<p> Behavior in higher eukaryotes is a complex process which integrates signals in the environment, the genetic makeup of the organism, and connectivity in the nervous system to produce extremely diverse adaptations to the phenomenon of existence. Unraveling the subcellular components that contribute to behavioral output is important for both understanding how behavior occurs in an unperturbed state, as well as understanding how behavior changes when the underlying systems that generate it are altered. Of the numerous molecular species that make up a cell, the regulation of messenger RNAs (mRNAs), the coding template of all proteins, is of key importance to the proper maintenance and functioning of cells of the brain, and thus the synaptic signals and information integration which underlie behavior. RNA binding proteins, a class of regulatory molecules, associate with mRNAs and facilitate their maturation from pre-spliced nascent transcripts, their stabilization and degradation ensuring appropriate levels are maintained, as well as their translation and subcellular compartmentalization, which ensures that proteins are translated at the appropriate level and in the places where they are required to fulfill their cellular functions. Our laboratory identified polymorphisms in the gene coding for the CUGBP and ELAV-like Factor 6 (CELF6) RNA binding protein to be associated with Autism Spectrum Disorder risk in humans. ASD is a spectrum of disorders of early neurodevelopment which present with lowered sociability and communication skills as well as restricted patterns of interests. When expression of the <i>Celf6</i> gene was ablated in mice, we found that they exhibited reductions to early communication as well as altered aspects of their exploratory behavior. In this dissertation, I explore the communication changes in young mouse pups with loss of CELF6 protein and identify that despite being able to produce vocalization patterns similar to their wild-type littermates, they nevertheless exhibit reduced response to maternal separation. Despite a history of literature on other CELF family proteins, the functions of the CELF6 protein in the brain have not been previously described. I provide characterization of the mRNA binding targets of CELF6 in the brain, and show that they share common UGU-containing sequence motifs which has been noted for other CELF proteins, and that CELF6 binding occurs primarily in the 3' untranslated regions (3' UTR) of mRNA. I hypothesized that this mode of interaction would result in regulation of mRNA degradation or translation efficiency as 3' UTR regions are known for providing binding sites for numerous regulators of such processes. In order to answer this question, I cloned sequence elements from the 3' UTRs of target mRNAs into a massively parallel reporter assay which has enabled me to test the effect of CELF6 expression on hundreds of binding targets simultaneously. When expressed in vitro, I found that CELF6 induced reduction to reporter library levels but exhibited few effects on translation efficiency, and I was able to rescue effects to reporter abundance mutation of binding motifs. Intriguingly, like CELF6, CELF3, CELF4, and CELF5 were all able to produce the same effect. CELF5 and CELF6 both showed similar, intermediate repression of reporter library mRNAs, while CELF3 and CELF4 exerted the strongest levels of repression. The level of repression under these conditions was somewhat predicted by number of motifs present per element, however a large amount of the variance in reporter levels is still unexplained and a mechanism for CELF6's action is unknown. Nevertheless, the work I present in this dissertation shows that CELF6 and other members of its family are key regulators of mRNA abundance levels which has direct implications to downstream consequence in the cell. As several of CELF6 binding target mRNAs are known regulators of neuronal signaling and synaptic function, the information I present is crucial for future experimentation. This work well help lead us to understand how behavior is altered when this protein is absent, along the way uncovering important mechanistic steps connecting the molecular landscape of cells to the behavior of organisms.</p><p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10824444 |
| Date | 23 June 2018 |
| Creators | Rieger, Michael A. |
| Publisher | Washington University in St. Louis |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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