الفهرس 
Introduction & Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
Some sea urchins, including the purple sea urchin Strongylocentrotus purpuratus, have been successfully used in aquaculture. They are harvested for their gonads, which are considered a high value sea food product with a high value nutrient source and are commercialized in many areas of the world, where they are frequently sold with expensive prices. The slow growth and late reproduction of S. purpuratus are challenging to overcome when developing efficient aquaculture production techniques. The specific objectives of this study were to: (1) assess the effect of different substrates on growth as well as gene expression patterns of Forkhead Box class O (FoxO) , Target of Rapamycin (TOR) and insulin like peptides (ILPs) in early post-settlement juveniles of S. purpuratus, (2) test how pre-settlement nutrition affects post-settlement growth, mortality as well as expression of marker genes and (3) gain a detailed understanding of juvenile development in relation to nutrient signaling. To test these objectives, the following steps were performed. (i) Juveniles sea urchins were grown on different substrates (biofilm, food, biofilm + food, filtered artificial seawater, natural inducer). For measurements, juveniles were imaged on a Nikon Ti microscope and images were analyzed using ImageJ. RNA was extracted, cDNAs were reverse transcribed from RNA and qRT-PCR were assessed. (ii) Larvae from a competent cohort were separated into two groups: (a) starved for 5 days before induction and (b) fed food (Rhodomonas lens at 6000 cells/ml). Growth as well as mortality were assessed at different time points; 0, 2, 4, 8 and 14 days post-settlement, before gene expression levels were evaluated. (iii) Performing a series of morphological analysis using scanning electron microscopy, phalloidin stain as well as whole mount in situ hybridization. The obtained results verified that the expression levels of TOR and ILPs were too variable to detect consistent trends. Meanwhile, FoxO provides a useful molecular marker in early juveniles as its expression was strongly correlated with the juvenile growth. The data have also shown that pre-settlement starvation affected juvenile growth trajectories as well as insulin/insulin-like growth factor signaling (IIS). The majority of juvenile feeding features, including skeletons, soft tissue and muscle tissue, were fully developed only after 8 days of juvenile development, leaving an extensive period of nutritional stress. FoxO gene expression was localized in juvenile tube feet, potentially associated with sensory structures involved in nutrient signaling. The above findings provide preliminary insights into the mechanisms underlying post-settlement growth and metabolism in S. purpuratus. This information can be used to develop new biomarkers for juvenile health in sea urchin aquaculture. The results also shed new light on the perimetamorphic period of S. purpuratus, with respect to nutrient signaling and the potential stressful pre-feeding period of juvenile sea urchins.
Keywords: Aquaculture, Sea urchin, Strongylocentrotus purpuratus, Metamorphosis, Nutrient signaling, Development, Aristotle’s lantern.