An abundant placental transcript containing an IAP-LTR is allelic to mouse pregnancy-specific glycoprotein 23 ( Psg23): cloning and genetic analysis

• Published in: Gene 2004-01, Vol.325, p.103-113
• Main Authors: Ball, Melanie, McLellan, Andrew, Collins, Ben, Coadwell, John, Stewart, Francesca, Moore, Tom
• Format: Article
• Language: English
• Subjects: Alleles; Animals; Base Sequence; Carcinoembryonic antigen; Cloning, Molecular; Crosses, Genetic; DNA, Complementary - chemistry; DNA, Complementary - genetics; DNA, Complementary - isolation & purification; Endogenous retrovirus; Evolution; Female; Gene Expression Profiling; Genes, Intracisternal A-Particle - genetics; Glycoproteins - genetics; Immunoglobulin superfamily; Intracisternal A-particle; Long terminal repeat; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C3H; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Inbred DBA; Mice, Inbred Strains; Models, Molecular; Molecular Sequence Data; Muridae; murine endogenous retrovirus; Physical Chromosome Mapping; Placenta - metabolism; Pregnancy Proteins - chemistry; Pregnancy Proteins - genetics; Pregnancy-specific glycoprotein 23; Protein Conformation; Rats; Sequence Alignment; Sequence Analysis, DNA; Sequence Homology, Nucleic Acid; Terminal Repeat Sequences - genetics; Transcription, Genetic; Trophoblast
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/j.gene.2003.10.001

Several families of endogenous retroviruses (ERVs) are expressed in mammalian placental tissues, and are implicated in aspects of placental development and function. We characterized the structure of abundant ERV-related transcripts in mouse placenta. In addition to the 7 kb full-length type I and 5 kb type I deleted intracisternal A-particle (IAP) transcripts, we identified and cloned an abundant 2 kb transcript encoding a novel member of the pregnancy-specific glycoprotein ( Psg) gene family, which contains an IAP long terminal repeat (LTR) in the 3′ untranslated region (UTR). The polyadenylation signal for the transcript is provided by the inserted LTR sequence. This sequence is allelic to Psg23 and is therefore denoted as Psg23 LTR . The transcript encodes a protein of 471 amino acids and has a domain organisation similar to previously described Psg proteins. Modelling of the protein N-domain produced a structure in good agreement with an existing crystalline structure for mouse sCEACAM1a. The LTR insertion is widely distributed among inbred mouse strains but is not found in 129/sv, CBA/2, or in wild mice. Cloning of the genomic region downstream of the LTR insertion site from the C57Bl/6J strain indicates that the insertion consists of a solo LTR without additional IAP sequence, and identified the original Psg23 polyadenylation signal sequence downstream of the insertion site. Psg23 LTR was mapped to proximal chromosome 7 using the European collaborative interspecific mouse backcross (EUCIB) panel, and to yeast artificial chromosome (YAC) E072, which contains other members of the Psg gene family, by polymerase chain reaction (PCR). Northern blot analysis of RNA from adult and fetal mouse tissues and in situ hybridization to mid-gestation mouse embryos indicated that Psg23 LTR is expressed predominantly in placental spongiotrophoblast. We detected a small, but statistically non-significant, bias in favour of transmission of Psg23 LTR to the offspring of heterozygous parents. However, a larger study would be required to determine whether this allele is selectively advantageous to the developing embryo.