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A developmental study of epiplexus cells and supraependymal cells and their possible relationship to microglia
Abstract:
Intraventricular macrophages are first seen attached to the presumptive choroid plexus in the 11 days postconception mouse. By 12 day postconception supraependymal macrophages are present as well as a few macrophages lying apparently free within the ventricles. The number of epiplexus, supraependymal and free macrophages increases rapidly and reaches a peak at 17 days postconception, then fall rapidly until 4 days post natum. A second increase in epiplexus and supraependymal cells occurs at 8 days post natum followed by another decrease up to 15 days post natum. Microglia were first observed in the brain at 13 days postconception and at 17 days postconception a microglial cell was observed apparently entering the ependyma from the ventricle. It is suggested that the large decrease in intraventricular macrophages after 17 days postconception is due to many of these cells migrating into the brain to give rise to microglia. The intraventricular macrophages themselves probably arise from within the choroid plexus, either from stromal cells or from blood-borne macrophages.
Insights
Early mouse brain development reveals intraventricular macrophages, crucial for forming microglia. These cells peak before birth and migrate into the brain, originating from the choroid plexus.
Area of Science:
- Neuroscience
- Developmental Biology
- Immunology
Background:
- Macrophages play critical roles in brain development and immune surveillance.
- The origin and developmental dynamics of brain-resident macrophages, like microglia, are not fully understood.
- Intraventricular macrophages represent a potential precursor population for microglia.
Purpose of the Study:
- To investigate the temporal and spatial dynamics of intraventricular macrophages during mouse embryonic and early postnatal development.
- To determine the origin of intraventricular macrophages.
- To explore the relationship between intraventricular macrophages and the emergence of microglia.
Main Methods:
- Histological analysis of mouse embryos and postnatal pups at various developmental stages (11 days postconception to 15 days post natum).
- Observation and quantification of epiplexus, supraependymal, and free intraventricular macrophages.
- Identification and tracking of microglia within the developing brain parenchyma.
- Morphological assessment of macrophage-ependymal interactions.
Main Results:
- Intraventricular macrophages (epiplexus, supraependymal, free) first appear at 11-12 days postconception, peaking at 17 days postconception.
- A significant decrease in intraventricular macrophages occurs postnatally, coinciding with the appearance of microglia.
- Microglia are first observed at 13 days postconception, with evidence of a microglial cell entering the brain from the ventricle at 17 days postconception.
- Intraventricular macrophages likely originate from the choroid plexus or blood-borne sources.
Conclusions:
- Intraventricular macrophages are a transient population during mouse brain development.
- The observed decrease in intraventricular macrophages correlates with microglial colonization of the brain, suggesting a precursor-progeny relationship.
- These findings support the hypothesis that intraventricular macrophages contribute to the microglial pool in the developing brain.