An in vivo genetic screen in Drosophila identifies the orthologue of human cancer/testis gene SPO11 among a network of targets to inhibit lethal(3)malignant brain tumour growth

Using transgenic RNAi technology, we have screened over 4000 genes to identify targets to inhibit malignant growth caused by the loss of function of lethal(3)malignant brain tumour in Drosophila in vivo. We have identified 131 targets, which belong to a wide range of gene ontologies. Most of these target genes are not significantly overexpressed in mbt tumours hence showing that, rather counterintuitively, tumour-linked overexpression is not a good predictor of functional requirement. Moreover, we have found that most of the genes upregulated in mbt tumours remain overexpressed in tumour-suppressed double-mutant conditions, hence revealing that most of the tumour transcriptome signature is not necessarily correlated with malignant growth. One of the identified target genes is meiotic W68 (mei-W68), the Drosophila orthologue of the human cancer/testis gene Sporulation-specific protein 11 (SPO11), the enzyme that catalyses the formation of meiotic double-strand breaks. We show that Drosophila mei-W68/SPO11 drives oncogenesis by causing DNA damage in a somatic tissue, hence providing the first instance in which a SPO11 orthologue is unequivocally shown to have a pro-tumoural role. Altogether, the results from this screen point to the possibility of investigating the function of human cancer relevant genes in a tractable experimental model organism like Drosophila.

A Variant Protein from φ29 Replication Gene, Gene 1, Did Not Form Homo-Polymer Due to a Single Amino Acid Substitution Near the Carboxyl Terminus

For study of the self-association of the product of psi29 gene 1, one variant which has a substitution at the 71(st) amino acid was used. By glycerol gradient sedimentation, the product of wild-type gene 1 existed both as large aggregate and oligomer, whereas the variant was detected as a single peak of monomer size. According to experiments using His-tagged proteins and Ni-NTA magnetic beads, the variant made only a little self-associated complex. From these results, a site essential for self-association was suggested to exist close to the carboxyl terminus of the product of psi29 gene 1.

Drosophila Sex lethal gene initiates female development in germline progenitors

Sex determination in the Drosophila germ line is regulated by both the sex of the surrounding soma and cell-autonomous cues. How primordial germ cells (PGCs) initiate sexual development via cell-autonomous mechanisms is unclear. Here, we demonstrate that, in Drosophila, the Sex lethal (Sxl) gene acts autonomously in PGCs to induce female development. Sxl is transiently expressed in PGCs during their migration to the gonads; this expression, which was detected only in XX PGCs, is necessary for PGCs to assume a female fate. Ectopic expression of Sxl in XY PGCs was sufficient to induce them to enter oogenesis and produce functional eggs when transplanted into an XX host. Our data provide powerful evidence that Sxl initiates female germline fate during sexual development.

Expression of genes involved in sumoylation in the Drosophila germline

Post-translational modification of proteins by the covalent addition of small ubiquitin-related modifier (SUMO) proteins has been reported to regulate a wide range of cellular processes. However, the spatiotemporal expression pattern of genes encoding the sumoylation machinery during development is largely unknown. Here, we report the expression of five sumoylation genes, Uba2, Aos1, smt3, Ulp1, and lesswright (lwr), in the Drosophila germline. Transcripts from all five genes were detected throughout the early embryo by whole-mount in situ hybridization, while they were predominantly expressed in the germline progenitors, or pole cells, in late stage embryos. These genes were also expressed in the germline during oogenesis and spermatogenesis. Finally, we found that SUMO protein was enriched in the nuclei of pole cells and gametogenic cells. Given that a large fraction of SUMO substrates are nuclear proteins, these data suggest that sumoylation is highly active in the germline. Our data provide a basis for understanding how sumoylation regulates germline development.

Drosophila Blimp-1 is a transient transcriptional repressor that controls timing of the ecdysone-induced developmental pathway

Regulatory mechanisms controlling the timing of developmental events are crucial for proper development to occur. ftz-f1 is expressed in a temporally regulated manner following pulses of ecdysteroid and this precise expression is necessary for the development of Drosophila melanogaster. To understand how insect hormone ecdysteroids regulate the timing of FTZ-F1 expression, we purified a DNA binding regulator of ftz-f1. Mass spectroscopy analysis revealed this protein to be a fly homolog of mammalian B lymphocyte-induced maturation protein 1 (Blimp-1). Drosophila Blimp-1 (dBlimp-1) is induced directly by 20-hydroxyecdysone, and its product exists during high-ecdysteroid periods and turns over rapidly. Forced expression of dBlimp-1 and RNA interference analysis indicate that dBlimp-1 acts as a repressor and controls the timing of FTZ-F1 expression. Furthermore, its prolonged expression results in delay of pupation timing. These results suggest that the transient transcriptional repressor dBlimp-1 is important for determining developmental timing in the ecdysone-induced pathway.

Effects of single amino acid substitutions at the predicted coiled-coil or hydrophobic region on the self-assembly of phi29 replication protein, gp1

Gp1, the product of one of the essential genes of phi29 replication, is an RNA binding protein and self-associates to form large complexes. Furthermore, gp1 suppresses the synthesis of phi29 DNA polymerase and primer protein in the post-transcriptional process. In this report, we have employed seven variants with single amino acid substitutions to analyze the self-assembly of gp1. Using chemical cross-linking and sedimentation assays, amino acid substitutions within the predicted coiled-coil or hydrophobic region were shown to strongly affect the formation of large complexes, suggesting that these two regions were required for the self-assembly of gp1. The self-association of gp1 was suggested to be necessary for the efficient binding to RNA and the translational repression.

Isolation of a series of single missense mutants of a dna gene of phage .PHI.29, gene 1, utilizing their inhibitory effect on E. coli growth

Gene 1 product (gp1) of Bacillus subtilis phage psi29 is known to promote DNA replication of the phage. Although its role in the DNA replication is not clear, gp1 is reported to exhibit multiple characteristics, including RNA binding, cell membrane localization, and self-association. To investigate these characteristics, we undertook the isolation of a series of missense mutants of gene 1 bearing substitutions at various regions. During cloning of gene 1, we found that its expression severely inhibited the growth of its host Escherichia coli cells. In this study, we utilized this growth-inhibition phenomenon to screen a random library muta-genized by error-prone PCR, expecting that mutants which could not inhibit cell growth would be affected in the authentic functions of gp1. Using this approach, we obtained 31 different mutants bearing single amino acid substitutions at 26 positions along the entire length of gp1. As a preliminary analysis of these mutants, we compared the deduced amino acid sequences of gp1s from psi29 and its related phages PZA, B103 and M2. Alignment of these sequences revealed three conserved regions, i.e. a hydrophobic region near the carboxyl terminus (assumed to be involved in the membrane localization and self-association of gp1), coiled-coil motif (essential for self-association), and a region of unknown function near the amino terminus. Interestingly, many of the substitutions in the isolated mutants occurred at strongly conserved residues in these regions and affected characteristic features of the regions (e.g. hydrophobicity of the hydrophobic region). These substitutions are expected to affect authentic functions of gp1, and the mutants will be useful for studies of the structure and functions of gp1.