Axis formation during Drosophila oogenesis

European Molecular Biology Laboratory, Meyerhofstrabetae 1, Postfach10.2209, D-69012, Heidelberg, Germany.
Current Opinion in Genetics & Development (Impact Factor: 7.57). 09/2001; 11(4):374-83. DOI: 10.1016/S0959-437X(00)00207-0
Source: PubMed


Recent advances shed light on the cellular processes that cooperate during oogenesis to produce a fully patterned egg, containing all the maternal information required for embryonic development. Progress has been made in defining the early steps in oocyte specification and it has been shown that progression of oogenesis is controlled by a meiotic checkpoint and requires active maintenance of the oocyte cell fate. The function of Gurken signalling in patterning the dorsal-ventral axis later in oogenesis is better understood. Anterior-posterior patterning of the embryo requires activities of bicoid and oskar mRNAs, localised within the oocyte. A microtubule motor, Kinesin, is directly implicated in localisation of oskar mRNA to the posterior pole of the oocyte.

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    • "For most members of this family, the interaction with dsRNA is not sequence-specific as documented by the atomic structure of dsRNA bound to various RBDs (5,6). The DRB protein Staufen was initially identified in Drosophila melanogaster as a maternal factor essential for the proper localization of bicoid and oskar mRNAs during the formation of the anteroposterior axis (7,8). The corresponding mammalian homologues Staufen1 and Staufen2 participate in various aspects of the mRNA life cycle. "
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    ABSTRACT: Cellular messenger RNAs (mRNAs) are associated to proteins in the form of ribonucleoprotein particles. The double-stranded RNA-binding (DRB) proteins play important roles in mRNA synthesis, modification, activity and decay. Staufen is a DRB protein involved in the localized translation of specific mRNAs during Drosophila early development. The human Staufen1 (hStau1) forms RNA granules that contain translation regulation proteins as well as cytoskeleton and motor proteins to allow the movement of the granule on microtubules, but the mechanisms of hStau1-RNA recognition are still unclear. Here we used a combination of affinity chromatography, RNAse-protection, deep-sequencing and bioinformatic analyses to identify mRNAs differentially associated to hStau1 or a mutant protein unable to bind RNA and, in this way, defined a collection of mRNAs specifically associated to wt hStau1. A common sequence signature consisting of two opposite-polarity Alu motifs was present in the hStau1-associated mRNAs and was shown to be sufficient for binding to hStau1 and hStau1-dependent stimulation of protein expression. Our results unravel how hStau1 identifies a wide spectrum of cellular target mRNAs to control their localization, expression and fate.
    Nucleic Acids Research 01/2014; 42(7). DOI:10.1093/nar/gku073 · 9.11 Impact Factor
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    • "In addition to oskar, bicoid mRNA localizes to the anterior margin of the oocyte and gurken mRNA localizes to the dorsal-anterior corner [14,15]. As with oskar, the spatial restriction of these mRNAs and subsequent protein products is essential for establishing the polarity of the oocyte and future embryo [16,17]. "
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    ABSTRACT: In order for eukaryotic cells to function properly, they must establish polarity. The Drosophila oocyte uses mRNA localization to establish polarity and hence provides a genetically tractable model in which to study this process. The spatial restriction of oskar mRNA and its subsequent protein product is necessary for embryonic patterning. The localization of oskar mRNA requires microtubules and microtubule-based motor proteins. Null mutants in Kinesin heavy chain (Khc), the motor subunit of the plus end-directed Kinesin-1, result in oskar mRNA delocalization. Although the majority of oskar particles are non-motile in khc nulls, a small fraction of particles display active motility. Thus, a motor other than Kinesin-1 could conceivably also participate in oskar mRNA localization. Here we show that Dynein heavy chain (Dhc), the motor subunit of the minus end-directed Dynein complex, extensively co-localizes with Khc and oskar mRNA. In addition, immunoprecipitation of the Dynein complex specifically co-precipitated oskar mRNA and Khc. Lastly, germline-specific depletion of Dhc resulted in oskar mRNA and Khc delocalization. Our results therefore suggest that efficient posterior localization of oskar mRNA requires the concerted activities of both Dynein and Kinesin-1.
    PLoS ONE 11/2013; 8(11):e80605. DOI:10.1371/journal.pone.0080605 · 3.23 Impact Factor
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    • "In each Drosophila egg chamber, sixteen germ cells (fifteen nurse cells and one oocyte) are encapsulated by an epithelial layer of somatic follicle cells. Whereas both somatic and germ-line cell lineages are instrumental in establishing and maintaining cell polarity in the oocyte [9]–[11], the primary roles of nurse cells are the production and synthesis of RNAs and proteins required for oocyte development, and deposition of maternal reserves needed during early embryogenesis before zygotic transcription is activated [12]. Once cell-fate identity in the germ line is established, prior to the egg chamber budding from the germarium, the nurse cells enter a variant developmental cycle known as the endocycle, in which mitosis is blocked and DNA is endoreplicated once every cycle [13]. "
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    ABSTRACT: During Drosophila oogenesis, the endopolyploid nuclei of germ-line nurse cells undergo a dramatic shift in morphology as oogenesis progresses; the easily-visible chromosomes are initially polytenic during the early stages of oogenesis before they transiently condense into a distinct '5-blob' configuration, with subsequent dispersal into a diffuse state. Mutations in many genes, with diverse cellular functions, can affect the ability of nurse cells to fully decondense their chromatin, resulting in a '5-blob arrest' phenotype that is maintained throughout the later stages of oogenesis. However, the mechanisms and significance of nurse-cell (NC) chromatin dispersal remain poorly understood. Here, we report that a screen for modifiers of the 5-blob phenotype in the germ line isolated the spliceosomal gene peanuts, the Drosophila Prp22. We demonstrate that reduction of spliceosomal activity through loss of peanuts promotes decondensation defects in NC nuclei during mid-oogenesis. We also show that the Prp38 spliceosomal protein accumulates in the nucleoplasm of nurse cells with impaired peanuts function, suggesting that spliceosomal recycling is impaired. Finally, we reveal that loss of additional spliceosomal proteins impairs the full decondensation of NC chromatin during later stages of oogenesis, suggesting that individual spliceosomal subcomplexes modulate expression of the distinct subset of genes that are required for correct morphology in endopolyploid nurse cells.
    PLoS ONE 11/2013; 8(11):e79048. DOI:10.1371/journal.pone.0079048 · 3.23 Impact Factor
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