Fibronectin isoforms in megakaryocytes

Area of Science:

• Cell Biology
• Hematology
• Biochemistry

Background:

• Fibronectin (FN) and its alternatively spliced variant, FN EIIIB, are important in cell development and migration.
• Megakaryocytes (MKs) are the cells responsible for platelet production.
• FN EIIIB is typically found in embryonic and developing cells, with limited presence in adult tissues.

Purpose of the Study:

• To investigate the synthesis and localization of fibronectin (FN) and FN EIIIB in megakaryocytes (MKs).
• To determine the effect of thrombin on FN and FN EIIIB secretion and localization in MKs.
• To explore the potential role of cell-surface bound FN EIIIB in MK function.

Main Methods:

• Immunohistochemistry and confocal microscopy were used to analyze FN and FN EIIIB expression in MKs.
• Bone marrow cells were treated with thrombin to observe changes in fibronectin localization.
• Analysis focused on differentiating between secreted and cell-surface bound fibronectin.

Main Results:

• Megakaryocytes (MKs) synthesize both general fibronectin (FN) and the alternatively spliced FN EIIIB.
• Unlike general FN, thrombin stimulation does not cause the secretion of FN EIIIB into the medium.
• Both general FN and FN EIIIB accumulate on the MK surface after thrombin treatment, indicating cell-surface binding rather than release into the extracellular space.

Conclusions:

• Megakaryocytes (MKs) and platelets are among the few adult cell types that synthesize and contain fibronectin EIIIB.
• Thrombin induces the cell-surface binding of FN EIIIB on MKs, suggesting it is released to bind the cell surface.
• The presence and localization of FN EIIIB on the MK surface may play a specific role in megakaryocyte migration and maturation processes.