The SLC7A7 Transporter Identifies Microglial Precursors prior to Entry into the Brain
Federico Rossi1, Alessandra Maria Casano1, Katrin Henke2
1Developmental Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidbelberg, Germany.
Abstract:
During development, macrophages invade organs to establish phenotypically and transcriptionally distinct tissue-resident populations. How they invade and colonize these organs is unclear. In particular, it remains to be established whether they arise from naive equivalents that colonize organs randomly or whether there are committed macrophages that follow pre-determined migration paths. Here, by using a combination of genetics and imaging approaches in the zebrafish embryo, we have addressed how macrophages colonize the brain to become microglia. Identification and cloning of a mutant that lacks microglia has shown that Slc7a7, a Leucine/Arginine transporter, defines a restricted macrophage sub-lineage and is necessary for brain colonization. By taking a photoconversion approach, we show that these macrophages give rise to microglia. This study provides direct experimental evidence for the existence of sub-lineages among embryonic macrophages.
Insights
Embryonic macrophages colonize organs to become resident cells. A specific transporter, Slc7a7, identifies a macrophage sub-lineage essential for brain colonization and microglia development in zebrafish.
Area of Science:
- Developmental biology
- Immunology
- Cell biology
Background:
- Macrophages differentiate into diverse tissue-resident populations during development.
- The mechanisms of organ colonization by embryonic macrophages remain largely unknown.
- It is unclear if macrophages migrate randomly or follow predetermined paths.
Purpose of the Study:
- To investigate the colonization process of macrophages in the zebrafish brain.
- To identify genetic factors and cellular mechanisms governing microglia development.
- To determine if committed macrophage sub-lineages exist during embryonic development.
Main Methods:
- Utilized zebrafish embryos for genetic and imaging studies.
- Identified and cloned a mutant lacking microglia.
- Employed a photoconversion technique to trace macrophage lineage.
Main Results:
- The Leucine/Arginine transporter Slc7a7 was identified as a marker for a restricted macrophage sub-lineage.
- Slc7a7 is crucial for the colonization of the brain by these macrophages.
- Photoconversion experiments confirmed that Slc7a7-expressing macrophages develop into microglia.
Conclusions:
- This study provides direct evidence for the existence of embryonic macrophage sub-lineages.
- Slc7a7 defines a specific sub-population of macrophages committed to brain colonization.
- These findings elucidate a key mechanism in microglia development and organ colonization by immune cells.
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