Baboon placentas express soluble and membrane-bound Paan-AG proteins encoded by alternatively spliced transcripts of the class Ib major histocompatibility complex gene, Paan-AG.
The human class Ib major histocompatibility complex (MHC) molecule, HLA-G, is unique in its limited polymorphism, high expression in the placenta and generation of multiple transcripts by alternative splicing. The proteins encoded by these transcripts are believed to modulate maternal-fetal immunological relationships during pregnancy. The baboon placenta contains messages encoded by a novel MHC gene, Paan-AG, which is evolutionarily related to the HLA-A locus, but shares unique characteristics with HLA-G. In this study, we show that the Paan-AG message is alternatively spliced to generate at least seven transcripts. One of these transcripts retains intron 4 and encodes a soluble glycoprotein with three external domains and a unique 21-amino-acid sequence at the carboxyl terminus, similar to soluble HLA-G1. This glycoprotein was detected in first trimester placental villous cytotrophoblast and syncytiotrophoblast, and in extravillous cytotrophoblast cells in the basal plate in term placenta. Four of the transcripts ( Paan-AG1, Paan-AG2, Paan-AG3, Paan-AG4) encode membrane-bound class Ib MHC glycoprotein isoforms. Paan-AG1 protein expression was similar to that of sPaan-AG, while Paan-AG2 protein was not detected in these tissues. The other two transcripts ( Paan-AGx and Paan-AGxi) contain a truncated exon 3 and multiple stop codons. Paan-AG1 and Paan-AGx transcripts were detected in a number of non-placental tissues, but these transcripts contained multiple stop codons. Because of the structural similarities and common features of organ-specific expression and splicing of the message, studies on Paan-AG may be of value in dissecting the functions of the class Ib proteins in human pregnancy.
Langat
Daudi K
DK
Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, 66160-7400, USA.
Morales
Pedro J
PJ
Fazleabas
Asgerally T
AT
Mwenda
Jason M
JM
Hunt
Joan S
JS
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005805:Genes, MHC Class I; D006680:HLA Antigens / Q000235:genetics; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis* / Q000235:genetics*; D008969:Molecular Sequence Data; D010215:Papio / Q000235:genetics* / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D014018:Tissue Distribution; D014158:Transcription, Genetic
D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D020033:Protein Isoforms; D012333:RNA, Messenger