Project description:We analyzed Origin Recognition Complex Subunit 2 (ORC2) ChIP-seq from hand-dissected fat body tissue from 68hr (after egg laying, AEL), 92hr AEL, and late-third wandering Drosophila melanogaster larvae. Fat body was dissected from wild-type (OrR) males and testes were removed. We examined ORC2 binding genome-wide with particular focus on the underreplicated regions in the fat body.
Project description:We performed mRNA-seq from hand-dissected fat body tissue from 68hr (after egg laying, AEL) and 92hr AEL Drosophila melanogaster larvae. Fat body was dissected from wild-type (OrR) males and testes were removed. We examined gene expression genome-wide with particular focus on genes in the underreplicated regions in the fat body.
Project description:In Drosophila, the humoral response characterised by the synthesis of antimicrobial peptides (AMPs) in the fat body (the equivalent of the mammalian liver) and the cellular response mediated by haemocytes (blood cells) engaged in phagocytosis represent two major reactions that counter pathogens. Although considerable analysis has permitted the elucidation of mechanisms pertaining to the two responses individually, the mechanism of their coordination has been unclear. To characterise the signals with which infection might be communicated between blood cells and fat body, we ablated circulating haemocytes and defined the parameters of AMP gene activation in larvae. We found that targeted ablation of blood cells influenced the levels of AMP gene expression in the fat body following both septic injury and oral infection. Expression of the AMP gene drosomycin (a Toll target) was blocked when expression of the Toll ligand Spätzle was knocked down in haemocytes. These results show that in larvae, integration of the two responses in a systemic reaction depend on the production of a cytokine (spz), a process that strongly parallels the mammalian immune response.
Project description:In Drosophila, the fat body undergoes a massive burst of autophagy at the end of larval development in preparation for the pupal transition. To identify genes involved in this process, we carried out a microarray analysis. We found that mRNA levels of the homologs of Atg8, the coat protein of early autophagic structures, and lysosomal hydrolases were upregulated, consistent with previous results. Genes encoding mitochondrial proteins and many chaperones were downregulated, including the inhibitor of eIF2alpha kinases and the peptidyl-prolyl cis-trans isomerase FK506-binding protein of 39 kDa (FKBP39). Genetic manipulation of FKBP39 expression had a significant effect on autophagy, potentially through modulation of the transcription factor Foxo. Accordingly, we found that Foxo mutants cannot properly undergo autophagy in response to starvation, and that overexpression of Foxo induces autophagy.
Project description:The alcohol dehydrogenase (Adh) gene in the Hawaiian species of fruit fly, Drosophila affinidisjuncta, like the Adh genes from all Drosophila species analyzed, is expressed at high levels in the larval fat body via a larval-specific promoter. To identify the cis-acting elements involved in this highly conserved aspect of Adh gene expression, deleted D. affinidisjuncta genes were introduced into D. melanogaster by somatic transformation. Unlike previously described methods, this transformation system allows analysis of Adh gene expression specifically in the larval fat body. The arrangement of sequences influencing expression of the proximal promoter of this gene in the larval fat body differs markedly from that described for the Adh gene from the distant relative, D. melanogaster. Multiple redundant elements dispersed 5' and 3' to the gene, only some of which map to regions carrying evolutionarily conserved sequences, affect expression in the fat body. D. affinidisjuncta employs a novel mode of Adh gene regulation in which the proximal promoter is influenced by sequences having roles in expression of the distal promoter. This gene is also unique in that far upstream sequences can compensate for loss of sequences within 200 bp of the proximal RNA start site. Furthermore, expression is influenced in an unusual, context-dependent manner by a naturally-occurring 3' duplication of the proximal promoter--a feature found only in Hawaiian species.
Project description:Spectrin cytoskeleton defects produce a host of phenotypes affecting the plasma membrane, cell polarity, and secretory membrane traffic. However, many of the underlying molecular mechanisms remain unexplained by prevailing models. Here we used the larval fat body of Drosophila melanogaster as a genetic model system to further elucidate mechanisms of ??-spectrin function. The results provide unexpected new insights into spectrin function as well as mechanisms of dietary fat uptake and storage. We show that loss of ?- or ?-spectrin in the fat body eliminated a population of small cortical lipid droplets and altered plasma membrane architecture, but did not affect viability of the organism. We present a novel model in which ??-spectrin directly couples lipid uptake at the plasma membrane to lipid droplet growth in the cytoplasm. In contrast, strong overexpression of ?-spectrin caused fat body atrophy and larval lethality. Overexpression of ?-spectrin also perturbed transport of dietary fat from the midgut to the fat body. This hypermorphic phenotype appears to be the result of blocking secretion of the lipid carrier lipophorin from fat cells. However, this midgut phenotype was never seen with spectrin loss of function, suggesting that spectrin is not normally required for lipophorin secretion or function. The ?-spectrin hypermorphic phenotype was ameliorated by co-overexpression of ?-spectrin. Based on the overexpression results here, we propose that ?-spectrin family members may be prone to hypermorphic effects (including effects on secretion) if their activity is not properly regulated.
