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Localization of a putative inositol 1,4,5-triphosphate receptor in the Limulus granulocyte
Abstract:
The horseshoe crab (Limulus polyphemus) granulocyte (GR) degranulates upon contact with bacteria and release factors that mediate an immune response. Stimulated cells produce IP3, which binds to receptors (IP3R, M.W.240-300 kD) that function to release stored Ca2+ into the cytoplasm that mediates degranulation. This mechanism is believed to mediate exocytosis in the Limulus GR but IP3R in the GR has not been shown. The present study utilized monoclonal antibody 4C11 and a commercially available anti-IP3R antibody, both of which label amino acids of the N-terminal of all known isoforms. Electron microscopy, immunohistochemistry, SDS-PAGE, and Western blot analysis, which employed the use of the two antibodies, demonstrates that a putative IP3R exists in the: plasma membrane, smooth surfaced vesicles, nucleus and nuclear membrane. We hypothesize that this putative IP3R is involved in mediating the immune response of the Limulus GR.
Insights
Horseshoe crab immune cells release factors when encountering bacteria. Researchers found evidence of a specific receptor (IP3R) in these cells, suggesting its role in the immune response.
Area of Science:
- Immunology
- Cell Biology
- Marine Biology
Background:
- Horseshoe crab granulocytes (GR) degranulate upon bacterial contact, releasing immune factors.
- This degranulation is linked to inositol trisphosphate (IP3) signaling and calcium (Ca2+) release via inositol trisphosphate receptors (IP3R).
- The presence of IP3R in Limulus GR, however, remained unconfirmed.
Purpose of the Study:
- To investigate the presence and localization of inositol trisphosphate receptors (IP3R) in horseshoe crab (Limulus polyphemus) granulocytes (GR).
- To determine if a putative IP3R is involved in the immune response mechanism of Limulus GR.
Main Methods:
- Utilized monoclonal antibody 4C11 and a commercial anti-IP3R antibody targeting the N-terminal of IP3R isoforms.
- Employed electron microscopy, immunohistochemistry, SDS-PAGE, and Western blot analysis to detect and localize IP3R.
Main Results:
- Demonstrated the existence of a putative IP3R in the plasma membrane, smooth surfaced vesicles, nucleus, and nuclear membrane of Limulus GR.
- Confirmed the presence of IP3R using multiple antibody-based detection methods.
Conclusions:
- A putative inositol trisphosphate receptor (IP3R) is present in various cellular compartments of the horseshoe crab granulocyte.
- This putative IP3R is hypothesized to play a crucial role in mediating the immune response and degranulation process in Limulus GR.