A retrotransposon 412 insertion within an exon of the Drosophila melanogaster vermilion gene is spliced from the precursor RNA.

Three alleles of the Drosophila melanogaster vermilion (v) gene are suppressed by recessive mutations at the suppressor of sable [su(s)], gene. Previous work has established that these alleles have identical insertions of the 412 retrotransposon in the 5'-untranslated region of the gene. Despite the transposon insertion in an exon, v mutants accumulate trace amounts of apparently wild-type-sized transcripts in a su(s)+ background, and the level of v transcript accumulation is increased by su(s) mutations. Here, we have characterized transcripts from a suppressible v mutant in both su(s)+ and su(s)- backgrounds by S1 nuclease protection experiments and sequence analysis of polymerase chain reaction (PCR) generated cDNA clones. We find that transposon sequences are imprecisely eliminated from v mutant transcripts by splicing at donor and acceptor sites located near the ends of the 412 retrotransposon. Four different 5' donor sites are alternatively spliced to a single 3' acceptor site. The implications of this finding are discussed in relation to possible functions of the su(s)+ gene product

Mutations in the Polycomb Group Gene polyhomeotic Lead to Epithelial Instability in both the Ovary and Wing Imaginal Disc in Drosophila

Most human cancers originate from epithelial tissues and cell polarity and adhesion defects can lead to metastasis. The Polycomb-Group of chromatin factors were first characterized in Drosophila as repressors of homeotic genes during development, while studies in mammals indicate a conserved role in body plan organization, as well as an implication in other processes such as stem cell maintenance, cell proliferation, and tumorigenesis. We have analyzed the function of the Drosophila Polycomb-Group gene polyhomeotic in epithelial cells of two different organs, the ovary and the wing imaginal disc.Clonal analysis of loss and gain of function of polyhomeotic resulted in segregation between mutant and wild-type cells in both the follicular and wing imaginal disc epithelia, without excessive cell proliferation. Both basal and apical expulsion of mutant cells was observed, the former characterized by specific reorganization of cell adhesion and polarity proteins, the latter by complete cytoplasmic diffusion of these proteins. Among several candidate target genes tested, only the homeotic gene Abdominal-B was a target of PH in both ovarian and wing disc cells. Although overexpression of Abdominal-B was sufficient to cause cell segregation in the wing disc, epistatic analysis indicated that the presence of Abdominal-B is not necessary for expulsion of polyhomeotic mutant epithelial cells suggesting that additional polyhomeotic targets are implicated in this phenomenon.Our results indicate that polyhomeotic mutations have a direct effect on epithelial integrity that can be uncoupled from overproliferation. We show that cells in an epithelium expressing different levels of polyhomeotic sort out indicating differential adhesive properties between the cell populations. Interestingly, we found distinct modalities between apical and basal expulsion of ph mutant cells and further studies of this phenomenon should allow parallels to be made with the modified adhesive and polarity properties of different types of epithelial tumors

Interactions cellulaires lors de la formation et la maturation des follicules ovariens chez Drosophila melanogaster (étude de la fonction du gène fused, et du processus de différenciation des cellules polaires)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Rôle de polyhomeotic dans le maintien de l'intégrité épithéliale chez Drosophila melanogaster

Le gène polyhomeotic (ph) de Drosophila melanogaster est un membre des gènes du groupe Polycomb (PcG) qui sont requis dans l établissement de la mémoire cellulaire en maintenant dans un état réprimé la transcription de leurs gènes cibles au cours du développement. Nous avons mis en évidence que les clones cellulaires mutants pour ph induits dans l'épithélium folliculaire ovarien et dans l'épithélium imaginal alaire perdent leur affinité avec les cellules voisines sauvages et sont expulsés de l'épithélium. L'adhésion intercellulaire est mise en place grâce à la formation de jonctions membranaires spécialisées qui polarisent les cellules épithéliales selon un axe apico-basal. Il apparaît ainsi que l'expulsion des cellules mutantes pour ph est accompagnée d'une réorganisation des jonctions adhérentes apicales. Nous avons également montré que le gène homéotique Abd-B, cible connue de ph, est impliqué dans cette nouvelle fonction de ph dans le maintien de l intégrité épithéliale.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Hedgehog signaling controls Soma-Germen interactions during Drosophila ovarian morphogenesis

The genetic analysis of Drosophila adult oogenesis has provided insights into the molecular mechanisms that control cell proliferation, differentiation, migration, and intercellular signaling. However, little is known about the larval and pupal cellular events leading to the formation of the highly organized adult ovary, which is composed of ovarioles each containing germline cells enveloped by specialized somatic cells. We describe here the presence of ovarioles devoid of any germ cells in adult females mutant for fused, which encodes a Hedgehog signal transducing serine/threonine kinase. We show that this phenotype corresponds to a requirement for fused function for the organization of germ cells with respect to ovarian somatic cells during ovariole formation specifically during pupal stages and provide some evidence by means of clonal analysis suggesting that fused function may be necessary in the germline. hedgehog is expressed specifically in somatic terminal filament cells in pupal ovaries, and females bearing hedgehog strong loss-of-function mutations also exhibit aberrant germ cell distribution and formation of agametic ovarioles. These results indicate a positive role for Fused in the transduction of somatic Hedgehog signaling instructing ovariole morphogenesis. We also provide evidence for the use of noncanonical Hedgehog signal transducer(s) within germline cells

JAK/STAT signaling is necessary for cell monosis prior to epithelial cell apoptotic extrusion

Epithelial cell extrusion is crucial for proper development and tissue homeostasis. High-resolution 3D reconstruction and 4D imaging, combined with genetic analyis, have allowed us to reveal the highly-sterotyped morphogenetic events controlled by JAK/STAT signaling in a developmentally-programmed case of epithelial cell extrusion. Specialized somatic cells, Polar Cells (PCs), are produced in excess and then undergo apoptotic elimination from the follicular epithelium in the Drosophila ovary. We show that supernumerary PCs are first systematically enveloped by PC neighbors on all sides, first laterally, then apically in conjunction with highly-reinforced adherens junctions, and finally basally. The PC to be removed thus loses all contact with follicle cells, germline cells and the basement membrane in a process we have called cell 'monosis', for 'isolation' in Greek. PC monosis takes several hours, and always precedes, and is independent of, activation of apoptosis. JAK/STAT signaling is necessary within the surrounding follicular epithelium for PC monosis. Minutes after monosis is complete, PC apoptotic corpses are formed and extruded laterally within the epithelium, in contrast to the apical and basal extrusions described to date. These apoptotic corpses are engulfed and eliminated by surrounding follicle cells, which are thus acting as non-professional phagocytes. This study therefore shows the non cell-autonomous impact of an epithelium, via JAK/STAT signaling activation, on cell morphogenesis events leading to apoptotic extrusion. It is likely that the use of high-resolution 3D and 4D imaging, which allows for better spatio-temporal understanding of morphogenetic events, will reveal that cell monosis and lateral extrusion within an epithelium are pertinent for other cases of epithelial cell extrusion as well

The steroid hormone receptor EcR finely modulates Drosophila lifespan during adulthood in a sex-specific manner

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JAK-STAT-dependent contact between follicle cells and the oocyte controls Drosophila anterior-posterior polarity and germline development

Abstract The number of embryonic primordial germ cells in Drosophila is determined by the quantity of germ plasm, whose assembly starts in the posterior region of the oocyte during oogenesis. Here, we report that extending JAK-STAT activity in the posterior somatic follicular epithelium leads to an excess of primordial germ cells in the future embryo. We show that JAK-STAT signaling is necessary for the differentiation of approximately 20 specialized follicle cells maintaining tight contact with the oocyte. These cells define, in the underlying posterior oocyte cortex, the anchoring of the germ cell determinant oskar mRNA. We reveal that the apical surface of these posterior anchoring cells extends long filopodia penetrating the oocyte. We identify two JAK-STAT targets in these cells that are each sufficient to extend the zone of contact with the oocyte, thereby leading to production of extra primordial germ cells. JAK-STAT signaling thus determines a fixed number of posterior anchoring cells required for anterior-posterior oocyte polarity and for the development of the future germline