Person:

Zhou, Yi

We completed two separate studies examining chemosensation in Drosophila. The first study investigated taste processing. It was our aim in this study to identify and characterize higher-order gustatory neurons. Our strategy for tackling this problem involved complementary functional and anatomical approaches. First, we used calcium imaging to screen for cells responding to stimulation of gustatory receptor neurons. Second, we used photo-activatable GFP to localize the cell bodies of neurons innervating the gustatory neuropil. Third, based on the information we gained from these imaging experiments, we were able to identify some promising Gal4 lines that labeled candidate gustatory neurons. Fourth and finally, we made whole-cell patch clamp recordings from these candidate gustatory neurons while stimulating the proboscis with tastants. Unfortunately, none of these candidates turned out to be gustatory neurons. However, this study illustrates a flexible and powerful general approach to identifying and characterizing sensory neurons in the Drosophila brain. The second study investigated olfactory transduction. Specifically, we examined the effect of air speed on olfactory receptor neuron responses (ORNs) in Drosophila. We constructed an odor delivery device that allowed us to independently vary concentration and air speed, and we used a fast photoionization detector to precisely measure the actual odor concentration at the antenna while simultaneously recording spikes from ORNs in vivo. Our results demonstrate that Drosophila ORN odor responses are invariant to air speed, as long as odor concentration is kept constant. This finding was true across a >100-fold range of air speeds. Because odor hydrophobicity has been proposed to affect the air speed dependence of olfactory transduction, we tested a >1,000-fold range of hydrophobicity values, and found that ORN responses are invariant to air speed across this full range. These results have implications for the mechanisms of odor delivery to Drosophila ORNs. Our findings are also significant because flies have a limited ability to control air flow across their antennae, unlike terrestrial vertebrates which can control air flow within their nasal cavity. Thus, for the fly, invariance to air speed may be adaptive because it confers robustness to changing wind conditions.

Interleukin-18 (IL18) participates in atherogenesis through several putative mechanisms1, 2. Interruption of IL18 action reduces atherosclerosis in mice3, 4. Here, we show that absence of the IL18 receptor (IL18r) does not affect atherosclerosis in apolipoprotein E–deficient (Apoe−/−) mice, nor does it affect IL18 cell surface binding to or signaling in endothelial cells. As identified initially by co-immunoprecipitation with IL18, we found that IL18 interacts with the Na-Cl co-transporter (NCC; also known as SLC12A3), a 12-transmembrane-domain ion transporter protein preferentially expressed in the kidney5. NCC is expressed in atherosclerotic lesions, where it colocalizes with IL18r. In Apoe−/− mice, combined deficiency of IL18r and NCC, but not single deficiency of either protein, protects mice from atherosclerosis. Peritoneal macrophages from Apoe−/− mice or from Apoe−/− mice lacking IL18r or NCC show IL18 binding and induction of cell signaling and cytokine and chemokine expression, but macrophages from Apoe−/− mice with combined deficiency of IL18r and NCC have a blunted response. An interaction between NCC and IL18r on macrophages was detected by co-immunoprecipitation. IL18 binds to the cell surface of NCC-transfected COS-7 cells, which do not express IL18r, and induces cell signaling and cytokine expression. This study identifies NCC as an IL18-binding protein that collaborates with IL18r in cell signaling, inflammatory molecule expression, and experimental atherogenesis.

Mast cells (MCs) contribute to the pathogenesis of obesity and diabetes. This study demonstrates that leptin deficiency slants MCs toward anti-inflammatory functions. MCs in the white adipose tissue (WAT) of lean humans and mice express negligible leptin. Adoptive transfer of leptin-deficient MCs expanded ex vivo mitigates diet-induced and pre-established obesity and diabetes in mice. Mechanistic studies show that leptin-deficient MCs polarize macrophages from M1 to M2 functions because of impaired cell signaling and an altered balance between pro-and anti-inflammatory cytokines, but do not affect T cell differentiation. Rampant body weight gain in ob/ob mice, a strain that lacks leptin, associates with reduced MC content in WAT. In ob/ob mice, genetic depletion of MCs exacerbates obesity and diabetes, and repopulation of ex vivo expanded ob/ob MCs ameliorates these diseases.