An Eye on Trafficking Genes: Identification of Four Eye Color Mutations inDrosophila

Abstract

Genes that code for proteins involved in organelle biogenesis and intracellular trafficking produce products that are critical in normal cell function . Conserved orthologs of these are present in most or all eukaryotes, including Drosophila melanogaster. Some of these genes were originally identified as eye color mutants with decreases in both types of pigments found in the fly eye. These criteria were used for identification of such genes, four eye color mutations that are not annotated in the genome sequence: chocolate, maroon, mahogany, and red Malpighian tubules were molecularly mapped and their genome sequences have been evaluated. Mapping was performed using deletion analysis and complementation tests. chocolate is an allele of the VhaAC39-1 gene, which is an ortholog of the Vacuolar H+ ATPase AC39 subunit 1. maroon corresponds to the Vps16A gene and its product is part of the HOPS complex, which participates in transport and organelle fusion. red Malpighian tubule is the CG12207 gene, which encodes a protein of unknown function that includes a LysM domain. mahogany is the CG13646 gene, which is predicted to be an amino acid transporter. The strategy of identifying eye color genes based on perturbations in quantities of both types of eye color pigments has proven useful in identifying proteins involved in trafficking and biogenesis of lysosome-related organelles. Mutants of these genes can form the basis of valuable in vivo models to understand these processes.

The road to lysosome‐related organelles: Insights from Hermansky‐Pudlak syndrome and other rare diseases

“…For example, mutations in any of the four subunits of AP‐3 result in a similar phenotype with a reduction in the number and size of the pigment granules and loss of both ommochrome and pteridine pigments. RNAi depletion of BLOC‐1 subunits, the pink mutation in the orthologue to the HPS5 subunit of BLOC‐2, the lightoid mutation in a Rab32/38 orthologue and the claret mutation in its putative guanine nucleotide exchange factor, and mutations in the Vps16, Vps33, Vps18 and Vps41 subunits of HOPS all cause altered eye color due to malformation of pigment granules. The availability of these models allows for relatively easy testing of genetic interactions among these and other genes.…”

“…Null mutations in vps18 and vps11 in zebrafish and medaka, respectively, cause hypopigmentation due to fewer melanosomes in epidermal and retinal pigment epithelia, suggesting a role for VPS‐C in the biogenesis of melanosomes. In D melanogaster , HOPS subunit genes—including those encoding homologues of VPS18, VPS41, VPS16A, and VPS33A—are among the granule group of genes that function in the formation of eye pigment granules . Deletion or loss‐of‐function alleles of the VPS18, VPS41 or VPS33A homologues are lethal because these genes are required for normal trafficking to lysosomes; however, hypomorphic alleles and clonal knockouts of these genes or of the VPS16A homologue in the eye cause changes in eye color due to defective protein trafficking to pigment granules .…”

“…In D melanogaster , HOPS subunit genes—including those encoding homologues of VPS18, VPS41, VPS16A, and VPS33A—are among the granule group of genes that function in the formation of eye pigment granules . Deletion or loss‐of‐function alleles of the VPS18, VPS41 or VPS33A homologues are lethal because these genes are required for normal trafficking to lysosomes; however, hypomorphic alleles and clonal knockouts of these genes or of the VPS16A homologue in the eye cause changes in eye color due to defective protein trafficking to pigment granules . Flies with eye‐specific knockdowns of HOPS subunits have strong retinal degeneration characterized by defective trafficking to lysosomes, aberrant autophagosome accumulation and loss of Type I and Type II pigment granules .…”

Iron Sulfur and Molybdenum Cofactor Enzymes Regulate the Drosophila Life Cycle by Controlling Cell Metabolism

“…Accounting for increased Xdh activity was harder, however, given the similar eye color between maroon, rosy , and mal . The demonstration that the maroon gene encodes for Vacuolar protein sorting 16A (Vps16A; Grant et al, 2016 ), a protein implicated in granule formation (Pulipparacharuvil et al, 2005 ; Lorincz et al, 2016 ), suggests a possible defect in the tissue localization of Xdh in maroon mutants, as the enzyme obviously remains functional in whole fly extracts and is even induced (Figure 7 ). It will be informative to test in maroon mutants whether the Xdh activity is localized in peripheral tissues, such as the Malpighian tubules, and not in the eyes.…”

CG4928 Is Vital for Renal Function in Fruit Flies and Membrane Potential in Cells: A First In-Depth Characterization of the Putative Solute Carrier UNC93A

“…The phenomena of accumulation of pigments and fluid in the Malpighian tubules have been observed earlier for the knockdown of genes important for transport and trafficking, e.g., w , cho , ma , mah , and red . Many of them are involved directly in the biosynthesis or the transport of components within the biosynthesis of eye pigments in flies ( Lloyd et al, 1998 ; Grant et al, 2016 ). For example, knockdown of Vps16A (vacuolar protein sorting 16A, also known as ma ), a gene that is a part of the HOPS complex that together with Syntaxin 17 mediates autophagosome–lysosome fusion ( Pulipparacharuvil et al, 2005 ; Jiang et al, 2014 ), leads to the accumulation of yellow pigments in Malpighian tubules ( Bridges, 1918 ).…”