Researcher(s)
- Cheryl Martinez, Biological Sciences, University of Delaware
Faculty Mentor(s)
- Veila Fowler, Biological Sciences, University of Delaware
Abstract
Erythropoiesis, the process of red blood cell (erythrocyte) formation, begins in the bone marrow with hematopoietic stem and progenitor cells (HSPCs). These cells differentiate through several intermediate stages, including erythroblasts and reticulocytes, before becoming mature, anucleate erythrocytes. As erythroblasts mature, they decrease in size and move their nucleus to one side of the cell (polarize) in preparation for enucleation, the process of expelling the nucleus. Successful enucleation requires coordinated cellular processes, including dynamic remodeling of the actin cytoskeleton. Actin exists as monomeric globular actin (G-actin) and polymerized filamentous actin (F-actin), comprised of many G-actins forming a long strand. These filaments continuously undergo remodeling through cycles of actin assembly and disassembly, allowing the cytoskeleton to rapidly reorganize and provide structural support and dynamic movements for the cell. During early erythroblast development, F-actin is distributed throughout the cytoplasm. As enucleation begins, F-actin reorganizes behind the polarizing nucleus to form the enucleosome, an actin-rich structure that supports nuclear expulsion; however, the mechanisms regulating its formation remain poorly understood. Cofilin is an actin-binding protein that severs and remodels F-actin filaments, promoting rapid cytoskeletal reorganization. Its activity is regulated by phosphorylation. When cofilin is phosphorylated (p-cofilin), it becomes inactive and unable to sever or disassemble F-actin, whereas dephosphorylation of cofilin activates cofilin to promote actin filament disassembly and turnover. To investigate the role of cofilin during erythroid differentiation, we performed immunofluorescence microscopy and observed that cofilin staining progressively decreased as cells got closer to enucleation. To determine whether cofilin activity also changed during differentiation, we performed Western blot analysis and observed that the ratio of p-cofilin to cofilin increased throughout differentiation. Overall, our findings suggest that cofilin activity decreases during differentiation, which may contribute to the cytoskeletal remodeling and F-actin assembly required for enucleation.