The FLAG-Ube3a BAC transgene (also called "Ube3a-isoform2,3-3XFlag: Strain L" transgene) has a 3xFLAG tag inserted in-frame into exon 12 of Ube3a on the BAC; this generates full-length, C-terminal FLAG-tagged Ube3a mRNA long isoforms (isoforms 2 and 3, L) that are subsequently translated into functional, FLAG-tagged Ube3a protein. Transgenic mice from founder line Fd1 (FLAG-Ube3a BAC Fd1 or FLAG-Ube3a BAC X0) are described here. The FLAG-Ube3a expression pattern matched that of endogenous Ube3a across multiple brain areas (including cortex, hippocampus and thalamus). Importantly, the endogenous Ube3a gene is expressed only from the maternal chromosome in neurons; a result of paternal imprinting (the antisense transcript functions to silence paternal expression in brain). Because the FLAG-Ube3a BAC transgene lacks the transcription initiation site of the antisense transcript, expression of FLAG-Ube3a is independent of parent-of-origin or sex of the animal. Compared to wildtype animals, expression levels of Ube3a protein in whole-brain lysates are two-fold greater in Ube3a 1xTg (i.e., hemizygous) mice and three-fold greater in Ube3a 2xTg (i.e., homozygous) mice.
This increased Ube3a gene dosage models maternal 15q11-13 duplication (dup15) and triplication (isodicentric extranumerary chromosome, idic15) that is associated with 1-3% of human autism spectrum disorder. By 16 weeks of age, homozygous mice display strong penetrance of three core autism-related behavior traits; defective social interaction, impaired communication and increased repetitive stereotypies (defective three chamber social interaction task, impaired social paired vocalizations in adults and increased repetitive self-grooming, respectively). Homozygous animals exhibit reduced glutamatergic (excitatory) synaptic transmission, but no defects in GABAergic (inhibitory) synaptic transmission. To date, homozygous mice have not displayed other major confounding traits or co-morbidities (no evidence of anxiety, motor behavior deficits, memory deficits or sensory behavior deficits). Hemizygous animals are viable and fertile, with a milder phenotype compared to homozygotes. The donating investigator does not recommend breeding homozygous animals as it could result in some heretofore unknown changes in phenotype.
