the DNA composition of post-mitotic versus mitotic and germ line nuclei occur during development in different organisms. Drosophila nasutoides possesses n=4 chromosomes which were quantified with a microphotometer in females. The diploid (2 C) DNA content was 0.79 pg or 7.7×10⁸ nucleotide pairs, calculated from brain metaphases and calibrated with hen erythrocyte nuclei. The individual elements comprised X=9%, 2=16%, 3=13%, and 4=62% of the total complement. In polytene nuclei of larval salivary glands which had undergone 11 endoreplication cycles, chromosome 4 contained only 1.55% of total Feulgen DNA. Thus, in contrast with other Drosophila genomes, where under-replicating material is dispersed to all elements, a huge quantity of non-endoreplicating DNA is restricted to a single chromosome. This permits accurate determination of the timing of under-replication in the single cell. The data presented here suggest that the schedule is tissue-specific. Larval hind gut and salivary duct nuclei begin under-replication during the first endocycle, whereas adult and larval salivary glands mainly begin during the second cycle. In Malpighian tubules the onset of selective DNA syntheses occurs during either the first or the second endocycle.     

Allatotropin expression during the development of the fourth instar larvae of the kissing-bug Triatoma infestans (Klüg)

Allatotropin (AT) is a neuropeptide originally isolated from the brain of Manduca sexta and then characterized in several insect species. It acts as a neurohormone, as well as a neuromodulator. While it was primarily characterized on the basis of its ability to stimulate the secretion of juvenile hormones, it was also found that it acts as a cardioaccelerator and myostimulator. The presence of AT in IV instar larvae of T. infestans was previously described at the level of the Malpighian tubules. In the present study we report the presence of the peptide at the level of the brain, retrocerebral complex, as well as in the anterior midgut and aorta. The presence of AT at the corpora allata suggests that the peptide is acting on the gland during the first days of the moulting cycle. Neural processes at the level of the aorta and the anterior midgut suggests that, like in adults, the hormone is acting as a cardioaccelerator and myostimulator. The peptide was also found in open-type cells of the midgut. Finally the presence of allatotropic neurons in the optical lobe of the brain suggests that as in other species, the peptide is related with the control of circadian rhythms.     

DNA values in somatic tissues of Dermestes (Dermestidae: Coleoptera)

The organisation of the male Malpighian tubule has been investigated in the coleopteran genus Dermestes. Nuclear number is found to be more or less constant between species. However, the DNA values of these nuclei do not, in general, reflect the germ-line DNA value of the species since many of them do not conform with members of a doubling series. These phenomena may be interpreted as aspects of the control of tissue and organ size, the final dimensions of the Malpighian tubules being similar in spite of presumed differences in 2C cell size in the different species.     

Development of the Drosophila entero-endocrine lineage and its specification by the Notch signaling pathway

In this paper we have investigated the developmental–genetic steps that shape the entero-endocrine system of Drosophila melanogaster from the embryo to the adult. The process starts in the endoderm of the early embryo where precursors of endocrine cells and enterocytes of the larval midgut, as well as progenitors of the adult midgut, are specified by a Notch signaling-dependent mechanism. In a second step that occurs during the late larval period, enterocytes and endocrine cells of a transient pupal midgut are selected from within the clusters of adult midgut progenitors. As in the embryo, activation of the Notch pathway triggers enterocyte differentiation and inhibits cells from further proliferation or choosing the endocrine fate. The third step of entero-endocrine cell development takes place at a mid-pupal stage. Before this time point, the epithelial layer destined to become the adult midgut is devoid of endocrine cells. However, precursors of the intestinal midgut stem cells (pISCs) are already present. After an initial phase of symmetric divisions which causes an increase in their own population size, pISCs start to spin off cells that become postmitotic and express the endocrine fate marker, Prospero. Activation of Notch in pISCs forces these cells into an enterocyte fate. Loss of Notch function causes an increase in the proliferatory activity of pISCs, as well as a higher ratio of Prospero-positive cells.     

Anatomy and fine structure of the alimentary canal of the spittlebug Lepyronia coleopterata (L.) (Hemiptera: Cercopoidea)

The alimentary canal of the spittlebug Lepyronia coleopterata (L.) differentiates into esophagus, filter chamber, midgut (conical segment, tubular midgut), and hindgut (ileum, rectum). The filter chamber is composed of the anterior extremity of the midgut, posterior extremity of the midgut, proximal Malpighian tubules, and proximal ileum; it is externally enveloped by a thin cellular sheath and thick muscle layers. The sac-like anterior extremity of the midgut is coiled around by the posterior extremity of the midgut and proximal Malpighian tubules. The tubular midgut is subdivided into an anterior tubular midgut, mid-midgut, posterior tubular midgut, and distal tubular midgut. Four Malpighian tubules run alongside the ileum, and each terminates in a rod closely attached to the rectum. Ultrastructurally, the esophagus is lined with a cuticle and enveloped by circular muscles; its cytoplasm contains virus-like fine granules of high electron-density. The anterior extremity of the midgut consists of two cellular types: (1) thin epithelia with well-developed and regularly arranged microvilli, and (2) large cuboidal cells with short and sparse microvilli. Cells of the posterior extremity of the midgut have regularly arranged microvilli and shallow basal infoldings devoid of mitochondria. Cells of the proximal Malpighian tubule possess concentric granules of different electron-density. The internal proximal ileum lined with a cuticle facing the lumen and contains secretory vesicles in its cytoplasm. Dense and long microvilli at the apical border of the conical segment cells are coated with abundant electron-dense fine granules. Cells of the anterior tubular midgut contain spherical secretory granules, oval secretory vesicles of different size, and autophagic vacuoles. Ferritin-like granules exist in the mid-midgut cells. The posterior tubular midgut consists of two cellular types: 1) cells with shallow and bulb-shaped basal infoldings containing numerous mitochondria, homocentric secretory granules, and fine electron-dense granules, and 2) cells with well-developed basal infoldings and regularly-arranged apical microvilli containing vesicles filled with fine granular materials. Cells of the distal tubular midgut are similar to those of the conical segment, but lack electron-dense fine granules coating the microvilli apex. Filamentous materials coat the microvilli of the conical segment, anterior and posterior extremities of the midgut, which are possibly the perimicrovillar membrane closely related to the nutrient absorption. The lumen of the hindgut is lined with a cuticle, beneath which are cells with poorly-developed infoldings possessing numerous mitochondria. Single-membraned or double-membraned microorganisms exist in the anterior and posterior extremities of the midgut, proximal Malpighian tubule and ileum; these are probably symbiotic.     

Excretory role of the midgut in larvae of the tobacco hornworm, Manduca sexta (L.).

Caterpillars of Manduca sexta use two distinct transport mechanisms for the excretion of dyes. One pump (Type A) has a high affinity for acid (anionic) dyes and occurs in the midgut and medial Malpighian tubules. Acid dyes accumulate rapidly in the lumen of the midgut while the Malpighian tubules appear to play only a minor role in the excretion of these dyes. The other pump (Type B) excretes basic (cationic) dyes and is located primarily in the proximal Malpighian tubules. Evidence is presented that hippuric acid competes with acid dyes for excretion by both midgut and Malpighian tubules. After the final-instar larva purges its gut the ability of the midgut and Malpighian tubules to excrete dyes gradually decreases. Sixty hours after the purge only the Malpighian tubules retain some dye excreting activity.     

Regulatory peptides in fruit fly midgut

Regulatory peptides were immunolocalized in the midgut of the fruit fly Drosophila melanogaster. Endocrine cells were found to produce six different peptides: allatostatins A, B and C, neuropeptide F, diuretic hormone 31, and the tachykinins. Small neuropeptide-F (sNPF) was found in neurons in the hypocerebral ganglion innervating the anterior midgut, whereas pigment-dispersing factor was found in nerves on the most posterior part of the posterior midgut. Neuropeptide-F (NPF)-producing endocrine cells were located in the anterior and middle midgut and in the very first part of the posterior midgut. All NPF endocrine cells also produced tachykinins. Endocrine cells containing diuretic hormone 31 were found in the caudal half of the posterior midgut; these cells also produced tachykinins. Other endocrine cells produced exclusively tachykinins in the anterior and posterior extemities of the midgut. Allatostatin-immunoreactive endocrine cells were present throughout the midgut. Those in the caudal half of the posterior midgut produced allatostatins A, whereas those in the anterior, middle, and first half of the posterior midgut produced allatostatin C. In the middle of the posterior midgut, some endocrine cells produced both allatostatins A and C. Allatostatin-C-immunoreactive endocrine cells were particularly prominent in the first half of the posterior midgut. Allatostatin B/MIP-immunoreactive cells were not consistently found and, when present, were only weakly immunoreactive, forming a subgroup of the allatostatin-C-immunoreactive cells in the posterior midgut. Previous work on Drosophila and other insect species suggested that (FM)RFamide-immunoreactive endocrine cells in the insect midgut could produce NPF, sNPF, myosuppressin, and/or sulfakinins. Using a combination of specific antisera to these peptides and transgenic fly models, we showed that the endocrine cells in the adult Drosophila midgut produced exclusively NPF. Although the Drosophila insulin gene Ilp3 was abundantly expressed in the midgut, Ilp3 was not expressed in endocrine cells, but in midgut muscle.     

X-ray microanalysis of the filter chamber of the cicada,Cyclochila australasiae Don.

X-ray microanalysis of frozen-hydrated specimens of the cicada filter chamber shows that there are concentration changes in K+ and Cl- in the various compartments of the filter chamber from feeding to non-feeding states. These changes are consistent with an osmotic transfer of water between the anterior midgut and the posterior midgut and Malpighian tubules. K+ and Cl- account for a large proportion of the osmotically active solutes in these compartments, and it is suggested that the osmotic gradients are generated by secretion of K+ and Cl- into the posterior midgut and Malpighian tubule lumina. Analysis of freeze-substituted sections of filter chamber supports the analysis of frozen-hydrated specimens and indicates that Na+ may also be secreted into the posterior midgut and the Malpighian tubules. The system functions as a water-shunting complex.     

Morphology and ultrastructure of the alimentary canal of the cicada Platypleura kaempferi (Hemiptera: Cicadidae)

The alimentary canal of cicada Platypleura kaempferi is described. It comprises the oesophagus, filter chamber, external midgut section and hindgut. The elongate oesophagus expands posteriorly, with its posterior end constricting to become a bulb. The filter chamber consists of two parts: a very thin sheath and a filter organ. The filter organ is composed of the anterior and posterior ends of the midgut (internal midgut section), and the internal proximal ends of the Malpighian tubules. The external midgut section differentiates into a collapsed sac and a midgut loop. The latter is divided into three distinct segments. The hindgut contains a dilated rectum and a long narrow ileum. The distal portions of the four Malpighian tubules are enclosed in a peritoneal sheath together with the distal ileum before reaching to the rectum. Ultrastructurally, the oesophagus and the hindgut are lined with a cuticle. The filter chamber sheath consists of cells with large irregular nuclei. Filamentous substances coat the microvilli of the cells of the internal midgut section. The posterior end of the midgut comprises two types of cells, with the first type of cells containing many vesicles and scattered elements of rough endoplasmic reticulum. The anterior and posterior segments of the midgut loop cells have ferritin‐like granules. The ileum cells have well‐developed apical leaflets associated with mitochondria. Accumulations of virus‐like particles enclosed in the membrane are observed in the esophagus, conical segment, mid‐ and posterior segments of the midgut loop.