Cronin Et Al

Essay

Cronin et al. (Science, 2009, 325: 340-343) used RNA interference to study the immune response of the fruit fly, Drosophila melanogaster, to the bacterial pathogen Serratia marcescens. They identified several members of the JAK-STAT cell-cell signaling pathway in their analysis.
a) The PIAS gene is a negative regulator of JAK-STAT signaling (that is, it inhibits the signaling pathway). RNAi to block PIAS activity causes flies to die significantly earlier than control flies when exposed to bacteria. Does JAK-STAT signaling appear to protect the flies from the bacteria? Explain.
b) The upd gene encodes a ligand that activates JAK-STAT signaling. RNAi that blocks upd function causes flies to survive longer than control flies when exposed to bacteria. Explain how this is or is not consistent with your answer from part (a).