A Novel Cell Death Gene Acts to Repair Patterning Defects in Drosophila melanogaster

Cell death is a mechanism utilized by organisms to eliminate excess cells during development. Here, we describe a novel regulator of caspase-independent cell death, Mabiki (Mabi), that is involved in the repair of the head patterning defects caused by extra copies of bicoid in Drosophila melanogaster. Mabiki functions together with caspase-dependent cell death mechanisms to provide robustness during development.     

The Integration Machinery of ZAM, a Retroelement from Drosophila melanogaster, Acts as a Sequence-Specific Endonuclease

Retroviruses and retrotransposons insert into the host genome with no obvious sequence specificity. We examined the target sites of the retroelement ZAM by sequencing each host-ZAM junction in the genome of Drosophila melanogaster. Our overall data provide compelling evidence that ZAM integration machinery recognizes and leads to ZAM insertion into the sequence 5'-GCGCGCg-3'. This unique property of ZAM will facilitate the development of new tools to study the integration process of retroelements.     

FAK Acts as a Suppressor of RTK-MAP Kinase Signalling in Drosophila melanogaster Epithelia and Human Cancer Cells

Receptor Tyrosine Kinases (RTKs) and Focal Adhesion Kinase (FAK) regulate multiple signalling pathways, including mitogen-activated protein (MAP) kinase pathway. FAK interacts with several RTKs but little is known about how FAK regulates their downstream signalling. Here we investigated how FAK regulates signalling resulting from the overexpression of the RTKs RET and EGFR. FAK suppressed RTKs signalling in Drosophila melanogaster epithelia by impairing MAPK pathway. This regulation was also observed in MDA-MB-231 human breast cancer cells, suggesting it is a conserved phenomenon in humans. Mechanistically, FAK reduced receptor recycling into the plasma membrane, which resulted in lower MAPK activation. Conversely, increasing the membrane pool of the receptor increased MAPK pathway signalling. FAK is widely considered as a therapeutic target in cancer biology; however, it also has tumour suppressor properties in some contexts. Therefore, the FAK-mediated negative regulation of RTK/MAPK signalling described here may have potential implications in the designing of therapy strategies for RTK-driven tumours.     

The trithorax Group Gene moira Encodes a Brahma-Associated Putative Chromatin-Remodeling Factor in Drosophila melanogaster

The genes of the trithorax group (trxG) in Drosophila melanogaster are required to maintain the pattern of homeotic gene expression that is established early in embryogenesis by the transient expression of the segmentation genes. The precise role of each of the diverse trxG members and the functional relationships among them are not well understood. Here, we report on the isolation of the trxG gene moira (mor) and its molecular characterization. mor encodes a fruit fly homolog of the human and yeast chromatin-remodeling factors BAF170, BAF155, and SWI3. mor is widely expressed throughout development, and its 170-kDa protein product is present in many embryonic tissues. In vitro, MOR can bind to itself and it interacts with Brahma (BRM), an SWI2-SNF2 homolog, with which it is associated in embryonic nuclear extracts. The leucine zipper motif of MOR is likely to participate in self-oligomerization; the equally conserved SANT domain, for which no function is known, may be required for optimal binding to BRM. MOR thus joins BRM and Snf5-related 1 (SNR1), two known Drosophila SWI-SNF subunits that act as positive regulators of the homeotic genes. These observations provide a molecular explanation for the phenotypic and genetic relationships among several of the trxG genes by suggesting that they encode evolutionarily conserved components of a chromatin-remodeling complex.     

The recent spread of a vertically transmitted virus through populations of Drosophila melanogaster

The sigma virus is a vertically transmitted pathogen that commonly infects natural populations of Drosophila melanogaster. This virus is the only known host-specific pathogen of D. melanogaster, and so offers a unique opportunity to study the genetics of Drosophila-viral interactions in a natural system. To elucidate the population genetic processes that operate in sigma virus populations, we collected D. melanogaster from 10 populations across three continents. We found that the sigma virus had a prevalence of 0-15% in these populations. Compared to other RNA viruses, we found that levels of viral genetic diversity are very low across Europe and North America. Based on laboratory measurements of the viral substitution rate, we estimate that most European and North American viral isolates shared a common ancestor approximately 200 years ago. We suggest two explanations for this: the first is that D. melanogaster has recently acquired the sigma virus; the second is that a single viral type has recently swept through D. melanogaster populations. Furthermore, in contrast to Drosophila populations, we find that the sigma viral populations are highly structured. This is surprising for a vertically transmitted pathogen that has a similar migration rate to its host. We suggest that the low structure in the viral populations can be explained by the smaller effective population size of the virus.     

Sodium Selenite Acts as an Otoprotectant against Neomycin-Induced Hair Cell Damage in a Zebrafish Model

Sodium selenite is a trace element essential for many physiological functions in the body. It is involved in various biological processes; it acts as a cofactor for antioxidant enzymes that protect against free radicals and is reported to limit metal-mediated oxidative DNA damage. In the present study, we investigated the effect of sodium selenite on neomycin ototoxicity in wild-type and transgenic zebrafish (Brn3C: EGFP). Five or six days post-fertilization, zebrafish larvae were co-exposed to 125 μM neomycin and various concentrations (10 μM, 100 μM, 250 μM, and 500 μM) of sodium selenite for 1 h. Hair cells within neuromasts of the supraorbital (SO1 and SO2), otic (O1), and occipital (OC1) lateral lines were analyzed by fluorescence microscopy (n = 10 fish per treatment). Hair cell survival was estimated as the ratio of the hair cell numbers in each group compared to those of the control group that were not exposed to neomycin. Apoptosis and hair cell damage of neuromasts were evaluated using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) assay and 2-[4-(dimethylamino) styryl]-N-ethylpyridinium iodide (DASPEI) assay, respectively. Ultrastructural changes were evaluated using scanning electron microscopy and transmission electron microscopy. Neuromast hair cells were preserved in zebrafish exposed to 125 μM neomycin and 500 μM sodium selenite for 1 h. Sodium selenite protected against neomycin-induced hair cell loss of neuromasts, reduced apoptosis, and prevented zebrafish ultrastructural changes. We propose that sodium selenite protects against neomycin-induced hair cell damage by inhibiting apoptosis, decreasing the disarray of stereocilia, and preventing ultrastructural changes in the neuromast hair cells of the zebrafish.     

Minos as a genetic and genomic tool in Drosophila melanogaster

Much of the information about the function of D. melanogaster genes has come from P-element mutagenesis. The major drawback of the P element, however, is its strong bias for insertion into some genes (hotspots) and against insertion into others (coldspots). Within genes, 5′-UTRs are preferential targets. For the successful completion of the Drosophila Genome Disruption Project, the use of transposon vectors other than P will be necessary. We examined here the suitability of the Minos element from Drosophila hydei as a tool for Drosophila genomics. Previous work has shown that Minos, a member of the Tc1/mariner family of transposable elements, is active in diverse organisms and cultured cells; it produces stable integrants in the germ line of several insect species, in the mouse, and in human cells. We generated and analyzed 96 Minos integrations into the Drosophila genome and devised an efficient “jump-starting” scheme for production of single insertions. The ratio of insertions into genes vs. intergenic DNA is consistent with a random distribution. Within genes, there is a statistically significant preference for insertion into introns rather than into exons. About 30% of all insertions were in introns and ~55% of insertions were into or next to genes that have so far not been hit by the P element. The insertion sites exhibit, in contrast to other transposons, little sequence requirement beyond the TA dinucleotide insertion target. We further demonstrate that induced remobilization of Minos insertions can delete nearby sequences. Our results suggest that Minos is a useful tool complementing the P element for insertional mutagenesis and genomic analysis in Drosophila.