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The growth of an organism and its size determination require the tight regulation of cell proliferation and cell growth. However, the mechanisms and regulatory networks that control and integrate these processes remain poorly understood. Here, we address the biological role of Arabidopsis translationally controlled tumor protein (AtTCTP) and test its shared functions in animals and plants. The data support a role of plant AtTCTP as a positive regulator of mitotic growth by specifically controlling the duration of the cell cycle. We show that, in contrast to animal TCTP, plant AtTCTP is not implicated in regulating postmitotic growth. Consistent with this finding, plant AtTCTP can fully rescue cell proliferation defects in Drosophila loss of function for dTCTP. Furthermore, Drosophila dTCTP is able to fully rescue cell proliferation defects in Arabidopsis tctp knockouts. Our data provide evidence that TCTP function in regulating cell division is part of a conserved growth regulatory pathway shared between plants and animals. The study also suggests that, although the cell division machinery is shared in all multicellular organisms to control growth, cell expansion can be uncoupled from cell division in plants but not in animals. Arabidopsis | Drosophila | organ development | cell division www.pnas.org/cgi/doi/ 10.1073/pnas.1007926107

We developed a multiscale approach for the computationally efficient modeling of morphogen gradients in the syncytial Drosophila embryo, a single cell with multiple dividing nuclei. By using a homogenization technique, we derived a coarse-grained model with parameters that are explicitly related to the geometry of the syncytium and kinetics of nucleocytoplasmic shuttling. One of our main results is an accurate analytical approximation for the effective diffusivity of a morphogen molecule as a function of the nuclear density. We used this expression to explore the dynamics of the Bicoid morphogen gradient, a signal that patterns the anterior-posterior axis of the embryo. A similar approach can be used to analyze the dynamics of all three maternal morphogen gradients in Drosophila. doi/ 10.1073/pnas.1001139107

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.12.023 Byline: Jason C. Maynard (a), Trang Pham (b), Tianli Zheng (a), Angela Jockheck-Clark (a), Helen B. Rankin (c), Christopher B. Newgard (b), Eric P. Spana (c), Christopher V. Nicchitta (a) Keywords: Drosophila; Gp93; Hsp90; GRP94; HSP90B1; Copper cell; Midgut; Epithelium; Endoderm; Growth control Abstract: GRP94, the endoplasmic reticulum Hsp90, is a metazoan-restricted chaperone essential for early development in mammals, yet dispensable for mammalian cell viability. This dichotomy suggests that GRP94 is required for the functional expression of secretory and/or membrane proteins that enable the integration of cells into tissues. To explore this hypothesis, we have identified the Drosophila ortholog of GRP94, Gp93, and report that Gp93 is an essential gene in Drosophila. Loss of zygotic Gp93 expression is late larval-lethal and causes prominent defects in the larval midgut, the sole endoderm-derived larval tissue. Gp93 mutant larvae display pronounced defects in the midgut epithelium, with aberrant copper cell structure, markedly reduced gut acidification, atypical septate junction structure, depressed gut motility, and deficits in intestinal nutrient uptake. The metabolic consequences of the loss of Gp93-expression are profound; Gp93 mutant larvae exhibit a starvation-like metabolic phenotype, including suppression of insulin signaling and extensive mobilization of amino acids and triglycerides. The defects in copper cell structure/function accompanying loss of Gp93 expression resemble those reported for mutations in labial, an endodermal homeotic gene required for copper cell specification, and [alpha]-spectrin, thus suggesting an essential role for Gp93 in the functional expression of secretory/integral membrane protein-encoding lab protein target genes and/or integral membrane protein(s) that interact with the spectrin cytoskeleton to confer epithelial membrane specialization. Author Affiliation: (a) Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA (b) Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA (c) Department of Biology, Duke University, Durham, NC 27710, USA Article History: Received 21 August 2009; Revised 14 December 2009; Accepted 17 December 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.10.042 Byline: Li-Lun Ho, Xiaomu Wei, Takeshi Shimizu, Zhi-Chun Lai Keywords: Drosophila eye and wing; Growth control; Proliferation; Apoptosis; Signaling; Mats; Warts; Hippo Abstract: Growth inhibition mediated by Hippo (Hpo) signaling is essential for tissue growth and organ size control in Drosophila. However, the cellular mechanism by which the core components like Mob as tumor suppressor (Mats) and Warts (Wts) protein kinase are activated is poorly understood. In this work, we found that the endogenous Mats is located at the plasma membrane in developing tissues. Membrane targeting constitutively activates Mats to promote apoptosis and reduce cell proliferation, which leads to reduced tissue growth and organ size. Moreover, the ability of membrane-targeted Mats to inhibit tissue growth required the wts gene activity and Wts kinase activity was increased by the activated Mats in developing tissues. Consistent with the idea that Mats is a key component of the Hpo pathway, Mats is required and sufficient to regulate Yki nuclear localization. These results support a model in which the plasma membrane is an important site of action for Mats tumor suppressor to control tissue growth and organ size. Article History: Received 3 September 2009; Revised 29 October 2009; Accepted 29 October 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.10.042 Byline: Li-Lun Ho (a), Xiaomu Wei (b), Takeshi Shimizu (c), Zhi-Chun Lai (a)(b)(c)(d) Keywords: Drosophila eye and wing; Growth control; Proliferation; Apoptosis; Signaling; Mats; Warts; Hippo Abstract: Growth inhibition mediated by Hippo (Hpo) signaling is essential for tissue growth and organ size control in Drosophila. However, the cellular mechanism by which the core components like Mob as tumor suppressor (Mats) and Warts (Wts) protein kinase are activated is poorly understood. In this work, we found that the endogenous Mats is located at the plasma membrane in developing tissues. Membrane targeting constitutively activates Mats to promote apoptosis and reduce cell proliferation, which leads to reduced tissue growth and organ size. Moreover, the ability of membrane-targeted Mats to inhibit tissue growth required the wts gene activity and Wts kinase activity was increased by the activated Mats in developing tissues. Consistent with the idea that Mats is a key component of the Hpo pathway, Mats is required and sufficient to regulate Yki nuclear localization. These results support a model in which the plasma membrane is an important site of action for Mats tumor suppressor to control tissue growth and organ size. Author Affiliation: (a) Intercollege Graduate Degree Program in Cell and Developmental Biology, The Pennsylvania State University, University Park, PA 16802, USA (b) Intercollege Graduate Degree Program in Genetics, The Pennsylvania State University, University Park, PA 16802, USA (c) Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA (d) Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA Article History: Received 3 September 2009; Revised 29 October 2009; Accepted 29 October 2009

Bicoid (Bcd) is the anterior determinant in Drosophila. Accordingly, loss of Bcd causes loss of head and thorax and their replacement with posterior structures, bed mRNA is maternally deposited at the anterior pole and Bcd forms an anterior-to-posterior (AP) concentration gradient. The expression of a series of zygotic head genes is thought to be differentially regulated by distinct threshold concentrations of the Bcd gradient. Thereby Bcd functions as a morphogen, instructing fields of cells to take on specific fates. Here, we show that spatial limits of anterior genes are also set in the absence of a Bcd gradient and depend on factors of the maternal terminal system. The receptor tyrosine kinase Torso (Tor), a key component of this system, is active in the pole regions of the embryo. Its activity downregulates the maternally deposited repressor Capicua (Cic), leaving high Cic activity in the central regions and decreasingly lower Cic activities toward the poles. We show that the positions of posterior boundaries of Bcd target genes are dependent not only on Bcd, but also on Tor-mediated Cic activity. The results indicate that Cic can mediate repression through distinct binding sites within a Bcd responsive enhancer and that gene activation by Bcd is antagonized by Cic. The activating and repressive effects of Bcd and Cic, respectively, are integrated by the Bcd target gene enhancer. We conclude that the spatial domains of head gene expression are determined by Bcd in concert with Tor-dependent repressors. bicoid antagonist | Drosophila development | gene regulation | head development | morphogen gradient doi/10.1073/pnas.0910225106

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.06.015 Byline: Camilla Larsen, Diana Shy, Shana R. Spindler, Siaumin Fung, Wayne Pereanu, Amelia Younossi-Hartenstein, Volker Hartenstein Keywords: Drosophila; Brain; Lineage; Pathfinding; Connectivity Abstract: The Drosophila central brain is composed of approximately 100 paired lineages, with most lineages comprising 100-150 neurons. Most lineages have a number of important characteristics in common. Typically, neurons of a lineage stay together as a coherent cluster and project their axons into a coherent bundle visible from late embryo to adult. Neurons born during the embryonic period form the primary axon tracts (PATs) that follow stereotyped pathways in the neuropile. Apoptotic cell death removes an average of 30-40% of primary neurons around the time of hatching. Secondary neurons generated during the larval period form secondary axon tracts (SATs) that typically fasciculate with their corresponding primary axon tract. SATs develop into the long fascicles that interconnect the different compartments of the adult brain. Structurally, we distinguish between three types of lineages: PD lineages, characterized by distinct, spatially separate proximal and distal arborizations; C lineages with arborizations distributed continuously along the entire length of their tract; D lineages that lack proximal arborizations. Arborizations of many lineages, in particular those of the PD type, are restricted to distinct neuropile compartments. We propose that compartments are 'scaffolded' by individual lineages, or small groups thereof. Thereby, the relatively small number of primary neurons of each primary lineage set up the compartment map in the late embryo. Compartments grow during the larval period simply by an increase in arbor volume of primary neurons. Arbors of secondary neurons form within or adjacent to the larval compartments, resulting in smaller compartment subdivisions and additional, adult specific compartments. Author Affiliation: Department of Molecular Cell and Developmental Biology, University of California Los Angeles, Los Angeles, CA 90095, USA Article History: Received 15 April 2009; Revised 9 June 2009; Accepted 11 June 2009

Drosophila melanogaster was used to identify genes with a potential role in genetic regulation of purine biosynthesis. In this study we examine two dominant genetic modifiers of the essential gene Prat, which encodes amidophosphoribosyltransferase (EC 2.4.2.14). We found that Mod(Prat:bw)3-1 enhances Prat expression only in female heads, whereas Mod(Prat:bw)3-5 suppresses Prat in all stages and tissues examined for both sexes. For Mod-3-5, gene expression microarrays were used to identify other genes that are affected by the modifier. Three mapping approaches were used to localize these modifiers. Deficiency and meiotic mapping showed that the complex lethal complementation group previously associated with Mod-3-1 and Mod-3-5 is actually due to shared second-site lethal mutations. Using male recombination mapping, Mod-3-1 was localized to a 21 kilobase region containing nine genes, and Mod-3-5 was localized to a 53 kilobase region containing eight genes. Key words: purine metabolism, genetic modifiers, Drosophila development, recombination mapping. Le Drosophila melanogaster a ete employe pour identifier des genes ayant un role potentiel dans la regulation de la biosynthese des purines. Dans ce travail, les auteurs examinent deux modificateurs genetiques dominants du gene essentiel Prat qui code pour l' amidophosphoribosyltransferase (EC 2.4.2.14). Les auteurs ont trouve que Mod(Prat:bw)3-1 augmentait l'expression de Prat seulement dans les tetes chez les femelles, tandis que Mod(Prat:bw)3-5 supprimait l'expression de Prat dans tous les tissus et a tous les stades examines chez les deux sexes. Pour Mod-3-5, des puces a ADN ont ete employees pour identifier d'autres genes qui seraient affectes par ces modificateurs. Trois approches de cartographie ont ete employees pour localiser ces modificateurs. Des analyses de deficience et de cartographie meiotique ont montre que le groupe de complementation letale complexe anterieurement associe a Mod-3-1 et Mod-3-5 serait en fait du a des mutations secondaires letales partagees. Au moyen de l'analyse de la recombinaison chez les males, Mod-3-1 a ete localise au sein d'une region de 21 kilobases contenant neuf genes et Mod-3-5 a ete localise dans une region de 53 kilobases comptant huit genes. Mots-cles : metabolisme des purines, modificateurs genetiques, developpement du Drosophila, cartographie par recombinaison., [Traduit par la Redaction] Introduction Purine nucleotides are supplied to most organisms by interconnected de novo synthesis, salvage, and interconversion pathways. With the exception of intracellular parasites such as Trypanosoma [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.07.035 Byline: Shana R. Spindler, Irma Ortiz, Siaumin Fung, Shigeo Takashima, Volker Hartenstein Keywords: Glia; Drosophila; Brain; Lineage Abstract: Glial cells play important roles in the developing brain during axon fasciculation, growth cone guidance, and neuron survival. In the Drosophila brain, three main classes of glia have been identified including surface, cortex, and neuropile glia. While surface glia ensheaths the brain and is involved in the formation of the blood-brain-barrier and the control of neuroblast proliferation, the range of functions for cortex and neuropile glia is less well understood. In this study, we use the nirvana2-GAL4 driver to visualize the association of cortex and neuropile glia with axon tracts formed by different brain lineages and selectively eliminate these glial populations via induced apoptosis. The larval central brain consists of approximately 100 lineages. Each lineage forms a cohesive axon bundle, the secondary axon tract (SAT). While entering and traversing the brain neuropile, SATs interact in a characteristic way with glial cells. Some SATs are completely invested with glial processes; others show no particular association with glia, and most fall somewhere in between these extremes. Our results demonstrate that the elimination of glia results in abnormalities in SAT fasciculation and trajectory. The most prevalent phenotype is truncation or misguidance of axon tracts, or abnormal fasciculation of tracts that normally form separate pathways. Importantly, the degree of glial association with a given lineage is positively correlated with the severity of the phenotype resulting from glial ablation. Previous studies have focused on the embryonic nerve cord or adult-specific compartments to establish the role of glia. Our study provides, for the first time, an analysis of glial function in the brain during axon formation and growth in larval development. Author Affiliation: Department of Molecular Cell and Developmental Biology, University of California Los Angeles, Los Angeles, CA 90095, USA Article History: Received 10 June 2009; Revised 23 July 2009; Accepted 23 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.03.029 Byline: Ji-Hoon Lee, Erin Overstreet, Erin Fitch, Stephen Fleenor, Janice A. Fischer Keywords: Epsin; Epsin-Related; Golgi; Endosome; Trafficking; Drosophila; Clathrin; ENTH domain; Patterning; Growth; Proliferation Abstract: Epsin and epsin-Related (epsinR) are multi-modular proteins that stimulate clathrin-coated vesicle formation. Epsin promotes endocytosis at the plasma membrane, and epsinR functions at the Golgi and early endosomes for trans-Golgi network/endosome vesicle trafficking. In Drosophila, endocytic epsin is known as Liquid facets, and it is essential specifically for Notch signaling. Here, by generating and analyzing loss-of-function mutants in the liquid facets-Related (lqfR) gene of Drosophila, we investigated the function of Golgi epsin in a multicellular context. We found that LqfR is indeed a Golgi protein, and that like liquid facets, lqfR is essential for Drosophila viability. In addition, primarily by analyzing mutant eye discs, we found that lqfR is required for cell proliferation, insulin-independent cell growth, and cell patterning, consistent with a role in one or several signaling pathways. Epsins in all organisms share an ENTH (epsin N-terminal homology) domain, which binds phosphoinositides enriched at the plasma membrane or the Golgi membrane. The epsinR ENTH domain is also the recognition element for particular cargos. By generating wild-type and mutant lqfR transgenes, we found that all apparent LqfR functions are independent of its ENTH domain. These results suggest that LqfR transports specific cargo critical to one or more signaling pathways, and lays the foundation for identifying those proteins. Author Affiliation: Section of Molecular Cell and Developmental Biology, Institute for Cell and Molecular Biology, The University of Texas at Austin, 1 University Station A4800, Austin, TX 78712, USA Article History: Received 4 February 2009; Revised 11 March 2009; Accepted 12 March 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2008.04.008 Byline: Georg Vogler (a), Joachim Urban (b) Keywords: Zfh1; Motoneuron; Synapse; Development, Neurogenesis; FRMFa; Neuromuscular junction; MARCM; Axonal outgrowth Abstract: Different aspects of neural development are tightly regulated and the underlying mechanisms have to be transcriptionally well controlled. Here we present evidence that the transcription factor Zfh1, the Drosophila member of the conserved zfh1 gene family, is important for different steps of neuronal differentiation. First, we show that late larval expression of the neuropeptide FMRFamide is dependent on correct levels of Zfh1 and that this regulation is presumably direct via a conserved zfh1 homeodomain binding site in the FMRFamide enhancer. Using MARCM analysis we additionally examined the requirement for Zfh1 during embryonic and larval stages of motoneuron development. We could show that Zfh1 cell autonomously regulates motoneuronal outgrowth and larval growth of neuromuscular junctions (NMJs). In addition, we find that the growth of NMJs is dependent on the dosage of Zfh1, suggesting it to be a downstream effector of the known NMJ size regulating pathways. Author Affiliation: (a) Center for Neuroscience and Aging, Burnham Institute for Medical Research, La Jolla, CA 92037, USA (b) Institut fur Genetik, Universitat Mainz, 55099 Mainz, Saarstra[beta]e 21, Germany Article History: Received 30 January 2007; Revised 28 March 2008; Accepted 7 April 2008

During cytokinesis, cleavage furrow invagination requires an actomyosin-based contractile ring and addition of new membrane. Little is known about how this actin and membrane traffic to the cleavage furrow. We address this through live analysis of fluorescently tagged vesicles in postcellularized Drosophila melanogaster embryos. We find that during cytokinesis, F-actin and membrane are targeted as a unit to invaginating furrows through formation of F-actin--associated vesicles. F-actin puncta strongly colocalize with endosomal, but not Golgi-derived, vesicles. These vesicles are recruited to the cleavage furrow along the central spindle and a distinct population of microtubules (MTs) in contact with the leading furrow edge (furrow MTs). We find that Rho-specific guanine nucleotide exchange factor mutants, pebble (pbl), severely disrupt this F-actin-associated vesicle transport. These transport defects are a consequence of the pbl mutants' inability to properly form furrow MTs and the central spindle. Transport of F-actin-associated vesicles on furrow MTs and the central spindle is thus an important mechanism by which actin and membrane are delivered to the cleavage furrow.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.12.026 Byline: Sarah B. Pierce (a), Cynthia Yost (a), Sarah A.R. Anderson (a), Erin M. Flynn (a), Jeffrey Delrow (b), Robert N. Eisenman (a) Keywords: Drosophila; Myc; Mnt; Growth; Transcription; Larval development; Ribosome biogenesis Abstract: Myc oncoproteins are essential regulators of the growth and proliferation of mammalian cells. In Drosophila the single ortholog of Myc (dMyc), encoded by the dm gene, influences organismal size and the growth of both mitotic and endoreplicating cells. A null mutation in dm results in attenuated endoreplication and growth arrest early in larval development. Drosophila also contains a single ortholog of the mammalian Mad/Mnt transcriptional repressor proteins (dMnt), which is thought to antagonize dMyc function. Here we show that animals lacking both dMyc and dMnt display increased viability and grow significantly larger and develop further than dMyc single mutants. We observe increased endoreplication and growth of larval tissues in these double mutants and disproportionate growth of the imaginal discs. Gene expression analysis indicates that loss of dMyc leads to decreased expression of genes required for ribosome biogenesis and protein synthesis. The additional loss of dMnt partially rescues expression of a small number of dMyc and dMnt genes that are primarily involved in rRNA synthesis and processing. Our results indicate that dMnt repression is normally overridden by dMyc activation during larval development. Therefore the severity of the dm null phenotype is likely due to unopposed repression by dMnt on a subset of genes critical for cell and organismal growth. Surprisingly, considerable growth and development can occur in the absence of both dMyc and dMnt. Author Affiliation: (a) Division of Basic Sciences, Fred Hutchinson Cancer Research Center, MS A2-025, POB 19024, Seattle, WA 98109-1024, USA (b) Genomics Resource, Fred Hutchinson Cancer Research Center, Seattle WA, USA Article History: Received 8 October 2007; Revised 3 December 2007; Accepted 11 December 2007

The regulation of segmentation gene expression is investigated by computational modeling using quantitative expression data. Previous tissue culture assays and transgene analyses raised the possibility that Hunchback (Hb) might function as both an activator and repressor of transcription. At low concentrations, Hb activates gene expression, whereas at high concentrations it mediates repression. Under the same experimental conditions, transcription factors encoded by other gap genes appear to function as dedicated repressors. Models based on dual regulation suggest that the Hb gradient can be sufficient for establishing the initial Kruppel (Kr) expression pattern in central regions of the precellular embryo. The subsequent refinement of the Kr pattern depends on the combination of Hb and the Giant (Gt) repressor. The dual-regulation models developed for Kr also explain some of the properties of the even-skipped (eve) stripe 3+7 enhancer. Computational simulations suggest that repression results from the dimerization of Hb monomers on the DNA template. computational model | Drosophila development | enhancer | dual transcriptional regulators | binding site

FOXO is thought to function as a repressor of growth that is, in turn, inhibited by insulin signaling. However, inactivating mutations in Drosophila melanogaster FOXO result in viable flies of normal size, which raises a question over the involvement of FOXO in growth regulation. Previously, a growth-suppressive role for FOXO under conditions of increased target of rapamycin (TOR) pathway activity was described. Here, we further characterize this phenomenon. We show that tuberous sclerosis complex 1 mutations cause increased FOXO levels, resulting in elevated expression of FOXO-regulated genes, some of which are known to antagonize growth-promoting pathways. Analogous transcriptional changes are observed in mammalian cells, which implies that FOXO attenuates TOR-driven growth in diverse species.

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 garA, which encodes the Drosophila homolog of glutamylt-RNA(GIn) 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 wildtype size, and gatA larvae die before pupariation, garA 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.

Studies in Drosophila have defined a new growth inhibitory pathway mediated by Fat (Ft), Merlin (Mer), Expanded (Ex), Hippo (Hpo), Salvador (Sav)/Shar-pei, Warts (Wts)/Large tumor suppressor (Lats), and Mob as tumor suppressor (Mats), which are all evolutionarily conserved in vertebrate animals. We previously found that the Mob family protein Mats functions as a coactivator of Wts kinase. Here we show that mats is essential for early development and is required for proper chromosomal segregation in developing embryos. Mats is expressed at low levels ubiquitously, which is consistent with the role of Mats as a general growth regulator. Like mammalian Mats, Drosophila Mats colocalizes with Wts/Lats kinase and cyclin E proteins at the centrosome. This raises the possibility that Mats may function together with Wts/Lats to regulate cyclin E activity in the centrosome for mitotic control. While Hpo/Wts signaling has been implicated in the control of cyclin E and diap1 expression, we found that it also modulates the expression of cyclin A and cyclin B. Although mats depletion leads to aberrant mitoses, this does hot seem to be due to compromised mitotic spindle checkpoint function.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.10.048 Byline: Deborah L. Berry (1)(2), Eric H. Baehrecke (1)(3) Keywords: CELLBIO; DEVBIO; SIGNALING Abstract: Autophagy is a catabolic process that is negatively regulated by growth and has been implicated in cell death. We find that autophagy is induced following growth arrest and precedes developmental autophagic cell death of Drosophila salivary glands. Maintaining growth by expression of either activated Ras or positive regulators of the class I phosphoinositide 3-kinase (PI3K) pathway inhibits autophagy and blocks salivary gland cell degradation. Developmental degradation of salivary glands is also inhibited in autophagy gene (atg) mutants. Caspases are active in PI3K-expressing and atg mutant salivary glands, and combined inhibition of both autophagy and caspases increases suppression of gland degradation. Further, induction of autophagy is sufficient to induce premature cell death in a caspase-independent manner. Our results provide in vivo evidence that growth arrest, autophagy, and atg genes are required for physiological autophagic cell death and that multiple degradation pathways cooperate in the efficient clearance of cells during development. Author Affiliation: (1) Center for Biosystems Research, University of Maryland Biotechnology Institute, College Park, MD 20742, USA (2) Present address: Children's National Medical Center, Washington, DC 20010, USA (3) Department of Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA Article History: Received 12 June 2007; Revised 7 September 2007; Accepted 16 October 2007 Article Note: (miscellaneous) Published: December 13, 2007

The Rho GTPases interact with multiple downstream effectors to exert their biological functions, which include important roles in tissue morphogenesis during the development of multicellular organisms. Among the Rho effectors are the protein kinase N (PKN) proteins, which are protein kinase C (PKC)-like kinases that bind activated Rho GTPases. The PKN proteins are well conserved evolutionarily, but their biological role in any organism is poorly understood. We previously determined that the single Drosophila ortholog of mammalian PKN proteins, Pkn, is a Rho/Rac-binding kinase essential for Drosophila development. By performing 'rescue' studies with various Pkn mutant constructs, we have defined the domains of Pkn required for its role during Drosophila development. These studies suggested that Rho, but not Rac binding is important for Pkn function in development. In addition, we determined that the kinase domain of PKC53E, a PKC family kinase, can functionally substitute for the kinase domain of Pkn during development, thereby exemplifying the evolutionary strategy of 'combining' functional domains to produce proteins with distinct biological activities. Interestingly, we also identified a requirement for Pkn in wing movphogenesis, thereby revealing the first postembryonic function for Pkn.

Allelic mutants exhibiting growth defects in Drosophila were isolated. Molecular cloning identified the responsible gene as a budding yeast Tim50 ortholog, and thus it was named tiny tim 50 (ttm50). The weak allele ([ttm50.sup.Gp99]) produced small flies due to reduced cell size and number, and growth terminated at the larval stage in the strong alleles ([ttm50.sup.IE1] and [ttm50.sup.IE2]). Twin-spot analysis showed fewer cells in [ttm50.sup.Gp99] clones, whereas [ttm50.sup.IE1] clones did not proliferate, suggesting that the gene has an essential cellular function. Tim50 is known to maintain mitochondrial membrane potential (MMP) while facilitating innermembrane protein transport. We found that tagged Ttm50 also localized to mitochondria and that mitochondrial morphology and MMP were affected in mutants, indicating that mitochondrial dysfunction causes the developmental phenotype. Conversely, ttm50 overexpression increased MMP and apoptosis. Co-expression of p35 suppressed this apoptosis, resulting in cell overproliferation. Interestingly, ttm50 transcription was tissue specific, corresponding to elevated MMP in the larval midgut, which was decreased in the mutant. The correlation of ttm50 expression levels with differences in MMP match its proposed role in mitochondrial permeability barrier maintenance. Thus a mitochondrial protein translocase component can play active roles in regulating metabolic levels, possibly for modulation of physiological function or growth in development.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.02.004 Byline: David M. Tyler, Nicholas E. Baker Keywords: Drosophila eye; Growth; Proliferation; Signaling; Wingless; Dpp; Warts; Hippo; Fat; Expanded; Sterol trafficking Abstract: Mutations in the expanded gene act as hyperplastic tumor suppressors, interfere with cell competition and elevate Dpp signaling. Unlike Dpp overexpression, ex causes few patterning defects. Our data suggest that patterning effects are partly masked by antagonistic roles of other signaling pathways that are also activated. ex causes proliferation of cells in the posterior eye disc that are normally postmitotic. ex mutations elevate Wg signaling, but Dpp signaling antagonizes patterning effects of Wg. By contrast, if Dpp signaling is blocked in ex mutant cells, the elevated Wg signaling preserves an immature developmental state and prevents retinal differentiation. An effect of ex mutations on vesicle transport is suggested by evidence for altered sterol distribution. Mutations in ft show effects on proliferation, Wg signaling and sterols very similar to those of ex mutations. During disc growth, ex was largely epistatic to ft, and the Warts pathway mutation hippo largely epistatic to ex. Our data suggest that ft and ex act partially through the Warts pathway. Author Affiliation: Department of Molecular Genetics, Albert Einstein College of Medicine 1300 Morris Park Avenue, Bronx, NY 10461, USA Article History: Received 24 August 2006; Revised 6 February 2007; Accepted 6 February 2007

The mechanisms responsible for controlling growth rates and size assessment in insects are discussed. Researchers have found that the insulin-dependent growth of the prothoracic gland is involved in assessing when critical weight is reached and mutations in DHR4, a repressor of ecdysone signaling, reduce critical weight and adult size.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.12.021 Byline: Brett J. Pellock (a)(b), Eugene Buff (b), Kristin White (a), Iswar K. Hariharan (b)(c) Keywords: Merlin; Expanded; Wingless; Hippo; Apoptosis; Tumor suppressor; Cell cycle Abstract: Mutations that inactivate either merlin (mer) or expanded (ex) result in increased cell growth and proliferation in Drosophila. Both Mer and Ex are members of the Band 4.1 protein superfamily, and, based on analyses of mer ex double mutants, they are proposed to function together in at least a partially redundant manner upstream of the Hippo (Hpo) and Warts (Wts) proteins to regulate cell growth and division. By individually analyzing ex and mer mutant phenotypes, we have found important qualitative and quantitative differences in the ways Mer and Ex function to regulate cell proliferation and cell survival. Though both mer and ex restrict cell and tissue growth, ex clones exhibit delayed cell cycle exit in the developing eye, while mer clones do not. Conversely, loss of mer substantially compromises normal developmental apoptosis in the pupal retina, while loss of ex has only mild effects. Finally, ex has a role in regulating Wingless protein levels in the eye that is not obviously shared by either mer or hpo. Taken together, our data suggest that Mer and Ex differentially regulate multiple downstream pathways. Author Affiliation: (a) Massachusetts General Hospital Cutaneous Biology Research Center, Charlestown, MA 02129, USA (b) Massachusetts General Hospital Cancer Center, Charlestown, MA 02129, USA (c) University of California, Berkeley, Department of Molecular and Cell Biology, Berkeley, CA 94720, USA Article History: Received 19 September 2006; Revised 5 December 2006; Accepted 10 December 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.07.050 Byline: Carlos M. Luque, Marco Milan Keywords: Notch; Growth; Eye; Head; Drosophila Abstract: Notch signaling is involved in cell differentiation and patterning, as well as in the regulation of growth and cell survival. Notch activation at the dorsal-ventral boundary of the Drosophila eye-head primordium leads to the expression of the secreted protein Unpaired, a ligand of the JAK-STAT pathway that induces cell proliferation in the undifferentiated tissue. The zinc finger proteins encoded by elbow and no ocelli are expressed in the highly proliferative region of the eye-head primordium. Loss of elbow and no ocelli activities induces overgrowths of the head capsule, without inducing Upd expression de novo. These overgrowths depend on Notch activity suggesting that elbow and noc repress a Upd independent role of Notch in driving cell proliferation. When the size of the overgrown tissue is increased, ectopic antenna and eye structures can be found. Thus, tight regulation of the size of the eye-head primordium by elbow and no ocelli is crucial for proper fate specification and generation of the adult structures. Author Affiliation: ICREA and Institute for Research in Biomedicine (IRB), Parc Cientific de Barcelona, Josep Samitier, 1-5, 08028 Barcelona, Spain Article History: Received 4 May 2006; Revised 27 July 2006; Accepted 28 July 2006

Mixed lineage kinases (MLKs) function as Jun-N-terminal kinase (JNK) kinase kinases to transduce extracellular signals during development and homeostasis in adults, slipper (slpr), which encodes the Drosophila homolog of mammalian MLKs, has previously been implicated in activation of the JNK pathway during embryonic dorsal epidermal closure. To further define the specific functions of SLPR, we analyzed the phenotypic consequences of slpr loss and gain of function throughout development, using a semiviable maternal-effect allele and wild-type or dominant-negative transgenes. From these analyses we confirm that failure of dorsal closure is the null phenotype in slpr germline clones. In addition, there is a functional maternal contribution, which can suffice for embryogenesis in the zygotic null mutant, but rarely suffices for pupal metamorphosis, revealing later functions for slpr as the maternal contribution is depleted. Zygotic null mutants that eclose as adults display an array of morphological defects, many of which are shared by hep mutant animals, deficient in the JNK kinase (JNKK/MKK7) substrate for SLPR, suggesting that the defects observed in slpr mutants primarily reflect loss of hep-dependent JNK activation. Consistent with this, the maternal slpr contribution is sensitive to the dosage of positive and negative JNK pathway regulators, which attenuate or potentiate SLPR-dependent signaling in development. Although SLPR and TAK1, another JNKKK family member, are differentially used in dorsal closure and TNF/Eiger-stimulated apoptosis, respectively, a Tak1 mutant shows dominant genetic interactions with slpr, suggesting potential redundant or combinatorial functions. Finally, we demonstrate that SLPR overexpression can induce ectopic JNK signaling and that the SLPR protein is enriched at the epithelial cell cortex.

Embryo development in Drosophila and biochemical process associated with this is examined.

Tube cell development and drosophila egg chamber and biochemical process associated with this is examined.

Embryo development in drosophila and biochemical impacts on this process is examined.

The negative effect of ultrabithorax in the development of haltere in Drosophila is discussed.

A study examines the role of decapentaplegic on the bone morphogenetic protein activity in the wing development of drosophila.

In Drosophila, the dosage compensation complex (DCC) mediates upregulation of transcription from the single male X chromosome. Despite coating the polytene male X, the DCC pattern looks discontinuous and probably reflects DCC dynamic associations with genes active at a given moment of development in a salivary gland. To test this hypothesis, we compared binding patterns of the DCC and of the elongating form of RNA polymerase II (PolIIo). We found that, unlike PolIIo, the DCC demonstrates a stable banded pattern throughout larval development and escapes binding to a subset of transcriptionally active areas, including developmental puffs. Moreover, these proteins are not completely colocalized at the electron microscopy level. These data combined imply that simple recognition of PolII machinery or of general features of active chromatin is either insufficient or not involved in DCC recruitment to its targets. We propose that DCC-mediated site-specific upregulation of transcription is not the fate of all active X-linked genes in males. Additionally, we found that DCC subunit MLE associates dynamically with developmental and heat-shock-induced puffs and, surprisingly, with those developing within DCC-devoid regions of the male X, thus resembling the PolIIo pattern. These data imply that, independently of other MSL proteins, the RNA-helicase MLE might participate in general transcriptional regulation or RNA processing.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.10.042 Byline: Karen L. Reddy, Margritte K. Rovani, Arthur Wohlwill, Alisa Katzen, Robert V. Storti Keywords: Drosophila; Pdp1; Growth; Replication; Endoreplication; Mitosis Abstract: PDP1 is a basic leucine zipper (bZip) transcription factor that is expressed at high levels in the muscle, epidermis, gut and fat body of the developing Drosophila embryo. We have identified three mutant alleles of Pdp1, each having a similar phenotype. Here, we describe in detail the Pdp1 mutant allele, Pdp1.sup.p205 , which is null for both Pdp1 RNA and protein. Interestingly, homozygous Pdp1.sup.p205 embryos develop normally, hatch and become viable larvae. Analyses of Pdp1 null mutant embryos reveal that the overall muscle pattern is normal as is the patterning of the gut and fat body. Pdp1.sup.p205 larvae also appear to have normal muscle and gut function and respond to ecdysone. These larvae, however, are severely growth delayed and arrested. Furthermore, although Pdp1 null larvae live a normal life span, they do not form pupae and thus do not give rise to eclosed flies. The stunted growth of Pdp1.sup.p205 larvae is accompanied by defects in mitosis and endoreplication similar to that associated with nutritional deprivation. The cellular defects resulting from the Pdp1.sup.p205 mutation are not cell autonomous. Moreover, PDP1 expression is sensitive to nutritional conditions, suggesting a link between nutrition, PDP1 isotype expression and growth. These results indicate that Pdp1 has a critical role in coordinating growth and DNA replication. Author Affiliation: Department of Biochemistry and Molecular Genetics M/C 669, University of Illinois College of Medicine, 900 S. Ashland Ave., Rm1008, Chicago, IL 60612, USA Article History: Received 26 January 2005; Revised 30 September 2005; Accepted 17 October 2005

Studies related to mutations in genes that could be termed growth-suppressors or tumor-suppressor that could provide insight into the genetic regulation of tissue growth in Drosophila and mammals are described. Evidence suggests that the phenotypes of endocytic neoplastic tumor-suppressor gene mutants are caused by an excess accumulation of various signaling receptors that fail to be turned over in mutant tissue.