A tetracycline transactivator (tTA) and a self-excising neo cassette (ACN, in reverse orientation) were inserted into exon 1 immediately downsteam of the initiation methionine. The neo cassette excision occurred within ES cells. Immunohistochemistry confirmed very low levels of protein expression in the brain. This is a hypomorphic allele that targets isoform 2, the main isoform expressed in the brain. (J:135447)