In Drosophila Melanogaster, Loss-Of-Function Mutations in Either Pink1 or Parkin

Multiple Choice

In Drosophila melanogaster, loss-of-function mutations in either Pink1 or Parkin show similar phenotypes including impaired ability to fly, male sterility, and degeneration of dopaminergic neurons. Transgenic overexpression of Parkin in mutants lacking Pink1 significantly ameliorates the loss-of-function phenotype, but overexpression of Pink1 cannot rescue the Parkin loss-of-function phenotype. According to these findings, which protein is more likely to act upstream of the other one? Assuming that the Parkin loss-of-function phenotype is merely due to defects in autophagy, would you expect Parkin overexpression to also rescue an ATG9 loss-of-function phenotype?

A) Parkin acts upstream of Pink1; yes
B) Parkin acts upstream of Pink1; no
C) Pink1 acts upstream of Parkin; yes
D) Pink1 acts upstream of Parkin; no