APOE polymorphisms are major genetic risk factors of Alzheimer's disease (AD). Compared with APOE3/E3, the APOE4/E4 genotype is associated with a > 14-fold increased risk. Therefore, we hypothesized t Show more
APOE polymorphisms are major genetic risk factors of Alzheimer's disease (AD). Compared with APOE3/E3, the APOE4/E4 genotype is associated with a > 14-fold increased risk. Therefore, we hypothesized that conversion of APOE4 to APOE3 would ameliorate AD-related pathologies. Accordingly, we generated a knock-in mouse model harboring an APOE4-FLEx (Flip-Excision) 4-to-3 construct enabling postnatal Cre-mediated APOE4-to-APOE3 switching. This construct comprised an APOE3 exon inserted in a reverse orientation downstream of the APOE4 exon, flanked by alternating loxP and mutant loxP sites, allowing Cre-mediated FLEx switching from APOE4-to-APOE3. For in vitro validation, HEK293T cells were transfected with APOE4-FLEx 4-to-3 plasmid, followed by AAV8-mediated iCre delivery. For in vivo studies, endogenous Apoe was replaced with the APOE4-FLEx 4-to-3 construct to generate APOE4-FLEx 4-to-3 knock-in mice, which were crossed with tamoxifen-inducible Rosa26-CreERT2 mice to yield Cre: APOE4-FLEx 4-to-3 double-knock-in mice. Tamoxifen was administered to induce APOE switching. Cre expression successfully induced APOE4-to-APOE3 switching in vitro. Tamoxifen administration in Cre: APOE4-FLEx 4-to-3 mice triggered APOE4-to-APOE3 switching in the liver, demonstrating the feasibility of postnatal isoform switching. However, brain APOE protein levels were below the detection limit. Investigation of the underlying cause involving transcript analysis revealed aberrant retention of intron 3 (APOE-I3). This abnormal splicing probably contributed to the decreased expression of fully spliced, translation-competent (mature) APOE mRNA, driving the subsequent protein reduction. Although APOE expression across organs in APOE4-FLEx 4-to-3 mice requires further optimization, our findings demonstrate that Cre-mediated FLEx switching can serve as a potential strategy to induce APOE genotype switching in vivo. Show less
The bHLH transcription factor Olig2 is required for sequential cell fate determination of both motor neurons and oligodendrocytes and for progenitor proliferation in the central nervous system. Howeve Show more
The bHLH transcription factor Olig2 is required for sequential cell fate determination of both motor neurons and oligodendrocytes and for progenitor proliferation in the central nervous system. However, the role of Olig2 in peripheral sensory neurogenesis remains unknown. We report that Olig2 is transiently expressed in the newly differentiated olfactory sensory neurons (OSNs) and is down-regulated in the mature OSNs in mice from early gestation to adulthood. Genetic fate mapping demonstrates that Olig2-expressing cells solely give rise to OSNs in the peripheral olfactory system. Olig2 depletion does not affect the proliferation of peripheral olfactory progenitors and the fate determination of OSNs, sustentacular cells, and the olfactory ensheathing cells. However, the terminal differentiation and maturation of OSNs are compromised in either Olig2 single or Olig1/Olig2 double knockout mice, associated with significantly diminished expression of multiple OSN maturation and odorant signaling genes, including Omp, Gnal, Adcy3, and Olfr15. We further demonstrate that Olig2 binds to the E-box in the Omp promoter region to regulate its expression. Taken together, our results reveal a distinctly novel function of Olig2 in the periphery nervous system to regulate the terminal differentiation and maturation of olfactory sensory neurons. Show less