RT Journal Article
SR Electronic
T1 Subfamily-specific differential contribution of individual monomers and the tether sequence to mouse L1 promoter activity
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.12.03.471143
DO 10.1101/2021.12.03.471143
A1 Lingqi Kong
A1 Karabi Saha
A1 Yuchi Hu
A1 Jada N. Tschetter
A1 Chase E. Habben
A1 Leanne S. Whitmore
A1 Changfeng Yao
A1 Xijin Ge
A1 Ping Ye
A1 Simon J. Newkirk
A1 Wenfeng An
YR 2021
UL http://biorxiv.org/content/early/2021/12/04/2021.12.03.471143.abstract
AB Background The internal promoter in L1 5’UTR is critical for autonomous L1 transcription and initiating retrotransposition. Unlike the human genome, which features one contemporarily active subfamily, four subfamilies (A_I, Gf_I and Tf_I/II) have been amplifying in the mouse genome in the last one million years. Moreover, mouse L1 5’UTRs are organized into tandem repeats called monomers, which are separated from ORF1 by a tether domain. In this study, we aim to compare promoter activities across young mouse L1 subfamilies and investigate the contribution of individual monomers and the tether sequence.Results We observed an inverse relationship between subfamily age and the average number of monomers among evolutionarily young mouse L1 subfamilies. The youngest subgroup (A_I and Tf_I/II) on average carry 3-4 monomers in the 5’UTR. Using a single-vector dual-luciferase reporter assay, we compared promoter activities across six L1 subfamilies (A_I/II, Gf_I and Tf_I/II/III) and established their antisense promoter activities in a mouse embryonic fibroblast cell line. Using consensus promoter sequences for three subfamilies (A_I, Gf_I and Tf_I), we dissected the differential roles of individual monomers and the tether domain in L1 promoter activity. We validated that, across multiple subfamilies, the second monomer consistently enhances the overall promoter activity. For individual promoter components, monomer 2 is consistently more active than the corresponding monomer 1 and/or the tether for each subfamily. Importantly, we revealed intricate interactions between monomer 2, monomer 1 and tether domains in a subfamily-specific manner. Furthermore, using three-monomer 5’UTRs, we established a complex nonlinear relationship between the length of the outmost monomer and the overall promoter activity.Conclusions The laboratory mouse is an important mammalian model system for human diseases as well as L1 biology. Our study extends previous findings and represents an important step toward a better understanding of the molecular mechanism controlling mouse L1 transcription as well as L1’s impact on development and disease.Competing Interest StatementThe authors have declared no competing interest.5’UTR5’ untranslated regionGFPgreen fluorescent proteinL1long interspersed element type 1M1monomer 1M2monomer 2M3monomer 3MYAmillion years agonon-LTRnon-long terminal repeat.