Bid Conditional Knockout mouse models

Bid, ortholog of human BID, encodes the BH3-only protein that couples receptor-initiated to mitochondrial apoptosis. Full-length BID is a compact eight-helix protein held inactive until caspase-8, activated within the FAS or TNFR1 death-inducing complex, cleaves it at Asp59 to yield tBID, which becomes N-myristoylated, targets cardiolipin-rich mitochondrial membranes, and directly activates BAK and BAX; granzyme B, calpains, and cathepsins cut BID at nearby sites, extending the same logic to cytotoxic lymphocyte killing and lysosomal damage. BID is also an ATM substrate implicated in the S-phase checkpoint. Nulls are viable, resist FAS-driven hepatocyte apoptosis, and eventually develop myeloid expansion, but the extrinsic-to-intrinsic bridge is partly covered by Bcl2l11 and Bbc3, so compound genetics is often required. A non-cleavable Asp59 knockin is the sharpest tool for isolating caspase-8-dependent amplification, whereas conditional nulls with hepatocyte or myeloid Cre address tissue-specific death sensitivity.

Tissue restricted knockout of Bid keeps wild type function everywhere else. Breeding is often more robust, and the setup mirrors patient biology where mutations arise in a subset of cells.