All ETDs from UAB

Advisory Committee Chair

Michael A Miller

Advisory Committee Members

Bradley Yoder

Chenbei Chang

Guillermo Marques

Rosa Serra

Weei-Chin Lin

Document Type

Dissertation

Date of Award

2010

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

The MSP domain is an evolutionarily conserved immunoglobulin-like structure of about 120 amino acids (Miller et al., 2001). A P56S missense mutation in the MSP domain of the human vapb gene is associated with a dominantly inherited form of Amyotropic Lateral Sclerosis (ALS) or Spinal Muscular Atrophy (SMA) (Nishimura et al., 2004). In C. elegans, secreted MSP binds to the VAB-1 Eph receptor and other receptors on oocyte and ovarian sheath cell surfaces (Miller et al., 2003). We have recently shown that the P56S mutation prevents secretion of the VAPB MSP domain, suggesting that the signaling function is important in ALS and SMA pathogenesis (Tsuda et al., 2008). Secreted MSPs bind to multiple receptors on oocyte and ovarian sheath cells to stimulate oocyte MPK-1 ERK MAP Kinase (MAPK) phosphorylation, but the function and mechanism of this phosphorylation event is not well understood. Here we show that the Shp class protein-tyrosine phosphatase PTP-2 acts in oocytes downstream of sheath/oocyte gap junctions to promote MSP-induced MPK-1 phosphorylation. PTP-2 inhibits multiple RasGAPs, resulting in sustained Ras activation necessary for high oocyte maturation rates. We also provide evidence that MSP promotes production of reactive oxygen species (ROS) to augment MPK-1 phosphorylation. The Cu/Zn superoxide dismutase SOD-1 inhibits MPK-1 phosphorylation downstream of, or in parallel to ptp-2. Our results support the model that MSP triggers PTP-2/Ras activation and ROS production to stimulate MPK-1 activity essential for oocyte maturation. The C. elegans vapb homolog VPR-1 (VAP Related) is required for wild type motility and body wall muscle mitochondrial function. We have investigated mutations in ptp-2 and let-60 Ras, which cause defects in mitochondrial shape due to abnormal fission and fusion (dynamics). These experiments help us delineate a signaling pathway that regulates mitochondrial function. This dissertation elaborates the signaling function of the MSP domain in oocyte maturation and muscle mitochondrial dynamics and may provide insight into the molecular mechanisms behind ALS and SMA. Moreover, VAP MSP domains are ligands for Eph receptors, the most abundant class of receptor tyrosine kinases in the human genome. Thus, these studies may be of broad significance.

Share

COinS