Stem cells depend on intrinsic and local factors to maintain their identity and activity, but they also sense and respond to changing external conditions. We previously showed that germline stem cells (GSCs) and follicle stem cells (FSCs) in the Drosophila ovary respond to diet via insulin signals. Insulin signals directly modulate the GSC cell cycle at the G2 phase, but additional unknown dietary mediators control both G1 and G2. Target of rapamycin, or TOR, is part of a highly conserved nutrient-sensing pathway affecting growth, proliferation, survival and fertility. Here, we show that optimal TOR activity maintains GSCs but does not play a major role in FSC maintenance, suggesting differential regulation of GSCs versus FSCs. TOR promotes GSC proliferation via G2 but independently of insulin signaling, and TOR is required for the proliferation, growth and survival of differentiating germ cells. We also report that TOR controls the proliferation of FSCs but not of their differentiating progeny. Instead, TOR controls follicle cell number by promoting survival, independently of either the apoptotic or autophagic pathways. These results uncover specific TOR functions in the control of stem cells versus their differentiating progeny, and reveal parallels between Drosophila and mammalian follicle growth.

The kinesin KIF1C is known to regulate podosomes, actin-rich adhesion structures, which remodel the extracellular matrix during physiological processes. Here we show that KIF1C is a player in the podosome-inducing signaling cascade. Upon induction of podosome formation by protein kinase C, KIF1C translocation to the cell periphery intensifies and KIF1C accumulates in the proximity of peripheral microtubules enriched with plus tip-associated proteins CLASPs and around podosomes. Importantly, without CLASPs, both KIF1C trafficking and podosome formation are suppressed. Moreover, chimeric mitochondria-targeted CLASP2 recruits KIF1C, suggesting a transient CLASP-KIF1C association. We propose that CLASP creates preferred microtubule tracks for KIF1C to promote podosome induction downstream of PKC.

On p. 2119, eukaryotic translation initiation factor 4E is incorrectly defined as 4eIF4E, instead of eIF4E. The online issue and print versions are correct.

The WASP family of proteins has emerged as important regulators that connect multiple signaling pathways to regulate the actin cytoskeleton. Dictyostelium cells express WASP, as well as a WASP related protein, WASP-B, endoded by wasB gene. WASP-B contains many of the domains present in WASP. Analysis of wild type, wasB null cells revealed that WASP-B is required for proper control of F-actin polymerization in response to a cAMP gradient. Due to the lack of tight control on actin polymerization, wasB null cells exhibited higher level of F-actin polymerization. wasB− cells extend more de novo pseudopods laterally and their average life span is longer than those of wild type cells, causing more turns and inefficient chemotaxis. YFP-WASP-B appears to be uniformly distributed in the cytosol and shows no translocation to cortical membrane upon cAMP stimulation. Active RacC pull-down assay reveals that the level of active RacC in wasB− cells is significantly higher than wild type cells. Moreover, the distribution of active RacC is not localized in wasB− cells. We conclude that chemotaxis defects of wasB− cells are likely to result from the aberrant regulation of RacC activation and localization.

Dual leucine zipper kinase (DLK) promotes growth cone motility and must be restrained to ensure normal development. PHR (Pam/ Highwire/RPM-1) ubiquitin ligases therefore target DLK for degradation unless axon injury occurs. Overall DLK levels decrease during development, but how DLK levels are regulated within a developing growth cone has not been examined. We analyzed the expression of the fly DLK Wallenda (Wnd) in R7 photoreceptor growth cones as they halt at their targets and become presynaptic boutons. We found that Wnd protein levels are repressed by the PHR protein Highwire (Hiw) during R7 growth cone halting, as has been observed in other systems. However, as R7 growth cones become boutons, Wnd levels are further repressed by a temporally expressed transcription factor, Tramtrack69 (Ttk69). Previously unobserved negative feedback from JNK also contributes to Wnd repression at both time points. We conclude that neurons deploy additional mechanisms to downregulate DLK as they form stable, synaptic connections. We use live imaging to probe the effects of Wnd and Ttk69 on R7 bouton development and conclude that Ttk69 coordinates multiple regulators of this process.