Targeted disruption within the CD3ζ/η/θ/Oct-1 locus in mouse

Abstract

To elucidate the role of the CD3η subunit of the T cell receptor (TCR) in thymic development, a CD3η(-/-) mouse was generated by gene targeting. Insertion of a neomycin resistance gene into exon 9 of the CD3ζ/η/θ locus disrupted expression of CD3η and CD3θ without affecting the expression of CD3ζ. Little difference was observed between wild type and CD3η(-/-) mice with regard to cellularity or subset composition in thymus and peripheral lymphoid organs. Furthermore, neither alloproliferative responses nor cytotoxic T lymphocyte generation and effector function was affected by the mutation. The effect of the CD3η-/-) mutation on thymic selection was examined by crossing the CD3η knockout animals with anti-HY TCR transgenic animals: the absence of the CD3η subunit altered neither positive nor negative selection. Thus, CD3η is not required for thymic selection. Of note, the birth rate of the CDη(-/-) animals was significantly lower than that of wild type or heterozygous animals (P = 0.041 - 0.002). This unexpected result is probably the consequence of an alteration in mRNA expression of the Oct-1 nuclear transcription factor in CD3η(-/-) animals. The CD3ζ/η/θ locus partially overlaps the gene encoding Oct-1 whose transcription is dysregulated by the CD3η(-/-) mutation. Our results clearly underscore the value of characterizing all products of a genetic locus disrupted by gene targeting.