Cx3cr1 Knockin mouse models

Cx3cr1, the mouse ortholog of human CX3CR1, encodes the Gi-coupled seven transmembrane receptor for fractalkine, the only CX3C chemokine, which is unusual in being tethered to the membrane by a mucin stalk so that it functions as an adhesion molecule until ADAM10 or ADAM17 shedding releases a soluble chemoattractant. The receptor marks microglia, patrolling monocytes and some natural killer and T cell subsets, and mediates neuron to microglia communication governing synaptic pruning. Allele design here carries a specific trap: the ubiquitous Cx3cr1-GFP and Cx3cr1-CreER tools are knockins that disrupt the coding sequence, so homozygous reporter animals are receptor nulls and heterozygous controls are essential. Humanized knockins additionally allow study of the human M280 variant associated with altered adhesion. Use tamoxifen-inducible deletion with appropriate chase periods to distinguish long-lived microglia from replenishing monocytes, then read process motility, synaptic engulfment, and lesion-associated recruitment.

An engineered Cx3cr1 allele can introduce a human coding region, a point change, or a fluorescent reporter without random transgene integration noise.