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A FRT-LoxP-Neomycin-FRT-LoxP selection cassette was inserted downstream of exon 4 and the third single LoxP site was inserted upstream of exon 4. The region flanked by the second and third LoxP sites is approximately 569 bp. Exon 4 encodes amino acids 337-386 and deletion of this sequence results in the creation of a premature stop codon. The neomycin selection cassette was removed via FLP-mediated recombination, leaving loxP sites flanking exon 4. Exon 4 was susequently removed via Cre-mediated recombination. In situ hybridization and RT-PCR analysis confirmed that this allele lacks expression of exon 4. qPCR analysis revealed that the medial ganglionic eminence of homozygous mutants expresses transcript downstream of the deleted region at ~35% of control levels at E13.5. (J:259070)