Abstracts - Society for Developmental Biology

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specific targets for the Ub/26S proteasome pathway. We performed a genome-wide screen in X. tropicalis for targets of
REST, the RE-1 Silencing Transcription factor, which silences neuronal genes in neural progenitors and non-neuronal cells
to restrict expression to neurons and identified Fbxo16 ubiquitin ligase. We determined that as expected for a neuronal
gene regulated by REST, Fbxo16 is expressed in the differentiating neurons in the brain but excluded from the neural
progenitor zone. Loss of function analysis using morpholino knock-down and a dominant negative construct showed that
Fbxo16 modulates neuron formation by affecting the function of the proneural protein Neurogenin (Ngn). This is
complemented bygain-of-function analysis, which shows elevated neurogenesis with increased Fbxo16. We found that the
effect of Fbxo16 on neurogenesis is not through cell cycle regulation but a direct consequence of its ability to regulate
proteins required for neurogenesis. In fact, our half-life analysis showed that Fbxo16 stabilizes Ngn, which is a short-lived
protein. Our findings suggest that Fbxo16 functions to protect Ngn from degradation to allow its accumulation as neural
progenitors differentiate, ensuring the activation of its transcriptional targets.
Program/Abstract # 256
Increased levels of hydrogen peroxide induce a HIF-1-dependent remodeling of lipid metabolism in C. elegans
Xie, Meng; Roy, Richard, McGill University, Montreal, Canada
Cells have evolved numerous mechanisms to circumvent environmental stresses caused by the environment, many of which
are regulated by the AMP-activated kinase (AMPK). Unlike most organisms, C. elegans AMPK null mutants are viable,
but die prematurely in the “long-lived” dauer stage due to rapid exhaustion of triglyceride energy stores. Using agenomewide
RNAi approach we found that the disruption of genes that increase hydrogen peroxide levels enhance the survival of
AMPK mutants by altering both the abundance and the nature of the fatty acid content in the animal by increasing the HIF-
1-dependent expression of several key rate-liming enzymes involved in de novo fatty acid biosynthesis. Our data provide a
mechanistic foundation to explain how an optimal level of hydrogen peroxide can provide cellular benefit; a phenomenon
described as hormesis, by instructing cells to readjust their lipid biosynthetic capacity through downstream HIF-1
activation, as a means to correct cellular energy deficiencies.
Program/Abstract # 257
AMPK is essential to mediate survival during nutrient stress in C. elegans
Demoinet, Emilie; Mantovani, Julie; Roy, Richard, McGill University, Montreal, Canada
During periods of prolonged nutrient stress, many organisms undergo developmental or reproductive diapause, which are
reversible states of developmental dormancy. When growth conditions are suboptimal, Caenorhabditis elegans can arrest
its development and execute a diapause like state.The best characterized of these are the first larval stage (L1) and dauer
diapause. The C. elegans L1 arrest is a response to an insufficient level of nutrient to initiate postembryonic development;
whereby development is suspended and environmental stress resistance is increased without obvious morphological
modification. Wild type L1 hatchlings can normally survive up to 2 weeks in the absence of food under these conditions.
We have shown that the maximal survival in the L1 diapause requires aak-2, one of the 2 homologues of the alpha subunit
of AMP-activated protein kinase (AMPK). AMPK is a metabolic master switch that is activated in response to various
nutritional and stress signals. Its main function is to maintain cellular energy homeostasis by up-regulating pathways that
produce ATP; while down-regulating energy-consuming anabolic processes. We found that in absence of AMPK (aak-0),
larvae lose their capacity to fold proteins and aggregates accumulate in the L1 larvae, leading to their premature death after
5 days in the L1 diapause. Under normal conditions, this accumulation of misfolded protein activates a highly conserved
adaptative signaling cascade known as the unfolded protein response (UPR). Based on genetic and cellular biological data,
we find that AMPK regulates a new UPR like response involving novels effectors to ensure organism survival during
condition of energy stress.
Program/Abstract # 258
Regulation of Pax3 neural expression by the Wnt-Cdx pathway
Sanchez, Oraly; Coutaud, Baptiste; Samani, Taraneh; Tremblay, Isabelle; Souchkova, Ouliana; Pilon, Nicolas, UQAM,
Montreal, Canada
Members of the vertebrate Cdx family, Cdx1, Cdx2, and Cdx4 are key regulators of posterior embryo development. Cdx
genes are strongly expressed in the posterior neurectoderm at the time of induction of neuralcrest cells (NCC), but their
role in these processes is still poorly understood because of functional redundancy and overlapping expression patterns.
Here we report that Cdx proteins act downstream of canonical Wnt signal to control the expression of Pax3, a known Wntinduced
gene essential for NCC induction. Pax3 and Cdx genes are co-expressed in the posterior neurectoderm and Pax3
expression is reduced in Cdx1-null embryos. RT-PCR analyses in undifferentiated P19 cells and in NCC-derived N2a cells
indicate that Pax3 expression is induced by the Wnt-Cdx pathway. Co-transfection analyses, electrophoretic mobility shift