Genetic analysis of protein kinase B (AKT) in Drosophila

Abstract

The decision between survival and death is an important aspect of cellular regulation during development and malignancy. Central to this regulation is the process of apoptosis, which is conserved in multicellular organisms [1]. A variety of signalling cascades have been implicated in modulation of apoptosis, including the phosphatidylinositol (Pl) 3-kinase pathway. Activation of Pl 3-kinase is protective, and inhibition of this lipid kinase enhances cell death under several conditions including deregulated expression of c-Myc, neurotrophin withdrawal and anoikis [2-7]. Recently, the protective effects of Pl 3-kinase have been linked to its activation of the pleckstrin homology (PH)-domain-containing protein kinase B (PKB or AKT) [8]. PKB/AKT was identified from an oncogene, v-akt, found in a rodent T-cell lymphoma [9]. To initiate a genetic analysis of PKB, we have isolated and characterized a Drosophila PKB/AKT mutant (termed Dakt1) that exhibits ectopic apoptosis during embryogenesis as judged by induction of membrane blebbing, DNA fragmentation and macrophage infiltration. Apoptosis caused by loss of Dakt function is rescued by caspase suppression but is distinct from the previously described reaper/grim/hid functions. These data implicate Dakt1 as a cell survival gene in Drosophila, consistent with cell protection studies in mammals.

The conserved PI3′K/PTEN/Akt signaling pathway regulates both cell size and survival in Drosophila

“…Germ line clone (GLC) analysis removing both maternal and zygotic expression of Dakt1 resulted in embryos that exhibit ectopic and widespread apoptosis (Figure 1) (Staveley et al, 1998). We also demonstrated that the ectopic apoptosis in Dakt1 GLC embryos was independent of the grim, reaper and hid genes but could be suppressed through the expression of the baculoviral caspase inhibitor P35 (Staveley et al, 1998). This maternal role for Dakt1 prompted us to test for a potential role for PI3'K signaling in early Drosophila embryos.…”

“…Our previous study described a null mutant allele of Dakt1 that resulted in zygotic larval lethality (Staveley et al, 1998). Germ line clone (GLC) analysis removing both maternal and zygotic expression of Dakt1 resulted in embryos that exhibit ectopic and widespread apoptosis (Figure 1) (Staveley et al, 1998).…”

“…Germ line clones (GLCs) of Dakt1 were generated as described in (Staveley et al, 1998). In all experiments, we used the q allele of Dakt1 (Staveley et al, 1998).…”

“…In all experiments, we used the q allele of Dakt1 (Staveley et al, 1998). We also used a P-element induced allele of Dakt1 (P1627).…”

“…Consistent with this hypothesis, Drosophila Akt (Dakt1) and Drosophila PTEN (DPTEN) have both been shown to play a role in cell growth during imaginal development (Verdu et al, 1999;Huang et al, 1999;Goberdham et al, 1999). Our previous studies on Dakt1 implicated a role for Dakt1 signaling in the regulation of cell survival during Drosophila embryogenesis (Staveley et al, 1998). In this study, we use biochemical and genetic tests to demonstrate the conservation of PI3'K/Akt signaling in Drosophila.…”