Genetic analysis of DAF-18/PTEN missense mutants for the ability to maintain quiescence of the somatic gonad and germ line in Caenorhabditis elegans dauer larvae.

The mammalian tumor suppressor PTEN has well-established lipid phosphatase and protein phosphatase activities. DAF-18, the Caenorhabditis elegans ortholog of PTEN, has a high degree of conservation in the catalytic domain, and human PTEN complements a null allele of daf-18, suggesting conserved protein function. Insights gleaned from studies of mammalian PTEN have been applied to studies of DAF-18 in C. elegans, including predicted enzymatic properties of mutants. Here, we characterize DAF-18 missense mutants previously treated as selectively disrupting either protein or lipid phosphatase activity in genetic assays to connect distinct phenotypes to specific enzymatic activities of DAF-18/PTEN. We analyze the ability of these mutants to maintain quiescence of the somatic gonad and germ line in dauer larvae, a state of diapause during which development is suspended. We show that transgenes expressing either the putative lipid phosphatase-deficient or putative protein phosphatase-deficient form fail to complement a daf-18 null allele, and that the corresponding homozygous endogenous missense mutant alleles fail to maintain developmental quiescence. We also show that the endogenous daf-18 missense alleles fail to complement each other, suggesting that one or both of the missense forms are not activity-selective. Furthermore, homozygous daf-18 missense mutants have a more severe phenotype than a daf-18 null mutant, suggesting the presence of functionally compromised mutant DAF-18 is more deleterious than the absence of DAF-18. We discuss how these genetic properties complicate the interpretation of genetic assays to associate specific enzymatic activities with specific phenotypes.

Signaling between somatic follicle cells and the germline patterns the egg and embryo of Drosophila.

In Drosophila, specification of the embryonic body axes requires signaling between the germline and the somatic follicle cells. These signaling events are necessary to properly localize embryonic patterning determinants in the egg or eggshell during oogenesis. There are three maternal patterning systems that specify the anterior-posterior axis, and one that establishes the dorsal-ventral axis. We will first review oogenesis, focusing on the establishment of the oocyte and nurse cells and patterning of the follicle cells into different subpopulations. We then describe how two coordinated signaling events between the oocyte and follicle cells establish polarity of the oocyte and localize the anterior determinant bicoid, the posterior determinant oskar, and Gurken/epidermal growth factor (EGF), which breaks symmetry to initiate dorsal-ventral axis establishment. Next, we review how dorsal-ventral asymmetry of the follicle cells is transmitted to the embryo. This process also involves Gurken-EGF receptor (EGFR) signaling between the oocyte and follicle cells, leading to ventrally-restricted expression of the sulfotransferase Pipe. These events promote the ventral processing of Spaetzle, a ligand for Toll, which ultimately sets up the embryonic dorsal-ventral axis. We then describe the activation of the terminal patterning system by specialized polar follicle cells. Finally, we present open questions regarding soma-germline signaling during Drosophila oogenesis required for cell identity and embryonic axis formation.

A Gene Expression Screen in Drosophila melanogaster Identifies Novel JAK/STAT and EGFR Targets During Oogenesis.

The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) and epidermal growth factor receptor (EGFR) signaling pathways are conserved regulators of tissue patterning, morphogenesis, and other cell biological processes. During Drosophila oogenesis, these pathways determine the fates of epithelial follicle cells (FCs). JAK/STAT and EGFR together specify a population of cells called the posterior follicle cells (PFCs), which signal to the oocyte to establish the embryonic axes. In this study, whole genome expression analysis was performed to identify genes activated by JAK/STAT and/or EGFR. We observed that 317 genes were transcriptionally upregulated in egg chambers with ectopic JAK/STAT and EGFR activity in the FCs. The list was enriched for genes encoding extracellular matrix (ECM) components and ECM-associated proteins. We tested 69 candidates for a role in axis establishment using RNAi knockdown in the FCs. We report that the signaling protein Semaphorin 1b becomes enriched in the PFCs in response to JAK/STAT and EGFR. We also identified ADAM metallopeptidase with thrombospondin type 1 motif A (AdamTS-A) as a novel target of JAK/STAT in the FCs that regulates egg chamber shape. AdamTS-A mRNA becomes enriched at the anterior and posterior poles of the egg chamber at stages 6 to 7 and is regulated by JAK/STAT. Altering AdamTS-A expression in the poles or middle of the egg chamber produces rounder egg chambers. We propose that AdamTS-A regulates egg shape by remodeling the basement membrane.