Movie S1.

Evolution of immune chemoreceptors into sensors of the outside world. This movie recapitulates three genomic accidents that occurred in the rodent Fpr/Vr gene cluster that are sufficient to explain all aspects of the complex expression patterns acquired by a receptor family that switched from sensing pathogens inside the organism to sensing the outside world through the nose. These accidents led to (i) the transcription of Fpr-rs3, -rs4, -rs6, and -rs7 in the apical part of the vomeronasal neuroepithelium; (ii), the transcription of Fpr-rs1 in the basal vomeronasal epithelium; and (iii) under specific conditions, the transcription of Fpr-rs1 in immune cells, via the generation of an intergenic splice variant linking the immune Fpr-rs2 and the vomeronasal Fpr-rs1 genes. For each step in the animation, the sequence of genomic events (duplications, inversions, gene shufflings, and pseudogenizations) are shown in an arbitrary order.