A Genetic Screen for Dominant Modifiers of a Small-Wing Phenotype in Drosophila melanogaster Identifies Proteins Involved in Splicing and Translation

Abstract

Studies in the fly, Drosophila melanogaster, have revealed that several signaling pathways are important for the regulation of growth. Among these, the insulin receptor/phosphoinositide 3-kinase (PI3K) pathway is remarkable in that it affects growth and final size without disturbing pattern formation. We have used a small-wing phenotype, generated by misexpression of kinase-dead PI3K, to screen for novel mutations that specifically disrupt organ growth in vivo. We identified several complementation groups that dominantly enhance this small-wing phenotype. Meiotic recombination in conjunction with visible markers and single-nucleotide polymorphisms (SNPs) was used to map five enhancers to single genes. Two of these, nucampholin and prp8, encode pre-mRNA splicing factors. The three other enhancers encode factors required for mRNA translation: pixie encodes the Drosophila ortholog of yeast RLI1, and RpL5 and RpL38 encode proteins of the large ribosomal subunit. Interestingly, mutations in several other ribosomal protein-encoding genes also enhance the small-wing phenotype used in the original screen. Our work has therefore identified mutations in five previously uncharacterized Drosophila genes and provides in vivo evidence that normal organ growth requires optimal regulation of both pre-mRNA splicing and mRNA translation.

Growth and cell survival are unevenly impaired inpixiemutant wing discs

“…These mutant cells succumb to the changing environment but do not fully interfere with the ability of the system to correct the defects that arise due to cell death or even perhaps extra cell proliferation. However, it is clear that this ability of the system to correct itself is compromised to the extent that proportion is not always maintained and mild overgrowth can occur (see Coelho et al, 2005). Studying the ability of mutant tissues to respond to growth constraints in vivo should advance our understanding of how the slowing down of growth is triggered.…”

“…1A-E) (Leevers et al, 1996;Coelho et al, 2005). Additional pixie alleles were obtained in a screen for mutations that are lethal in combination with a deficiency that uncovers pixie (Dahanukar et al, 1999).…”

The molecular chaperone Hsp90 is a component of the cap-binding complex and interacts with the translational repressor Cup during Drosophila oogenesis

“…Several already known components of the active cap-binding complex could be detected (Table 1), namely: eukaryotic translation initiation factor 4E (eIF4E-1 and eIF4E-2; CG4035; Hernandez et al, 2005); eukaryotic translation initiation factor 4G (eIF4G; CG10811; Hernandez et al, 1998); Poly(A) binding protein (PABP; CG5119; Johnstone and Lasko, 2001); eukaryotic translation elongation factor 2b (EF-2; CG2238-PA; Grinblat et al, 1989); Suppressor of variegation 3-9 (eIF-2γ; CG6476-PB; Lasko, 2000); eukaryotic translation initiation factor 2α (eIF-2α; CG9946; Lasko, 2000); Trip1 (eIF-3β; CG8882; Lasko, 2000); Ribosomal protein S3 (RpS3; CG6779; Lyamouri et al, 2002); Ribosomal protein S3A (RpS3A; CG2168; Lyamouri et al, 2002); Ribosomal protein L5 (RpL5; CG17489; Coelho et al, 2005). We further isolated Cap-binding protein 80 (Cbp80; CG7035), which appears to replace eIF4E, for binding to the cap structure, during premRNA maturation and nonsense-mediated mRNA decay processes (Maquat, 2004).…”

Mutations in the Drosophila Mitochondrial tRNA Amidotransferase, bene/gatA, Cause Growth Defects in Mitotic and Endoreplicating Tissues

“…The Minute genes, which have long been known to mediate cell growth and cell competition, encode many cytoplasmic ribosomal proteins (Lambertsson 1998). Mutations in three other cytoplasmic ribosomal proteins, Pixie, RpL5, and RpL38, disrupt wing development downstream of the insulin pathway (Coelho et al 2005). Defects in Bonsai, a mitochondrial ribosomal protein, result in small larvae that exhibit cell proliferation defects (Galloni and Edgar 1999;Galloni 2003).…”