Ivanna Ihnatovych¹, Ryu P. Dorn¹, Eduardo Cortes Gomez², Harneet Sandhu¹, David A. Bennett³, Jianmin Wang², Kinga Szigeti¹

Human specific gene CHRFAM7A, a fusion product between ULK4/FAM7A and CHRNA7, is present in 99% of human population in different copy number (CN) and orientation. Both the direct and inverted alleles are transcribed with similar frequency, suggesting they underwent similar selective pressure and that both are functional. The direct allele is translated, and the protein incorporates into a7 nAChR modifying its function; the mechanism of the inverted allele is unclear. As the inverted allele (CHRFAM7A_Δ2bp) is not translated and its expression does not affect CHRNA7, we hypothesized that the CHRFAM7A_Δ2bp mechanism is RNA mediated regulation of ULK4. Human brain RNAseq data, brain tissue, primary macrophages (MΦ), and the iPSC model were used to study ULK4 expression and regulation. Analyzing RNAseq data from ROSMAP, we detected the long and short ULK4 transcripts and demonstrated that the long isoform expression correlates with CHRFAM7A_Δ2bp CN. qPCR with isoform-specific primers further confirmed that with increasing CHRFAM7A_Δ2bp CN, correlation between the isoforms decreases in human brain and MΦ. In the iPSC model, the increased long to short isoform ratio - both at the mRNA and protein level - was detected in neuronal progenitors and MΦ containing CHRFAM7A_Δ2bp compared to CHRFAM7A null cells. In the inverted line, higher ULK4 Long/ ULK4 Short ratio correlated with higher level of α-tubulin acetylation and polymerization. These findings suggest that the CHRFAM7A_Δ2bp exerts genetic epistasis on ULK4 resulting in increased long to short ULK4 isoform ratio. Our iPSC model presents an opportunity to elucidate the molecular mechanism of ULK4 regulation.

¹ Department of Neurology, State University of New York at Buffalo, 875 Ellicott St., Buffalo, NY, 14203, USA, ² Roswell Park Comprehensive Cancer Center, 665 Elm St, Buffalo, NY 14203, USA, ³ Rush Alzheimer’s Disease Center, Rush University Medical Center, Chicago, IL, USA

Funding Support: Community Foundation for Greater Buffalo (Kinga Szigeti). ROSMAP is supported by NIA grants P30AG10161, P30AG72975, R01AG15819, R01AG17917, U01AG46152, and U01AG61356.