Abstract The Drosophila oocyte develops from a cluster of 16 interconnected cells that derive from a common progenitor. One of these cells, the oocyte, arrests in meiosis. The other cells endoreplicate their DNA and produce mRNAs and proteins that they traffic to the oocyte along a polarized microtubule cytoskeleton shared by the entire cyst. Therefore, Drosophila oogenesis is an attractive system for the study of cell cycle control and cell polarity. We carried out a clonal screen on the right arm of chromosome 3 for female sterile mutations using the FLP-FRT-ovoD system to identify new genes required for early oogenesis. We identified alleles of oo18 RNA binding protein (orb) and Darkener of apricot (Doa), which had previously been shown to exhibit oogenesis defects. We also identified several lethal alleles of the male sterile mutant, bobble (bob). In addition, we identified eight new lethal complementation groups that exhibit early oogenesis phenotypes. We analyzed mutant clones to determine the aspects of oogenesis disrupted by each complementation group. We assayed for the production and development of egg chambers, localization of ORB to and within the oocyte, and proper execution of the nurse cell cycle (endoreplication of DNA) and the oocyte cell cycle (karyosome formation). Here we discuss the identification, mapping, and phenotypic characterization of these new genes: omelet, soft boiled, hard boiled, poached, fried, over easy, sunny side up, and benedict.
Recent work on Drosophila oogenesis has uncovered connections between cell-cycle checkpoints and pattern formation. Genes of the spindle class, which encode double-strand break repair enzymes and RNA helicases, affect oocyte polarity and the decision whether to differentiate as an oocyte or a nurse cell.
Cyclins regulate progression through the cell cycle. Control of cyclin levels is essential in Drosophila oogenesis for the four synchronous divisions that generate the 16 cell germ line cyst and for ensuring that one cell in each cyst, the oocyte, is arrested in meiosis, while the remaining fifteen cells become polyploid nurse cells. Changes in cyclin levels could be achieved by regulating transcription, translation or protein stability. The proteasome limits cyclin protein levels in the Drosophila ovary, but the mechanisms regulating RNA turnover or translation remain largely unclear. Here, we report the identification of twin, a homolog of the yeast CCR4 deadenylase. We show that twin is important for the number and synchrony of cyst divisions and oocyte fate. Consistent with the deadenylase activity of CCR4 in yeast, our data suggest that Twin controls germ line cyst development by regulating poly(A) tail lengths of several targets including Cyclin A (CycA) RNA. twin mutants exhibit very low expression of Bag-of-marbles (Bam), a regulator of cyst division, indicating that Twin/Ccr4 activity is necessary for wild-type Bam expression. Lowering the levels of CycA or increasing the levels of Bam suppresses the defects we observe in twin ovaries, implicating CycA and Bam as downstream effectors of Twin. We propose that Twin/Ccr4 functions during early oogenesis to coordinate cyst division, oocyte fate specification and egg chamber maturation.
Rapid larval growth is essential in the development of most metazoans. In this article, we show that bene, a gene previously identified on the basis of its oogenesis defects, is also required for larval growth and viability. We show that all bene alleles disrupt gatA, which encodes the Drosophila homolog of glutamyl-tRNA(Gln) amidotransferase subunit A (GatA). bene alleles are now referred to as gatA. GatA proteins are highly conserved throughout eukaryotes and many prokaryotes. These enzymes are required for proper translation of the proteins encoded by the mitochondrial genome and by many eubacterial genomes. Mitotic and endoreplicating tissues in Drosophila gatA loss-of-function mutants grow slowly and never achieve wild-type size, and gatA larvae die before pupariation. gatA mutant eye clones exhibit growth and differentiation defects, indicating that gatA expression is required cell autonomously for normal growth. The gatA gene is widely expressed in mitotic and endoreplicating tissues.
There is an intricate network of molecules called cell fate determinants that instruct the cells of the embryo to take on either an anterior or posterior fate. In a lively Perspective, Lehmann and her colleagues discuss new findings in the fruit fly that identify a key protein, PAR-1, which ensures that the cell fate determinants are themselves located in the correct region of the oocyte. In this way, the anterior-posterior axis is set up in the fruit fly egg before fertilization.
Institutional review boards have a dual goal: first, to protect the rights and welfare of human research subjects, and second, to support and facilitate the conduct of valuable research. In striving to achieve these goals, IRBs must often consider conflicting interests. In the discussion below, we characterize research oversight as having three elements: (i) research regulations, which establish a minimum acceptable standard for research conduct; (ii) ethical principles, which help us identify and define relevant ethical issues; and (iii) virtue ethics, which guides the prioritization of relevant issues. We describe specific ways in which the lessons of virtue ethics suggest revisions to the IRB structure and review process, the education and training of IRB members, and the appropriate limits of regulations in research ethics oversight.
David Carpenter argues in favour of Internal Review Boards taking a virtue ethics approach to their reviews of research proposals. Carpenter views principle- and code-based approaches as in competition with virtue ethics, and he describes reliance on principles and codes as neither necessary nor sufficient. We agree with Carpenter’s thesis that a virtue ethics approach would be beneficial and even necessary for exemplary review of research proposals. We disagree with Carpenter, however, about the weight that should be given to principles and codes. We defend here our view that principles and regulations are indispensible to ethical review of research, in spite of the fact that principles often conflict with each other. In those situations, the reviewer’s virtue of practical wisdom is necessary to adjudicate between competing ethical claims.
Assigning the appropriate moral status to different stages of human development is an urgent problem in bioethics. Many philosophers have attempted to assess developmental events using strict ontological principles to determine when a developing entity becomes essentially human. This approach is not consistent with recent findings in reproductive and stem cell biology, including the discovery of the plasticity of early embryonic development and the advent of induced pluripotent stem cells. Substance ontology should therefore not be used to determine the moral status of the embryo.
