Maspardin's Effects on BMP Signaling Molecules

Document Type


Degree Name

Master of Science (MS)


Biological and Environmental Sciences

Date of Award

Spring 2014


The hereditary spastic paraplegias (HSPs) are a group of upper motor neuron disorders characterized by continuous degradation of efferent neurons in the corticospinal tract. Mast syndrome (SPG21) is an autosomal-recessive complicated form of HSP that originates from a mutation of the ACP33/maspardin gene.Bone Morphogenetic Proteins (BMPs) are multifunctional growth factors that, along with forming bone and cartilage, influence axonal synaptic growth and function. Upon activation by BMP ligand, type II BMP receptors phosphorylate type I receptors - activating intracellular signaling molecules Smad 1, 5 and 8. These bind Smad 4 and the Smad complex enters the cell nucleus to drive gene transcription. Previous studies have shown multiple HSP-associated proteins to be inhibitors of BMP signaling. Thus, we propose that maspardin is involved in BMP signaling as an additional BMP inhibitor. In fact, previous results demonstrate that neurons that are depleted of maspardin exhibit increased axonal branching. My working hypothesis is that maspardin is indispensable in regulating BMP signaling via protein trafficking and degradation.Levels of phosphorylated Smad 1/5 were examined in mouse embryonic fibroblasts (MEFs) by western blot analysis and compared to total Smad levels after stimulation with BMP4 ligand. Comparable experiments were performed in primary neuron cultures from wildtype and knockout mice. Pixel densities were used to compare PSmad/Smad ratios in western blots, as well as confirm quantities of protein present. Results were statistically analyzed via unpaired two-tailed t tests. Increases in PSmad 1/5 signaling were insignificant in wildtype stimulated neurons when compared to controls (P=0.0911). In contrast, knockout neurons demonstrated significant increases in levels of PSmad 1/5 in stimulated cells versus controls (P=0.0462; *P<0.05). Significant increases were also observed between stimulated and control samples in knockout MEFs (P=0.0466; *P<0.05). These increases were similarly found to be insignificant in wildtype cells (P=0.6061). Further investigation is needed to determine the exact mechanism by which maspardin regulates these molecules.


Lani Lyman-Henley

Subject Categories

Biochemistry, Biophysics, and Structural Biology | Life Sciences