Germ-line transmission of a disrupted β₂microglobulin gene produced by homologous recombination in embryonic stem cells

Abstract

MAJOR histocompatibility complex (MHC) class I molecules are integral membrane proteins present on virtually all vertebrate cells and consist of a heterodimer between the highly polymorphic α-chain and the β₂microglobulin (β2-m) protein of relative molecular mass 12,000 (ref. 1). These cell-surface molecules play a pivotal part in the recognition of antigens, the cytotoxic response of T cells, and the induction of self tolerance^1,2. It is possible, however, that the function of MHC class I molecules is not restricted to the immune system, but extends to a wide variety of biological reactions including cell–cell interactions. For example, MHC class I molecules seem to be associated with various cell-surface proteins, including the receptors for insulin, epidermal growth factor, luteinizing hormone and the β-adrenergic receptor^3–6. In mice, class I molecules are secreted in the urine and act as highly specific olfactory cues which influence mating preference^{7, 8}. The β2-m protein has also been identified as the smaller component of the Fc receptor in neonatal intestinal cells⁹, and it has been suggested that the protein induces collagenase in fibrob-lasts¹⁰. Cells lacking β2-m are deficient in the expression of MHC class I molecules, indicating that the association with β2-m is crucial for the transport of MHC class I molecules to the cell surface¹. The most direct means of unravelling the many biological functions of β2-mis to create a mutant mouse with a defective β2-mgene. We have now used the technique of homologous recombination to disrupt the β2-mgene. We report here that introduction of a targeting vector into embryonic stem cells resulted in β2-mgene disruption with high frequency. Chimaeric mice derived from blastocysts injected with mutant embryonic stem cell clones transmit the mutant allele to their offspring.