SPG20 Protein Spartin Associates with Cardiolipin via Its Plant-Related Senescence Domain and Regulates Mitochondrial Ca2+ Homeostasis

Hereditary spastic paraplegias (HSPs) are a group of neurological disorders characterized clinically by spasticity of lower limbs and pathologically by degeneration of the corticospinal tract. Troyer syndrome is an autosomal recessive HSP caused by a frameshift mutation in the spartin (SPG20) gene. Previously, we established that this mutation results in a lack of expression of the truncated mutant spartin protein. Spartin is involved in many cellular processes and associates with several intracellular organelles, including mitochondria. Spartin contains a conserved plant-related senescence domain at its C-terminus. However, neither the function of this domain nor the roles of spartin in mitochondrial physiology are currently known. In this study, we determined that the plant-related senescence domain of spartin interacts with cardiolipin but not with two other major mitochondrial phospholipids, phosphatidylcholine and phosphatidylethanolamine. We also found that knockdown of spartin by small interfering RNA in a human neuroblastoma cell line resulted in depolarization of the mitochondrial membrane. In addition, depletion of spartin resulted in a significant decrease in both mitochondrial calcium uptake and mitochondrial membrane potential in cells treated with thapsigargin. Our results suggest that impairment of mitochondrial calcium uptake might contribute to the neurodegeneration of long corticospinal axons and the pathophysiology of Troyer syndrome

Private Wage Returns To Schooling In Nigeria: 1996-1999

In the last two decades, primary and secondary school enrollment rates have declined in Nigeria while enrollment rates in post-secondary school have increased. This paper estimates from the General Household Survey for Nigeria the private returns to schooling associated with levels of educational attainment for wage and self-employed workers. The estimates for both men and women are small at primary and secondary levels, 2 to 4 percent, but are substantial at post-secondary education level, 10-15 percent. These schooling return estimates may account for the recent trends in enrollments. Thus, increasing public investment to encourage increased attendance in basic education is not justifiable on grounds of private efficiency, unless investments to increase school quality have higher private returns. With high private returns to postsecondary schooling, students at this level should pay tuition, to recoup more of the public costs of schooling, which may be redistributed to poor families through scholarships. Key words: Schooling Investment; Private Wage Returns; Efficiency; Equity; Nigeria JEL Classifications: O15, I12, J24 1