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Originally published as Genetics Published Articles Ahead of Print on July 18, 2006.
Genetics, Vol. 174, 309-316, September 2006, Copyright © 2006
doi:10.1534/genetics.106.061499
Effects of Sex and Insulin/Insulin-Like Growth Factor-1 Signaling on Performance in an Associative Learning Paradigm in Caenorhabditis elegans
Tibor Vellai*,1,
Diana McCulloch
,
David Gems and
Attila L. Kovács
* Department of Genetics and Department of Anatomy, Cell and Developmental Biology, Eötvös Loránd University, Budapest, H-1117, Hungary and Centre for Research on Ageing, Department of Biology, University College, London, WCIE 6BT, United Kingdom
1 Corresponding author: Department of Genetics, Eötvös Loránd University, Pázmány Péter sétány 1/C, Budapest, H-1117, Hungary.
E-mail: vellai{at}falco.elte.hu
Learning is an adaptive change in behavior in response to environmental stimuli. In mammals, there is a distinct female bias to learn skills that is still unprecedented in other animal taxa. Here we have investigated the biological determinants of performance in an associative learning paradigm in the nematode Caenorhabditis elegans. Using an assay of chemotactic reactions associated with food deprivation, wild-type male worms show inferior learning ability relative to hermaphrodites. Sex-based learning difference is therefore an ancient evolutionary feature appearing even in relatively simple animals. C. elegans mutants with reduced insulin/IGF-1 signaling also exhibit a greatly reduced learning ability in this assay. In addition, hyperactivation of insulin/IGF-1 signaling through loss-of-function mutations in the PTEN phosphatase daf-18, a negative regulator of insulin/IGF-1 signaling, enhances learning ability beyond that of wild type. According to our epistasis analysis, the effect of DAF-2 on learning acts via phosphatidylinositol 3,4,5-trisphosphate (PIP3) production, but not the DAF-16 FOXO transcription factor. This implies that the signaling pathway from DAF-2 affecting this learning paradigm branches between PIP3 production and DAF-16. However, learning capacity of nematodes is lowered by loss-of-function mutations in daf-16, suggesting involvement of noninsulin/IGF-1 signaling-dependent DAF-16 activation in learning. Potentially, sex and insulin/IGF-1 signaling affect performance in this learning assay via effects on the neurobiology of learning.
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