When reporter positivity is not lineage identity: A four-gate validation framework for stress-exposed Cre-loxP...

Cre-loxP systems provide powerful tools for cell-specific manipulation and lineage tracing, but their interpretation depends on the assumption that reporter activation faithfully reflects cell-autonomous recombinase activity. Recent evidence that Cre recombinase protein may transfer from oligodendroglial cells to neurons under pathological stress raises an important methodological question: does reporter positivity invariably establish lineage identity? We propose a four-gate lineage-certainty framework that distinguishes driver confirmation, recombination confirmation, independent cell-identity confirmation, and a stress-transfer challenge. This framework separates four biologically distinct events, recombinase transcription, recombinase protein localization, genomic recombination, and lineage identityand encourages orthogonal validation when unexpected reporter-positive populations emerge. A resource-adaptive implementation, ranging from conventional immunohistochemistry and transcript localization to cell-resolved recombination analysis and spatial or single-cell approaches, could improve applicability across laboratory settings. Reporter activation should therefore be regarded as evidence of recombination-dependent reporter activity rather than automatic proof of lineage derivation. This distinction may strengthen the reproducibility and interpretability of Cre-loxP histochemistry across experimental models of development, injury, degeneration, and regeneration.