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Poster Full Abstracts - Physiology and Aging
Poster board number is above title. The first author is the presenter
325
energy demands as the animal progresses through each stage in the life cycle. At the onset of metamorphosis, for example, the growing larva ceases feeding
and enters a period of developmentally-programmed starvation until adult eclosion. The nuclear receptor dHNF4 is a critical regulator of energy homeostasis
during starvation in larvae, where it is required to activate a transcriptional program for the catabolism of stored fat (triacylglycerol). In addition, under
standard growth conditions, dHNF4 mutants display lethality just prior to, or immediately following, eclosion from the pupal case. This suggests that dHNF4
may also play a vital role in energy homeostasis during metamorphosis and possibly adulthood. Consistent with this, dHNF4 mutants display significantly
reduced amounts of glycogen (stored sugar) and trehalose (circulating sugar) during late pupal stages. Surprisingly however, they maintain relatively normal
levels of triacylglycerol, in contrast to what is seen in starved dHNF4 mutant larvae. Interestingly, decreasing the amount of dietary sugar, either during
development (larval diet) or adulthood, dramatically suppresses the lethality of dHNF4 mutants. Metabolite measurements are currently being performed
using these different dietary conditions. Our findings suggest a critical role for dHNF4 in the regulation of carbohydrate metabolism during both
metamorphosis and adulthood.
724A
The Let-7 microRNA Complex Extends Longevity and Alters Fat Metabolism in
Drosophila Melanogaster
.
Christi Gendron, Scott Pletcher. Molecular
and Integrative Physiology, University of Michigan, Ann Arbor, MI.
Objective: Given the wide range of physiological processes that microRNAs (miRNAs) are involved in, we hypothesized that specific miRNAs will
influence organismal longevity and fat metabolism. An initial screen for miRNAs that influence
Drosophila
longevity identified the let-7-complex
(containing let-7, miR-100, and miR-125 miRNAs) as candidates. Therefore, our goal was two-fold: (1) to confirm if the let-7-complex influences both
organismal longevity and fat metabolism and (2) to identify which component within the let-7-complex was responsible for the observed changes. Methods:
Mated female flies were maintained on standard sugar/yeast food with 12:12 light/dark cycle and constant humidity for longevity experiments. Fly
triglyceride (TAG) and protein levels were measured using the Infinity TAG assay or the Pierce BCA Protein assay, respectively, according to the
manufacturer’s instructions. Starvation assays were performed with young female flies kept on agar-only media. Results: Let-7-complex over-expression
resulted in a significant increase in lifespan over control flies. This effect is likely due to miR-100, because over-expression of let-7 or miR-125 individually
did not extend lifespan. Whole body let-7-complex over-expression led to increased TAG stores in female flies, with little effect in males. Increased female
TAG stores were also observed with let-7 over-expression alone. Conversely, let-7 deletion leads to thinner flies. Let-7-complex over-expression does not
provide additional starvation resistance, suggesting that there are alterations in the ability of these flies to mobilize fat stores. Conclusions: We identified the
let-7-complex, and likely miR-100, as having the ability to extend fly longevity. Surprisingly, this was not due to miR-125 overexpression, which has been
shown to increase longevity in
C. elegans
. Furthermore, over-expression of the let-7-complex, and let-7 itself, alters female fat levels and mobilization.
Work is ongoing to identify the mechanisms behind these observations.
725B
Biosynthesis and regulation of
Drosophila
molybdoenzymes.
Marina L Georgiou
1
, Zvonimir Marelja
2
, Silke Leimkühler
2
, Fanis Missirlis
1
. 1) School of
Biological and Chemical Sciences, Queen Mary, University of London, London, UK; 2) Institute of Biochemistry and Biology, University of Potsdam,
Potsdam, Germany.
The
rosy
,
maroon
,
maroon-like
and
cinnamon
fly mutants were named after a characteristic brownish eye color phenotype. The studies of Art Chovnick,
Victoria Finnerty and their co-workers showed that rosy represents the structural gene of xanthine dehydrogenase (XDH) and that the gene products of
cinnamon
and
maroon-like
are involved in the maturation of XDH. XDH is an enzyme composed of two identical and independent subunits, binding one
molybdenum cofactor (Moco), two non-identical iron sulfur (FeS) clusters and a flavin adenine dinucleotide. As a continuation of the studies of rosy
maturation, we screened for genes that play a role in Moco and FeS cluster biosynthesis by analyzing the activities of the
Drosophila
molybdoenzymes
XDH, aldehyde oxidase and sulfite oxidase following RNA interference of various candidate genes that are suggested by sequence homologies to play a role
in Moco and FeS cluster biosnythesis. Furthermore, we are interested in the
maroon
locus that was isolated by Calvin Bridges in 1912. Our preliminary
experiments suggest that
maroon
differentially regulates molybdoenzyme activities and we are using the genome sequence in an effort to map the original
mutation. Finally, although a single aldehyde oxidase activity is revealed following native protein gel separations, four aldehyde oxidase homologues are
present in the
Drosophila
genome and show distinct developmental expression patterns. We wish to uncover their respective functions.
726C
Identification of metabolic phenotypes and mechanisms of metabolic regulation by TGF-β signaling in
Drosophila melanogaster
.
Arpan Ghosh,
Michael O'Connor. GCD, University of Minnesota, Minneapolis, MN.
The TGF-β superfamily is a highly conserved and frequently employed signaling pathway in the animal kingdom that regulates many developmental
events. Recent evidence indicates that TGF-β signaling is involved in regulating metabolism and homeostatic processes in vertebrates. However, the
mechanism(s) by which TGF-β signaling regulates metabolism remain unknown. We have found that loss of TGF-β-signaling components manifests a
number of metabolic defects in
Drosophila
. Loss of the TGF-β ligand
dawdle
(
daw
) causes larval lethality on standard cornmeal food. This phenotype can
be rescued by rearing the larvae on yeast food and, as substitution experiments show, is partly caused by sensitivity to propionic acid present in the cornmeal
food recipe. Loss of
daw
also leads to a unique sugar-dependent pupal lethality phenotype, causes a small drop in total TAG content, and affects total
glycogen content in the larvae. Notably, loss of
daw
causes a significant increase in circulating sugar (CS) concentration in both feeding and starving third
instar larvae. The phenotype is aggravated by simultaneous loss of
dAct
indicating that these related ligands function redundantly. While
daw
mutants do not
show significant change in
dIlp
(
2,3&5
) expression, IHC experiments show that
daw
larvae are defective in secretion of the dIlp2 peptide from the IPCs. The
diabetic phenotype is also observed in feeding
smox
and
babo
larvae. However, unlike
daw
, starvation suppresses the phenotype in
smox
and
babo
mutants
indicating an alternate role of the pathway in positively regulating CS levels during starvation. Consistently we observe that loss of
smox
(RNAi clones) in
fatbody cells leads to loss of dFOXO nuclear localization upon starvation. Since FOXO is known to be involved in nutrient mobilization during starvation
we believe that loss of dFOXO translocation in
smox
mutants impairs release of stored sugar and counteracts the diabetic phenotype caused by loss of
daw
.
Current work is focused on defining the mechanisms by which TGF-β signaling regulates CS levels in both feeding and starving conditions.