Cell type-specific expression of LINE-1 open reading frames 1 and 2 in fetal and adult human tissues.
The LINE-1 (L1) family of non-long terminal repeat retrotransposons is a major force shaping mammalian genomes, and its members can alter the genome in many ways. Mutational analyses have shown that coexpression of functional proteins encoded by the two L1-specific open reading frames, ORF1 and ORF2, is an essential prerequisite for the propagation of L1 elements in the genome. However, all efforts to identify ORF2-encoded proteins have failed so far. Here, applying a novel antibody we report the presence of proteins encoded by ORF2 in a subset of cellular components of human male gonads. Immunohistochemical analyses revealed coexpression of ORF1 and ORF2 in prespermatogonia of fetal testis, in germ cells of adult testis, and in distinct somatic cell types, such as Leydig, Sertoli, and vascular endothelial cells. Coexpression of both proteins in male germ cells is necessary for the observed genomic expansion of the number of L1 elements. Peptide mass fingerprinting analysis of a approximately 130-kDa polypeptide isolated from cultured human dermal microvascular endothelial cells led to the identification of ORF2-encoded peptides. An isolated approximately 45-kDa polypeptide was shown to derive from nonfunctional copies of ORF2 coding regions. The presence of both ORF1- and ORF2-encoded proteins in vascular endothelial cells and its apparent association with certain stages of differentiation and maturation of blood vessels may have functional relevance for vasculogenesis and/or angiogenesis.
Ergün
Süleyman
S
Institut für Anatomie, Universitätsklinikum Hamburg-Eppendorf, Germany.
Buschmann
Christian
C
Heukeshoven
Jochen
J
Dammann
Kristin
K
Schnieders
Frank
F
Lauke
Heidrun
H
Chalajour
Fariba
F
Kilic
Nerbil
N
Strätling
Wolf H
WH
Schumann
Gerald G
GG
D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D004822:Epididymis / Q000166:cytology / Q000378:metabolism; D005333:Fetus / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D007985:Leydig Cells / Q000378:metabolism; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics*; D010449:Peptide Mapping; D010920:Placenta / Q000166:cytology / Q000378:metabolism; D014176:Protein Biosynthesis; D011506:Proteins / Q000032:analysis / Q000235:genetics; D012708:Sertoli Cells / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013094:Spermatozoa / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
D011506:Proteins