Shinya Kato

The phosphatidylinositol 3-kinase (PI3K) pathway regulates many cellular functions, but its roles in the nervous system are still poorly understood. We found that a newly discovered insulin receptor isoform, DAF-2c, is translocated from the cell body to the synaptic region of the chemosensory neuron in Caenorhabditis elegans by a conditioning stimulus that induces taste avoidance learning. This translocation is essential for learning and is dependent on the mitogen-activated protein kinase-regulated interaction of CASY-1 (the calsyntenin ortholog) and kinesin-1. The PI3K pathway is required downstream of the receptor. Light-regulated activation of PI3K in the synaptic region, but not in other parts of the cell, switched taste-attractive behavior to taste avoidance, mimicking the effect of conditioning. Thus, synaptic PI3K is crucial for the behavioral switch caused by learning.

Corpora lutea disappear from ovaries in the absence of conception. The present study was undertaken to examine the hypothesis that disappearance of corpora lutea is accomplished through apoptosis-dependent phagocytosis of luteal cells. When bone marrow cells expressing green fluorescence protein were transplanted into X-ray-irradiated mice, macrophages derived from donor mice were detected within corpora lutea, suggesting macrophage infiltration into the tissue. Dispersed rat luteal cells underwent spontaneous apoptosis during culture and were phagocytosed by luteal macrophages. Treatment with doxorubicin increased the extent of apoptosis in luteal cells, and those cells were more efficiently phagocytosed than cells left untreated. The phagocytosis was inhibited by liposomes containing phosphatidylserine or a peptide containing the integrin-targeted sequence, and was stimulated by milk fat globule epidermal growth factor 8. These results collectively indicate that apoptotic luteal cells are phagocytosed by macrophages in a manner mediated by phosphatidylserine and integrin.

During phagocytosis, the FcGR-IgG bond is thought to be necessary to promote cell-membrane extension as the zipper mechanism. However, does this zipper mechanism provide a spatial antigen discrimination capability that allows macrophages to selectively phagocytose only antigens, especially for clusters with a mixture of antigens and non-antigens? To elucidate the ability and limitation of the zipper mechanism, we fed a coupled 2 μm IgG-coated and 4.5 μm non-coated polystyrene bead mixtures to macrophages and observed their phagocytosis. Macrophage engulfed the mixed clusters, including the 4.5 μm non-coated polystyrene part, indicating that the non-coated particles can be engulfed even without the zipper mechanism as far as coupled to the opsonized particles. In contrast, when the non-opsonized particle part was held by the microcapillary manipulation assay, macrophages pinched off the non-coated polystyrene particle part and internalized the opsonized particle part only. The results suggest that (1) an IgG-coated surface is needed to anchor phagocytosis by cell-membrane protrusion; however, (2) once the antibody-dependent cell phagocytosis is started, phagocytosis can proceed with the uncoated objects as the followers of the internalizing opsonized particles even without the support of the zipper mechanism. They may also indicate the concern of misleading the immune system to target unexpected objects because of their aggregation with target pathogens and the possibility of new medical applications to capture the non-opsonized target objects by the aggregation with small antigens to activate an immune response.