Igh^tm1Cog

A loxP site flanked neomycin resistance gene cassette was inserted upstream of the E mu enhancer (Rr150) in the intergenic region following the Igh-J region, such that E mu and its flanking matrix-associated regions (MARs) were left intact. Flow cytometric analysis showed a lack of surface IgM+ B cells, while ELISA indicated an absence of all serum immunoglobulin classes. The insertion blocked transcription of the Igh-J region and prevented rearranged VDJ segments. Excision of the neo cassette resulted in rescue, indicating the observed phenotypes were the result of the presence of neo cassette rather than a deletion of a regulatory element. (J:80654)