Human epidermal growth factor receptor-1 expression renders Chinese hamster ovary cells sensitive to alternative aldosterone signaling

The epidermal growth factor (EGF) regulates cell proliferation, differentiation, and ion transport using ERK1/2 as a downstream effector. Furthermore, the EGF receptor (EGFR) is involved in signaling by G-protein-coupled receptors, growth hormone, and cytokines via transactivation. It has been suggested that steroids interact with peptide hormones. Previously, we have shown that aldosterone modulates EGF responses in Madin-Darby canine kidney cells (Gekle, M., Freudinger, R., Mildenberger, S., and Silbernagl, S. (2002) Am. J. Physiol. 282, F669-F679). Here, we tested the hypothesis that human EGFR-1 can confer alternative aldosterone responsiveness with respect to ERK1/2 phosphorylation to Chinese hamster ovary cells, which do not express EGFR. Wild-type Chinese hamster ovary cells did not respond to EGF or aldosterone. After transfection of human EGFR-1, the cells responded to EGF, but not to aldosterone. However, when submaximal concentrations of EGF were used, nanomolar concentrations of aldosterone potentiated the action of EGF within minutes, resulting in a leftward shift of the EGF dose-response curve. This was not the case in mock-transfected cells. The EGFR kinase inhibitor tyrphostin AG1478 or the MEK1/2 inhibitor U0126 completely prevented the effect. Furthermore, aldosterone enhanced Tyr phosphorylation of c-Src and EGFR, and an inhibitor of cytosolic tyrosine kinases (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyriociaine) prevented the action of aldosterone. Our data show that aldosterone uses the EGF-EGFR-MEK1/2-ERK1/2 signaling cascade to elicit its alternative effects. In the presence of EGF, aldosterone leads to EGFR transactivation via cytosolic tyrosine kinases of the Src family.     

Cracking open cell death in the Drosophila ovary

The Drosophila melanogaster ovary is a powerful yet simple system with only a few cell types. Cell death in the ovary can be induced in response to multiple developmental and environmental signals. These cell deaths occur at distinct stages of oogenesis and involve unique mechanisms utilizing apoptotic, autophagic and perhaps necrotic processes. In this review, we summarize recent progress characterizing cell death mechanisms in the fly ovary.     

Half-pint: alternative splicing in the Drosophila ovary

A new study from the Schüpbach lab implicates a splicing factor, Half-pint, in the regulation of oogenesis in Drosophila. Through processing of the otu mRNA, Hfp appears to control both mitosis and RNA localization in the germline.     

Mitochondrial regulation of cell death in the Drosophila ovary

Interactions between the Bcl-2 family proteins and the mitochondrial fission and fusion machinery regulate cell death in mammals and worms. In Drosophila, the Bcl-2 family proteins have not been shown to be major regulators of cell death. However, emerging evidence suggests that mitochondrial remodeling may be important in Drosophila cell death. We recently demonstrated a series of events that occur during follicle removal in the Drosophila ovary that included mitochondrial remodeling and clustering, followed by uptake and degradation in the follicle cells. Importantly, the Bcl-2 family proteins, mitochondrial dynamics, and autophagic proteins regulate these events.     

A genome analysis of endoreplication in the Drosophila ovary

Gene amplification is used by follicle cells to increase the copy number of Drosophila chorion genes, which encode structural components of the eggshell. A new study by Claycomb et al. in this issue of Developmental Cell raises the possibility that gene amplification might also be used for the developmental patterning of the egg chamber and oocyte.     

Caprin controls follicle stem cell fate in the Drosophila ovary

Adult stem cells must balance self-renewal and differentiation for tissue homeostasis. The Drosophila ovary has provided a wealth of information about the extrinsic niche signals and intrinsic molecular processes required to ensure appropriate germline stem cell renewal and differentiation. The factors controlling behavior of the more recently identified follicle stem cells of the ovary are less well-understood but equally important for fertility. Here we report that translational regulators play a critical role in controlling these cells. Specifically, the translational regulator Caprin (Capr) is required in the follicle stem cell lineage to ensure maintenance of this stem cell population and proper encapsulation of developing germ cells by follicle stem cell progeny. In addition, reduction of one copy of the gene fmr1, encoding the translational regulator Fragile X Mental Retardation Protein, exacerbates the Capr encapsulation phenotype, suggesting Capr and fmr1 are regulating a common process. Caprin was previously characterized in vertebrates as Cytoplasmic Activation/Proliferation-Associated Protein. Significantly, we find that loss of Caprin alters the dynamics of the cell cycle, and we present evidence that misregulation of CycB contributes to the disruption in behavior of follicle stem cell progeny. Our findings support the idea that translational regulators may provide a conserved mechanism for oversight of developmentally critical cell cycles such as those in stem cell populations.     

Eggs over easy: cell death in the Drosophila ovary

Programmed cell death is the most common fate of female germ cells in Drosophila and many animals. In Drosophila, oocytes form in individual egg chambers that are supported by germline nurse cells and surrounded by somatic follicle cells. As oogenesis proceeds, 15 nurse cells die for every oocyte that is produced. In addition to this developmentally regulated cell death, groups of germ cells or entire egg chambers may be induced to undergo apoptosis in response to starvation or other insults. Recent findings suggest that these different types of cell death involve distinct genetic pathways. This review focuses on progress towards elucidating the molecular mechanisms acting during programmed cell death in Drosophila oogenesis.     

Hofbauer-Buchner eyelet affects circadian photosensitivity and coordinates TIM and PER expression in Drosophila clock neurons

Extraretinal photoreception is a common input route for light resetting signals into the circadian clock of animals. In Drosophila melanogaster, substantial circadian light inputs are mediated via the blue light photoreceptor CRYPTOCHROME (CRY) expressed in clock neurons within the brain. The current model predicts that, upon light activation, CRY interacts with the clock proteins TIMELESS (TIM) and PERIOD (PER), thereby inducing their degradation, which in turn leads to a resetting of the molecular oscillations within the circadian clock. Here the authors investigate the function of another putative extraretinal circadian photoreceptor, the Hofbauer-Buchner eyelet (H-B eyelet), located between the retina and the medulla in the fly optic lobes. Blocking synaptic transmission between the H-B eyelet and its potential target cells, the ventral circadian pacemaker neurons, impaired the flies' ability to resynchronize their behavior under jet-lag conditions in the context of nonfunctional retinal photoreception and a mutation in the CRY-encoding gene. The same manipulation also affected synchronized expression of the clock proteins TIM and PER in different subsets of the clock neurons. This shows that synaptic communication between the H-B eyelet and clock neurons contributes to synchronization of molecular and behavioral rhythms and confirms that the H-B eyelet functions as a circadian photoreceptor. Blockage of synaptic transmission from the H-B eyelet in the presence of functional compound eyes and the absence of CRY also results in increased numbers of flies that are unable to synchronize to extreme photoperiods, supplying independent proof for the role of the H-B eyelet as a circadian photoreceptor.     

Neuromuscular organization and aminergic modulation of contractions in the Drosophila ovary

Background  

The processes by which eggs develop in the insect ovary are well characterized. Despite a large number of Drosophila mutants that cannot lay eggs, the way that the egg is moved along the reproductive tract from ovary to uterus is less well understood. We remedy this with an integrative study on the reproductive tract muscles (anatomy, innervation, contractions, aminergic modulation) in female flies.     

Ectopic HP1 promotes chromosome loops and variegated silencing in Drosophila

A transgene inserted in euchromatin exhibits mosaic expression when targeted by a fusion protein made of the DNA-binding domain of GAL4 and the heterochromatin-associated protein HP1. The silencing responds to the loss of a dose of the dominant modifiers of position-effect variegation Su(var)3-7 and Su(var)2-5, the locus encoding HP1. The genomic environs of the insertion site at 87C1 comprise the dispersed repetitive elements micropia and alphagamma. In the presence of the GAL4-HP1 chimera, the polytene chromosomes of this line form loops between the insertion site of the transgene and six other sections of chromosome 3R, as well as, rarely, with pericentric and telomeric heterochromatin. In contrast to the insertion site of the transgene at 87C, the six loop-forming sites in the euchromatic arm were each previously described as intercalary heterochromatin. Moreover, GAL4-HP1 tethering on one homologue trans-inactivates the reporter on the other. HP1, probably together with other partners, could thus facilitate the coalescence of dispersed middle repetitive sequences, and organize the heterochromatic structure responsible for the variegated silencing of nearby euchromatic genes.     

An epithelial niche in the Drosophila ovary undergoes long-range stem cell replacement

Adult epithelial stem cells are thought to reside in specific niches, where they are maintained by adhesion to stromal cells and by intercellular signals. In niches that harbor multiple adjacent stem cells, such as those maintaining Drosophila germ cells, lost stem cells are replaced by division of neighboring stem cells or reversion of transit cells. We have characterized the Drosophila follicle stem cell (FSC) niche as a model of the epithelial niche to learn whether nonneighboring cells can also generate stem cell replacements. Exactly two stroma-free FSC niches holding single FSCs are located in fixed locations on opposite edges of the Drosophila ovariole. FSC daughters regularly migrate across the width of the ovariole to the other niche before proliferating and contributing to the follicle cell monolayer. Crossmigrating FSC daughters compete with the resident FSC for niche occupancy and are the source of replacement FSCs. The ability of stem cell daughters to target a distant niche and displace its resident stem cell suggests that precancerous mutations might spread from niche to niche within stem cell-based tissues.     

Notch signaling controls germline stem cell niche formation in the Drosophila ovary

Stem cells, which can self-renew and generate differentiated cells, have been shown to be controlled by surrounding microenvironments or niches in several adult tissues. However, it remains largely unknown what constitutes a functional niche and how niche formation is controlled. In the Drosophila ovary, germline stem cells (GSCs), which are adjacent to cap cells and two other cell types, have been shown to be maintained in the niche. In this study, we show that Notch signaling controls formation and maintenance of the GSC niche and that cap cells help determine the niche size in the Drosophila ovary. Expanded Notch activation causes the formation of more cap cells and bigger niches, which support more GSCs, whereas compromising Notch signaling during niche formation decreases the cap cell number and niche size and consequently the GSC number. Furthermore, the niches located away from their normal location can still sufficiently sustain GSC self-renewal by maintaining high local BMP signaling and repressing bam as in normal GSCs. Finally, loss of Notch function in adults results in rapid loss of the GSC niche, including cap cells and thus GSCs. Our results indicate that Notch signaling is important for formation and maintenance of the GSC niche, and that cap cells help determine niche size and function.     

Hsp83 regulates the fate of germline stem cells in Drosophila ovary

正In adult tissues,stem cells are defined by their unique capacity to self-renew and produce differentiated cells to maintain tissue homeostasis.Drosophila ovarian germline stem cells(GSCs)provide a powerful model for investigating the regulatory mechanisms underlying stem cell fate determination in vivo(Chen and Mckearin,     

Stage-specific differences in the requirements for germline stem cell maintenance in the Drosophila ovary

In this study, we uncover a role for microRNAs in Drosophila germline stem cell (GSC) maintenance. Disruption of Dicer-1 function in GSCs during adult life results in GSC loss. Surprisingly, however, loss of Dicer-1 during development does not result in a GSC maintenance defect, although a defect is seen if both Dicer-1 and Dicer-2 function are disrupted. Loss of the bantam microRNA mimics the Dicer-1 maintenance defect when induced in adult GSCs, suggesting that bantam plays a key role in GSC self-renewal. Mad, a component of the TGF-beta pathway, behaves similarly to Dicer-1: adult GSC maintenance requires Mad if it is lost during adult life, but not if it is lost during pupal development. Overall, these results show stage-specific differential sensitivity of GSC maintenance to certain perturbations, and suggest that there may be Dcr-2 dependent redundancy of GSC maintenance mechanisms during development that is lost in later life.     

The Transposon Galileo Generates Natural Chromosomal Inversions in Drosophila by Ectopic Recombination

Background

Transposable elements (TEs) are responsible for the generation of chromosomal inversions in several groups of organisms. However, in Drosophila and other Dipterans, where inversions are abundant both as intraspecific polymorphisms and interspecific fixed differences, the evidence for a role of TEs is scarce. Previous work revealed that the transposon Galileo was involved in the generation of two polymorphic inversions of Drosophila buzzatii.

Methodology/Principal Findings

To assess the impact of TEs in Drosophila chromosomal evolution and shed light on the mechanism involved, we isolated and sequenced the two breakpoints of another widespread polymorphic inversion from D. buzzatii, 2z ³. In the non inverted chromosome, the 2z ³ distal breakpoint was located between genes CG2046 and CG10326 whereas the proximal breakpoint lies between two novel genes that we have named Dlh and Mdp. In the inverted chromosome, the analysis of the breakpoint sequences revealed relatively large insertions (2,870-bp and 4,786-bp long) including two copies of the transposon Galileo (subfamily Newton), one at each breakpoint, plus several other TEs. The two Galileo copies: (i) are inserted in opposite orientation; (ii) present exchanged target site duplications; and (iii) are both chimeric.

Conclusions/Significance

Our observations provide the best evidence gathered so far for the role of TEs in the generation of Drosophila inversions. In addition, they show unequivocally that ectopic recombination is the causative mechanism. The fact that the three polymorphic D. buzzatii inversions investigated so far were generated by the same transposon family is remarkable and is conceivably due to Galileo''s unusual structure and current (or recent) transpositional activity.