Haploinsufficiency of retinoic acid induced 1 (RAI1) in humans causes Smith-Magenis syndrome (SMS), which is associated with diverse neurodevelopmental and behavioral symptoms as well as obesity. RAI1 encodes a nuclear protein with emerging functions in the expression of genes involved in circuit assembly and neuronal communication.
The Rai1flox allele has loxP sites flanking exon 3 of the retinoic acid induced 1 gene. Mice homozygous for this floxed allele are viable and fertile with no reported abnormalities. When bred to mice that express Cre recombinase, the resulting offspring will have the floxed region (encoding amino acid 1-1837) deleted in cre-expressing tissues; creating a knock-out allele (Rai1Δ).
For example, when bred to mice with Cre-expression throughout the central and peripheral nervous system (Nestin-Cre; Stock No. 003771), the resulting NestinCre;Rai1CKO homozygotes have pan-neural loss of Rai1 and exhibit three major characteristics of SMS - deficits in body weight homeostasis, motor function and associative learning and memory. They are smaller than control littermates prior to weaning and show prominent hindlimb clasping. More than 80% die by 25 weeks of age. Females (but not males) show obesity beginning ~5 weeks of age.
Furthermore, individual aspects of these three major SMS phenotypes may be observed by crossing Rai1flox to different cre-expressing mice.
Breeding to Gad2-IRES-Cre mice (Stock No. 010802) results in Rai1 knock-out in most GABAergic inhibitory neurons. Those Gad2Cre;Rai1CKO mice show learning deficits, but no motor function abnormalities, obesity or early lethality.
When bred to Vglut2-ires-cre mice (Stock No. 016963), the resulting Vglut2Cre;Rai1Tag mice have Rai1 knock-out in subcortical excitatory neurons - leading to increased body weight, poor motor function and learning deficits, with no early lethality. In addition, Rai1 knock-out specifically in neurons of the paraventricular nucleus of hypothalamus (PVH ; via breeding to Sim1-cre [see Stock No. 006395]) or ventromedial nucleus of hypothalamus (VMH ; via breeding to Sf1-Cre [Stock No. 012462]) both contributed to the obesity phenotype observed in Vglut2Cre;Rai1CKO mice.
No SMS-like characteristics were observed for mice with Rai1 knock-out in astrocytes and subsets of adult neural progenitors (via breeding to Gfap-Cre73.12 ; Stock No. 012886) or with Rai1 knock-out in cortical and hippocampal excitatory neurons and glia (via breeding to Emx1-IRES-Cre; Stock No. 005628).
