Functional analysis of anastral spindle 3 in wg signaling, and cell death

Abstract

Apoptosis, and compensatory proliferation are essential for normal development: removal of damaged cells and replacement by newly formed cells. Mis-regulation of centrosomal proteins, damaged DNA, and defects in mitosis results in mitotic catastrophe. Ana3 is a member of pericentriolar matrix proteins, and known as a key component of centriolar cohesion and basal body formation. Here, I report that ana3$^{m19}$ is a suppressor of lethality induced by overexpression of Sol narae (Sona), one of ADAMTS family. ana3$^{m19}$ has a nonsense mutation that truncates 252 amino acid residues at the carboxyl terminus. Ana3 contains multiple armadillo repeats, and the armadillo repeats at the C- terminus that are truncated in ana3$^{m19}$ is highly conserved. Overexpression of Ana3 did not induce any phenotypes, while knockdown of Ana3 caused decrease in wing size and malformation of hinge. The wing phenotypes of ana3 knockdown flies were rescued by overexpression of Sona, demonstrating the positive genetic interaction between ana3 and sona. Cell death was responsible for small wing phenotype, and was rescued by p35 co-expression. This led me to hypothesize that overexpression of Ana3 may promote cell survival. Indeed, the small eye phenotype of GMR>Grim flies was rescued by overexpression of Ana3. Overexpression of Ana3 also enhanced resistance against γ-irradiation, and the resistance was dependent on the level of Ana3. Interestingly, the levels of both intracellular and extracellular Ana3 increased in response to irradiation, and overexpression of Ana3 was capable of repressing cell death by irradiation. The secretion of Ana3 by exosomal secretion pathway was demonstrated by sequential ultracentrifugation of culture media of S2 cells. Western analysis showed that Ana3 promotes processing of Sona whose rate correlates with the amount of Ana3. This suggests that Ana3 plays key roles in resistance against irradiation by accelerating the processing of Sona.