In a recent lab journal club we discussed a paper from the lab of Seung Kim:

A genetic strategy to measure circulating Drosophila insulin reveals genes regulating insulin production and secretion. Park S, Alfa RW, Topper SM, Kim GE, Kockel L, Kim SK. (2014) PLoS Genetics, Aug 7;10(8):e1004555.

This paper described a new approach to measure circulating insulins in Drosophila. The authors generated transgenic flies that carry epitope-tagged versions of a drosophila insulin-like peptide (dILP). They then developed an efficient and high- throughput ELISA approach to measure levels of circulating dILP within the hemeolymph of these flies. Using this approach they defined new genes required for controlling dILP release (vs expression). They also showed that changes in circulating dILPs often are not reflected in altered mRNA or protein levels, and that dILP release from neurosecretory cells can be influenced by peripheral insulin signaling.

Measuring circulating dILPs in flies is not straightforward. Many papers have relied on indirect measures (such as dILP mRNA or protein in neurosecretory cells, or assays for downstream insulin/PI3K/FOXO signaling) to infer changes in circulating dILPs. We liked the paper because it provides a powerful new tool to actually measure hemolymph dILP levels. These flies and ELISA assays will help with future studies on the genetic and signaling mechanisms that control insulin function.

In a recent lab journal club, we discussed a recent paper from the Miguel-Aliaga lab:

Neuronal Control of Metabolism through Nutrient-Dependent Modulation of Tracheal Branching, 2014, Cell, 156, 69.

In this paper, the Miguel-Aliaga group show that nutrient rich conditions promote tracheal branching in the larval, especially the gut, whereas upon starvation this branching is reduced . This control of branching relies on both systemic insulin signaling and also local signaling to trachea via VIP- and insulin-secreting neurons, whose activity is regulated by dietary nutrients. Moreover, the starvation effects on branching could mimicked by genetically inhibiting the insulin/PI3K pathway in tracheal termini (we wondered whether cell-autonomous overexpression of insulin/PI3K signaling could also promote branching, especially in starved animals)

We really liked this paper: Another great example of how the simplicity and versatility of fly genetics can be used to unravel important cell-to-cell and tissue-to-tissue signaling mechanisms that govern whole animal physiology.

It’s been a while since I updated on our regular lab journal clubs (I’ll blame grants and paper writing). So here are a few of the papers we’ve discussed in recent weeks. Although they each tackle a different research question, they highlight the versatility of Drosophila genetics to uncover key mechanisms governing animal physiology – the power and simplicity of the Drosophila genetic toolkit, means that the only major limitations to discovery are our ideas. Each of these papers has some very clever ideas.

Muscle mitohormesis promotes longevity via systemic repression of insulin signaling. Owusu-Ansah E, Song W, Perrimon N. Cell. 2013 Oct 24;155(3):699-712.

A very nice paper showing how limited mitochondrial stress in adult Drosophila muscle can extend lifespan, in part by limiting systemic insulin signaling.

Cell-nonautonomous effects of dFOXO/DAF-16 in aging. Alic N, Tullet JM, Niccoli T, Broughton S, Hoddinott MP, Slack C, Gems D, Partridge L. Cell Rep. 2014 Feb 27;6(4):608-16.

A clever study delineating the differential non-autonmous requirements for FOXO on controlling lifespan and metabolism in adult flies

Sensing of amino acids in a dopaminergic circuitry promotes rejection of an incomplete diet in Drosophila. Bjordal M, Arquier N, Kniazeff J, Pin JP, Léopold P. Cell. 2014 Jan 30;156(3):510-21

A paper that elegantly combines genetics, behavioural measurements and neural imaging to identify a role for the AA-regulate kinase GCN2 in the neuronal and behavioral response to limitation of dietary amino acids

Changes in rRNA transcription influence proliferation and cell fate within a stem cell lineage. Zhang Q, Shalaby NA, Buszczak M. Science. 2014 Jan 17;343(6168):298-301

This paper adds to a growing literature that points to the importance of differential regulation of mRNA translation and protein synthesis in controlling the behaviour of stem cells. The importance of this paper is that it suggests that rRNA synthesis and Pol I function may be an important control point in the regulation of stem cell protein synthesis.

In our last lab journal club, we discussed the recent paper from Matt Piper (@piperlab) (along with the Ribeiro (@RibeiroLab), Partridge and Pletcher labs) in which they define a holidic diet for Drosophila research:

A holidic medium for Drosophila Melanogaster (2013) Nat Methods

Variations in fly food between different labs (and even within labs) can profoundly influence organismal phenotypes, particularly behavioural, lifespan and stress responses. So, this very nice, meticulous paper provides an important, defined set of dietary conditions upon which to carry out these type of experiments.

As larval growth researchers, we were particularly interested in the finding that on the holidic diet, larvae took several days longer to pupate than on a ‘normal’ yeast/sugar-based food. Moreover, this delayed development could be abrogated by adding a small amount of yeast extract to the holidic diet. So what is the magic yeast ingredient?  A gustatory cue? An olfactory cue?  – (given the recent paper from the Banerjee lab – coming up next on lab journal club – on how olfactory cues can influence physiological responses in larvae). Also Or83B (olfactory receptor) mutant larvae show a (modest) delay in development, which is more pronounced when they have to compete with wildtype flies to forage for food (from – Vosshall lab @pollyp1)

In a recent journal club, we discussed a paper from the Cagan lab: Transformed Drosophila cells evade diet-mediated insulin resistance through wingless signaling.

This paper continues with a theme from a previous lab journal club and describes how diet-induced changes in fly physiology can influence localized imaginal tissue growth caused by altered oncogene/tumor suppressor signaling pathways. Here, the Cagan lab show that rasv12/csk- clones  show little or no growth phenotype in flies fed their ‘standard’ lab diet, but on a high sugar diet, these clones show massive overgrowth and invasive behaviour. The authors go on to show that this high sugar-phenotype can be explained in part by elevated Wg signaling in the rsv12/csk- cells, which leads to increased expression of the fly insulin receptor (InR) and increased insulin/PI3K signaling. Given that InR is also a transcriptional target of FOXO, we wondered whether some of the phenotype in RasV12/csk- may be explained by interactions with PI3K-FOXO signaling.

We liked this paper, which like the previous PTEN paper, is built upon an interesting finding that diet can interact with genotype to influence tissue growth. These two papers in particular illustrate the utility and power of fly genetics to explore how the micro and macro–environment can influence tissue growth.

For our first journal club after the summer we picked an interesting paper from Hugo Stocker and co:

“Nutrient restriction enhances the proliferative potential of cells lacking the tumor suppressor PTEN in mitotic tissues”  published in elife.

The paper describes the interesting behaviour of pten mutant imaginal disc cells under different dietary protein (yeast) conditions. In rich food (high yeast) pten mutant cells overgrow compared to neighboring wild-type cells (which was already known). However, under nutrient-restricted conditions (low yeast) , the pten cells show massive overgrowth and a strong proliferative advantage versus their wildtype neighbours. This over-poliferation requires amino acid import and TOR signaling, but appears distinct from the cell competition and supercompetitor effects of factors such as Myc (e.g. see Moreno and Basler or De La Cova et al). Interestingly, under nutrient restrictive conditions the overgrowth of pten mutant cell clones in the eye disc triggered a systemic growth impairment  (other tissues such as the wing and fat body were smaller – although marginally so)

We liked this paper a lot. A few quick comments and thoughts that we tried to wrap our heads around:

– Do PTEN cells actively upregulate their AA or nutrient import under nutrient-deprivation conditions? It would be interesting (although difficult) to measure nutrient uptake in pten cells to see if they actively switch (upregulate) to ‘nutrient scavenging mode’ upon a switch to poor food, or whether their basal level of nutrient uptake is already high under rich food and just remains so when nutrients are scarce.

-what underlies the switch from hypertrophic growth (rich nutrients) to hyperplastic growth (poor nutrients) in pten cell clones? Is it simply due to increased cellular nutrient import? Or is there some ‘organ-level’ control of growth?

– What underlies the systemic growth impairment? Is it the case that the pten cells are very efficient at nutrient and growth factor ‘scavenging’ that growth in other tissues is reduced? The systemic growth impairment didn’t appear marked, so this ‘scavenging’ explanation may be right. Alternatively, is there some kind of signaling triggered by pten cells that induces a systemic endocrine response – similar to dilp8 release from damaged discs, which influences ecdysone release and whole body development (Colombani et al , Carelli et al)

– what about tsc1 mutant cells? they have overactive TOR signaling – would they phenocopy the pten cells with respect to growth in rich vs poor food? The editor/reviewer comments did suggest that the authors address this, and intriguingly, in their response, the authors indicated that the experiments were done but that the story was ‘rather complex’ – we look forward to hearing about this complex story.

Finally, we enjoyed reading the paper in elife, especially with the transparent reviewer comments and author responses. All journals should adopt this policy.