Strand-specific LINE-1 transcription in mouse F9 cells originates from the youngest phylogenetic subgroup of LINE-1 elements.
LINE-1 (L1) is a mammalian family of highly repeated DNA sequences that are members of a class of transposable elements whose movement involves an RNA intermediate. Both structural and evolutionary data indicate that the L1 family consists of a small number of active transposable elements interspersed with a large number of L1 pseudogenes. In the mouse, the longest, characterized L1 sequences span about 7000 base-pairs and contain two long open reading frames. Two subfamilies of mouse L1 elements, A and F, have been defined on the basis of the type of putative transcriptional regulatory sequence found at the 5' end. In order to identify a transcribed subset of L1 elements in mouse F9 teratocarcinoma cells, we have examined the strand-specificity of L1 transcription by Northern analysis and compared the open reading frame-1 sequences of ten A-type cDNAs with fifteen genomic A-type L1 elements. Transcripts containing A-type sequence are far more abundant than those containing F-type sequence. Although the majority of L1 RNA in F9 cells appears to be transcribed non-specifically from both strands, our results provide evidence for a subpopulation of variable length, strand-specific transcripts arising from A-type transcriptional regulatory sequences. F9 cell cDNA sequences, which share greater than 99.5% sequence identity with one another, represent a homogeneous subset of the genomic L1 population. Examination of genomic mouse L1 sequences reveals three types of length polymorphism in a defined segment of the first open reading frame. Phylogenetic analysis shows a correlation between the type of length polymorphism in the first open reading frame and the relative age of an individual A-type genomic L1 element. Comparison of the cDNA and genomic sequences indicates that the youngest subgroup of A-type L1 elements is preferentially transcribed in F9 cells. This subgroup may be currently dominating the L1 dispersal process in mice.
Schichman
S A
SA
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill 27599.
Severynse
D M
DM
Edgell
M H
MH
Hutchison
C A
CA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D015342:DNA Probes; D004251:DNA Transposable Elements; D004273:DNA, Neoplasm / Q000737:chemistry; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D011110:Polymorphism, Genetic; D012334:RNA, Neoplasm / Q000737:chemistry; D012091:Repetitive Sequences, Nucleic Acid; D013724:Teratoma / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D015342:DNA Probes; D004251:DNA Transposable Elements; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm