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The annual killifish, Austrofundulus limnaeus, may enter embryonic diapause at three distinct points of development, termed diapause I, II, and III. Previous studies suggest a role for steroid hormones in the regulation of diapause in annual killifish. This study concerns the hormonal and genomic components involved in the developmental decision to enter or escape diapause II from both a maternal and embryonic perspective. Steroid hormone levels were measured in tissues isolated from adult female fish that were producing either high or low proportions of escape embryos. Levels of steroid hormones were also measured in new fertilized embryos that were known to be on either an escape or diapausing developmental trajectory. In addition, cDNA microarray gene expression analysis was used to identify gene sequences that may be associated with the regulation of entry into diapause in this species. Decreases in maternal estrogen levels associated with aging are correlated with decreasing escape embryo production, but there is no direct association between measured steroid hormone levels and escape embryo production. However, maternal production of escape embryos is correlated with increased ratios of 17 ß-estradiol to testosterone in ovary tissue, and cDNA microarray gene expression analysis indicates differentially regulated sequences associated with escape embryo production in maternal tissues. Both of these independent measures suggest hormonal involvement in the regulation of diapause. Embryonic levels of steroid hormones in newly fertilized embryos are not correlated with entry or escape from diapause II, although incubation in exogenous cortisol and 17 ß-estradiol causes an increase in the proportion of escape embryos. Gene expression analysis again suggests hormonal involvement. Interestingly, genes involved in epigenetic control of gene expression though chromatin condensation are differentially regulated in both maternal tissues producing escape embryos, and in embryos on the different developmental trajectories. These data suggest that hormonal control of gene expression through alterations of chromatin condensation may regulate the decision to enter or escape diapause II.

Thesis (Ph. D.)--York University, 2001. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 102-132). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ66369.

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Diapause embryos of the animal extremophile Artemia franciscana, a crustacean, are metabolically dormant and exceptionally tolerant to stressors such as heat and anoxia, characteristics thought to depend on the protective activity of molecular chaperones. RNAi methodology was developed and used to knock down individual molecular chaperones which are normally up-regulated during Artemia diapause. DsRNA and siRNAs injected into females were effective in knocking down proteins in embryos into the fifth release. Five proteins were knocked down including the ?-crystallin related small heat shock proteins (sHsps) p26, ArHsp21 and ArHsp22, artemin, a species-specific chaperone as well as p8 a transcription co-factor. The individual sHsps, artemin and p8 exhibited different roles during cyst development and diapause with only some of these proteins contributing to stress tolerance. p26, for example, enhances stress resistance in Artemia embryos, facilitates embryo development and prevents diapause termination indicated by spontaneous hatching. ArHsp21, another ?-crystallin type small heat shock protein contributes only slightly to freezing and desiccation stress and is not protective during heat stress. DsRNA specific to ArHsp22 is lethal to both male and female adults. Artemin contributes to stress tolerance but to a lesser extent than p26. Artemin also extended the period of time over which cysts were released. Cysts that did not contain p8 were also less stress resistant than those that did contain p8 and hatched upon release 10% for the time, suggesting an important role in diapause. By revealing separate and novel roles for molecular chaperones this work contributes substantially to our understanding of diapause, an important, phylogenetically widespread developmental process.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). "November 2008." Includes bibliographical references (p. 167-182). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 74-86).