Jak3 Knockout mouse models

Jak3, the mouse ortholog of human JAK3, encodes a Janus kinase whose expression is largely restricted to hematopoietic cells and which associates exclusively with the Il2rg common gamma chain, making it the obligate partner for interleukin 2, 4, 7, 9, 15, and 21 signaling through Stat5 and Stat6; loss-of-function mutations in humans cause autosomal recessive T-negative, B-positive, NK-negative severe combined immunodeficiency. Homozygous null mice are viable but profoundly lymphopenic with blocked thymopoiesis and absent NK cells, which makes the null a useful chassis for immunodeficient host strains supporting human graft engraftment, often alongside Il2rg or Prkdc alleles. Conditional deletion addresses lineage-autonomous requirements after development, kinase-dead knockins separate catalysis from receptor assembly, and humanization is essential when the question is covalent inhibitor engagement of the JAK3-specific Cys909 residue. No paralog substitutes for gamma-chain coupling, so phenotypes report cleanly; choose allele class according to whether the endpoint is host permissiveness or drug selectivity.

Whole body loss of Jak3 gives the clearest readout when the question is whether the gene is required at all. Follow up tissue work can still move to a conditional allele if lethality or compensation appears.