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Senthil Selvam, Andrew Scott, Sidath E Liyanage, Michael Powner, Marcus Fruttiger; Mouse Model for Tamoxifen-inducible Cre Targeting of Retinal Microglia. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3556. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Microglia are a specialised population of the mononuclear phagocyte lineage. Resident microglia are distinct to invading populations of circulating monocyte-derived macrophages in their localisation to the central nervous system (CNS) and their homeostatic role in the neurogeneis and angiogenesis of the developing retina. Microglial activation is commonly seen in inflammatory and degenerative pathologies of the retina. Resident retinal microglia are known to specifically express the protein ionized calcium binding adaptor molecule 1 (Iba1; also known as allograft inflammatory factor-1, Aif1). Using the Aif1 gene we present a mouse model of tamoxifen inducible, cre-recombinase activation that allows the genetic targeting of resident central nervous system microglia.
A bacterial artificial chromosome (BAC), containing the Aif1 gene was obtained and a construct coding for a tamoxifen inducible form of Cre (CreERT2) was recombined into the open reading frame of the Aif1 gene. The modified BAC was then used for transgenesis by pronuclear injections and resulting offspring was screened for founders by PCR. In vivo recombination efficiency was tested in a ROSA-EGFP reporter strain (Gt(ROSA)26Sortm4(ACTB-tdTomato,-EGFP)Luo/J) using flow cytometry in both p7 neonatal mice and 6 week old adult mice. Using the same strain we demonstrate the use of this tool to label Iba1 expressing resident retinal microglia in murine models of oxygen induced retinopathy (OIR), laser induced choroidal neovasculairsation (CNV) and endotoxin induced uveitis (EIU).
Two founders were obtained and a transgenic line was established from one of them (Aif1-CreER). Flow cytometry of the ROSA-EGFP reporter mice showed that recombination could be achieved in upto 72% of resident microglia in the p7 perinatal retina and upto 95% in the 6 week adult retina. The brain, choroid and spleen also showed GFP expression. Immunohistochemistry performed on retinal flat mounts of ROSA-EGFP reporter mice undergoing OIR, laser induced CNV and EIU demonstrated co-localisation of GFP expression and Iba1 antibody labelling.
This model of Aif1-CreER provides a valuable research tool to genetically target resident microglia in the central nervous system of mice in various murine models of retinal disease.
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