Characterization of the cell morphology differences between pre‐diapause and diapause embryos of the killifish Austrofundulus limnaeus

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Austrofundulus limnaeus is a freshwater annual killifish from Venezuela that produces embryos capable of entering three distinct stages of diapause. Diapause II is a state of developmental arrest that can last over 100 days and confers extreme anoxia tolerance. Diapause I and III are inducible while II is obligate. Diapause II occurs in ideal conditions (25oC) whereas incubation at 30oC induces a bypass of diapause II. Diapause II provides an opportunity to study an arrest of development in a vertebrate animal without exposing the organism to compounding stresses. Currently, little is known about the molecular mechanisms that induce and maintain this developmentally arrested state. We hypothesize that down regulation of gene expression is central to inducing diapause II. Our aim is to use assays that are principally based upon immunohistochemistry to characterize at the cellular level differences in cell morphology between pre‐DII and DII embryos. We are looking at changes in chromatin modifications, which are known to be involved in the repression or activation of developmental genes, as well as changes in mitotic cell division. Preliminary results show a change in the signal of H3K27 chromatin modifiers as the animal transitions between stages of pre‐DII and DII. This research is leading to a greater molecular understanding of the remarkable phenomenon of obligate developmental arrest in a vertebrate embryo.