A Cre-deleter specific for embryo-derived brain macrophages reveals distinct features of microglia and border macrophages

• Published in: Immunity (Cambridge, Mass.) Vol. 56; no. 5; pp. 1027 - 1045.e8
• Main Authors: Brioschi, Simone, Belk, Julia A., Peng, Vincent, Molgora, Martina, Rodrigues, Patrick Fernandes, Nguyen, Khai M., Wang, Shoutang, Du, Siling, Wang, Wei-Le, Grajales-Reyes, Gary E., Ponce, Jennifer M., Yuede, Carla M., Li, Qingyun, Baer, John M., DeNardo, David G., Gilfillan, Susan, Cella, Marina, Satpathy, Ansuman T., Colonna, Marco
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09-05-2023
• Subjects: Animals; BAMs; Brain - metabolism; fate-mapping; Integrases - genetics; Integrases - metabolism; Macrophages - metabolism; macrophages ontogeny; Mice; microglia; Microglia - metabolism; SMAD4; macrophages ontogeny; SMAD4; fate-mapping; BAMs; microglia
• ISSN: 1074-7613; 1097-4180
• DOI: 10.1016/j.immuni.2023.01.028

Genetic tools to target microglia specifically and efficiently from the early stages of embryonic development are lacking. We generated a constitutive Cre line controlled by the microglia signature gene Crybb1 that produced nearly complete recombination in embryonic brain macrophages (microglia and border-associated macrophages [BAMs]) by the perinatal period, with limited recombination in peripheral myeloid cells. Using this tool in combination with Flt3-Cre lineage tracer, single-cell RNA-sequencing analysis, and confocal imaging, we resolved embryonic-derived versus monocyte-derived BAMs in the mouse cortex. Deletion of the transcription factor SMAD4 in microglia and embryonic-derived BAMs using Crybb1-Cre caused a developmental arrest of microglia, which instead acquired a BAM specification signature. By contrast, the development of genuine BAMs remained unaffected. Our results reveal that SMAD4 drives a transcriptional and epigenetic program that is indispensable for the commitment of brain macrophages to the microglia fate and highlight Crybb1-Cre as a tool for targeting embryonic brain macrophages.
[Display omitted]
•Generated Crybb1-Cre line that recombines in microglia and BAMs in embryonic development•Embryonic BAMs are CD38+MHC2−, while monocyte-derived BAMs are CD38−MHC2+•Used Crybb1-Cre to delete SMAD4 in microglia and embryonic BAMs•SMAD4 deletion arrests microglia development and impairs mouse memory skills
Tools to target microglia specifically and efficiently from the embryonic development are lacking. Brioschi et al. generated the Crybb1-Cre line, which recombines in microglia and border-associated macrophages during the embryonic stage. Combining Crybb1-Cre and other tools, they resolved embryonic-derived versus monocyte-derived BAMs in the mouse cortex. Deletion of the transcription SMAD4 using Crybb1-Cre revealed that microglia require SMAD4 for differentiation.