Date of Award

12-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biological Sciences

Advisor

Dr. Lisa Bain

Committee Member

Dr. Charles Rice

Committee Member

Dr. David Feliciano

Abstract

Epidemiological studies have shown that arsenic exposure during early embryogenesis can cause reduced weight gain and neurological deficits later on in life. In addition, in vitro and in vivo studies have indicated that arsenic suppresses neurogenesis and myogenesis. The exact mechanism of how arsenic causes these undesired developmental outcomes is poorly understood, however both skeletal muscle and sensory neuron development require the Wnt/β-catenin signaling pathway to initiate the specific differentiation of precursor cells. We were interested in determining the target cell population of arsenic and its metabolites. Arsenic's metabolites were of interest because they have been shown to be more toxic than arsenic itself. We found that arsenic and its metabolites, monomethylarsonous (MMA III) acid and dimethylarsinous (DMA III) acid, target a specific population of progenitor cells termed the neural plate border specifier (NPBS) cells by reducing the expression of signals required for neurogenesis (Pax3, Sox10, and NeuroD1) and myogenesis (Msx1, MyoD, and Myogenin). Pluripotent P19 embryonic stem cells were differentiated into embryoid bodies (EBs) in the presence of 0.1μM and 0.5μM sodium arsenite, 0.01μM and 0.05μM MMA III, or 0.001μM and 0.005μM DMA III. The expression of myogenic and neurogenic signals was determined by immunohistochemistry in EBs after 2-5 days of differentiation. Starting on day 2, in the neurogenic pathway, and day 3 in the myogenic pathway, arsenic is targeting the neural plate border specifier (NPBS) cells, which resulted in reduced transcription factor expression of Pax3 and Msx1. Arsenic also altered nuclear localization of Msx1 (day 2), MyoD (days 2-5), NeuroD1 (days 4-5), and altered co-localization patterns in both the neurogenic and myogenic lineages. After exposure to arsenic's metabolites, MMA III and DMA III, more drastic patterns were seen. In the neurogenic pathway, it appears that MMA III is targeting the neural plate border specifier cells on day 3, while DMA III does not affect transcription factor expression until day 5. Co-localization patterns were again changed after exposure. After 3 days of MMA III and DMA III exposure, co-localization patterns were significantly changed in the myogenic pathway. In regards to nuclear localization MyoD's nuclear localization was significantly decreased on days 3 and 5 in both the MMA and DMA treatments. In the neurogenic pathway, NeuroD1's nuclear localization was significantly decreased in day 5 EBs after exposure to both MMA and DMA. Overall, these results suggest that arsenic and its metabolites are targeting the precursor cells to skeletal muscles and sensory neurons, and are therefore suppressing neurogenesis and myogenesis.

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