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Accumulation and massive cell death of polymorphonuclear neutrophils in the developing bone marrow of the mouse: a
1Department of Anatomy, Kawasaki Medical School, Kurashiki, Japan.
Abstract:
Accumulation and cell death of neutrophils were studied by light and electron microscopy in neonatal mouse bone marrow. At the beginning of bone marrow hematopoiesis, the marrow cavity contained a large number of polymorphonuclear leukocytes. Polymorphs comprised approximately 75% of the total nucleated cells in the hematopoietic compartment of the newborn marrow, the majority being neutrophils. Mature neutrophils were sometimes crossing the endothelium of the marrow blood sinus. Neutrophils in neonatal marrow show features typical of apoptosis, e.g. formation of nuclear pockets and blebs, margination of compact nuclear chromatin to form sharply circumscribed masses, condensation of cytoplasm, and convolution of cell outlines. Dying neutrophils were devoured and digested by phagocytes. The occurrence of large-scale neutrophil death and removal of neutrophils by phagocytes in neonatal bone marrow are discussed in relation to programmed cell death in development of the fetal hematopoietic system.
Insights
Neonatal mouse bone marrow exhibits extensive neutrophil apoptosis and phagocytosis. This programmed cell death is crucial for the developing fetal hematopoietic system.
Area of Science:
- Hematology
- Developmental Biology
- Cell Biology
Background:
- Neonatal bone marrow is rich in hematopoietic cells, including a high proportion of polymorphonuclear leukocytes.
- Neutrophils constitute a significant majority of nucleated cells in the newborn marrow's hematopoietic compartment.
- Observational evidence suggests mature neutrophils may migrate across the endothelium of marrow blood sinusoids.
Purpose of the Study:
- To investigate the processes of neutrophil accumulation and cell death in neonatal mouse bone marrow.
- To characterize the morphological features of neutrophil apoptosis in this specific developmental context.
- To explore the role of phagocytosis in the clearance of dying neutrophils within the neonatal marrow.
Main Methods:
- Light microscopy was employed to observe cellular morphology and distribution.
- Electron microscopy was utilized for detailed ultrastructural analysis of neutrophils.
- The study focused on the hematopoietic compartment of neonatal mouse bone marrow.
Main Results:
- Neutrophils in neonatal bone marrow display characteristic morphological signs of apoptosis, including nuclear and cytoplasmic changes.
- Dying neutrophils were actively engulfed and digested by phagocytic cells.
- A significant proportion of neutrophils were observed undergoing programmed cell death and subsequent clearance.
Conclusions:
- Large-scale neutrophil death via apoptosis is a prominent feature of neonatal mouse bone marrow.
- Phagocytosis plays a critical role in removing apoptotic neutrophils during early hematopoiesis.
- These findings contribute to understanding programmed cell death in the development of the fetal hematopoietic system.