First Advisor

Jason Podrabsky

Date of Publication

Spring 8-31-2016

Document Type


Degree Name

Master of Science (M.S.) in Biology






Somatomedin, Killifishes -- Embryology, Fishes -- Embryology, Diapause



Physical Description

1 online resource (xi, 124 pages)


Development in the annual killifish Austrofundulus limnaeus can follow two distinct developmental trajectories. Typical development includes the entrance of embryos into a state of metabolic and developmental arrest termed diapause. Alternately, embryos can escape diapause and develop directly without pause. These two trajectories are characterized by differences in the rate and timing of developmental, morphological, and physiological traits. Insulin and Insulin-like growth factor (IGF) signaling (IIS) is known to regulate entrance into diapause in a variety of invertebrates. In this thesis I explore the possible role of IGFs in the regulation of development and diapause in embryos of A. limnaeus. Here I report stage-specific expression of IGF-I and II proteins and their associated mRNA transcripts. Patterns of IGF-I protein expression are consistent with IGF signaling playing a major role in supporting the escape trajectory. In addition, treatment of embryos with a potent inhibitor of the IGF-I receptor (IGF1R) mimics the diapause developmental pattern even under conditions that should favor direct development. Evaluation of mRNA gene expression patterns in the two developmental trajectories suggests a role for IGF-I signaling through the RAS-MAPK-ERK pathway, which may be promoting the escape phenotype. Additionally, IGF-I activity may be enhanced in escape trajectory embryos though upregulation of IGF binding protein 2 (IGFBP-2) mRNA. These data suggest a major role for IGF signaling in the promotion of the escape trajectory, and thus we predict that specific mechanisms are in place in diapause-bound embryos that block IGF signaling and thus promote entrance into diapause. The data presented here suggest that blocking IGF signaling is critical for induction of diapause, but also suggests that other signaling pathways are likely also at play. Other pathways such at the TGF-beta signaling molecules and SMAD pathway, may also be involved in the direct regulation of the diapause phenotype, as has been shown for other animal models of developmental arrest.


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