Fibroblast Growth Factor Receptor Function in Muscle Stem Cells

Hackett, Tashi

Undergraduate Honors Thesis

Fibroblast Growth Factor Receptor Function in Muscle Stem Cells Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/jw827c11f

Abstract

Skeletal muscle has a remarkable ability to regenerate itself following injury and this is reliant upon a group of stem cells known as muscle stem cells Muscle stem cell dysfunction contributes to variety of muscle wasting diseases and insights into mechanisms that regulate MuSC function could lead to new therapies and further our understanding of stem cell biology in general. Fibroblast Growth Factor 2 (FGF2) is a protein that regulates muscle stem cell behavior through stimulation of cell surface tyrosine receptor kinases known as Fibroblast Growth Factor Receptors (Jones, 2001). Activation of the receptors by FGF will induce intracellular signaling pathways that control cell behaviors including activation, replication, differentiation and self-renewal. There are four Fibroblast Growth Factor Receptors (FGFR1, FGFR2, FGFR3 and FGFR4) and the role each of these individual receptors has in regulating muscle stem cell behavior is currently unclear. Receptor 1 and receptor 4 are highly expressed in muscle stem cells, while receptor 3 expression is weak and receptor 2 expression cannot be detected. Ablation of any single receptor has only a slight impact as compared to pharmacological inhibition targeting all four receptors, which significantly alters muscle stem cell behavior, thus suggesting that the receptors act in a complementary manner. My main goal in this thesis work is to genetically delete the Fibroblast Growth Factor Receptors individually and in combination to investigate their role in regulating satellite cell behavior. To knockout receptor expression I used both a CRISPR-Cas9 methodology and a Cre-Floxed approach. In both cases, I was able to achieve low-level knock down of receptors 1, 2, and 3, verified by RT-PCR and immunofluorescence. FGF receptor 1 and 3 double mutant muscle stem cells were slightly impaired compared to wild type controls. Overall however, my inability to entirely delete these receptors using well-established methods was unexpected. The deletion of FGF receptors and additional receptor complex proteins in turn proves to be much more problematic compared to other proteins possibly suggesting that these genes required for FGF signaling are vital to cell function and thus protected from modification.

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