Developmental changes in fat body and midgut chromosomes of Drosophila auraria

Changes in puffing activity of fat body (FB) and midgut (MG) chromosomes of Drosophila auraria during late larval and white prepupal development as well as after in vitro culture with or without ecdysterone were studied and compared with those of the salivary gland (SG). The Balbiani Rings characteristic of the SG chromosomes of D. auraria, are not formed in FB and MG. Most of the inverted tandem chromosomal duplications that have been found to be common to all three tissues showed differentiation of puffing activity of the bands considered to be homologous. The major early ecdysone puffs 73A and 73B (considered to be homologues of D. melanogaster puffs 74EF and 75B, respectively), together with other early ecdysone puffs were present in all three tissues. Clear intermoult and postintermoult puffs were not evident in FB and MG chromosomes. However, a small set of late ecdysone puffs could be scored in FB, while no late ecdysone puffs were abserved in MG. Other tissue-specific puffs were identified, but a very small number of them were limited to MG.by W. Beermann     

Structure and activity of salivary gland chromosomes of Drosophila gibberosa

In Drosophila gibberosa the maximum secretory output of the salivary glands is in the prepupa rather than in the late third-instar larva. Using salivary chromosome maps provided here we have followed puff patterns from late second-instar larvae through the time of histolysis of the salivary glands 28–32 h after pupariation and find low puff activity correlated with low secretory activity throughout much of the third larval instar. Ecdysteroid-sensitive puffs were not observed at the second larval molt but do appear prior to pupariation initiating an intense cycle of gene activity. The second cycle of ecdysteroid-induced gene activity a day later, at the time of pupation, appears somewhat damped, especially for late puffs. Salivary chromosome maps provided here may also be used to identify homologous loci in fat body, Malpighian, and midgut chromosomes.     

Developmental changes in genome activity in Drosophila lebanonensis casteeli pipkin

Puparium formation in Drosophila lebanonensis casteeli is obviously restricted to a certain phase in circadian oscillation. The question whether or not the release of molting hormone is the actual process which is controlled by the circadian oscillation could be approached by using molting hormone-specific changes in genome activity as indication for changes in hormone titer. The identification of hormone specific changes in the puffing pattern of polytene chromosomes should provide a basis for this study.—To this end, a chromosome map of the 7 polytene chromosome arms (1 acrocentric and 3 metacentric chromosomes) of the species was made. Changes in the puffing pattern associated with puparium formation are described and compared with those occurring in response to experimental administration of -ecdysone.—89 puffs were regularly observed in midthird instar larvae. Prior to puparium formation 5 new puffs arise, one at an early stage and 4 attaining their maximum size immediately before puparium formation. Concomitantly, 5 puffs increase considerably in size. These changes in the puffing pattern can be reproduced by injection of ecdysone.—Upon injection of the hormone a clear differentiation between fast reacting loci (within 30–60 min) and slow reacting loci (after 3–4 hours) can be found. As in other Drosophila species the immediate response (within 30–60 min) comprises more than one (5) locus.In memory of Professor Dr. J. Schultz.     

An overview of gene activity in the fat body of Drosophila gibberosa

In the larval fat body of Drosophila gibberosa, polytene chromosome structure and activity exhibit cytological differences from chromosomes of midgut and salivary glands. These differences include long-persisting puffs, transient puffs and long-persisting band modulations. Some early ecdysteroid-induced puffs are present in all three organs but few late puffs are present in the fat body. Comparative studies reveal, therefore, that late larval-early pupal puffing is enhanced in salivary glands relative to gut, fat body and Malpighian tubules. After the fat body breaks up in the prepupa, the rate of programmed cell death and the corresponding slow decline of chromosomal activity also differ from cell to cell and from other organs.by M.L. Pardue     

Replication in Drosophila chromosomes

DNA fibre autoradiography of highly polytenized nuclei in salivary glands of Drosophila nasuta larvae reveals two distinct types of active replicons. Type I replicons are longer (mean size=64 m), have a very high rate of fork migration (average rate=0.95 m/min) and generally occur in large arrays often extending over several thousand m. In contrast, the type II replicons are smaller (mean size= 20 m), slow replicating (average rate=0.07 m/min) and occur in short arrays containing only a few closely spaced active replicons. Evidence is presented that type I replicons are active in the early S and type II in the late S. Observations on autoradiographic labelling of partially lysed polytene chromosomes provide evidence for a lack of temporal and spatial agreement in the activation of origin points in homologous regions of the lateral polytene strands; these observations also suggest local variations in levels of polyteny within a chromosome. On the basis of this and other available information on replication in polytene chromosomes the possible roles of the two replicon types in the generation of the different ³H-thymidine labelling patterns of polytene chromosomes are discussed.We take pleasure in dedicating this paper to our inspiring teacher Prof. S.P. Ray Chaudhuri on his completing 75 years of fruitful life     

Replication in Drosophila chromosomes

The temporal order of replication of specific sites in polytene chromosomes from salivary glands and gastric caeca of Drosophila nasuta larvae was compared using ³H-thymidine autoradiography. Labelling of different cytological regions in segments of chromosome 2R (section 47 A to 49 C) and chromosome 3 (section 80 A to 82 C) was examined in detail in nuclei showing late S-period labelling (2 D and 1D types) in both cell types. The different labelling sites (22 on the 2R segment and 38 on the chromosome 3 segment) are cytologically similar in the two cell types. However, there are profound differences in the labelling frequencies of certain sites in polytene nuclei from salivary glands and gastric caeca during the late S-phase. This suggests that even though a comparable number of chromosomal replicating units operates in the two polytene cell types, the temporal order of completion of replication differs.     

Replication in Drosophila chromosomes

It is widely known that the bulk of the pericentromeric heterochromatin (-heterochromatin) does not replicate during polytenization in Drosophila. However, a recent DNA-Feulgen cytophotometric study (Dennhöfer 1982a) has claimed equal polytenization of all heterochromatin regions. To re-examine this issue, the amount of Hoechst 33258-bright heterochromatin in non-polytene and polytene nuclei in salivary glands and Malpighian tubules of late third instar larvae of D. nasuta has been compared by cytofluorometry. Since the amount of Hoechst 33258-bright heterochromatin is similar in non-polytene and polytene nuclei in spite of the latter having an enormously high euchromatin DNA content, it is concluded that the -heterochromatin does not replicate during polytenization. The present results further indicate that in the polytene nuclei of Malpighian tubules the -heterochromatin remains at the 2C level whereas in salivary gland polytene nuclei it varies between the 2C and 4C levels.I would like to dedicate this paper to the memory of E. Heitz to commemorate 50 years of - and -heterochromatin     

Replication in Drosophila chromosomes

Prolongation of larval life in Drosophila melanogaster, by growing wild type larvae at lower temperature, or in animals carrying the X-linked mutation giant is known to result in a greater proportion of nuclei in salivary glands showing the highest level of polyteny. We have examined by autoradiography the patterns of ³H-thymidine incorporation during 10 min or 1 min pulses in salivary gland polytene chromosomes of older giant larvae and of wild type late third instar larvae of D. melanogaster grown since hatching either at 24 ° C or at 10 ° C. The various patterns of labelling and their relative frequencies are generally similar in glands from the warm-(24 ° C) or cold (10 ° C)-reared wild type larvae, except the interband (IB) labelling patterns which are very frequent in the later group but rare in the former. The IB type labelled nuclei in cold-reared wild type larvae show labelling ranging from only a few puffs/interbands labelled to nearly all puffs/interbands labelled. In warm-reared wild type larvae, very low labelled IB patterns are not seen. In older giant larvae, the ³H-thymidine labelling patterns are in most respects similar to those seen in cold-reared wild type larvae. In 1 min pulsed preparations from all larvae, the IB patterns are relatively more frequent than in corresponding 10 min pulsed preparations. No nuclei with the continuous (2C or 3C) type of labelling pattern, with all bands and interbands/puffs labelled, were seen in 1 min pulsed preparations from cold-reared wild type or in giant larvae, and only a few nuclei in 1 min pulsed preparations from warm-reared wild type larvae exhibited the 2C labelling pattern. Analysis of silver grain density on specific late replicating sites in late discontinuous (1D) type labelled nuclei suggests that the rate of DNA synthesis per chromosomal site is not different at the two developmental temperatures. It is suggested that correlated with the prolongation of larval life under cold-rearing conditions or in giant larvae, the polytene replication cycles are also prolonged. It is further suggested that the polytene S-period in these larvae is longer due to a considerable asynchrony in the initiation and termination of replication of different sites during a replication cycle.     

Developmental changes in midgut trehalase activity and its localization in the silkworm, Bombyx mori

The changes in trehalase activity and its localization in the midgut of the silkworm, Bombyx mori, were studied during larval-pupal-adult development. Trehalase activity in larval midgut epithelium increased with the larval growth, reached a maximum level at the middle of the fifth instar, and then decreased gradually. Trehalase activity in larval midgut was found in the epithelial tissue but not in the digestive juice or the midgut contents.The trehalase activity in the whole midgut started to rise at the onset of spinning and increased abruptly at larval-pupal ecdysis to reach an extremely high level 3 days later. This high activity was maintained throughout the subsequent pharate adult development and dropped suddenly at emergence. The midgut trehalase activity during pupal-adult development was mainly found in the midgut contents but scarcely any in the epithelium.Subcellular distribution of midgut trehalase depended upon larval-pupal-adult development. The activity was concentrated in a precipitate fraction of the epithelium until the middle of the fifth instar. During larval-pupal development, however, the activity increased in the soluble fraction with a concomitant decrease in the precipitate fraction. Almost all the trehalase activity in pupal and pharate adult midgut was recovered in the soluble fraction of the midgut contents. The data are discussed from a viewpoint of the histolysis.     

Identification of adult midgut precursors in Drosophila

The adult Drosophila midgut is thought to arise from an endodermal rudiment specified during embryogenesis. Previous studies have reported the presence of individual cells termed adult midgut precursors (AMPs) as well as “midgut islands” or “islets” in embryonic and larval midgut tissue. Yet the precise relationship between progenitor cell populations and the cells of the adult midgut has not been characterized. Using a combination of molecular markers and directed cell lineage tracing, we provide evidence that the adult midgut arises from a molecularly distinct population of single cells present by the embryonic/larval transition. AMPs reside in a distinct basal position in the larval midgut where they remain through all subsequent larval and pupal stages and into adulthood. At least five phases of AMP activity are associated with the stepwise process of midgut formation. Our data shows that during larval stages AMPs give rise to the presumptive adult epithelium; during pupal stages AMPs contribute to the final size, cell number and form. Finally, a genetic screen has led to the identification of the Ecdysone receptor as a regulator of AMP expansion.     

Developmental changes in Drosophila melanogaster following exposure to alternating electromagnetic fields

This study investigated the biological effects of alternating electromagnetic fields (EMFs) on developmental stages of Drosophila melanogaster eggs and the first, second and third instar larvae stages. D. melanogaster eggs and larval stages were exposed to a 11 mT 50 Hz field produced by a pair of Helmholtz coils. Each stage was exposed to aEMFs for 2, 4, 6 and 8 h. Features of adult flies such as head, thorax, abdomen and other morphological changes were studied and compared. The frequency of abnormal flies was calculated using statistical methods at P <.05. The results obtained from exposing larvae in different stages of development showed a significant increase in the number of abnormal adult flies, whereas no significant increase was observed in the group arising from eggs exposed to aEMFs. Also, it appeared that duration of exposure correlates with the increase in the number of abnormal flies. There was no significant difference in mortality rate and sex distribution of the abnormal flies between field exposed and the control groups.     

Synthesis and secretion of salivary gland proteins in Drosophila gibberosa during larval and prepupal development

Summary The late larvae of Drosophila gibberosa Patterson and Mainland choose different pupariation sites than the larvae of Drosophila melanogaster Meigen. Since the larvae of D. gibberosa do not attach themselves to the substratum, the salivary glands contain only a small amount of the glue proteins before pupariation. Proteins comprising the salivary gland secretions of late larvae of these two species were compared and found to be qualitatively quite different. Only five polypeptides with the same molecular masses were identified in both species. The rate of protein synthesis in the salivary glands of D. gibberosa continued to increase through the late larval stage and pupariation. As a consequence, the total amount of protein contained in the salivary glands also continued to increase after pupariation. To demonstrate temporal changes in protein synthesis from 48 h before pupariation to 28 h after pupariation, newly synthesized polypeptides were pulse labeled by culturing salivary glands in vitro. The patterns of polypeptide synthesis fell into four major groups depending upon whether the synthesis of a protein stopped shortly after pupariation, stopped during late pupariation, increased at pupariation, or was initiated after pupariation. Changing patterns of protein synthesis are correlated with the known changes in gene puffing during this developmental period.     

A comparative study of the location of mobile dispersed genes in salivary gland and midgut polytene chromosomes of Drosophila melanogaster

The location of DNA fragments representing mobile dispersed genes (MDG) in salivary gland and midgut polytene chromosomes was compared by means of in situ hybridization. In the Drosophila stock under study the average number of hybridization sites in the polytene chromosomes of one nucleus was 20 for MDG-1 and 10 for MDG-3. The total numbers of hybridization sites and their relative positions proved to be same in the polytene chromosomes of the two tissues. These results support the idea of a stable location of the mobile dispersed genes in the course of ontogenesis.     

Developmental studies in Drosophila

A study of the puffing patterns of the salivary gland chromosomes of D. pseudoobscura was carried out through several larval, prepupal, and pupal stages of development. A total of 176 puffs were found, 111 of which changed during the stages studied. As described in previous investigations with other Drosophila species there are two major peaks of puffing activity. These two peaks occur during puparium formation and pupation. Additionally, a minor activity-peak occurs during mid-prepupal life. Attempts have been made to establish correlations between the puffing data and those obtained from electrophoretic and ultrastructural studies.Supported in part by grants GM-16736-03 and FR-05426-09 from the U.S. Department of Health, Education, and Welfare. Ann Jacob Stocker was a holder of a University of Texas predoctoral fellowship.     

Developmental Studies in Drosophila

The salivary gland chromosomes of 3rd instar Drosophila pseudoobscura larvae were observed for puffing changes after injection of larvae with ecdysterone solution. Chromosomes from the salivary glands of 3rd instar larvae and prepupae were similarly examined after incubation in ecdysterone-containing medium. The larvae, after treatment, showed advancement of the puffing process with the occurrence of a pattern similar to that observed during the pre-spiracle eversion period of normal development. At least 92 puffs showed changes in size. For the prepupae, the puffing changes resembled those occurring normally during the late prepupal period. A group of puffs were selected for detailed study. Among these were four puffs on the XR chromosome which exhibited large increases before spiracle eversion and pupation in normal development. As in normal development, two of these became the most prominent puffs observed within h after hormone treatment. In chromosomes from larval glands, the other two XR chromosome puffs were among the largest puffs to appear later in the sequence. However, in chromosomes from prepupal glands one of these later puffs failed to appear. The significance of this large number of hormone-inducible puffing changes at two different periods in development is discussed.     

Intestinal stem cells in the adult Drosophila midgut

Drosophila has long been an excellent model organism for studying stem cell biology. Notably, studies of Drosophila's germline stem cells have been instrumental in developing the stem cell niche concept. The recent discovery of somatic stem cells in adult Drosophila, particularly the intestinal stem cells (ISCs) of the midgut, has established Drosophila as an exciting model to study stem cell-mediated adult tissue homeostasis and regeneration. Here, we review the major signaling pathways that regulate the self-renewal, proliferation and differentiation of Drosophila ISCs, discussing how this regulation maintains midgut homeostasis and mediates regeneration of the intestinal epithelium after injury.     

Heparan sulfate maintains adult midgut homeostasis in Drosophila

Tissue homeostasis is controlled by the differentiated progeny of residential progenitors (stem cells). Adult stem cells constantly adjust their proliferation/differentiation rates to respond to tissue damage and stresses. However, how differentiated cells maintain tissue homeostasis remains unclear. Here, we find that heparan sulfate (HS), a class of glycosaminoglycan (GAG) chains, protects differentiated cells from loss to maintain intestinal homeostasis. HS depletion in enterocytes (ECs) leads to intestinal homeostasis disruption, with accumulation of intestinal stem cell (ISC)‐like cells and mis‐differentiated progeny. HS‐deficient ECs are prone to cell death/stress and induced cytokine and epidermal growth factor (EGF) expression, which, in turn, promote ISC proliferation and differentiation. Interestingly, HS depletion in ECs results in the inactivation of decapentaplegic (Dpp) signaling. Moreover, ectopic Dpp signaling completely rescued the defects caused by HS depletion. Together, our data demonstrate that HS is required for Dpp signal activation in ECs, thereby protecting ECs from ablation to maintain midgut homeostasis. Our data shed light into the regulatory mechanisms of how differentiated cells contribute to tissue homeostasis maintenance.     

Comparison of the polytene chromosomes of the salivary gland,the fat body and the midgut nuclei of Drosophila auraria

Photo-maps of the fat body and midgut polytene chromosomes of Drosophila auraria were constructed. These photo-maps are compared with a new, more detailed photo-map of the salivary gland chromosomes of the same species. Seven, not previously described inverted tandem-duplications were detected, raising the number of such structures found in this species to 31. The constancy of the banding pattern based on the analysis of the above chromosomes is discussed.