Disruption of Drosophila melanogaster Lipid Metabolism Genes Causes Tissue Overgrowth Associated with Altered Developmental Signaling.

Developmental patterning requires the precise interplay of numerous intercellular signaling pathways to ensure that cells are properly specified during tissue formation and organogenesis. The spatiotemporal function of many developmental pathways is strongly influenced by the biosynthesis and intracellular trafficking of signaling components. Receptors and ligands must be trafficked to the cell surface where they interact, and their subsequent endocytic internalization and endosomal trafficking is critical for both signal propagation and its down-modulation. In a forward genetic screen for mutations that alter intracellular Notch receptor trafficking in Drosophila melanogaster, we recovered mutants that disrupt genes encoding serine palmitoyltransferase and acetyl-CoA carboxylase. Both mutants cause Notch, Wingless, the Epidermal Growth Factor Receptor (EFGR), and Patched to accumulate abnormally in endosomal compartments. In mosaic animals, mutant tissues exhibit an unusual non-cell-autonomous effect whereby mutant cells are functionally rescued by secreted activities emanating from adjacent wildtype tissue. Strikingly, both mutants display prominent tissue overgrowth phenotypes that are partially attributable to altered Notch and Wnt signaling. Our analysis of the mutants demonstrates genetic links between abnormal lipid metabolism, perturbations in developmental signaling, and aberrant cell proliferation

Cell Chirality Drives Left-Right Asymmetric Morphogenesis

Most macromolecules found in cells are chiral, meaning that they cannot be superimposed onto their mirror image. However, cells themselves can also be chiral, a subject that has received little attention until very recently. In our studies on the mechanisms of left-right (LR) asymmetric development in Drosophila, we discovered that cells can have an intrinsic chirality to their structure, and that this “cell chirality” is generally responsible for the LR asymmetric development of certain organs in this species. The actin cytoskeleton plays important roles in the formation of cell chirality. In addition, Myosin31DF (Myo31DF), which encodes Drosophila Myosin ID, was identified as a molecular switch for cell chirality. In other invertebrate species, including snails and Caenorhabditis elegans, chirality of the blastomeres, another type of cell chirality, determines the LR asymmetry of structures in the body. Thus, chirality at the cellular level may broadly contribute to LR asymmetric development in various invertebrate species. Recently, cell chirality was also reported for various vertebrate cultured cells, and studies suggested that cell chirality is evolutionarily conserved, including the essential role of the actin cytoskeleton. Although the biological roles of cell chirality in vertebrates remain unknown, it may control LR asymmetric development or other morphogenetic events. The investigation of cell chirality has just begun, and this new field should provide valuable new insights in biology and medicine

The <i>lace</i> overproliferation phenotype is partially rescued by activated Armadillo.

<p>Mutant clones of <i>lace²</i> (A, C) or <i>ACC¹</i> (B, D) were induced using <i>sd-GAL4; UAS-FLP</i>, and examined for tissue overgrowth in the absence (A, B) or presence (C, D) of a constitutively activated form of Armadillo (armS10), expressed using a <i>UAS-armS10</i> transgene. For each image pair, panel i shows tissue growth patterns as revealed by Phalloidin (red in A–D), the mutant clone marker (green indicates non-mutant cells in A, B), or armS10 expression (blue in C, D), with the Phalloidin signal alone shown in panel ii. Complete genotypes are listed in Supplemental <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003917#pgen.1003917.s009" target="_blank">Table S4</a>. Note that tissue overgrowth in the wing hinge region was not suppressed (C, D) because armS10 is not expressed in the hinge at this stage. Scale bars, 50 µm.</p

Notch and Delta accumulate abnormally in <i>lace</i> and <i>ACC</i> mutant tissues.

<p>Confocal optical sections through <i>D. melanogaster</i> wing imaginal discs bearing homozygous mutant clones of <i>lace¹⁸</i> (A–C) or <i>ACC¹</i> (D–F) showing accumulation of Notch (A, D) and Delta (C, F) in fixed tissue samples, and endocytic internalization of Notch in live tissue samples (B, E). Areas devoid of GFP marker gene expression (green) correspond to mutant cell regions. Each set of five images (i–v) depict an apical (i, ii) and basal (iii–iv) horizontal section showing Notch (red in A, B, D and E) or Delta (magenta in C and F) accumulation, the same images overlaid with corresponding GFP expression to indicate clone locations (ii and iv), and a representative z-series showing the distribution of Notch or Delta along the apicobasal axis of the disc tissue (v). Scale bars, 20 µm.</p

Colocalization of Notch with endosomal and lysosomal markers in <i>lace</i> and <i>ACC</i> mutant tissue clones.

<p>Each confocal image triplet (i–iii) depicts <i>lace²</i> (E–I) or <i>ACC¹</i> (J–N) mutant wing disc clones, showing Notch overaccumulation (red in i for E–H, J–M) or mutant clone locations (absence of blue signal in i for I and N), the subcellular localization of the indicated organelle marker (green in ii), and the corresponding merged images at right (iii). Corresponding wildtype control images for each marker are shown in A–D; <i>da-GAL4; UAS-Rab5-YFP</i>, <i>Rab7-YFP</i>, or <i>Rab11-YFP</i> and <i>UAS-LAMP-HRP</i> were utilized for controls. Organelle markers in each panel are as follows: Rab5-YFP (Rab5; A, E, J), Rab7-YFP (Rab7; B, F, K), Rab11-YFP (Rab11; C, G, L), and LAMP-HRP (LAMP; D, H, I, M, N). Note elevated LAMP-HRP expression in <i>lace²</i> and <i>ACC¹</i> mutant clones in I and N. Scale bars, 10 µm.</p

Notch and Wingless signaling abnormalities in <i>lace</i> and <i>ACC</i> mutants.

<p>(A–I) Wing disc mutant clones of <i>lace²</i> (B, E, H) and <i>ACC¹</i> (C, F, I) analyzed for expression of the Notch pathway reporters Cut (B, C; green), <i>vestigial boundary enhancer</i> (E, F; vgBE; green), and <i>Gbe+Su(H)_m8</i> (H, I; green). Mutant cell territories are indicated by absence of blue Myc or <i>lacZ</i> signal, and Notch accumulation is shown in red in B, C, E, F, H, and I. Wildtype expression patterns of the indicated Notch reporters are shown in A, D, and G (green). (J–O) Wing disc clones for <i>lace²</i> (L, M) and <i>ACC¹</i> (N, O) were examined for activity of Wingless pathway reporters Senseless (Sens; J, L, N) and Distalless (Dll; K, M, O). For each panel i, mutant clone locations are indicated by absence of blue Myc or lacZ expression, Notch accumulation is shown in green, and Sens or Dll expression is in red; panel ii depicts the corresponding red channel only. Scale bars, 20 µm.</p

Analysis of molecular lesions associated with <i>lace</i> and <i>ACC</i> mutants and alignment of human and <i>D. melanogaster</i> ACC protein domains.

<p>(A) Diagram of the Lace protein (SPT-II, serine palmitoyltransferase II) showing amino acid substitutions in the AAT I (amino-acid acetyltransferase I) domain in <i>lace¹⁸</i>, <i>lace¹⁹</i>, and <i>lace²</i> mutants, and diagram of the ACC protein showing mutant lesions associated with <i>ACC¹</i> and <i>ACC²</i> mutants. (B) Alignment of human and <i>D. melanogaster</i> ACC activity domains BC (biotin carboxylase), BCCP (biotin carboxyl carrier protein), and CT (carboxyltransferase) as depicted in panel A. Black boxes indicate identical residues; shaded boxes indicate conservative substitutions; percent identity is denoted at left for each domain.</p

Cells with Broken Left–Right Symmetry: Roles of Intrinsic Cell Chirality in Left–Right Asymmetric Epithelial Morphogenesis

Chirality is a fundamental feature in biology, from the molecular to the organismal level. An animal has chirality in the left&#8211;right asymmetric structure and function of its body. In general, chirality occurring at the molecular and organ/organism scales has been studied separately. However, recently, chirality was found at the cellular level in various species. This &#8220;cell chirality&#8222; can serve as a link between molecular chirality and that of an organ or animal. Cell chirality is observed in the structure, motility, and cytoplasmic dynamics of cells and the mechanisms of cell chirality formation are beginning to be understood. In all cases studied so far, proteins that interact chirally with F-actin, such as formin and myosin I, play essential roles in cell chirality formation or the switching of a cell&#8217;s enantiomorphic state. Thus, the chirality of F-actin may represent the ultimate origin of cell chirality. Links between cell chirality and left&#8211;right body asymmetry are also starting to be revealed in various animal species. In this review, the mechanisms of cell chirality formation and its roles in left&#8211;right asymmetric development are discussed, with a focus on the fruit fly Drosophila, in which many of the pioneering studies were conducted