TARGETED DISRUPTION WITHIN THE CD3-ZETA ETA/THETA/OCT-1 LOCUS IN MOUSE/

To elucidate the role of the CD3 eta subunit of the T cell receptor (T CR) in thymic development, a CD3 eta(-/-) mouse was generated by gene targeting. Insertion of a neomycin resistance gene into exon 9 of the CD3 zeta/eta/theta locus disrupted expression of CD3 eta and CD3 theta without affecting the expression of CD3 zeta. Little difference was o bserved between wild type and CD3 eta(-/-) mice with regard to cellula rity or subset composition in thymus and peripheral lymphoid organs. F urthermore, neither alloproliferative responses nor cytotoxic T lympho cyte generation and effector function was affected by the mutation. Th e effect of the CD3 eta(-/-) mutation on thymic selection was examined by crossing the CD3 eta knockout animals with anti-HY TCR transgenic animals: the absence of the CD3 eta subunit altered neither positive n or negative selection. Thus, CD3 eta is not required for thymic select ion. Of note, the birth rate of the CD3 eta(-/-) animals was significa ntly lower than that of wild type or heterozygous animals (P = 0.041-0 .002). This unexpected result is probably the consequence of an altera tion in mRNA expression of the Oct-1 nuclear transcription factor in C D3 eta(-/-) animals. The CD3 zeta/eta/theta locus partially overlaps t he gene encoding Oct-1 whose transcription is dysregulated by the CD3 eta(-/-) mutation. Our results clearly underscore the value of charact erizing all products of a genetic locus disrupted by gene targeting.