Date Thesis Awarded

4-2015

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Shantá D. Hinton

Committee Member

Diane C. Shakes

Committee Member

Beverly T. Sher

Committee Member

Jonathan Mott

Abstract

MK-STYX [MAPK (mitogen activated protein kinase) phosphoserine/threonine/tyrosine binding protein] is a pseudophosphatase member of the MAPK phosphatase family. Though structurally related to the MAPK phosphatases, MK-STYX lacks the nucleophilic cysteine and histidine residues essential for catalysis. Despite its lack of catalytic activity, MK-STYX maintains its ability to bind to phosphorylated proteins, but not dephosphorylating them. This thesis focuses on further characterizing the role of MK-STYX in PC12 neuronal differentiation. The PC12 cell line is widely used as a model to study neuronal differentiation. Our previous data demonstrated that MK-STYX induces neuronal differentiation in PC12 cells. The results presented here also show that MK-STYX induces neuronal differentiation in PC12 cells. We further investigated whether MK-STYX induced a unique branching pattern in PC12 cells when they differentiate. In the presence and absence of nerve growth factor (NGF), both primary and secondary neurite distributions are changed, suggesting that MK-STYX changes neurite branching patterns. To investigate what caused this pattern, we turned to the cytoskeleton. Actin polymerization drives the protrusion of lamellipodia and filopodia in growth cones, while tubulin is responsible for making up the ‘core’ of a developing neurite. In the presence of NGF, PC12 cells overexpressing MK-STYX caused an increase in actin protrusions commonly associated with growth cones, dendritic spines, and future dendritic branches. In addition, MK-STYX induced neurites exhibit presynaptic and post-synaptic qualities, as shown through immunostaining with anti-Tau and MAP2 antibodies, respectively. Cofilin, an actin binding and severing protein, has been shown to play a role in regulating neurite outgrowth and branching. MK-STYX further regulates actin dynamics, and thus branching through a possible temporal regulation of cofilin phosphorylation and dephosphorylation. A transient decrease in cofilin phosphorylation at 72 hours of NGF stimulation allows MK-STYX-induced neurites to branch. This strongly supports a model in which the pseudophosphatase MK-STYX has a critical role as a regulator in PC12 neuronal differentiation and morphology.

Available for download on Friday, May 11, 2018

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