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Translational regulation plays an important role in gene expression. In this work, I focus on Nanos (Nos), a conserved RNA-binding protein that acts as a translational repressor to control a number of biological processes. In Chapter 1, I summarize current knowledge about the mechanism of action of Nos and briefly discuss the known regulatory targets of Nos. By utilizing Upf1-Nos chimera protein, I aimed to identify mRNA regulatory targets of Nos. As described in Chapter 2, I show that Nos potentially regulates approximately 32% of the transcriptome in the early embryo. I demonstrate that the majority of Upf1-Nos depleted mRNAs are likely regulated by the cooperative action of Nos and Pumilio (Pum) in Chapter 2. I identify molecular mechanisms for recognition of this diverse population of mRNAs in Chapter 3. In Chapter 4, I describe evidence suggesting that Bruno may be a novel partner that mediates a minor fraction of Nos activity in vivo. This work dramatically expands the list of potential Nos regulatory targets, from the previous number of 11 to 2554.

We investigated the natural variation in silk composition and mechanical performance within and among individual spiders of Argiope trifasciataat multiple spatial and temporal scales. Major ampullate spider silk consists of two proteins (known as MaSp1 and MaSp2) with different amino acid compositions and proposed microstructures. We assessed the reliability and precision of the Waters AccQ-Tag[TM] amino acid analysis kit for spider silk. Variation in chemical composition was not detectable within silk spun by a spider on a single day. However, we found that variation within a single spider's silk across days could be greater than variation among individuals. We showed that major ampullate silk of a single species of orb spiders varies in chemical composition among individuals, but is in general homogeneous among individuals of the same population. Most of the variation in silk composition in our investigation resulted from a small number of outliers (three out of sixteen individuals) with a recent history of stress. Based on reported sequences for MaSp genes, we developed a model showing the covariation of the most abundant amino acids in major ampullate silk. The model supports that the silk composition is mostly determined by relative abundance of MaSp1 and MaSp2. Finally, we showed that silk composition (proline content) strongly correlates with shrink capacity after supercontraction as well as their breaking strains. This suggests that spiders are able to change the relative expression rate of different MaSp genes to produce silk fibers with different mechanical properties.