The Functions of Auxilin and Rab11 in Drosophila Suggest That the Fundamental Role of Ligand Endocytosis in Notch Signaling Cells Is Not Recycling

Notch signaling requires ligand internalization by the signal sending cells. Two endocytic proteins, epsin and auxilin, are essential for ligand internalization and signaling. Epsin promotes clathrin-coated vesicle formation, and auxilin uncoats clathrin from newly internalized vesicles. Two hypotheses have been advanced to explain the requirement for ligand endocytosis. One idea is that after ligand/receptor binding, ligand endocytosis leads to receptor activation by pulling on the receptor, which either exposes a cleavage site on the extracellular domain, or dissociates two receptor subunits. Alternatively, ligand internalization prior to receptor binding, followed by trafficking through an endosomal pathway and recycling to the plasma membrane may enable ligand activation. Activation could mean ligand modification or ligand transcytosis to a membrane environment conducive to signaling. A key piece of evidence supporting the recycling model is the requirement in signaling cells for Rab11, which encodes a GTPase critical for endosomal recycling. Here, we use Drosophila Rab11 and auxilin mutants to test the ligand recycling hypothesis. First, we find that Rab11 is dispensable for several Notch signaling events in the eye disc. Second, we find that Drosophila female germline cells, the one cell type known to signal without clathrin, also do not require auxilin to signal. Third, we find that much of the requirement for auxilin in Notch signaling was bypassed by overexpression of both clathrin heavy chain and epsin. Thus, the main role of auxilin in Notch signaling is not to produce uncoated ligand-containing vesicles, but to maintain the pool of free clathrin. Taken together, these results argue strongly that at least in some cell types, the primary function of Notch ligand endocytosis is not for ligand recycling

Understanding of an effect of plenum volume of a low porosity bend skewed casing treatment on the performance of single-stage transonic axial flow compressor

The present study intends to improve the performance of transonic axial flow compressor stage and its operating range by implementing passive flow control technique, a Casing Treatment. A plenum chamber with two different volumes placed above the bend skewed slots was implemented. The objective was to understand the effect of plenum volume on the performance of transonic axial flow compressor retrofitted with bend skewed casing treatment. The porosity of the selected bend skewed casing treatment was 33%. A detailed steady-state CFD analysis has been carried out for the compressor operating at six different speeds. Axial location of the casing treatment above the rotor tip was chosen based upon the previous experiments reported in literature [1]. For the same axial location and porosity, plenum chamber depth was varied from zero depth to full plenum depth to understand effect of a plenum volume. The results were compared with baseline model with solid casing wall. Significant improvement in stall margin was observed at all rotational speeds. Minor deviation was observed in stage total pressure ratio with reduction in efficiency at design speed

Rab11 Plays an Indispensable Role in the Differentiation and Development of the Indirect Flight Muscles in Drosophila

Rab11, an evolutionary conserved, ubiquitously expressed subfamily of small monomeric GTPase has been known to regulate diverse cellular and developmental events, by regulating the exocytotic and transcytotic events inside the cell. Our studies show that Rab11 regulates Drosophila adult myogenesis by controlling proliferation and differentiation of the Adult muscle precursors (AMPs). Blocking Rab11 in the AMPs, which fuse to form the Indirect Flight Muscles (IFMs) of fly, renders flies completely flightless and non-viable. The indirect flight musculature, comprising of the differentially patterned dorsal longitudinal muscles (DLMs) and dorsal ventral muscles (DVMs), is affected to different extents. Abrogating or knocking down normal Rab11 function results in severely disrupted IFMs. DLMs forming from larval templates are reduced in number along with a significant reduction in their fibre size. The de novo developing DVMs are frequently absent. The DLMs in Rab11 hypomorphs are highly reduced, showing as a small constricted mass in one half of the thorax. Further, Rab11 function is essential for growth of these muscles during later half of adult myogenesis, as down regulation of Rab11 in IFMs results in degenerated muscles and broken fibres. Finally, we show that loss of Rab11 activity in the AMPs result in acquisition of migratory characteristic of myoblast as they show cellular protrusion at their polar ends accompanied with loss of cell-cell contacts. Our data provide the first evidence of a trafficking protein playing an indispensable role in regulating early stages of adult muscle development

Weight gain prior to entry into a weight-loss intervention study among overweight and obese breast cancer survivors

PURPOSE: Changes in cancer therapy, in addition to changes in obesity prevalence, suggest the need for a current assessment of weight gain patterns following breast cancer diagnosis. The aim of this study was to evaluate factors associated with weight gain among breast cancer survivors prior to enrolling into a behavioral weight loss intervention. METHODS: Anthropometric measures and data on weight-related factors were collected at baseline on 665 breast cancer survivors. Postdiagnosis weight gain was determined between entry into the trial and previous diagnosis up to 5 years. Multivariate logistic regression analyses were used to evaluate the association between weight gain and influencing factors. RESULTS: The mean weight gain was 4.5 % body weight (standard deviation=10.6); 44 % of women experienced ≥5 % body weight gain. The risk of weight gain was inversely associated with age (adjusted odds ratio (OR(adj))=0.97, 95 % confidence interval (95 % CI) 0.95–0.99), Hispanic ethnicity (OR(adj)=0.30, 95 % CI 0.13–0.68), and overweight (OR(adj)= 0.11, 95 % CI 0.05–0.23) or obese (OR(adj)=0.03, 95 % CI 0.02–0.07) status at diagnosis and positively associated with time elapsed since diagnosis (OR(adj)=1.19/year, 95 % CI 1.04–1.36). Women prescribed aromatase inhibitors were 46 % less likely to gain weight compared to women prescribed selective estrogen-receptor modulators (OR(adj)=0.54, 95 % CI 0.31–0.93). The risk of weight gain was positively associated with smoking at diagnosis (OR(adj)=2.69, 95 % CI 1.12–6.49) although this was attributable to women who subsequently quit smoking. CONCLUSIONS: Postdiagnosis weight gain is common and complex and influenced by age, ethnicity, weight, smoking status, time elapsed since diagnosis, and endocrine-modulating therapy. IMPLICATIONS FOR CANCER SURVIVORS: Weight gain continues to be a concern following a diagnosis of breast cancer. Factors influencing this weight gain include age, ethnicity, weight, smoking status, time elapsed since diagnosis, and endocrine-modulating therapy. Effective weight management strategies are needed for this population of women