The Id2-EGFP knockin allele was designed to both abolish inhibitor of DNA binding 2 (Id2) gene function and express enhanced green fluorescent protein (eGFP) from the Id2 promoter/enhancer elements. No Id2 expression is observed from the endogenous Id2 gene. The donating investigator reports that homozygote mice mice are runted with defective lung alveolarization. Other organ systems have not been evaluated. However, Id2-eGFP homozygotes may be expected to exhibit the same phenotype as mice homozygous for other null mutations of this gene (including postnatal lethality and defects of the immune system, digestive tract, kidneys, adipose tissue and mammary gland development). The donating investigator also reports eGFP expression recapitulates the endogenous Id2 expression pattern. In the lungs, immunohistochemical detection of eGFP recapitulates the epithelial expression of the endogenous gene (distal tip lung epithelial multipotent precursor cells of the developing lung throughout branching morphogenesis up to embryonic day (E)16.5). The donating investigator reports immunohistochemical and FACS detection of eGFP in immune cell populations is observed for single-positive CD4 thymocytes and single-positive CD8 thymocytes, CD4-positive splenocytes, and CD8-positive splenocytes. No eGFP expression is observed in CD4/CD8 double-positive thymocytes, and direct eGFP fluorescence was too weak to be observed microscopically for any cell type. Heterozygous mice are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities.

Of note, the same group designed an identically-targeted Id2-CreERT2 knockin mouse line to express the tamoxifen-inducible CreER^T2 fusion protein (rather than eGFP) from the Id2 promoter/enhancer elements. That Id2-CreERT2 knockin mouse line is available as Stock No. 016222.